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T4B

AMATEUR RADIO PRACTICES

Operating controls: frequency tuning, use of filters, squelch function, AGC, memory channels, noise blanker, microphone gain, receiver incremental tuning (RIT), bandwidth selection, scanning function; Digital transceiver configuration; DMR code plugs and talk groups

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T4B011 of 11

What is the effect of excessive microphone gain on SSB transmissions?

Why Microphone gain sets how hard your voice drives the transmitter's audio stages. Turn it up too far and the audio peaks are clipped and flattened by the ALC and the modulator, so the SSB signal comes out distorted and splattering into adjacent frequencies. The correct setting is the one where the ALC meter just barely moves into its range on voice peaks, not pinned.
Watch out Increased SWR is tempting because both are transmitter problems, but SWR depends only on the match between the radio, feed line and antenna, not on how loud your audio is.
Mic gain drives audio, not RF: too much gain means mush and splatter. Set it so ALC just flickers on peaks.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B022 of 11

Which of the following can be used to enter a transceiver's operating frequency?

Why Frequency entry on a modern transceiver is done either by typing the digits directly on the front-panel or microphone keypad, or by turning the VFO (variable frequency oscillator) knob to tune up and down the band. Both methods set the same thing: the VFO frequency the radio transmits and receives on. Memory channels are a third way, but they just recall a frequency that was entered by one of these methods.
Watch out CTCSS and DTMF encoders generate subaudible or touch-tone tones for repeater access and control, and automatic frequency control makes small corrections to hold a signal centered, so none of them let you choose an operating frequency.
Type it on the keypad or spin the VFO knob. Tones and AFC do not pick the frequency.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B033 of 11

How is squelch adjusted so that a weak FM signal can be heard?

Why Squelch mutes the receiver audio until an incoming signal is strong enough to cross a threshold you set. A weak signal may not be strong enough to open a normally set squelch, so you back the control off until the rushing noise is heard continuously, meaning the gate is open all the time. With the squelch open you will hear the noise, but you will also hear the weak station when it transmits.
Watch out Raising the audio (volume) control does nothing to the squelch gate, it only changes how loud the already unmuted audio is. There are no functions called anti-squelch or squelch enhancement, those are invented names.
Squelch gates the audio, volume only sets loudness. Weak signal? Open the gate until you hear hiss.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B044 of 11

What does an FM signal sound like when received slightly off frequency?

Why An FM receiver recovers audio by measuring instantaneous frequency deviation against the center of its discriminator (detector) response curve. That curve is only linear over a limited range centered on the carrier, so if the incoming signal sits off to one side, the deviation swings run into the curved, nonlinear part of the response and the recovered audio comes out distorted, often sounding harsh or clipped on loud peaks.
Watch out Rising or falling pitch is what you hear when you mistune an SSB or CW signal, where the tuning offset shifts the beat frequency directly; FM detection does not work that way, and a simple amplitude drop is what you would expect from a weak signal rather than a mistuned one.
Mistune SSB and the pitch changes; mistune FM and the audio just gets ugly.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B055 of 11

What does the scanning function of an FM transceiver do?

Why Scanning is an automated tuning feature: the radio steps through a programmed range of frequencies or a list of memory channels, pausing when the squelch opens because a signal is present. It is a way to monitor many channels without turning the dial by hand. Most FM radios let you scan memory channels, a band segment, or a set of limits you define.
Watch out Checking deviation is a transmitter measurement done with test equipment, and finding an antenna's resonant frequency is what an antenna analyzer or SWR sweep does, not the receiver's scan function.
Scan = search for activity. The radio does the dial-turning for you and stops when someone talks.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B066 of 11

Which of the following controls could be used if the voice pitch of a single-sideband signal returning to your CQ call seems too high or low?

Why In SSB the carrier is suppressed, so the audio pitch you hear depends entirely on how closely your receive frequency matches the other station's transmit frequency. If the other station is a few hundred hertz off, every voice frequency shifts by that amount and the voice sounds too high (chipmunk) or too low (growly). Receiver incremental tuning, also called the clarifier, nudges the receive frequency slightly without moving your transmit frequency, so you can correct the pitch and stay on their frequency when you answer.
Watch out Changing bandwidth only narrows or widens the filter passband, which affects how much noise and adjacent signals you hear, not the pitch of the recovered audio; AGC controls gain and tone squelch is an FM subaudible tone feature.
RIT = Receive-only tuning. Clarifier 'clarifies' the Donald Duck voice by shifting RX a few hundred Hz.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B077 of 11

What is a DMR "code plug"?

Why DMR radios are not tuned like analog rigs; nearly everything is preprogrammed. A code plug is the configuration file, built on a computer with the manufacturer's programming software and uploaded to the radio, that holds channels, repeater frequencies, color codes, time slots, talkgroup IDs, contacts and zones. Without a current code plug the radio cannot key up the digital repeaters or join the right talkgroups.
Watch out The CODEC answer describes the AMBE+2 vocoder that digitizes your voice, which is hardware/firmware inside the radio and has nothing to do with the configuration file.
Code plug = the radio's settings file, not a cable, not software, not a codec.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B088 of 11

What is the advantage of having a choice of receiver filter bandwidths in a multimode transceiver?

Why A receiver filter passes only a slice of spectrum to the detector, so everything outside that slice, noise and adjacent signals alike, is rejected. Matching the filter to the mode's actual bandwidth lets the wanted signal through while throwing away the rest: roughly 500 Hz or less for CW, about 2.4 kHz for SSB, and 10 to 15 kHz for FM. Using a wider filter than the mode needs just lets in extra noise and interference with no gain in readability.
Watch out Monitoring several modes at once is not what multiple filters do; a receiver still demodulates one signal at a time, and the filters are alternatives, not parallel channels. Memory count and transmit offset are unrelated functions.
Filter bandwidth = mode bandwidth. CW narrow (~500 Hz), SSB medium (~2.4 kHz), FM wide. Wider than needed means more noise.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B099 of 11

How is a specific group of stations selected on a DMR digital voice transceiver?

Why DMR organizes users into talk groups, and each talk group has a numeric ID. Your radio only passes audio from the talk group ID programmed into the channel you are using, so selecting a group means entering or selecting that talk group number (usually stored in the radio's code plug along with frequency, color code and time slot).
Watch out CTCSS is an analog subaudible tone system for FM squelch and has nothing to do with DMR's digital signaling. A 'code plug' in DMR is a software configuration file loaded into the radio, not a physical five-pin plug.
DMR groups are numbers: talk group ID, not a tone. Code plug = the programming file, not hardware.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B1010 of 11

Which of the following receiver filter bandwidths provides the best signal-to-noise ratio for SSB reception?

Why A receiver filter should be just wide enough to pass the signal and no wider, because every extra hertz of bandwidth admits more noise without adding any signal. A voice SSB transmission occupies roughly 2.4 kHz, so a 2400 Hz filter passes all of the speech energy while rejecting noise and adjacent signals outside it, giving the best signal-to-noise ratio.
Watch out The 500 Hz setting is a CW filter; it would chop off most of the speech energy and make SSB audio muffled and unintelligible, while 5000 Hz is about right for AM and just lets in twice the noise for an SSB signal.
Match the filter to the mode: about 500 Hz for CW, 2400 Hz for SSB, 5 kHz or more for AM/FM.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T4B1111 of 11

Which of the following must be programmed into a D-STAR digital transceiver before transmitting?

Why D-STAR sends your call sign as digital data in every transmission, so the radio must have MYCALL programmed before it will identify you properly on the air. This is the digital equivalent of station identification, and many repeaters and gateways will reject or ignore a transmission from a radio with no call sign entered. Other D-STAR fields like UR, RPT1 and RPT2 control routing, but the call sign is the one that must be set.
Watch out The codec is not a user choice: D-STAR uses the AMBE voice codec exclusively, so there is nothing to program. Output power is set with a control or menu item like any FM radio and is not part of the digital data stream.
D-STAR stands for Digital Smart Technologies; the smart part is that your call sign rides along in the data.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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