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
This group covers the front-panel controls you use every day, such as frequency entry, squelch, filters, scanning, RIT, and microphone gain. It also covers the setup basics of digital voice radios such as DMR and D-STAR.
Frequency entry and scanning
You enter a frequency with the keypad or the VFO knob. CTCSS and DTMF encoders send tones, and AFC corrects drift; none enter a frequency. Scanning steps through a range of frequencies or memory channels to check for activity and stops when it finds a signal.
Squelch
Squelch silences receiver audio when no signal is present. To hear a weak FM signal, set the squelch threshold so that audio is on all the time. Then the weak signal is not blocked by the squelch, though you hear noise between transmissions.
FM tuning
FM receivers detect frequency deviation, and their filters and detector are centered on the channel. If a received signal is slightly off frequency, part of its deviation falls outside the receiver’s passband, so the audio becomes distorted. Unlike SSB, the pitch does not shift.
SSB controls
Microphone gain: too much overdrives the audio stage, causing distorted audio and splatter on adjacent frequencies.
RIT (receiver incremental tuning) or Clarifier: shifts only your receive frequency. If a station answering your CQ sounds too high or too low in pitch, use RIT to adjust without moving your transmit frequency.
Receiver filters
A multimode transceiver offers selectable bandwidths so you can match the filter to the mode. A narrower filter reduces noise and nearby interference. Typical choices:
Mode
Typical filter
CW
250 to 500 Hz
SSB voice
about 2400 Hz
FM voice
10 to 15 kHz
For SSB, 2400 Hz gives the best signal-to-noise ratio because it passes the voice and rejects extra noise.
DMR
DMR radios use a code plug, a configuration file loaded into the radio. It contains channels, repeaters, talkgroups, contacts, and color codes. You select a group of stations by entering the group’s identification code, called a talkgroup ID, rather than by tone or frequency alone.
D-STAR
Before transmitting on D-STAR you must program your call sign into the radio, because it is sent with each transmission. Output power and codec type are not required entries.
Key facts to memorize
SSB voice bandwidth: about 2.4 kHz, so a 2400 Hz filter is best.
Excess mic gain: distorted audio.
RIT or Clarifier: adjusts receive frequency only.
Open squelch (audio always on) to hear weak signals.
Off-frequency FM: distorted audio.
DMR code plug: configuration data for repeaters and talkgroups.
DMR group selection: group identification code.
D-STAR: your call sign must be programmed.
Memory hooks
RIT: “Receive Is Tunable”, transmit stays put.
Code plug equals “contact list and channel list for your radio”.
Questions in this group (11): answers shown
T4B01
What is the effect of excessive microphone gain on SSB transmissions?
A. Frequency instability
B. Distorted transmitted audio ✓ Correct answer
C. Increased SWR
D. Sideband inversion
Too much microphone gain overdrives the modulator, which distorts the transmitted audio and widens the signal, causing splatter. It does not shift the frequency or change SWR, and sideband inversion is unrelated.
T4B02
Which of the following can be used to enter a transceiver’s operating frequency?
A. The keypad or VFO knob ✓ Correct answer
B. The CTCSS or DTMF encoder
C. The Automatic Frequency Control
D. All these choices are correct
You can enter a frequency with the keypad or turn the VFO knob. CTCSS and DTMF encoders send tones, and AFC corrects tuning drift, so none of those enter a frequency, which makes 'all choices' wrong.
T4B03
How is squelch adjusted so that a weak FM signal can be heard?
A. Set the squelch threshold so that receiver output audio is on all the time ✓ Correct answer
B. Turn up the audio level until it overcomes the squelch threshold
C. Turn on the anti-squelch function
D. Enable squelch enhancement
To hear a weak FM signal, open the squelch by setting its threshold so the receiver output audio is on all the time, then you can hear the weak signal's noisy audio. Turning up volume does not move the squelch threshold.
T4B04
What does an FM signal sound like when received slightly off frequency?
A. The audio increases in pitch
B. The audio decrease in pitch
C. There is no effect except for reduction in amplitude
D. The audio becomes distorted ✓ Correct answer
An FM receiver's filters and detector are centered on the channel. When a signal is slightly off frequency, part of its deviation falls outside the receiver's passband and the detector's linear range, so the audio sounds distorted. Unlike SSB, the pitch does not shift, and the effect is more than reduced amplitude.
T4B05
What does the scanning function of an FM transceiver do?
A. Checks incoming signal deviation
B. Prevents interference to nearby repeaters
C. Tunes through a range of frequencies to check for activity ✓ Correct answer
D. Tunes through a range of frequencies to determine the antenna’s resonant frequency
Scanning makes the FM transceiver step through a range of frequencies or memory channels to find activity, stopping when it finds a signal. It does not check deviation, protect repeaters, or find antenna resonance.
T4B06
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?
A. The AGC or limiter
B. The bandwidth selection
C. The tone squelch
D. The RIT or Clarifier ✓ Correct answer
On SSB, a received voice that sounds too high or low means you are tuned off the other station's frequency. The RIT (receiver incremental tuning) or Clarifier adjusts receive frequency without moving your transmit frequency.
T4B07
What is a DMR “code plug”?
A. An adapter cable used to connect a DMR radio to a computer for internet access
B. Configuration data loaded onto your radio to access repeaters and talkgroups ✓ Correct answer
C. An upgrade to DMR programming software provided by the radio manufacturer to accommodate new radio models
D. A Coder-Decoder (CODEC) that converts analog voice data to DMR digital data and vice versa
A DMR code plug is a configuration file loaded into the radio. It holds the channels, repeaters, talkgroups, contacts, and color codes you need. It is not a cable, a software upgrade, or a codec.
T4B08
What is the advantage of having a choice of receiver filter bandwidths in a multimode transceiver?
A. Permits monitoring several modes simultaneously by selecting a separate filter for each mode
B. Permits noise or interference reduction by selecting a bandwidth matching the mode ✓ Correct answer
C. Increases the number of frequencies that can be stored in memory
D. Increases the amount of offset between receive and transmit frequencies
Selectable receive filter widths let you match bandwidth to the mode, such as narrower for CW and wider for SSB. This cuts noise and adjacent-signal interference without losing the wanted signal. It does not monitor several modes at once.
T4B09
How is a specific group of stations selected on a DMR digital voice transceiver?
A. By retrieving the frequencies from transceiver memory
B. By enabling the group’s CTCSS tone
C. By entering the group’s identification code ✓ Correct answer
D. By inserting a five-pin, pre-programmed code plug
DMR radios select a group (talkgroup) by its identification number, which you program as a contact and select. One repeater frequency carries many talkgroups, so recalling a frequency from memory is not enough, CTCSS is an analog access tone, and a code plug is configuration data, not a physical plug.
T4B10
Which of the following receiver filter bandwidths provides the best signal-to-noise ratio for SSB reception?
A. 500 Hz
B. 1000 Hz
C. 2400 Hz ✓ Correct answer
D. 5000 Hz
SSB voice occupies about 2.4 kHz, so a 2400 Hz filter passes the whole signal while rejecting most noise. The 500 Hz and 1000 Hz filters are too narrow and cut off part of the voice, while 5000 Hz lets in extra noise and interference.
T4B11
Which of the following must be programmed into a D-STAR digital transceiver before transmitting?
A. Your call sign ✓ Correct answer
B. Your output power
C. The codec type being used
D. All these choices are correct
D-STAR needs your call sign programmed into the radio, because it is sent as part of every transmission to identify you. Power level and codec type are not required to be programmed, so 'all choices' is incorrect.