Every question in the official Element 4 Amateur Extra pool, with the correct answer and an explanation. Your exam will be 50 of these questions, one from each group.
Source: NCVEC Question Pool Committee, 2024-2028 Amateur Extra Class FCC Element 4 Question Pool (public domain). Question and answer text are reproduced exactly; explanations are written by HamTestHub. See all sources.
Withdrawn questions: NCVEC has removed E2A13, E4D05, E6D07, E9E10 from the pool. They will not appear on exams and are not listed here.
6 exam questions from this subelement. Practice E1 · Study notes
Why is it not legal to transmit a 3 kHz bandwidth USB signal with a carrier frequency of 14.348 MHz?
Answer D. 20 meters ends at 14.350 MHz. A 3 kHz USB signal at 14.348 MHz extends to 14.351 MHz, so its upper 1 kHz is outside the band.
When using a transceiver that displays the carrier frequency of phone signals, which of the following displayed frequencies represents the lowest frequency at which a properly adjusted LSB emission will be totally within the band?
Answer D. LSB extends about 3 kHz below the displayed carrier, so the display must be at least 3 kHz above the lower band edge.
What is the highest legal carrier frequency on the 20-meter band for transmitting a 2.8 kHz wide USB data signal?
Answer C. The 20-meter data segment ends at 14.150 MHz. A 2.8 kHz USB signal needs the carrier at or below 14.150 - 0.0028 = 14.1472 MHz.
May an Extra class operator answer the CQ of a station on 3.601 MHz LSB phone?
Answer C. The 75-meter phone segment starts at 3.600 MHz. LSB at 3.601 MHz extends down to about 3.598 MHz, below the phone segment edge.
Who must be in physical control of the station apparatus of an amateur station aboard any vessel or craft that is documented or registered in the United States?
Answer C. On a U.S.-documented or registered vessel, any person with an FCC-issued amateur license, or authorized for alien reciprocal operation, may control the station apparatus.
What is the required transmit frequency of a CW signal for channelized 60 meter operation?
Answer B. On the 60-meter channels, CW must be transmitted at the center frequency of the channel.
What is the maximum power permitted on the 2200-meter band?
Answer C. The 2200-meter band is limited to 1 watt EIRP.
If a station in a message forwarding system inadvertently forwards a message that is in violation of FCC rules, who is primarily accountable for the rules violation?
Answer B. In a message forwarding system, the control operator of the originating station is primarily accountable for a violation.
Except in some parts of Alaska, what is the maximum power permitted on the 630-meter band?
Answer D. Except in parts of Alaska, the 630-meter band is limited to 5 watts EIRP.
If an amateur station is installed aboard a ship or aircraft, what condition must be met before the station is operated?
Answer A. An amateur station on a ship or aircraft may operate only with the approval of the ship's master or the aircraft's pilot in command.
What licensing is required when operating an amateur station aboard a US-registered vessel in international waters?
Answer B. Any FCC-issued amateur license is enough to operate aboard a U.S.-registered vessel in international waters.
Which of the following constitutes a spurious emission?
Answer D. A spurious emission is outside the necessary bandwidth and can be reduced or eliminated without affecting the information sent. Harmonics are an example.
Which of the following is an acceptable bandwidth for digital voice or slow-scan TV transmissions made on the HF amateur bands?
Answer A. Digital voice and SSTV on HF should be kept to about 3 kHz, the same as an SSB voice signal.
Within what distance must an amateur station protect an FCC monitoring facility from harmful interference?
Answer A. Amateur stations within 1 mile of an FCC monitoring facility must protect it from harmful interference.
What must the control operator of a repeater operating in the 70-centimeter band do if a radiolocation system experiences interference from that repeater?
Answer C. Amateurs are secondary on 70 cm. If a radiolocation system receives interference, the repeater must cease operation or be changed to fix the interference.
What is the National Radio Quiet Zone?
Answer C. The National Radio Quiet Zone surrounds the National Radio Astronomy Observatory in Green Bank, West Virginia.
Which of the following additional rules apply if you are erecting an amateur station antenna structure at a site at or near a public use airport?
Answer A. Near a public-use airport, an antenna structure may require FAA notification and FCC registration under Part 17.
To what type of regulations does PRB-1 apply?
Answer C. PRB-1 applies to state and local zoning regulations, not to private homeowner association covenants.
What limitations may the FCC place on an amateur station if its signal causes interference to domestic broadcast reception, assuming that the receivers involved are of good engineering design?
Answer D. If a station interferes with well-designed broadcast receivers, the FCC may require it to avoid transmitting during certain hours on the offending frequencies (quiet hours).
Which amateur stations may be operated under RACES rules?
Answer C. Any FCC-licensed amateur station certified by the responsible civil defense organization may operate under RACES rules.
What frequencies are authorized to an amateur station operating under RACES rules?
Answer A. A RACES station may use all amateur frequencies authorized to its control operator.
What does PRB-1 require of state and local regulations affecting amateur radio antenna size and structures?
Answer B. PRB-1 requires state and local regulations to make reasonable accommodation for amateur radio.
What is the maximum bandwidth for a data emission on 60 meters?
Answer D. Data emissions on 60 meters are limited to 2.8 kHz bandwidth.
Which of the following apply to communications transmitted to amateur stations in foreign countries?
Answer C. International communications must be incidental to the purposes of the Amateur Service, or remarks of a personal nature.
How long must an operator wait after filing a notification with the Utilities Technology Council (UTC) before operating on the 2200-meter or 630-meter band?
Answer B. After notifying the UTC, you may operate after 30 days, unless you have been told you are within 1 km of power-line carrier (PLC) systems on those frequencies.
What is an IARP?
Answer A. An IARP (International Amateur Radio Permit) lets U.S. amateurs operate in certain countries of the Americas.
Under what situation may a station transmit third party communications while being automatically controlled?
Answer B. An automatically controlled station may transmit third-party communications only when using RTTY or data emissions.
Which of the following is required in order to operate in accordance with CEPT rules in foreign countries where permitted?
Answer C. To operate under CEPT rules, you must carry a copy of FCC Public Notice DA 16-1048.
What notifications must be given before transmitting on the 630- or 2200-meter bands?
Answer D. Before using 630 or 2200 meters, you must notify the Utilities Technology Council (UTC) of your call sign and station coordinates.
What is the maximum permissible duration of a remotely controlled station’s transmissions if its control link malfunctions?
Answer B. If the control link fails, a remotely controlled station must stop transmitting within 3 minutes.
What is the highest modulation index permitted at the highest modulation frequency for angle modulation below 29.0 MHz?
Answer B. Below 29.0 MHz, angle modulation (FM/PM) is limited to a modulation index of 1.0 at the highest modulation frequency.
What is the maximum mean power level for a spurious emission below 30 MHz with respect to the fundamental emission?
Answer A. Below 30 MHz, spurious emissions must be at least 43 dB below the fundamental.
Which of the following operating arrangements allows an FCC-licensed US citizen to operate in many European countries, and amateurs from many European countries to operate in the US?
Answer A. The CEPT arrangement lets U.S. citizens operate in many European countries, and vice versa.
In what portion of the 630-meter band are phone emissions permitted?
Answer D. Phone emissions are permitted throughout the 630-meter band.
What is the definition of telemetry?
Answer A. Telemetry is one-way transmission of measurements from a distance.
Which of the following may transmit encrypted messages?
Answer B. Telecommand signals sent from a space telecommand station may be encrypted.
What is a space telecommand station?
Answer B. A space telecommand station sends commands that start, change or stop functions of a space station.
Which of the following is required in the identification transmissions from a balloon-borne telemetry station?
Answer A. A balloon-borne telemetry station must identify with its call sign.
What must be posted at the location of a station being operated by telecommand on or within 50 kilometers of the Earth’s surface?
Answer D. A telecommanded station near Earth must have a label with the station licensee's and control operator's name, address and phone number, plus a copy of the license.
What is the maximum permitted transmitter output power when operating a model craft by telecommand?
Answer A. Model craft telecommand transmitters are limited to 1 watt output.
Which of the following HF amateur bands include allocations for space stations?
Answer A. On HF, space stations are authorized in parts of 40, 20, 15 and 10 meters (and 17 and 12 meters).
Which VHF amateur bands have frequencies authorized for space stations?
Answer D. On VHF, space stations are authorized on 2 meters.
Which UHF amateur bands have frequencies authorized for space stations?
Answer B. On UHF, space stations are authorized on 70 centimeters and 13 centimeters.
Which amateur stations are eligible to be telecommand stations of space stations, subject to the privileges of the class of operator license held by the control operator of the station?
Answer B. Any amateur station designated by the space station licensee may be a telecommand station, within its control operator's privileges.
Which amateur stations are eligible to operate as Earth stations?
Answer D. Any amateur station may be an Earth station, subject to its control operator's license privileges.
Which of the following amateur stations may transmit one-way communications?
Answer A. Space stations, beacons and telecommand stations may make one-way transmissions.
For which types of out-of-pocket expenses do the Part 97 rules state that VEs and VECs may be reimbursed?
Answer A. VEs and VECs may be reimbursed for out-of-pocket expenses of preparing, processing, administering and coordinating exams.
Who is tasked by Part 97 with maintaining the pools of questions for all US amateur license examinations?
Answer C. Part 97 gives the VECs (through the NCVEC) the job of maintaining the question pools.
What is a Volunteer Examiner Coordinator?
Answer C. A VEC is an organization that has an agreement with the FCC to coordinate amateur license exams.
What is required to be accredited as a Volunteer Examiner?
Answer D. A VEC accredits a VE after confirming the applicant meets FCC requirements.
What must the VE team do with the application form if the examinee does not pass the exam?
Answer B. If the examinee fails, the VE team returns the application document to the examinee.
Who is responsible for the proper conduct and necessary supervision during an amateur operator license examination session?
Answer C. Each administering VE is responsible for the proper conduct and supervision of the exam session.
What should a VE do if a candidate fails to comply with the examiner’s instructions during an amateur operator license examination?
Answer B. A candidate who fails to comply with the examiners' instructions has their exam terminated immediately.
To which of the following examinees may a VE not administer an examination?
Answer C. A VE may not examine their relatives as listed in the FCC rules.
What may be the penalty for a VE who fraudulently administers or certifies an examination?
Answer A. A VE who fraudulently administers or certifies an exam may lose their station license and have their operator license suspended.
What must the administering VEs do after the administration of a successful examination for an amateur operator license?
Answer C. After a successful exam, the VEs submit the application to the coordinating VEC according to its instructions.
What must the VE team do if an examinee scores a passing grade on all examination elements needed for an upgrade or new license?
Answer B. Three VEs must certify that the examinee is qualified and that they followed the VE requirements.
On what frequencies are spread spectrum transmissions permitted?
Answer B. Spread spectrum is permitted only on amateur frequencies above 222 MHz.
What privileges are authorized in the US to persons holding an amateur service license granted by the government of Canada?
Answer C. Canadian amateurs in the U.S. may operate under the terms of their Canadian license, not exceeding U.S. Amateur Extra privileges.
Under what circumstances may a dealer sell an external RF power amplifier capable of operation below 144 MHz if it has not been granted FCC certification?
Answer D. An uncertified amplifier capable of operation below 144 MHz may be sold if it was built or modified by an amateur for use at an amateur station.
Which of the following geographic descriptions approximately describes "Line A"?
Answer A. Line A runs roughly parallel to the U.S.-Canada border, just south of it.
Amateur stations may not transmit in which of the following frequency segments if they are located in the contiguous 48 states and north of Line A?
Answer D. North of Line A, U.S. amateurs may not transmit on 420 to 430 MHz.
Under what circumstances might the FCC issue a Special Temporary Authority (STA) to an amateur station?
Answer A. The FCC may issue a Special Temporary Authority (STA) for experimental amateur communications.
When may an amateur station send a message to a business?
Answer D. You may send a message to a business only if neither you nor your employer has a financial (pecuniary) interest in it.
Which of the following types of amateur station communications are prohibited?
Answer A. Communications for hire or material compensation are prohibited, except where the rules allow it.
Which of the following cannot be transmitted over an amateur radio mesh network?
Answer C. Messages encoded to obscure their meaning are prohibited on amateur mesh networks, as on any amateur station.
Who may be the control operator of an auxiliary station?
Answer B. Technician, General, Advanced and Amateur Extra class operators may control an auxiliary station.
Which of the following best describes one of the standards that must be met by an external RF power amplifier if it is to qualify for a grant of FCC certification?
Answer D. To be certified, an amplifier must meet FCC spurious emission standards at 1500 watts or its full output, whichever is less.
5 exam questions from this subelement. Practice E2 · Study notes
What is the direction of an ascending pass for an amateur satellite?
Answer C. An ascending pass is one where the satellite moves from south to north.
Which of the following is characteristic of an inverting linear transponder?
Answer D. In an inverting transponder, signal positions are reversed, USB becomes LSB, and Doppler shifts on uplink and downlink partly cancel. All are true.
How is an upload signal processed by an inverting linear transponder?
Answer D. An inverting transponder mixes the uplink with a local oscillator and transmits the difference product, which inverts the spectrum.
What is meant by the “mode” of an amateur radio satellite?
Answer B. A satellite's mode is its uplink and downlink frequency bands.
What do the letters in a satellite’s mode designator specify?
Answer D. Mode designator letters specify the uplink and downlink frequency ranges, for example U/V.
What are Keplerian elements?
Answer A. Keplerian elements are the parameters that define a satellite's orbit.
Which of the following types of signals can be relayed through a linear transponder?
Answer D. A linear transponder relays any signal in its passband: FM, CW, SSB, SSTV, PSK and packet.
Why should effective radiated power (ERP) be limited to a satellite that uses a linear transponder?
Answer B. A linear transponder shares its power among all signals. Excess uplink power takes a larger share and reduces downlink power for everyone else.
What do the terms “L band” and “S band” specify?
Answer A. L band is the 23-centimeter band and S band is the 13-centimeter band.
What type of satellite appears to stay in one position in the sky?
Answer B. A geostationary satellite orbits at the same rate Earth rotates, so it appears fixed in the sky.
What type of antenna can be used to minimize the effects of spin modulation and Faraday rotation?
Answer B. Circularly polarized antennas reduce fading from satellite spin and Faraday rotation.
What is the purpose of digital store-and-forward functions on an amateur radio satellite?
Answer C. Store-and-forward satellites hold digital messages for later download.
In digital television, what does a coding rate of 3/4 mean?
Answer A. A 3/4 coding rate means 3 of every 4 bits are data and 1 is error correction, so 25% is FEC.
How many horizontal lines make up a fast-scan (NTSC) television frame?
Answer C. An NTSC fast-scan TV frame has 525 lines.
How is an interlaced scanning pattern generated in a fast-scan (NTSC) television system?
Answer D. Interlacing scans the odd-numbered lines in one field and the even-numbered lines in the next.
How is color information sent in analog SSTV?
Answer A. Analog SSTV sends color lines sequentially (for example red, green, blue).
Which of the following describes the use of vestigial sideband in analog fast-scan TV transmissions?
Answer C. Vestigial sideband reduces bandwidth while preserving fidelity of the low-frequency video components.
What is vestigial sideband modulation?
Answer A. VSB is AM that transmits one complete sideband plus a portion (vestige) of the other.
Which types of modulation are used for amateur television DVB-T signals?
Answer B. DVB-T digital TV uses QAM and QPSK modulation.
What technique allows commercial analog TV receivers to be used for fast-scan TV operations on the 70-centimeter band?
Answer A. Transmitting on 70-cm frequencies that match cable TV channels lets ordinary cable-ready TVs receive amateur fast-scan TV.
What kind of receiver can be used to receive and decode SSTV using the Digital Radio Mondiale (DRM) protocol?
Answer D. DRM digital SSTV is received with an SSB receiver feeding decoding software.
What aspect of an analog slow-scan television signal encodes the brightness of the picture?
Answer A. In analog SSTV, brightness is encoded as tone frequency.
What is the function of the vertical interval signaling (VIS) code sent as part of an SSTV transmission?
Answer B. The VIS code identifies which SSTV mode is being sent.
What signals SSTV receiving software to begin a new picture line?
Answer A. Specific tone frequencies (sync tones) signal the start of each new picture line.
What indicator is required to be used by US-licensed operators when operating a station via remote control and the remote transmitter is located in the US?
Answer D. When remotely operating a station located in the U.S., no additional indicator is required.
Which of the following file formats is used for exchanging amateur radio log data?
Answer C. ADIF is the standard format for exchanging amateur log data.
From which of the following bands is amateur radio contesting generally excluded?
Answer A. By convention, contests are not held on 30 meters (or 17 and 12 meters).
Which of the following frequencies can be used for amateur radio mesh networks?
Answer B. Mesh networks use frequencies shared with unlicensed wireless data services, such as Wi-Fi channels in amateur bands.
What is the function of a DX QSL Manager?
Answer B. A QSL manager handles receiving and sending contact confirmations for a DX station.
During a VHF/UHF contest, in which band segment would you expect to find the highest level of SSB or CW activity?
Answer C. In VHF/UHF contests, most SSB and CW activity is in the weak-signal segment near the calling frequency.
What is the Cabrillo format?
Answer A. Cabrillo is the standard format for submitting electronic contest logs.
Which of the following contacts may be confirmed through the Logbook of The World (LoTW)?
Answer D. LoTW can confirm all of these contacts: domestic special events, international contacts and Worked All States credit.
What type of equipment is commonly used to implement an amateur radio mesh network?
Answer C. Amateur mesh networks are commonly built with wireless routers running custom firmware.
Why do DX stations often transmit and receive on different frequencies?
Answer D. Working split helps when the DX station's frequency is prohibited to some callers, separates callers from the DX station, and improves efficiency.
How should you generally identify your station when attempting to contact a DX station during a contest or in a pileup?
Answer A. In a pileup, send your full call sign once or twice.
What indicates the delay between a control operator action and the corresponding change in the transmitted signal?
Answer C. Latency is the delay between a control action and the resulting change in the transmitted signal, an important factor in remote operating.
Which of the following digital modes is designed for meteor scatter communications?
Answer B. MSK144 is designed for meteor scatter.
What information replaces signal-to-noise ratio when using the FT8 or FT4 modes in a VHF contest?
Answer D. In VHF contests using FT8 or FT4, the grid square replaces the signal report.
Which of the following digital modes is designed for EME communications?
Answer D. Q65 is designed for EME (moonbounce) and other weak-signal paths.
What technology is used for real-time tracking of balloons carrying amateur radio transmitters?
Answer C. APRS is used for real-time tracking of balloons carrying amateur transmitters.
What is the characteristic of the JT65 mode?
Answer B. JT65 can decode signals with very low signal-to-noise ratios.
Which of the following is a method for establishing EME contacts?
Answer A. EME contacts often use time-synchronous transmissions, with stations alternating fixed transmit periods.
What digital protocol is used by APRS?
Answer C. APRS uses the AX.25 packet protocol.
What type of packet frame is used to transmit APRS beacon data?
Answer C. APRS beacons are sent as Unnumbered Information (UI) frames, which need no connection.
What type of modulation is used by JT65?
Answer A. JT65 uses multitone AFSK (65 tones).
What does the packet path WIDE3-1 designate?
Answer C. WIDE3-1 requests three digipeater hops, with one hop remaining.
How do APRS stations relay data?
Answer D. APRS data is relayed by packet digipeaters.
Which of the following types of modulation is used for data emissions below 30 MHz?
Answer B. FSK is the common modulation for data emissions below 30 MHz.
Which of the following synchronizes WSJT-X digital mode transmit/receive timing?
Answer B. WSJT-X modes depend on accurately synchronized computer clocks.
To what does the "4" in FT4 refer?
Answer B. The "4" in FT4 refers to its four-tone continuous-phase FSK.
Which of the following is characteristic of the FST4 mode?
Answer D. FST4 uses four-tone Gaussian FSK, variable transmit/receive periods and several tone spacings. All are characteristic.
Which of these digital modes does not support keyboard-to-keyboard operation?
Answer A. WSPR is a one-way beacon mode with no keyboard-to-keyboard chat.
What is the length of an FT8 transmission cycle?
Answer C. An FT8 cycle is 15 seconds.
How does Q65 differ from JT65?
Answer C. Q65 can average multiple receive cycles to decode very weak signals, unlike JT65.
Which of the following HF digital modes can be used to transfer binary files?
Answer B. PACTOR can transfer binary files, with error correction.
Which of the following HF digital modes uses variable-length character coding?
Answer D. PSK31 uses Varicode, a variable-length character code.
Which of these digital modes has the narrowest bandwidth?
Answer C. FT8 occupies only about 50 Hz, the narrowest of these modes.
What is the difference between direct FSK and audio FSK?
Answer A. Direct FSK shifts the transmitter's VFO (oscillator) frequency directly. Audio FSK uses tones fed into an SSB transmitter.
How do ALE stations establish contact?
Answer A. ALE radios constantly scan a list of frequencies and activate when they receive their designated call sign.
Which of these digital modes has the highest data throughput under clear communication conditions?
Answer D. PACTOR IV has the highest data throughput of these modes under good conditions.
3 exam questions from this subelement. Practice E3 · Study notes
What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by EME?
Answer D. EME (moonbounce) works between any two stations that can both see the Moon, up to about 12,000 miles apart on Earth's surface.
What characterizes libration fading of an EME signal?
Answer B. Libration fading is a fluttery, irregular fading caused by the Moon's slight rocking motion, which changes the many reflection paths.
When scheduling EME contacts, which of these conditions will generally result in the least path loss?
Answer A. Path loss is lowest when the Moon is at perigee, its closest point to Earth.
In what direction does an electromagnetic wave travel?
Answer D. An electromagnetic wave travels at right angles to both its electric and magnetic fields.
How are the component fields of an electromagnetic wave oriented?
Answer C. The electric and magnetic fields of an electromagnetic wave are at right angles to each other.
What should be done to continue a long-distance contact when the MUF for that path decreases due to darkness?
Answer B. When darkness lowers the MUF, switch to a lower-frequency band that the ionosphere still supports.
Atmospheric ducts capable of propagating microwave signals often form over what geographic feature?
Answer C. Microwave ducts often form over large bodies of water, where temperature and humidity layers are common.
When a meteor strikes the Earth’s atmosphere, a linear ionized region is formed at what region of the ionosphere?
Answer A. Meteors create linear ionized trails in the E region, about 85 to 120 km up.
Which of the following frequency ranges is most suited for meteor-scatter communications?
Answer C. Meteor scatter works best from about 28 to 148 MHz, with 6 meters especially popular.
What determines the speed of electromagnetic waves through a medium?
Answer D. The index of refraction of a medium determines how fast electromagnetic waves travel through it.
What is a typical range for tropospheric duct propagation of microwave signals?
Answer B. Tropospheric ducting typically carries microwave signals about 100 to 300 miles.
What is most likely to result in auroral propagation?
Answer C. Severe geomagnetic storms produce the auroras that support auroral propagation.
Which of these emission modes is best for auroral propagation?
Answer A. Auroral reflection badly distorts signals. CW stays readable best.
What are circularly polarized electromagnetic waves?
Answer B. In a circularly polarized wave, the electric and magnetic fields rotate as the wave travels.
Where is transequatorial propagation (TEP) most likely to occur?
Answer A. TEP is most likely between stations 2,000 to 3,000 miles apart on a path that crosses the geomagnetic equator at right angles.
What is the approximate maximum range for signals using transequatorial propagation?
Answer C. Transequatorial propagation can reach up to about 5,000 miles.
At what time of day is transequatorial propagation most likely to occur?
Answer C. TEP is most likely in the afternoon or early evening.
What are “extraordinary” and “ordinary” waves?
Answer B. In the ionosphere, Earth's magnetic field splits a wave into two independently propagating, elliptically polarized waves: ordinary and extraordinary.
Which of the following paths is most likely to support long-distance propagation on 160 meters?
Answer D. 160-meter signals are absorbed in daylight, so long-distance 160-meter paths work best when the whole path is in darkness.
On which of the following amateur bands is long-path propagation most frequent?
Answer B. Long-path propagation is most frequent on 40 and 20 meters.
What effect does lowering a signal’s transmitted elevation angle have on ionospheric HF skip propagation?
Answer C. Lowering the elevation (takeoff) angle makes each skip hop cover more distance.
How does the maximum range of ground-wave propagation change when the signal frequency is increased?
Answer C. Ground-wave range decreases as frequency increases, which is why ground wave is most useful on MF and low HF.
At what time of year is sporadic-E propagation most likely to occur?
Answer A. Sporadic E peaks around the solstices, especially the summer solstice (with a smaller peak in winter).
What is the effect of chordal-hop propagation?
Answer A. Chordal hop skips the lossy ground reflections of multi-hop paths, so signals suffer less loss.
At what time of day is sporadic-E propagation most likely to occur?
Answer D. Sporadic E is most common during daylight, between sunrise and sunset.
What is chordal-hop propagation?
Answer B. Chordal hop is a series of ionospheric refractions without the signal bouncing off the ground in between.
What type of polarization is supported by ground-wave propagation?
Answer A. Ground-wave propagation supports vertical polarization. Horizontally polarized ground waves are quickly attenuated.
What is the cause of short-term radio blackouts?
Answer D. Short-term radio blackouts are caused by solar flares, whose X-rays increase D-region absorption.
What is indicated by a rising A-index or K-index?
Answer A. Rising A or K index values indicate increasing disturbance of Earth's magnetic field.
Which of the following signal paths is most likely to experience high levels of absorption when the A-index or K-index is elevated?
Answer B. When the A or K index is high, paths through the auroral oval suffer the most absorption.
What does the value of Bz (B sub z) represent?
Answer C. Bz is the north-south component of the interplanetary magnetic field.
What orientation of Bz (B sub z) increases the likelihood that charged particles from the Sun will cause disturbed conditions?
Answer A. A southward Bz couples more easily with Earth's field and makes disturbed conditions more likely.
How does the VHF/UHF radio horizon compare to the geographic horizon?
Answer A. Atmospheric refraction makes the VHF/UHF radio horizon about 15 percent farther than the geographic horizon.
Which of the following indicates the greatest solar flare intensity?
Answer D. Solar flares are classed A, B, C, M and X. Class X is the most intense.
Which of the following is the space-weather term for an extreme geomagnetic storm?
Answer D. On NOAA's space weather scales, G5 is an extreme geomagnetic storm.
What type of data is reported by amateur radio propagation reporting networks?
Answer D. Propagation reporting networks report received digital-mode and CW signals, showing where signals are being heard.
What does the 304A solar parameter measure?
Answer B. The 304A parameter measures ultraviolet emissions at 304 angstroms, which correlate with the solar flux index.
What does VOACAP software model?
Answer C. VOACAP is software that models HF propagation.
Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum?
Answer B. A sudden rise in background noise across much of HF suggests a CME impact or a solar flare.
5 exam questions from this subelement. Practice E4 · Study notes
Which of the following limits the highest frequency signal that can be accurately displayed on a digital oscilloscope?
Answer A. A digital scope's highest accurately displayed frequency is limited by its ADC sampling rate. It must sample at more than twice the signal frequency.
Which of the following parameters does a spectrum analyzer display on the vertical and horizontal axes?
Answer B. A spectrum analyzer shows amplitude on the vertical axis and frequency on the horizontal axis.
Which of the following test instruments is used to display spurious signals and/or intermodulation distortion products generated by an SSB transmitter?
Answer B. A spectrum analyzer shows spurious signals and intermodulation products from a transmitter.
How is compensation of an oscilloscope probe performed?
Answer A. To compensate a scope probe, display a square wave and adjust the probe until the flat (horizontal) parts are as flat as possible.
What is the purpose of using a prescaler with a frequency counter?
Answer D. A prescaler divides a high input frequency down to a range the counter can handle.
What is the effect of aliasing on a digital oscilloscope when displaying a waveform?
Answer A. Aliasing from too low a sample rate shows a false, jittery, low-frequency version of the waveform.
Which of the following is an advantage of using an antenna analyzer compared to an SWR bridge?
Answer B. An antenna analyzer computes SWR and impedance automatically. An SWR bridge needs a transmitter and manual calculation.
Which of the following is used to measure SWR?
Answer D. Directional wattmeters, vector network analyzers and antenna analyzers can all measure SWR.
Which of the following is good practice when using an oscilloscope probe?
Answer A. Keep the probe's ground connection as short as possible to avoid ringing and pickup.
Which trigger mode is most effective when using an oscilloscope to measure a linear power supply’s output ripple?
Answer D. Line triggering syncs the scope to the AC power line, ideal for viewing ripple at the line frequency.
Which of the following can be measured with an antenna analyzer?
Answer D. An antenna analyzer can measure velocity factor, cable length and the resonant frequency of a tuned circuit.
Which of the following factors most affects the accuracy of a frequency counter?
Answer B. A frequency counter's accuracy depends mainly on the accuracy of its time base.
What is the significance of voltmeter sensitivity expressed in ohms per volt?
Answer A. Full-scale voltage multiplied by the ohms-per-volt rating gives the meter's input impedance on that range.
Which S parameter is equivalent to forward gain?
Answer C. S21 is forward gain (transmission from port 1 to port 2).
Which S parameter represents input port return loss or reflection coefficient (equivalent to VSWR)?
Answer A. S11 is the input reflection coefficient (return loss), equivalent to VSWR.
What three test loads are used to calibrate an RF vector network analyzer?
Answer B. A VNA is calibrated with a short circuit, an open circuit and a 50-ohm load.
How much power is being absorbed by the load when a directional power meter connected between a transmitter and a terminating load reads 100 watts forward power and 25 watts reflected power?
Answer D. Absorbed power = forward - reflected = 100 W - 25 W = 75 W.
What do the subscripts of S parameters represent?
Answer A. S-parameter subscripts give the ports involved: the first is the output port, the second the input port.
Which of the following can be used to determine the Q of a series-tuned circuit?
Answer C. Q of a resonant circuit equals resonant frequency divided by bandwidth, so the bandwidth of its frequency response gives Q.
Which of the following can be measured by a two-port vector network analyzer?
Answer B. A two-port VNA can measure a filter's frequency response.
Which of the following methods measures intermodulation distortion in an SSB transmitter?
Answer B. Measure SSB intermodulation by modulating with two non-harmonically related audio tones and observing the RF output on a spectrum analyzer.
Which of the following can be measured with a vector network analyzer?
Answer D. A VNA can measure input impedance, output impedance and reflection coefficient.
What is an effect of excessive phase noise in an SDR receiver’s master clock oscillator?
Answer D. Phase noise in an SDR's master clock can mix with strong nearby signals and create interference (reciprocal mixing).
Which of the following receiver circuits can be effective in eliminating interference from strong out-of-band signals?
Answer A. A front-end filter (preselector) removes strong out-of-band signals before they reach later stages.
What is the term for the suppression in an FM receiver of one signal by another stronger signal on the same frequency?
Answer C. Capture effect is an FM receiver suppressing a weaker signal on the same frequency in favor of a stronger one.
What is the noise figure of a receiver?
Answer D. Noise figure is the ratio in dB of the noise a receiver generates to the theoretical minimum noise.
What does a receiver noise floor of -174 dBm represent?
Answer B. -174 dBm is the theoretical thermal noise in a 1 Hz bandwidth at room temperature for a perfect receiver.
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor?
Answer D. Noise rises 10 x log(1000 / 50) = 10 x log(20), about 13 dB.
What does the MDS of a receiver represent?
Answer B. MDS means minimum discernible signal, the weakest signal the receiver can detect.
An SDR receiver is overloaded when input signals exceed what level?
Answer D. An SDR overloads when the input exceeds the ADC's reference voltage (full-scale level).
Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF communications receiver?
Answer C. A high IF puts the image frequency far from the desired signal, so front-end filters can reject it more easily.
What is an advantage of having a variety of receiver bandwidths from which to select?
Answer C. Matching receive bandwidth to the signal's bandwidth maximizes signal-to-noise ratio and reduces interference.
Why does input attenuation reduce receiver overload on the lower frequency HF bands with little or no impact on signal-to-noise ratio?
Answer D. On the lower HF bands, atmospheric noise is much stronger than receiver noise, so attenuation reduces overload without hurting signal-to-noise ratio.
How does a narrow-band roofing filter affect receiver performance?
Answer C. A narrow roofing filter blocks strong nearby signals early in the receiver, improving blocking dynamic range.
What is reciprocal mixing?
Answer D. Reciprocal mixing is local oscillator phase noise mixing with strong adjacent signals, putting noise on the desired signal.
What is the purpose of the receiver IF Shift control?
Answer C. IF shift moves the passband relative to the signal, reducing interference from adjacent stations.
What is meant by the blocking dynamic range of a receiver?
Answer A. Blocking dynamic range is the difference between the noise floor and the signal level that causes 1 dB of gain compression.
Which of the following describes problems caused by poor dynamic range in a receiver?
Answer A. Poor dynamic range causes cross modulation and desensitization from strong nearby signals.
What creates intermodulation interference between two repeaters in close proximity?
Answer B. Intermodulation between nearby repeaters happens when their output signals mix in the final amplifier of one or both transmitters.
Which of the following is used to reduce or eliminate intermodulation interference in a repeater caused by a nearby transmitter?
Answer B. A properly terminated circulator at the transmitter output keeps other signals from entering the final amplifier and mixing.
What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency?
Answer C. Desensitization is reduced receiver sensitivity caused by a strong signal near the received frequency.
Which of the following reduces the likelihood of receiver desensitization?
Answer A. Attenuation before the first RF stage reduces strong signals and the chance of desensitization.
What causes intermodulation in an electronic circuit?
Answer C. Intermodulation is caused by nonlinear circuits or devices.
What is the purpose of the preselector in a communications receiver?
Answer C. A preselector increases rejection of signals outside the band being received.
What does a third-order intercept level of 40 dBm mean with respect to receiver performance?
Answer C. A +40 dBm third-order intercept is where the third-order products would theoretically equal the input signals in amplitude. Higher is better.
Why are odd-order intermodulation products, created within a receiver, of particular interest compared to other products?
Answer A. Odd-order products (such as 2F1 - F2) from two in-band signals usually also fall in the band, so they cause interference.
What is the link margin in a system with a transmit power level of 10 W (+40 dBm), a system antenna gain of 10 dBi, a cable loss of 3 dB, a path loss of 136 dB, a receiver minimum discernable signal of -103 dBm, and a required signal-to-noise ratio of 6 dB?
Answer C. Received level = 40 + 10 - 3 - 136 = -89 dBm. Required = -103 + 6 = -97 dBm. Margin = -89 - (-97) = +8 dB.
What is the received signal level with a transmit power of 10 W (+40 dBm), a transmit antenna gain of 6 dBi, a receive antenna gain of 3 dBi, and a path loss of 100 dB?
Answer A. Received level = 40 + 6 + 3 - 100 = -51 dBm.
What power level does a receiver minimum discernible signal of -100 dBm represent?
Answer D. -100 dBm is 10^-10 milliwatts, which is 10^-13 watts or 0.1 picowatts.
What problem can occur when using an automatic notch filter (ANF) to remove interfering carriers while receiving CW signals?
Answer A. An automatic notch filter can mistake a steady CW signal for an interfering carrier and remove it.
Which of the following types of noise can often be reduced by a digital noise reduction?
Answer D. DSP noise reduction can reduce broadband white noise, ignition noise and power line noise.
Which of the following types of noise are removed by a noise blanker?
Answer B. A noise blanker removes impulse noise, short sharp pulses such as ignition noise.
How can conducted noise from an automobile battery charging system be suppressed?
Answer D. Ferrite chokes on the charging system leads suppress conducted alternator noise.
What is used to suppress radio frequency interference from a line-driven AC motor?
Answer B. A brute-force AC-line filter in series with a motor's power leads suppresses its RF interference.
What type of electrical interference can be caused by computer network equipment?
Answer C. Network equipment can produce unstable modulated or unmodulated signals at specific frequencies.
Which of the following can cause shielded cables to radiate or receive interference?
Answer B. Common-mode currents on the shield and conductors make shielded cables radiate or pick up interference.
What current flows equally on all conductors of an unshielded multiconductor cable?
Answer B. Common-mode current flows equally (in the same direction) on all conductors of a cable.
What undesirable effect can occur when using a noise blanker?
Answer C. A noise blanker can distort strong signals, making them appear to have spurious emissions.
Which of the following can create intermittent loud roaring or buzzing AC line interference?
Answer D. Arcing thermostat contacts, defective doorbell transformers and faulty illuminated signs can all cause loud intermittent AC line noise.
What could be the cause of local AM broadcast band signals combining to generate spurious signals on the MF or HF bands?
Answer B. Corroded metal connections nearby can act as nonlinear mixers and reradiate combined broadcast signals (the "rusty bolt" effect).
What causes interference received as a series of carriers at regular intervals across a wide frequency range?
Answer A. Switch-mode power supplies produce a series of carriers at regular intervals across a wide range.
Where should a station AC surge protector be installed?
Answer C. Install the station's AC surge protector on the single point ground panel.
What is the purpose of a single point ground panel?
Answer D. A single point ground panel keeps all protectors at the same reference, so they activate at the same time during a surge.
4 exam questions from this subelement. Practice E5 · Study notes
What can cause the voltage across reactances in a series RLC circuit to be higher than the voltage applied to the entire circuit?
Answer A. At resonance, the voltages across L and C in a series circuit can be much larger than the applied voltage (multiplied by Q). They cancel each other, but each is large.
What is the resonant frequency of an RLC circuit if R is 22 ohms, L is 50 microhenries, and C is 40 picofarads?
Answer C. f = 1 / (2π√(LC)) = 1 / (2π√(50 µH x 40 pF)), about 3.56 MHz. R does not affect the resonant frequency.
What is the magnitude of the impedance of a series RLC circuit at resonance?
Answer D. In a series RLC circuit at resonance, the reactances cancel and impedance equals the circuit resistance.
What is the magnitude of the impedance of a parallel RLC circuit at resonance?
Answer A. In a parallel RLC circuit at resonance, the impedance is approximately equal to the circuit resistance (high for a good tank circuit).
What is the result of increasing the Q of an impedance-matching circuit?
Answer A. Higher Q means a sharper response, so the matching bandwidth decreases.
What is the magnitude of the circulating current within the components of a parallel LC circuit at resonance?
Answer B. In a parallel LC circuit at resonance, current circulating between L and C is at a maximum.
What is the magnitude of the current at the input of a parallel RLC circuit at resonance?
Answer A. At resonance a parallel RLC circuit has maximum impedance, so the current drawn at its input is at a minimum.
What is the phase relationship between the current through and the voltage across a series resonant circuit at resonance?
Answer C. At resonance the reactances cancel, so voltage and current are in phase.
How is the Q of an RLC parallel resonant circuit calculated?
Answer C. For a parallel circuit, Q = R / X, where X is the reactance of either L or C.
What is the resonant frequency of an RLC circuit if R is 33 ohms, L is 50 microhenries, and C is 10 picofarads?
Answer A. f = 1 / (2π√(50 µH x 10 pF)), about 7.12 MHz.
What is the half-power bandwidth of a resonant circuit that has a resonant frequency of 7.1 MHz and a Q of 150?
Answer C. Bandwidth = f / Q = 7.1 MHz / 150, about 47.3 kHz.
What is the half-power bandwidth of a resonant circuit that has a resonant frequency of 3.7 MHz and a Q of 118?
Answer C. Bandwidth = f / Q = 3.7 MHz / 118, about 31.4 kHz.
What is an effect of increasing Q in a series resonant circuit?
Answer C. Higher Q in a series resonant circuit raises the internal voltages across L and C.
What is the term for the time required for the capacitor in an RC circuit to be charged to 63.2% of the applied voltage or to discharge to 36.8% of its initial voltage?
Answer B. One time constant (R x C) is the time to charge to 63.2% or discharge to 36.8%.
What letter is commonly used to represent susceptance?
Answer D. Susceptance is represented by the letter B.
How is impedance in polar form converted to an equivalent admittance?
Answer B. To convert polar impedance to admittance, take the reciprocal of the magnitude and change the sign of the angle.
What is the time constant of a circuit having two 220-microfarad capacitors and two 1-megohm resistors, all in parallel?
Answer D. Parallel capacitors add: 440 µF. Two 1 MΩ resistors in parallel: 0.5 MΩ. Time constant = 0.5 MΩ x 440 µF = 220 seconds.
What is the effect on the magnitude of pure reactance when it is converted to susceptance?
Answer D. Converting pure reactance to susceptance replaces it with its reciprocal (B = 1 / X).
What is susceptance?
Answer C. Susceptance is the imaginary part of admittance.
What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 500 ohms, R is 1 kilohm, and XL is 250 ohms?
Answer C. Net reactance = 250 - 500 = -250 ohms (capacitive). Angle = arctan(-250 / 1000), about -14 degrees: voltage lags current.
What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 300 ohms, R is 100 ohms, and XL is 100 ohms?
Answer A. Net reactance = 100 - 300 = -200 ohms. Angle = arctan(-200 / 100), about -63 degrees: voltage lags current.
What is the relationship between the AC current through a capacitor and the voltage across a capacitor?
Answer D. In a capacitor, current leads voltage by 90 degrees.
What is the relationship between the AC current through an inductor and the voltage across an inductor?
Answer A. In an inductor, voltage leads current by 90 degrees. Memory aid: ELI the ICE man.
What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 25 ohms, R is 100 ohms, and XL is 75 ohms?
Answer B. Net reactance = 75 - 25 = +50 ohms (inductive). Angle = arctan(50 / 100), about 27 degrees: voltage leads current.
What is admittance?
Answer A. Admittance is the inverse of impedance.
Which of the following represents pure capacitive reactance of 100 ohms in rectangular notation?
Answer A. Capacitive reactance is negative imaginary, so pure capacitive 100 ohms is 0 - j100.
How are impedances described in polar coordinates?
Answer C. Polar coordinates describe impedance by magnitude and phase angle.
Which of the following represents a pure inductive reactance in polar coordinates?
Answer C. Pure inductive reactance has a phase angle of +90 degrees.
What type of Y-axis scale is most often used for graphs of circuit frequency response?
Answer D. Frequency response graphs usually use a logarithmic Y-axis (decibels).
What kind of diagram is used to show the phase relationship between impedances at a given frequency?
Answer C. A phasor diagram shows the phase relationships between impedances.
What does the impedance 50 - j25 ohms represent?
Answer B. 50 - j25 means 50 ohms resistance in series with 25 ohms of capacitive reactance (negative j).
Where is the impedance of a pure resistance plotted on rectangular coordinates?
Answer D. Pure resistance has no reactance, so it lies on the horizontal (real) axis.
What coordinate system is often used to display the phase angle of a circuit containing resistance, inductive, and/or capacitive reactance?
Answer D. Polar coordinates are often used to show a circuit's phase angle.
When using rectangular coordinates to graph the impedance of a circuit, what do the axes represent?
Answer A. In rectangular coordinates, the X axis is resistance and the Y axis is reactance.
Which point on Figure E5-1 best represents the impedance of a series circuit consisting of a 400-ohm resistor and a 38-picofarad capacitor at 14 MHz?
Answer B. XC = 1 / (2π x 14 MHz x 38 pF), about 299 ohms, so Z is about 400 - j300. That is point 4 in figure E5-1.
Which point in Figure E5-1 best represents the impedance of a series circuit consisting of a 300-ohm resistor and an 18-microhenry inductor at 3.505 MHz?
Answer B. XL = 2π x 3.505 MHz x 18 µH, about 396 ohms, so Z is about 300 + j400. That is point 3 in figure E5-1.
Which point on Figure E5-1 best represents the impedance of a series circuit consisting of a 300-ohm resistor and a 19-picofarad capacitor at 21.200 MHz?
Answer A. XC = 1 / (2π x 21.2 MHz x 19 pF), about 395 ohms, so Z is about 300 - j400. That is point 1 in figure E5-1.
What is the result of conductor skin effect?
Answer A. Skin effect makes RF current flow near the conductor's surface, so resistance increases with frequency.
Why is it important to keep lead lengths short for components used in circuits for VHF and above?
Answer B. At VHF and above, even short leads add significant inductive reactance, so keep them short.
What is the phase relationship between current and voltage for reactive power?
Answer C. For reactive power, current and voltage are 90 degrees out of phase.
Why are short connections used at microwave frequencies?
Answer B. At microwave frequencies even short connections cause phase shift, so they are kept very short.
What parasitic characteristic causes electrolytic capacitors to be unsuitable for use at RF?
Answer C. Electrolytic capacitors have significant internal inductance, which makes them unsuitable at RF.
What parasitic characteristic creates an inductor’s self-resonance?
Answer D. Capacitance between an inductor's turns creates its self-resonance.
What combines to create the self-resonance of a component?
Answer B. A component's self-resonance comes from its nominal reactance combined with its parasitic reactance.
What is the primary cause of loss in film capacitors at RF?
Answer D. In film capacitors at RF, skin effect in the thin conductors is the main source of loss.
What happens to reactive power in ideal inductors and capacitors?
Answer B. Ideal inductors and capacitors store energy in fields and return it. Reactive power is not dissipated.
As a conductor’s diameter increases, what is the effect on its electrical length?
Answer D. A thicker conductor has a slightly greater electrical length (it resonates lower), which is why thick elements are cut a bit shorter.
How much real power is consumed in a circuit consisting of a 100-ohm resistor in series with a 100-ohm inductive reactance drawing 1 ampere?
Answer B. Only the resistor consumes real power: P = I² x R = 1² x 100 = 100 watts.
What is reactive power?
Answer D. Reactive power is wattless, nonproductive power that moves back and forth without being consumed.
6 exam questions from this subelement. Practice E6 · Study notes
In what application is gallium arsenide used as a semiconductor material?
Answer C. Gallium arsenide is used in microwave circuits because of its high electron mobility.
Which of the following semiconductor materials contains excess free electrons?
Answer A. N-type semiconductor material has excess free electrons from donor impurities.
Why does a PN-junction diode not conduct current when reverse biased?
Answer C. Reverse bias pulls holes and electrons away from the junction, widening the depletion region so no current flows.
What is the name given to an impurity atom that adds holes to a semiconductor crystal structure?
Answer C. An acceptor impurity adds holes to the crystal, creating P-type material.
How does DC input impedance at the gate of a field-effect transistor (FET) compare with that of a bipolar transistor?
Answer C. An FET's gate draws almost no current, so its DC input impedance is much higher than a bipolar transistor's.
What is the beta of a bipolar junction transistor?
Answer B. Beta is the current gain: change in collector current divided by change in base current.
Which of the following indicates that a silicon NPN junction transistor is biased on?
Answer D. A silicon NPN transistor is biased on when the base-emitter voltage is about 0.6 to 0.7 volts.
What is the term for the frequency at which the grounded-base current gain of a bipolar junction transistor has decreased to 0.7 of the gain obtainable at 1 kHz?
Answer D. Alpha cutoff frequency is where grounded-base current gain falls to 0.7 of its 1 kHz value.
What is a depletion-mode field-effect transistor (FET)?
Answer A. A depletion-mode FET conducts between source and drain with no gate voltage. Gate voltage reduces the current.
In Figure E6-1, which is the schematic symbol for an N-channel dual-gate MOSFET?
Answer B. In figure E6-1, symbol 4 is an N-channel dual-gate MOSFET: two insulated gates, with the arrow pointing in for N-channel.
In Figure E6-1, which is the schematic symbol for a P-channel junction FET?
Answer A. In figure E6-1, symbol 1 is a P-channel junction FET, with the gate arrow pointing out for P-channel.
What is the purpose of connecting Zener diodes between a MOSFET gate and its source or drain?
Answer D. Zener diodes between the gate and source or drain protect the thin gate insulation from static damage.
What is the most useful characteristic of a Zener diode?
Answer B. A Zener diode keeps a nearly constant voltage drop as current varies, making it a voltage reference.
Which characteristic of a Schottky diode makes it a better choice than a silicon junction diode for use as a power supply rectifier?
Answer D. Schottky diodes have a lower forward voltage drop, so they waste less power as rectifiers.
What property of an LED's semiconductor material determines its forward voltage drop?
Answer B. An LED's forward voltage is set by its semiconductor band gap, which also sets its color.
What type of semiconductor device is designed for use as a voltage-controlled capacitor?
Answer A. A varactor diode works as a voltage-controlled capacitor.
What characteristic of a PIN diode makes it useful as an RF switch?
Answer D. PIN diodes have low junction capacitance, so they make good RF switches.
Which of the following is a common use of a Schottky diode?
Answer D. Schottky diodes are commonly used as VHF/UHF mixers and detectors because they switch fast.
What causes a junction diode to fail from excessive current?
Answer B. Excessive current overheats the junction, and excessive junction temperature destroys the diode.
Which of the following is a Schottky barrier diode?
Answer A. A Schottky barrier diode uses a metal-semiconductor junction.
What is a common use for point-contact diodes?
Answer C. Point-contact diodes are commonly used as RF detectors.
In Figure E6-2, which is the schematic symbol for a Schottky diode?
Answer B. In figure E6-2, symbol 6 is the Schottky diode, shown by the S-shaped bar on the cathode.
What is used to control the attenuation of RF signals by a PIN diode?
Answer A. A PIN diode's RF attenuation is controlled by its forward DC bias current.
What is the function of hysteresis in a comparator?
Answer A. Hysteresis gives a comparator separate switching thresholds, so noise near the threshold cannot cause unstable output.
What happens when the level of a comparator’s input signal crosses the threshold voltage?
Answer B. When the input crosses the threshold voltage, the comparator changes output state.
What is tri-state logic?
Answer A. Tri-state logic outputs can be 0, 1 or high-impedance (effectively disconnected), so many devices can share a bus.
Which of the following is an advantage of BiCMOS logic?
Answer C. BiCMOS combines CMOS's high input impedance with bipolar transistors' low output impedance.
Which of the following digital logic families has the lowest power consumption?
Answer D. CMOS has the lowest power consumption of these logic families.
Why do CMOS digital integrated circuits have high immunity to noise on the input signal or power supply?
Answer C. CMOS switches at about half the supply voltage, giving a large margin against noise.
What best describes a pull-up or pull-down resistor?
Answer B. A pull-up or pull-down resistor connects to the positive or negative supply to set a defined voltage when an input or output is otherwise open.
In Figure E6-3, which is the schematic symbol for a NAND gate?
Answer B. In figure E6-3, symbol 2 is a NAND gate: an AND gate shape with a small circle (inversion) at the output.
What is used to design the configuration of a field-programmable gate array (FPGA)?
Answer B. FPGAs are configured with a hardware description language (HDL) such as VHDL or Verilog.
In Figure E6-3, which is the schematic symbol for a NOR gate?
Answer D. In figure E6-3, symbol 4 is a NOR gate: an OR gate shape with a circle at the output.
In Figure E6-3, which is the schematic symbol for the NOT operation (inversion)?
Answer C. In figure E6-3, symbol 5 is the NOT gate (inverter): a triangle with a circle at the output.
What is piezoelectricity?
Answer C. Piezoelectric materials generate a voltage when stressed and flex when a voltage is applied. Quartz crystals use this effect.
What is the equivalent circuit of a quartz crystal?
Answer A. A crystal's equivalent circuit is a series RLC in parallel with a shunt capacitance from the electrodes and stray capacitance.
Which of the following is an aspect of the piezoelectric effect?
Answer A. Mechanical deformation when a voltage is applied is part of the piezoelectric effect.
Why are cores of inductors and transformers sometimes constructed of thin layers?
Answer B. Thin insulated layers (laminations) break up eddy currents in the core, reducing power loss.
How do ferrite and powdered iron compare for use in an inductor core?
Answer C. Ferrite cores usually have higher permeability, so fewer turns are needed for a given inductance.
What core material property determines the inductance of an inductor?
Answer D. A core's permeability determines how much it increases inductance.
Which of the following materials has the highest temperature stability of its magnetic characteristics?
Answer B. Powdered iron has better temperature stability of its magnetic properties than ferrite.
What devices are commonly used as VHF and UHF parasitic suppressors at the input and output terminals of a transistor HF amplifier?
Answer C. Ferrite beads on transistor amplifier terminals suppress VHF and UHF parasitic oscillations.
What is a primary advantage of using a toroidal core instead of a solenoidal core in an inductor?
Answer A. A toroidal core keeps most of the magnetic field inside the core, reducing coupling to nearby components.
Which type of core material decreases inductance when inserted into a coil?
Answer B. A brass core reduces inductance. Eddy currents in the nonmagnetic conductor oppose the coil's field.
What causes inductor saturation?
Answer C. Saturation happens when the core is driven with excessive magnetic flux and cannot magnetize further.
Why is gallium arsenide (GaAs) useful for semiconductor devices operating at UHF and higher frequencies?
Answer B. GaAs has higher electron mobility than silicon, which suits UHF and microwave devices.
Which of the following device packages is a through-hole type?
Answer A. DIP (dual in-line package) is a through-hole package. The others are surface-mount types.
Which of the following materials supports the highest frequency of operation when used in MMICs?
Answer D. Gallium nitride supports the highest operating frequencies of these MMIC materials.
Which is the most common input and output impedance of MMICs?
Answer A. MMICs most commonly have 50-ohm input and output impedances.
Which of the following noise figure values is typical of a low-noise UHF preamplifier?
Answer A. A good low-noise UHF preamp has a noise figure around 0.5 dB.
What characteristics of MMICs make them a popular choice for VHF through microwave circuits?
Answer D. MMICs offer controlled gain, low noise figure, and constant input and output impedance over their frequency range.
What type of transmission line is often used for connections to MMICs?
Answer D. MMICs are usually connected with microstrip transmission lines on the circuit board.
How is power supplied to the most common type of MMIC?
Answer C. Common MMICs get power through a resistor and/or RF choke connected to the output lead.
Which of the following component package types have the least parasitic effects at frequencies above the HF range?
Answer D. Surface-mount packages have the least parasitic effects above HF, because their leads are very short.
What advantage does surface-mount technology offer at RF compared to using through-hole components?
Answer D. Surface-mount parts give smaller circuit area, shorter traces, and less parasitic inductance and capacitance.
What is a characteristic of DIP packaging used for integrated circuits?
Answer D. DIP means dual in-line package: two rows of pins on opposite sides.
Why are DIP through-hole package ICs not typically used at UHF and higher frequencies?
Answer C. DIP leads are too long for UHF and higher, adding parasitic inductance.
What absorbs the energy from light falling on a photovoltaic cell?
Answer C. In a photovoltaic cell, electrons absorb the energy of incoming light.
What happens to photoconductive material when light shines on it?
Answer A. Light lowers the resistance of photoconductive material.
What is the most common configuration of an optoisolator or optocoupler?
Answer D. An optoisolator is most commonly an LED and a phototransistor in one package.
What is the photovoltaic effect?
Answer B. The photovoltaic effect is the conversion of light into electrical energy.
Which of the following describes an optical shaft encoder?
Answer A. An optical shaft encoder detects rotation by a patterned wheel interrupting a light beam. It is common in radio tuning knobs.
Which of these materials is most commonly used to create photoconductive devices?
Answer C. Photoconductive devices are usually made from crystalline semiconductor material.
What is a solid-state relay?
Answer B. A solid-state relay uses semiconductors to do the job of an electromechanical relay.
Why are optoisolators often used in conjunction with solid-state circuits that control 120 VAC circuits?
Answer C. Optoisolators electrically isolate a control circuit from the 120 VAC circuit being switched.
What is the efficiency of a photovoltaic cell?
Answer D. Photovoltaic efficiency is the fraction of light energy converted into electrical energy.
What is the most common material used in power-generating photovoltaic cells?
Answer B. Silicon is the most common material for power-generating solar cells.
What is the approximate open-circuit voltage produced by a fully illuminated silicon photovoltaic cell?
Answer A. A fully illuminated silicon cell produces about 0.5 volts open-circuit.
8 exam questions from this subelement. Practice E7 · Study notes
Which circuit is bistable?
Answer C. A flip-flop is bistable: it stays in either of two states until triggered.
What is the function of a decade counter?
Answer A. A decade counter outputs one pulse for every 10 input pulses.
Which of the following can divide the frequency of a pulse train by 2?
Answer B. A flip-flop changes state every other input pulse, dividing the frequency by 2.
How many flip-flops are required to divide a signal frequency by 16?
Answer A. Each flip-flop divides by 2, and 2⁴ = 16, so four flip-flops are needed.
Which of the following circuits continuously alternates between two states without an external clock signal?
Answer D. An astable multivibrator continuously alternates between two states on its own.
What is a characteristic of a monostable multivibrator?
Answer A. A monostable multivibrator switches to its alternate state for a set time when triggered, then returns.
What logical operation does a NAND gate perform?
Answer D. A NAND gate outputs 0 only when all inputs are 1. Otherwise it outputs 1.
What logical operation does an OR gate perform?
Answer A. An OR gate outputs 1 if any input is 1.
What logical operation is performed by a two-input exclusive NOR gate?
Answer C. An exclusive NOR (XNOR) outputs 0 when exactly one input is 1, and 1 when the inputs match.
What is a truth table?
Answer B. A truth table lists every input combination and the corresponding output of a digital device.
What does “positive logic” mean in reference to logic devices?
Answer B. In positive logic, a high voltage represents 1 and a low voltage represents 0.
For what portion of the signal cycle does each active element in a push-pull, Class AB amplifier conduct?
Answer A. In Class AB push-pull, each device conducts for more than 180 but less than 360 degrees.
What is a Class D amplifier?
Answer A. A Class D amplifier uses switching techniques for high efficiency.
What circuit is required at the output of an RF switching amplifier?
Answer A. A switching amplifier's output is rich in harmonics, so a filter is required to remove them.
What is the operating point of a Class A common emitter amplifier?
Answer A. A Class A amplifier is biased about halfway between saturation and cutoff.
What can be done to prevent unwanted oscillations in an RF power amplifier?
Answer C. Parasitic suppressors and neutralization prevent unwanted oscillations in RF power amplifiers.
What is a characteristic of a grounded-grid amplifier?
Answer B. A grounded-grid amplifier has low input impedance.
Which of the following is the likely result of using a Class C amplifier to amplify a single-sideband phone signal?
Answer D. Class C is non-linear, so amplifying SSB with it causes distortion and excessive bandwidth.
Why are switching amplifiers more efficient than linear amplifiers?
Answer B. Switching devices spend most of their time fully on (saturated) or fully off (cutoff), where little power is lost.
What is characteristic of an emitter follower (or common collector) amplifier?
Answer D. An emitter follower's output is in phase with its input, with voltage gain slightly below 1.
In Figure E7-1, what is the purpose of R1 and R2?
Answer B. In figure E7-1, R1 and R2 form a voltage divider that sets the transistor's base bias.
In Figure E7-1, what is the purpose of R3?
Answer D. In figure E7-1, R3 in the emitter provides self bias, stabilizing the operating point.
What type of amplifier circuit is shown in Figure E7-1?
Answer C. Figure E7-1 shows a common emitter amplifier: input at the base, output at the collector.
How are the capacitors and inductors of a low-pass filter Pi-network arranged between the network’s input and output?
Answer D. A low-pass pi-network has a capacitor from input to ground, a capacitor from output to ground, and an inductor between input and output.
What is the frequency response of a T-network with series capacitors and a shunt inductor?
Answer B. Series capacitors pass high frequencies and a shunt inductor shorts low frequencies to ground, giving a high-pass response.
What is the purpose of adding an inductor to a Pi-network to create a Pi-L-network?
Answer A. Adding an output inductor to make a pi-L network improves harmonic suppression.
How does an impedance-matching circuit transform a complex impedance to a resistive impedance?
Answer C. A matching network cancels the reactive part of the load and transforms the resistive part to the desired value.
Which filter type has ripple in the passband and a sharp cutoff?
Answer D. A Chebyshev filter has ripple in the passband in exchange for a sharp cutoff.
What are the characteristics of an elliptical filter?
Answer C. An elliptical filter has an extremely sharp cutoff, with one or more notches in the stop band.
Which describes a Pi-L network?
Answer B. A pi-L network is a pi-network with an additional series inductor at the output.
Which of the following is most frequently used as a band-pass or notch filter in VHF and UHF transceivers?
Answer B. Helical filters are common band-pass or notch filters in VHF and UHF transceivers.
What is a crystal lattice filter?
Answer D. A crystal lattice filter uses quartz crystals for very selective filtering of low-level signals, such as in IF stages.
Which of the following filters is used in a 2-meter band repeater duplexer?
Answer B. Repeater duplexers use high-Q cavity filters to isolate the transmitter from the receiver.
Which of the following measures a filter’s ability to reject signals in adjacent channels?
Answer C. Shape factor (the ratio of bandwidths at two attenuation levels) measures how well a filter rejects adjacent signals.
How does a linear electronic voltage regulator work?
Answer D. A linear regulator varies the conduction of a control element to keep the output voltage constant.
How does a switchmode voltage regulator work?
Answer B. A switchmode regulator varies the duty cycle of pulses fed to a filter to set the output voltage.
What device is used as a stable voltage reference?
Answer A. A Zener diode is a common stable voltage reference.
Which of the following describes a three-terminal voltage regulator?
Answer B. A three-terminal regulator (such as the 78xx series) is a series regulator.
Which of the following types of linear voltage regulator operates by loading the unregulated voltage source?
Answer D. A shunt regulator works by loading the source, diverting current to hold the voltage steady.
What is the purpose of Q1 in the circuit shown in Figure E7-2?
Answer C. In figure E7-2, Q1 is the pass transistor: it controls the current to keep the output voltage constant.
What is the purpose of C2 in the circuit shown in Figure E7-2?
Answer A. In figure E7-2, C2 bypasses rectifier ripple around the Zener reference D1.
What type of circuit is shown in Figure E7-2?
Answer C. Figure E7-2 is a linear voltage regulator.
How is battery operating time calculated?
Answer C. Battery operating time = capacity in amp-hours divided by average current.
Why is a switching type power supply less expensive and lighter than an equivalent linear power supply?
Answer C. Switching supplies run at high frequency, so they need much smaller, lighter transformers and filter parts.
What is the purpose of an inverter connected to a solar panel output?
Answer D. An inverter converts the solar panel's DC output to AC.
What is the dropout voltage of a linear voltage regulator?
Answer C. Dropout voltage is the minimum input-to-output voltage difference needed to stay in regulation.
Which of the following calculates power dissipated by a series linear voltage regulator?
Answer C. A series regulator dissipates (input voltage - output voltage) x output current.
What is the purpose of connecting equal-value resistors across power supply filter capacitors connected in series?
Answer D. Equal resistors across series filter capacitors equalize their voltages, discharge them when power is removed, and give a minimum load. All three.
What is the purpose of a step-start circuit in a high-voltage power supply?
Answer D. A step-start circuit limits inrush current so filter capacitors charge gradually.
Which of the following can be used to generate FM phone signals?
Answer B. FM can be generated by reactance modulation of an oscillator.
What is the function of a reactance modulator?
Answer D. A reactance modulator varies capacitance (or inductance) to produce PM or FM.
What is a frequency discriminator?
Answer D. A frequency discriminator detects (demodulates) FM signals.
What is one way to produce a single-sideband phone signal?
Answer A. SSB can be made with a balanced modulator (producing DSB) followed by a filter that removes one sideband.
What is added to an FM speech channel to boost the higher audio frequencies?
Answer D. Pre-emphasis boosts the higher audio frequencies before FM transmission.
Why is de-emphasis used in FM communications receivers?
Answer A. Phase modulation boosts high audio frequencies, like FM with pre-emphasis. De-emphasis in the receiver restores a flat response, keeping FM receivers compatible with PM transmitters.
What is meant by the term “baseband” in radio communications?
Answer B. Baseband is the frequency range of the message signal before modulation.
What are the principal frequencies that appear at the output of a mixer?
Answer C. A mixer's output contains the two input frequencies plus their sum and difference.
What occurs when the input signal levels to a mixer are too high?
Answer A. Overdriving a mixer generates spurious mixer products.
How does a diode envelope detector function?
Answer A. An envelope detector rectifies the RF signal and filters out the RF, leaving the audio envelope.
Which type of detector is used for demodulating SSB signals?
Answer C. SSB signals are demodulated with a product detector.
What is meant by “direct sampling” in software defined radios?
Answer C. Direct sampling digitizes the incoming RF directly with an ADC, without mixing it with a local oscillator.
What kind of digital signal processing audio filter is used to remove unwanted noise from a received SSB signal?
Answer A. An adaptive filter is used to remove noise from received SSB audio.
What type of digital signal processing filter is used to generate an SSB signal?
Answer C. A Hilbert-transform filter creates the 90-degree phase shift used to generate SSB digitally.
Which method generates an SSB signal using digital signal processing?
Answer D. DSP generates SSB by combining signals in a quadrature (90-degree) phase relationship.
How frequently must an analog signal be sampled to be accurately reproduced?
Answer B. By the Nyquist criterion, sample at least twice the highest frequency in the signal.
What is the minimum number of bits required to sample a signal with a range of 1 volt at a resolution of 1 millivolt?
Answer D. 1 V / 1 mV = 1000 levels. 2¹⁰ = 1024, so at least 10 bits are needed.
What function is performed by a Fast Fourier Transform?
Answer C. A Fast Fourier Transform converts signals from the time domain to the frequency domain.
What is the function of decimation?
Answer B. Decimation reduces the effective sample rate by removing samples.
Why is an anti-aliasing filter required in a decimator?
Answer A. Without an anti-aliasing filter, high-frequency components would alias into false lower-frequency signals after decimation.
What aspect of receiver analog-to-digital conversion determines the maximum receive bandwidth of a direct-sampling software defined radio (SDR)?
Answer A. A direct-sampling SDR's maximum receive bandwidth is set by its ADC sample rate.
What sets the minimum detectable signal level for a direct-sampling software defined receiver in the absence of atmospheric or thermal noise?
Answer B. Without external noise, the minimum detectable signal depends on the ADC's reference voltage and its number of bits.
Which of the following is generally true of Finite Impulse Response (FIR) filters?
Answer A. FIR filters can delay all frequency components equally (linear phase), avoiding phase distortion.
What is the function of taps in a digital signal processing filter?
Answer D. Taps provide incremental signal delays used by the filter algorithm.
Which of the following would allow a digital signal processing filter to create a sharper filter response?
Answer B. More taps give a DSP filter a sharper response.
What is the typical output impedance of an op-amp?
Answer A. An op-amp has very low output impedance.
What is the frequency response of the circuit in E7-3 if a capacitor is added across the feedback resistor?
Answer B. A capacitor across the feedback resistor lowers the gain at high frequencies, making a low-pass filter.
What is the typical input impedance of an op-amp?
Answer D. An op-amp has very high input impedance.
What is meant by the term “op-amp input offset voltage”?
Answer C. Input offset voltage is the differential input voltage needed to bring the open-loop output to zero.
How can unwanted ringing and audio instability be prevented in an op-amp audio filter?
Answer A. Limiting both gain and Q prevents ringing and instability in op-amp audio filters.
What is the gain-bandwidth of an operational amplifier?
Answer B. Gain-bandwidth is the frequency at which the op-amp's open-loop gain falls to one.
What voltage gain can be expected from the circuit in Figure E73 when R1 is 10 ohms and RF is 470 ohms?
Answer C. Inverting gain = RF / R1 = 470 / 10 = 47.
How does the gain of an ideal operational amplifier vary with frequency?
Answer D. An ideal op-amp's gain does not vary with frequency.
What will be the output voltage of the circuit shown in Figure E7-3 if R1 is 1,000 ohms, RF is 10,000 ohms, and 0.23 volts DC is applied to the input?
Answer D. Gain = -RF / R1 = -10,000 / 1,000 = -10, so the output is -10 x 0.23 V = -2.3 V. The inverting amplifier reverses the sign.
What absolute voltage gain can be expected from the circuit in Figure E7-3 when R1 is 1,800 ohms and RF is 68 kilohms?
Answer C. Gain = RF / R1 = 68,000 / 1,800, about 38.
What absolute voltage gain can be expected from the circuit in Figure E7-3 when R1 is 3,300 ohms and RF is 47 kilohms?
Answer B. Gain = RF / R1 = 47,000 / 3,300, about 14.
What is an operational amplifier?
Answer A. An op-amp is a high-gain, direct-coupled differential amplifier with very high input impedance and very low output impedance.
What are three common oscillator circuits?
Answer D. Colpitts, Hartley and Pierce are three common oscillator circuits.
What is a microphonic?
Answer C. Microphonics are changes in oscillator frequency caused by mechanical vibration.
What is a phase-locked loop?
Answer C. A PLL is a servo loop with a phase detector, a low-pass filter, a VCO and a stable reference oscillator.
How is positive feedback supplied in a Colpitts oscillator?
Answer C. A Colpitts oscillator gets its feedback through a capacitive divider.
How is positive feedback supplied in a Pierce oscillator?
Answer D. A Pierce oscillator gets its feedback through a quartz crystal.
Which of these functions can be performed by a phase-locked loop?
Answer B. A PLL can perform frequency synthesis and FM demodulation.
How can an oscillator’s microphonic responses be reduced?
Answer D. Mechanically isolating the oscillator from its enclosure reduces microphonics.
Which of the following components can be used to reduce thermal drift in crystal oscillators?
Answer A. NP0 (C0G) capacitors have nearly zero temperature coefficient, reducing thermal drift.
What type of frequency synthesizer circuit uses a phase accumulator, lookup table, digital-to-analog converter, and a low-pass anti-alias filter?
Answer A. A DDS uses a phase accumulator, a lookup table, a DAC and an anti-alias low-pass filter.
What information is contained in the lookup table of a direct digital synthesizer (DDS)?
Answer B. A DDS lookup table holds amplitude values for the desired waveform, such as a sine wave.
What are the major spectral impurity components of direct digital synthesizers?
Answer C. DDS outputs mainly contain spurious signals at discrete frequencies.
Which of the following ensures that a crystal oscillator operates on the frequency specified by the crystal manufacturer?
Answer B. A crystal oscillates at its specified frequency only when given the specified parallel (load) capacitance.
Which of the following is a technique for providing highly accurate and stable oscillators needed for microwave transmission and reception?
Answer D. GPS references, rubidium standards and temperature-controlled dielectric resonators all provide highly stable microwave oscillators.
4 exam questions from this subelement. Practice E8 · Study notes
What technique shows that a square wave is made up of a sine wave and its odd harmonics?
Answer A. Fourier analysis shows that a square wave is a sine wave plus its odd harmonics.
Which of the following is a type of analog-to-digital conversion?
Answer A. Successive approximation is a common type of analog-to-digital conversion.
Which of the following describes a signal in the time domain?
Answer B. A time-domain signal shows amplitude at different times, as on an oscilloscope.
What is “dither” with respect to analog-to-digital converters?
Answer B. Dither is a small amount of noise added to the ADC input to reduce quantization noise and distortion.
What is the benefit of making voltage measurements with a true-RMS calculating meter?
Answer D. A true-RMS meter gives correct RMS readings for both sine waves and non-sinusoidal signals.
What is the approximate ratio of PEP-to-average power in an unprocessed single-sideband phone signal?
Answer A. Unprocessed SSB voice has a PEP-to-average power ratio of about 2.5 to 1.
What determines the PEP-to-average power ratio of an unprocessed single-sideband phone signal?
Answer B. The PEP-to-average ratio of unprocessed SSB depends on the characteristics of the speech.
Why are direct or flash conversion analog-to-digital converters used for a software defined radio?
Answer C. Direct (flash) ADCs are very fast, so they can digitize high frequencies in SDRs.
How many different input levels can be encoded by an analog-to-digital converter with 8-bit resolution?
Answer D. 8 bits can represent 2⁸ = 256 different levels.
What is the purpose of a low-pass filter used at the output of a digital-to-analog converter?
Answer C. A low-pass filter after a DAC removes spurious sampling artifacts from the output.
Which of the following is a measure of the quality of an analog-to-digital converter?
Answer A. Total harmonic distortion is one measure of ADC quality.
What is the modulation index of an FM signal?
Answer A. FM modulation index = frequency deviation divided by modulating frequency.
How does the modulation index of a phase-modulated emission vary with RF carrier frequency?
Answer D. PM modulation index does not depend on the RF carrier frequency.
What is the modulation index of an FM phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency if the highest modulating frequency is 1000 Hz?
Answer A. Modulation index = 3000 Hz / 1000 Hz = 3.
What is the modulation index of an FM phone signal having a maximum carrier deviation of plus or minus 6 kHz if the highest modulating frequency is 2 kHz?
Answer B. Modulation index = 6 kHz / 2 kHz = 3.
What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 5 kHz if the highest modulation frequency is 3 kHz?
Answer D. Deviation ratio = maximum deviation / highest modulating frequency = 5 / 3, about 1.67.
What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 7.5 kHz if the highest modulation frequency is 3.5 kHz?
Answer A. Deviation ratio = 7.5 / 3.5, about 2.14.
Orthogonal frequency-division multiplexing (OFDM) is a technique used for which types of amateur communication?
Answer A. OFDM is used for digital modes.
What describes orthogonal frequency-division multiplexing (OFDM)?
Answer D. OFDM is a digital technique using many subcarriers whose frequencies are chosen to avoid intersymbol interference.
What is deviation ratio?
Answer B. Deviation ratio is maximum carrier deviation divided by the highest audio modulating frequency.
What is frequency division multiplexing (FDM)?
Answer B. FDM divides the signal into separate frequency bands, each carrying its own data stream.
What is digital time division multiplexing?
Answer B. Time division multiplexing gives each signal its own time slots in the transmission.
What is Quadrature Amplitude Modulation or QAM?
Answer B. QAM modulates the amplitude of two same-frequency carriers that are 90 degrees apart.
What is the definition of symbol rate in a digital transmission?
Answer C. Symbol rate is the rate at which the waveform changes to convey information.
Why should the phase of a PSK signal be changed at the zero crossing of the RF signal?
Answer A. Changing PSK phase at the RF zero crossing avoids abrupt jumps, minimizing bandwidth.
What technique minimizes the bandwidth of a PSK31 signal?
Answer C. PSK31 uses sinusoidally shaped data pulses to minimize bandwidth.
What is the approximate bandwidth of a 13-WPM International Morse Code transmission?
Answer C. CW bandwidth is roughly 4 x WPM: 4 x 13, about 52 Hz.
What is the bandwidth of an FT8 signal?
Answer B. An FT8 signal is about 50 Hz wide.
What is the bandwidth of a 4,800-Hz frequency shift, 9,600-baud ASCII FM transmission?
Answer A. Bandwidth = baud rate + 1.2 x shift = 9,600 + (1.2 x 4,800) = 15,360 Hz, or 15.36 kHz.
How does ARQ accomplish error correction?
Answer D. ARQ detects errors and requests retransmission of the bad data.
Which digital code allows only one bit to change between sequential code values?
Answer D. In Gray code, only one bit changes between consecutive values.
How can data rate be increased without increasing bandwidth?
Answer C. A more efficient digital code can carry more data in the same bandwidth.
What is the relationship between symbol rate and baud?
Answer A. Baud is the symbol rate. They are the same thing.
What factors affect the bandwidth of a transmitted CW signal?
Answer C. CW bandwidth depends on keying speed and the rise and fall times (shape) of the keying.
What is described by the constellation diagram of a QAM or QPSK signal?
Answer B. A constellation diagram shows the possible phase and amplitude states for each symbol.
What type of addresses do nodes have in a mesh network?
Answer C. Mesh network nodes have Internet Protocol (IP) addresses.
What technique do individual nodes use to form a mesh network?
Answer C. Mesh nodes use discovery and link establishment protocols to find each other and form the network.
Why are received spread spectrum signals resistant to interference?
Answer A. A spread spectrum receiver uses the same spreading algorithm, so signals not using it are suppressed.
What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?
Answer B. Direct sequence spread spectrum uses a high-speed bit stream to shift the carrier's phase.
Which describes spread spectrum frequency hopping?
Answer D. Frequency hopping rapidly changes the transmit frequency in a pseudorandom sequence.
What is the primary effect of extremely short rise or fall time on a CW signal?
Answer C. Very short rise and fall times on CW create key clicks.
What is the most common method of reducing key clicks?
Answer A. Lengthening the rise and fall times of the keying waveform reduces key clicks.
What is the advantage of including parity bits in ASCII characters?
Answer D. Parity bits allow some types of errors to be detected.
What is a common cause of overmodulation of AFSK signals?
Answer D. Excessive transmit audio level is a common cause of AFSK overmodulation.
What parameter evaluates distortion of an AFSK signal caused by excessive input audio levels?
Answer D. IMD (intermodulation distortion) measures AFSK distortion from excessive audio levels.
What is considered an acceptable maximum IMD level for an idling PSK signal?
Answer D. An idling PSK signal should have IMD of -30 dB or better.
What are some of the differences between the Baudot digital code and ASCII?
Answer B. Baudot uses 5 data bits and two shift codes (letters and figures). ASCII uses 7 or 8 bits and needs no shift codes.
What is one advantage of using ASCII code for data communications?
Answer C. ASCII can send both uppercase and lowercase text.
8 exam questions from this subelement. Practice E9 · Study notes
What is an isotropic radiator?
Answer C. An isotropic radiator is a hypothetical, lossless antenna radiating equally in all directions. It is the reference for dBi.
What is the effective radiated power (ERP) of a repeater station with 150 watts transmitter power output, 2 dB feed line loss, 2.2 dB duplexer loss, and 7 dBd antenna gain?
Answer D. Net gain = 7 - 2 - 2.2 = +2.8 dB. ERP = 150 W x 10^0.28, about 286 watts.
What term describing total radiated power takes into account all gains and losses?
Answer C. Effective radiated power accounts for transmitter power and all gains and losses.
Which of the following factors affect the feed point impedance of an antenna?
Answer B. Antenna height affects feed point impedance through interaction with the ground.
What does the term “ground gain” mean?
Answer D. Ground gain is the increase in signal strength from ground reflections around the antenna.
What is the effective radiated power (ERP) of a repeater station with 200 watts transmitter power output, 4 dB feed line loss, 3.2 dB duplexer loss, 0.8 dB circulator loss, and 10 dBd antenna gain?
Answer A. Net gain = 10 - 4 - 3.2 - 0.8 = +2 dB. ERP = 200 W x 10^0.2, about 317 watts.
What is the effective isotropic radiated power (EIRP) of a repeater station with 200 watts transmitter power output, 2 dB feed line loss, 2.8 dB duplexer loss, 1.2 dB circulator loss, and 7 dBi antenna gain?
Answer B. Net gain = 7 - 2 - 2.8 - 1.2 = +1 dB. EIRP = 200 W x 10^0.1, about 252 watts.
Which frequency band has the smallest first Fresnel zone?
Answer A. Fresnel zone size shrinks as frequency rises, so 5.8 GHz has the smallest first Fresnel zone.
What is antenna efficiency?
Answer B. Antenna efficiency = radiation resistance / total resistance.
Which of the following improves the efficiency of a ground-mounted quarter-wave vertical antenna?
Answer A. A ground radial system reduces ground losses and improves a ground-mounted vertical's efficiency.
Which of the following determines ground losses for a ground-mounted vertical antenna operating on HF?
Answer C. Soil conductivity determines the ground losses of an HF vertical.
How much gain does an antenna have compared to a half-wavelength dipole if it has 6 dB gain over an isotropic radiator?
Answer A. dBd = dBi - 2.15, so 6 dBi - 2.15 = 3.85 dBd.
What is the 3 dB beamwidth of the antenna radiation pattern shown in Figure E9-1?
Answer B. In figure E9-1, the main lobe falls 3 dB from its peak at points about 50 degrees apart.
What is the front-to-back ratio of the antenna radiation pattern shown in Figure E9-1?
Answer D. In figure E9-1, the back lobe is about 18 dB below the main lobe.
What is the front-to-side ratio of the antenna radiation pattern shown in Figure E9-1?
Answer D. In figure E9-1, the side response is about 14 dB below the main lobe.
What is the front-to-back ratio of the radiation pattern shown in Figure E92?
Answer B. In figure E9-2, the rearward lobe is about 28 dB below the forward peak.
What type of antenna pattern is shown in Figure E9-2?
Answer A. Figure E9-2 is an elevation pattern: radiation plotted against vertical angle.
What is the elevation angle of peak response in the antenna radiation pattern shown in Figure E9-2?
Answer C. In figure E9-2, peak radiation is at about 7.5 degrees elevation.
What is the difference in radiated power between a lossless antenna with gain and an isotropic radiator driven by the same power?
Answer C. A lossless antenna with gain radiates the same total power as an isotropic radiator. It only concentrates it in certain directions.
What is the far field of an antenna?
Answer D. The far field is the region where the pattern's shape no longer changes with distance.
What type of analysis is commonly used for modeling antennas?
Answer B. Antenna modeling software (such as NEC) commonly uses the Method of Moments.
What is the principle of a Method of Moments analysis?
Answer A. Method of Moments models a wire as a series of segments, each with a uniform current.
What is a disadvantage of decreasing the number of wire segments in an antenna model below 10 segments per half-wavelength?
Answer C. Too few segments (under about 10 per half wavelength) can make the computed feed point impedance incorrect.
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?
Answer D. Two verticals 1/2 wavelength apart fed 180 degrees out of phase give a figure-eight pattern along the axis of the array (end-fire).
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?
Answer A. Two verticals 1/4 wavelength apart fed 90 degrees out of phase give a cardioid pattern.
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase?
Answer C. Two verticals 1/2 wavelength apart fed in phase give a figure-eight broadside to the array.
What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased?
Answer B. As a long wire gets longer, more lobes form and the major lobes align more closely with the wire's axis.
What is the purpose of feeding an off-center-fed dipole (OCFD) between the center and one end instead of at the midpoint?
Answer A. Feeding a dipole off-center gives a similar feed point impedance on several bands.
What is the effect of adding a terminating resistor to a rhombic or long-wire antenna?
Answer B. A terminating resistor absorbs the reflected wave, making a rhombic or long wire unidirectional.
What is the approximate feed point impedance at the center of a two-wire half-wave folded dipole antenna?
Answer A. A two-wire half-wave folded dipole has a feed point impedance of about 300 ohms.
What is a folded dipole antenna?
Answer C. A folded dipole is a half-wave dipole with an additional parallel wire connecting its two ends.
Which of the following describes a G5RV antenna?
Answer A. A G5RV is a wire antenna center-fed through a specific length of open-wire line, then a balun and coax.
Which of the following describes a Zepp antenna?
Answer B. A Zepp is an end-fed half-wave dipole.
How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil?
Answer D. Seawater is an excellent ground, so a vertical over seawater radiates more at low angles.
Which of the following describes an extended double Zepp antenna?
Answer C. An extended double Zepp is a center-fed dipole about 1.25 wavelengths long.
How does the radiation pattern of a horizontally polarized antenna vary with increasing height above ground?
Answer B. Raising a horizontal antenna lowers the takeoff angle of its lowest elevation lobe.
How does the radiation pattern of a horizontally-polarized antenna mounted above a long slope compare with the same antenna mounted above flat ground?
Answer B. Over a downward slope, the main lobe takeoff angle decreases in the downhill direction.
How much does the gain of an ideal parabolic reflector antenna increase when the operating frequency is doubled?
Answer D. Doubling frequency makes a dish four times larger in wavelengths, so gain rises 6 dB.
How can two linearly polarized Yagi antennas be used to produce circular polarization?
Answer C. Two Yagis on the same boom at right angles to each other, driven elements at the same point, fed 90 degrees out of phase, give circular polarization.
What is the most efficient location for a loading coil on an electrically short whip?
Answer A. A loading coil near the center of a short whip is the most efficient location.
Why should antenna loading coils have a high ratio of reactance to resistance?
Answer C. Loading coils need a high reactance-to-resistance ratio (high Q) to minimize loss and maximize efficiency.
Approximately how long is a Yagi’s driven element?
Answer D. A Yagi's driven element is about 1/2 wavelength long.
What happens to SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna?
Answer B. Loading coils on a short antenna reduce its SWR bandwidth.
What is an advantage of top loading an electrically short HF vertical antenna?
Answer D. Top loading increases current in the vertical section, improving radiation efficiency.
What happens as the Q of an antenna increases?
Answer B. Higher antenna Q means narrower SWR bandwidth.
What is the function of a loading coil in an electrically short antenna?
Answer D. A loading coil cancels a short antenna's capacitive reactance to make it resonant.
How does radiation resistance of a base-fed whip antenna change below its resonant frequency?
Answer B. Below its resonant frequency, a whip is electrically shorter, so its radiation resistance decreases.
Why do most two-element Yagis with normal spacing have a reflector instead of a director?
Answer D. With normal spacing, a driven element plus a reflector gives higher gain than one plus a director.
What is the purpose of making a Yagi’s parasitic elements either longer or shorter than resonance?
Answer C. Making parasitic elements longer or shorter than resonance controls their phase shift, which creates directivity.
Which matching system for Yagi antennas requires the driven element to be insulated from the boom?
Answer B. The beta (hairpin) match requires the driven element to be split and insulated from the boom.
What antenna matching system matches coaxial cable to an antenna by connecting the shield to the center of the antenna and the conductor a fraction of a wavelength to one side?
Answer A. In a gamma match, the shield goes to the element's center and the center conductor to a point partway out on one side.
What matching system uses a short length of transmission line connected in parallel with the feed line at or near the feed point?
Answer D. A stub match uses a short piece of transmission line in parallel with the feed line near the feed point.
What is the purpose of the series capacitor in a gamma match?
Answer B. The series capacitor in a gamma match cancels the gamma rod's inductive reactance.
What Yagi driven element feed point impedance is required to use a beta or hairpin matching system?
Answer A. A hairpin match needs a capacitive driven element, electrically shorter than 1/2 wavelength.
Which of these transmission line impedances would be suitable for constructing a quarter-wave Q-section for matching a 100-ohm feed point impedance to a 50-ohm transmission line?
Answer C. A quarter-wave Q-section needs Z = √(100 x 50), about 71 ohms, so 75-ohm line is suitable.
What parameter describes the interaction of a load and transmission line?
Answer B. The reflection coefficient describes how a load interacts with a transmission line.
What is a use for a Wilkinson divider?
Answer C. A Wilkinson divider splits power equally between two 50-ohm loads while keeping a 50-ohm input.
Which of the following is used to shunt feed a grounded tower at its base?
Answer C. A gamma match can shunt-feed a grounded tower at its base.
What is the purpose of using multiple driven elements connected through phasing lines?
Answer A. Multiple driven elements connected through phasing lines control the antenna's radiation pattern.
What is the velocity factor of a transmission line?
Answer D. Velocity factor = wave velocity in the line divided by the speed of light in a vacuum.
Which of the following has the biggest effect on the velocity factor of a transmission line?
Answer C. The dielectric (insulating) material has the biggest effect on velocity factor.
Why is the electrical length of a coaxial cable longer than its physical length?
Answer D. Waves travel slower in coax than in air, so a cable's electrical length is longer than its physical length.
What impedance does a 1/2-wavelength transmission line present to an RF generator when the line is shorted at the far end?
Answer B. A half-wave line repeats its load impedance, so a shorted far end looks like a very low impedance.
What is microstrip?
Answer D. Microstrip is precision circuit board conductors over a ground plane, giving constant-impedance connections at microwave frequencies.
What is the approximate physical length of an air-insulated, parallel conductor transmission line that is electrically 1/2 wavelength long at 14.10 MHz?
Answer C. Air line has a velocity factor of about 1. Half wavelength = 300 / 14.10 / 2, about 10.6 meters.
How does parallel conductor transmission line compare to coaxial cable with a plastic dielectric?
Answer A. Parallel-conductor line has lower loss than plastic-dielectric coax.
Which of the following is a significant difference between foam dielectric coaxial cable and solid dielectric coaxial cable, assuming all other parameters are the same?
Answer D. Compared with solid dielectric, foam coax has a lower voltage rating, lower loss and higher velocity factor.
What impedance does a 1/4-wavelength transmission line present to an RF generator when the line is shorted at the far end?
Answer A. A quarter-wave line inverts impedance, so a short at the far end looks like a very high impedance.
What impedance does a 1/8-wavelength transmission line present to an RF generator when the line is shorted at the far end?
Answer C. A shorted line less than 1/4 wavelength long (such as 1/8) looks like an inductive reactance.
What impedance does a 1/8-wavelength transmission line present to an RF generator when the line is open at the far end?
Answer C. An open line less than 1/4 wavelength long (such as 1/8) looks like a capacitive reactance.
What impedance does a 1/4-wavelength transmission line present to an RF generator when the line is open at the far end?
Answer D. A quarter-wave line inverts impedance, so an open far end looks like a very low impedance.
Which of the following can be calculated using a Smith chart?
Answer A. A Smith chart can be used to calculate impedance along transmission lines.
What type of coordinate system is used in a Smith chart?
Answer B. A Smith chart uses resistance circles and reactance arcs.
Which of the following is often determined using a Smith chart?
Answer C. Smith charts are often used to find impedance and SWR values on transmission lines.
What are the two families of circles and arcs that make up a Smith chart?
Answer C. The two families on a Smith chart are resistance circles and reactance arcs.
Which of the following is a common use for a Smith chart?
Answer A. A common use of the Smith chart is finding the length and position of a matching stub.
On the Smith chart shown in Figure E9-3, what is the name for the large outer circle on which the reactance arcs terminate?
Answer B. The outer circle of a Smith chart, where the reactance arcs end, is the reactance axis.
On the Smith chart shown in Figure E9-3, what is the only straight line shown?
Answer D. The only straight line on a Smith chart is the horizontal resistance axis.
How is a Smith chart normalized?
Answer C. A Smith chart is normalized by reassigning the impedance value at the prime center, such as 50 ohms.
What third family of circles is often added to a Smith chart during the process of designing impedance matching networks?
Answer A. Constant-SWR circles are often added when designing matching networks.
What do the arcs on a Smith chart represent?
Answer D. Smith chart arcs represent points of constant reactance.
In what units are the wavelength scales on a Smith chart calibrated?
Answer B. Smith chart wavelength scales are in fractions of the line's electrical wavelength.
When constructing a Beverage antenna, which of the following factors should be included in the design to achieve good performance at the desired frequency?
Answer D. A Beverage antenna should be at least one wavelength long for good performance.
Which is generally true for 160- and 80-meter receiving antennas?
Answer A. On 160 and 80 meters, atmospheric noise is so high that directivity matters far more than antenna losses.
What is receiving directivity factor (RDF)?
Answer D. RDF compares an antenna's peak gain to its average gain over the hemisphere around and above it.
What is the purpose of placing an electrostatic shield around a small-loop direction-finding antenna?
Answer B. An electrostatic shield removes unbalanced capacitive coupling, giving deeper nulls on a direction-finding loop.
What challenge is presented by a small wire-loop antenna for direction finding?
Answer A. A small loop has two nulls 180 degrees apart, so a bearing is ambiguous between two directions.
What indicates the correct value of terminating resistance for a Beverage antenna?
Answer D. The correct Beverage termination gives the least variation in SWR across the desired frequency range.
What is the function of a Beverage antenna’s termination resistor?
Answer B. A Beverage's termination resistor absorbs signals arriving from the reverse direction.
What is the function of a sense antenna?
Answer A. A sense antenna modifies a DF antenna's pattern so it has a null in only one direction, resolving ambiguity.
What type of radiation pattern is created by a single-turn, terminated loop such as a pennant antenna?
Answer A. A terminated single-turn loop such as a pennant has a cardioid pattern.
How can the output voltage of a multiple-turn receiving loop antenna be increased?
Answer C. More turns and/or a larger loop area increase a receiving loop's output voltage.
What feature of a cardioid pattern antenna makes it useful for direction-finding antennas?
Answer B. A cardioid pattern has a single null, which makes the direction unambiguous for direction finding.
1 exam question from this subelement. Practice E0 · Study notes
What is the primary function of an external earth connection or ground rod?
Answer B. An external ground rod's primary function is to dissipate lightning charge into the earth.
When evaluating RF exposure levels from your station at a neighbor’s home, what must you do?
Answer B. Neighbors are the general public, so their exposure must stay below the uncontrolled (general population) MPE limits.
Over what range of frequencies are the FCC human body RF exposure limits most restrictive?
Answer C. Exposure limits are most restrictive from 30 to 300 MHz, where the human body absorbs RF most efficiently.
When evaluating a site with multiple transmitters operating at the same time, the operators and licensees of which transmitters are responsible for mitigating over-exposure situations?
Answer C. At multi-transmitter sites, every transmitter producing 5% or more of its MPE limit where the total is exceeded shares responsibility.
What hazard is created by operating at microwave frequencies?
Answer B. Microwave antennas often have high gain, which can concentrate energy into high exposure levels.
Why are there separate electric (E) and magnetic (H) MPE limits at frequencies below 300 MHz?
Answer D. Below 300 MHz, the body responds to both E and H fields, ground reflections vary field strength, and E and H peaks can occur in different places. All three explain separate limits.
What is meant by “100% tie-off” regarding tower safety?
Answer B. 100% tie-off means at least one lanyard is attached to the tower at all times.
What does SAR measure?
Answer C. SAR (specific absorption rate) measures the rate at which the body absorbs RF energy.
Which of the following types of equipment are exempt from RF exposure evaluations?
Answer C. Hand-held transceivers sold before May 3, 2021 are exempt from RF exposure evaluations.
When must an RF exposure evaluation be performed on an amateur station operating on 80 meters?
Answer A. Under the current rules, an RF exposure evaluation must always be performed for an 80-meter station.
To what should lanyards be attached while climbing?
Answer D. Attach lanyards to the tower legs, the strongest structural members.
Where should a shock-absorbing lanyard be attached to a tower when working above ground?
Answer A. Attach a shock-absorbing lanyard above head level to limit fall distance.
Take a 50-question exam built from this pool.