T4 Amateur Radio Practices

D. 13.8 volts at 12 amperes

Mobile transceivers are built for a vehicle's electrical system, which runs at about 13.8 V while the engine is running. A 50 W FM transmitter is not 100 percent efficient, so it draws well over 50 W of input power; a supply rated 13.8 V at 12 A can deliver 13.8 V x 12 A = 165.6 W, enough for full output.

• A. 24.0 V is the wrong voltage for equipment designed for a 12 V vehicle system, and 4 A is too little current.
• B. 13.8 V is correct, but 4 A supplies only 13.8 V x 4 A = 55.2 W, not enough for a transmitter producing 50 W of RF output.
• C. 12 A is a reasonable current, but 24.0 V is far above the voltage the transceiver is designed for and could damage it.

A. The frequency and power level at which the measurements will be made

An SWR meter is designed for a particular frequency range and maximum power. Choose one rated for the bands and power levels you will measure, since a meter used outside its ratings may read inaccurately or be damaged.

• B. The meter's distance from the antenna is not a selection factor; the meter is usually installed at the transmitter end of the feed line.
• C. An SWR meter displays whatever SWR is present; the expected maximum SWR does not determine which meter to choose.
• D. An SWR meter only measures; compensating for a mismatch is the job of an antenna tuner or matching network.

A. To minimize voltage drop when transmitting

A transceiver draws high current when transmitting, and every wire has some resistance. The voltage lost in the wire is current times resistance (E = I x R), so short, heavy-gauge wire keeps the resistance low and the radio receives close to full supply voltage.

• B. A DC power supply is not impedance matched to its load; the goal is low resistance in the wiring, not a match.
• C. Wire gauge and length are chosen to limit voltage drop; RF interference is handled with filtering and bonding.
• D. DC power cables do not radiate meaningful power; the loss that matters is the resistive voltage drop.

B. To the audio output and input of a computer running FT8 software

FT8 is generated and decoded by software on a computer, such as WSJT-X. The transceiver's receive audio goes to the computer's audio input, and the computer's audio output goes to the transceiver's audio input, often through a USB audio interface.

• A. A terminal program with a terminal node controller (TNC) is the setup for packet radio, not FT8.
• C. There is no separate FT8 conversion unit; the computer software does the encoding and decoding.
• D. FT8 does not run through a conversion website; the software runs on the computer connected to the radio.

A. In the feed line, between the transmitter and antenna

An RF power meter measures the radio frequency power flowing to the antenna, so it is connected in the feed line between the transmitter and the antenna.

• B. The power supply output carries DC, not RF, so a meter there cannot measure transmitted RF power.
• C. The push-to-talk line is a keying circuit, and an RF power meter is connected in series in the feed line, not in parallel with other lines.
• D. The power supply cable carries DC to the radio; RF power is measured in the feed line.

C. Receive audio, transmit audio, and transmitter keying

A computer-radio interface for digital modes carries three signals: receive audio from the radio to the computer, transmit audio from the computer to the radio, and a keying signal (push-to-talk) that switches the transmitter on and off.

• A. Mode, status and location are not the signals a digital mode interface carries; it carries audio in each direction plus transmitter keying.
• B. Antenna and RF power connections run between the radio and the antenna, not through the computer interface.
• D. GPS location data and DC power are not part of the audio and keying connections a digital mode interface provides.

C. Computer “line in” to transceiver speaker connector

The computer must hear what the radio receives, so the transceiver's speaker (audio output) connects to the computer's line input. The other connections are computer line out to the transceiver's microphone or data input, and a keying line to push-to-talk.

• A. Line out carries transmit audio to the radio's microphone or data input; push-to-talk needs a keying signal, not audio.
• B. Line in receives audio from the radio's speaker output; it does not connect to push-to-talk.
• D. Line out and the speaker connector are both outputs, so connecting them does not carry audio where it is needed.

D. Flat copper strap

At radio frequencies, current flows mostly on the surface of a conductor (skin effect), and wide, flat conductors have low inductance. Flat copper strap provides a large surface area and low impedance, which is why it is preferred for RF bonding.

• A. Braid removed from coax has many fine strands that corrode and loosen over time, raising its resistance, and it lacks the low inductance of wide strap.
• B. Copper-clad steel wire is strong and suits antenna elements, but a round wire has more inductance and less surface area than a wide strap.
• C. Twisted-pair cable uses small conductors intended for data and signals, not low-impedance RF bonding.

B. Divide the battery ampere-hour rating by the average current draw of the equipment

A battery's ampere-hour (Ah) rating states how much current it can supply for how long. Dividing it by the equipment's average current draw gives the run time: for example, 20 Ah / 2.5 A = 8 hours.

• A. Using peak power gives too short an estimate, because equipment draws its peak power only part of the time; average consumption sets the run time.
• C. “Watts per hour” is not a unit of energy use, and multiplying by the battery rating does not produce a time.
• D. Current squared times resistance (I² x R) gives power in watts, not run time.

A. Communication with a digital voice or data network

A digital mode hotspot is a small, low-power transceiver connected to the internet. Nearby digital radios (such as DMR, D-STAR or System Fusion) talk to the hotspot by radio, and it links them to a digital voice or data network.

• B. A hotspot does not make FT8 contacts through a smartphone; FT8 runs on a computer connected to a transceiver.
• C. A hotspot does not encode or decode RTTY; it relays digital voice and data network traffic.
• D. A hotspot is a low-power, short-range link to a network, not a high-speed system for meteor scatter.

A. At the 12-volt battery chassis ground

Connect the negative lead where the battery's negative terminal is grounded to the vehicle chassis. That gives the transceiver's high current a solid, low-resistance return path to the battery and helps keep noise from other vehicle circuits out of the radio's supply.

• B. The shell of the power connector is not designed to carry the transceiver's return current.
• C. An arbitrary metal part may be painted, corroded or poorly connected to the battery, causing voltage drop and noise.
• D. A mounting bracket is a mechanical support; its connection to the chassis is not a reliable path for high current.

C. A device that assists in manual sending of Morse code

An electronic keyer helps you send Morse code by hand: when you press its paddle, it automatically produces correctly timed dots and dashes at the speed you set, while you form the characters.

• A. Switching an antenna between transmit and receive is done by a transmit/receive (T/R) switch or relay.
• B. Voice-activated switching from receive to transmit is VOX, not a keyer.
• D. An interlock that prevents unauthorized use is a security feature, not a keyer.

B. Distorted transmitted audio

Too much microphone gain overdrives the transmitter's audio and RF stages on SSB, producing distorted, hard-to-understand audio. It can also widen the signal (splatter) and cause interference to nearby frequencies.

• A. Microphone gain affects audio level, not the stability of the transmitter's frequency.
• C. SWR depends on the match between the antenna and the feed line, not on audio level.
• D. Which sideband is transmitted is set by the radio's mode, not by microphone gain.

A. The keypad or VFO knob

You set the operating frequency by entering it on the keypad or by turning the VFO (variable frequency oscillator) tuning knob.

• B. CTCSS and DTMF encoders generate tones for repeater access and control; they do not set the radio's frequency.
• C. Automatic Frequency Control (AFC) makes small automatic corrections to keep a receiver tuned to a signal; it is not used to enter a frequency.
• D. Only the keypad or VFO knob enters a frequency, so not every choice is correct.

A. Set the squelch threshold so that receiver output audio is on all the time

Squelch mutes the audio until a signal exceeds the threshold, so a very weak signal may never open it. Setting the threshold so that the audio is on all the time (open squelch) lets you hear weak signals along with the background noise.

• B. The volume control sets loudness after the squelch; turning it up does not open a closed squelch.
• C. There is no standard anti-squelch function; opening the squelch is done with the squelch control.
• D. Squelch enhancement is not a standard control; to hear weak signals you open the squelch.

D. The audio becomes distorted

An FM receiver tuned slightly off frequency places the signal off-center in its filter, so part of the signal's deviation falls outside the passband and the demodulated audio becomes distorted. Pitch changes from mistuning are characteristic of SSB, not FM.

• A. A rise in pitch from mistuning happens with SSB; FM audio pitch does not shift this way.
• B. A drop in pitch from mistuning also describes SSB, not FM.
• C. Being off frequency on FM does more than reduce the level; the audio distorts.

C. Tunes through a range of frequencies to check for activity

Scanning makes the transceiver step through a range of frequencies or memory channels, stopping when it finds a signal. It lets you check many frequencies for activity without tuning by hand.

• A. Measuring incoming signal deviation requires a deviation meter or service monitor, not the scan function.
• B. Scanning only listens; it does nothing to prevent interference to repeaters.
• D. Finding an antenna's resonant frequency requires an antenna analyzer or SWR measurements, not a receiver scan.

D. The RIT or Clarifier

On SSB, a station slightly off your frequency sounds too high or too low in pitch. RIT (receiver incremental tuning), also called a clarifier, shifts your receive frequency without moving your transmit frequency, so you can correct the pitch.

• A. AGC and limiters control signal levels, not the received pitch.
• B. Bandwidth selection changes how wide the receive filter is; it does not retune the signal's pitch.
• C. Tone squelch is an FM function that opens the audio on a CTCSS tone; it does not affect SSB pitch.

B. Configuration data loaded onto your radio to access repeaters and talkgroups

A DMR code plug is the configuration file loaded into the radio. It holds the channels, frequencies, color codes, talkgroups and contact lists needed to access repeaters and talkgroups.

• A. A cable that connects the radio to a computer is a programming cable; the code plug is the data loaded through it.
• C. An update to the programming software is a software release, not the code plug, which is the radio's configuration data.
• D. The codec (vocoder) is built into the radio; a code plug is configuration data, not a converter.

B. Permits noise or interference reduction by selecting a bandwidth matching the mode

Each mode needs a certain bandwidth, for example about 2.4 kHz for SSB and a few hundred hertz for CW. Choosing a filter that matches the signal passes the signal while rejecting noise and interference outside it, which improves readability.

• A. Selectable filters do not let one receiver monitor several modes at once; you select one bandwidth for the mode you are copying.
• C. Filter bandwidth has nothing to do with how many frequencies can be stored in memory.
• D. The offset between transmit and receive frequencies is set separately from receiver filter bandwidth.

C. By entering the group’s identification code

On DMR, each talkgroup has an identification number. You select a group by entering or choosing its ID (usually stored in your code plug as a channel or contact), and your radio then sends and receives traffic tagged with that ID.

• A. Many talkgroups can share one DMR repeater frequency, so recalling a frequency alone does not select a group.
• B. CTCSS tones are used with analog FM; DMR groups are selected by a digital ID.
• D. A code plug is configuration data loaded through software, not a five-pin plug you insert.

C. 2400 Hz

An SSB voice signal occupies roughly 2.4 to 3 kHz. A 2400 Hz filter passes the important voice frequencies while rejecting noise and interference outside them, which gives a better signal-to-noise ratio for SSB than the narrower or wider widths listed.

• A. 500 Hz is a CW filter width; it cuts off most of a voice signal and makes SSB unintelligible.
• B. 1000 Hz is too narrow to pass the voice frequencies an SSB signal contains.
• D. 5000 Hz is wider than an SSB signal, so it admits extra noise and interference; a width like that is closer to what AM needs.

A. Your call sign

D-STAR transmits your call sign digitally with every transmission, and the system uses it for identification and routing. You must program your call sign into the radio before you can transmit.

• B. Output power is chosen with a control; it is not something you must program before transmitting on D-STAR.
• C. D-STAR uses a single built-in voice codec, so you do not choose or program a codec type.
• D. Only your call sign must be programmed before transmitting, so not every choice is correct.