T4B

Radio operating controls

Set squelch, filters, RIT, mic gain and digital-radio settings so you can hear and be heard clearly.

11 pool questions1 on the exam

Syllabus: 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

Squelch mutes what is weaker than its threshold

Squelch silences the speaker when no signal is present. Set higher, it also mutes weak signals. To hear a weak FM signal, lower the threshold until the audio is on all the time.

Audio plays only for signals that reach past the threshold line.

Squelch65

ResultWeak signal muted

RememberWeak signal? Open the squelch so audio is always on.

Match filter bandwidth to the mode

A narrower filter blocks noise and nearby interference, but too narrow cuts the signal itself. Choose the bandwidth that matches the mode. An SSB voice signal fits best in 2400 Hz.

Shaded window = filter passband. Orange bars = noise that gets through.

RememberFilter width matches the mode: SSB voice, 2400 Hz.

Tuning: keypad, VFO, scan and RIT

Control	What it does
Keypad or VFO knob	Enters the operating frequency
Scan	Tunes through a range of frequencies to check for activity
RIT / Clarifier	Shifts receive frequency only, to fix voice pitch on SSB

CTCSS and DTMF are tones, not ways to enter a frequency.

Ghost lines: how the voice should sound. Solid lines: what you hear.

Their frequency is off by+200 HzYour RIT / Clarifier0 Hz

You hearToo high

Off-frequency FM sounds distorted. Off-frequency SSB sounds too high or too low, and RIT corrects it.

RememberSSB pitch wrong? RIT or Clarifier. Off-frequency FM? Distorted.

Too much microphone gain distorts

Dashed lines: the most audio the transmitter can handle cleanly.

Microphone gain

Transmitted audioClean

Keep the peaks inside the limit. Excess gain gives distorted transmitted audio.

RememberExcessive mic gain means distorted audio.

Digital radios are programmed before use

Digital radios must be configured before they work on the network.

Question	Answer
Code plug	Configuration data loaded into your radio for repeaters and talkgroups
Picking a DMR group	Enter the group's ID code
Required in a D-STAR radio	Your call sign

RememberCode plug = config. Talkgroup = ID code. D-STAR = your call sign.

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Go deeper

Compendium articles on the ideas in this lesson, beyond what the exam asks.

Check what stuck

Practise the 11 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".

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