Working Repeaters, Tones, and Digital Voice

When the repeater will not hear you

Which of the following could be the reason you are unable to access a repeater whose output you can hear?

All these choices are correct.

The three, and they are the three to check in order:

1. Wrong offset — you are transmitting on the output frequency instead of the input.
2. No tone, or the wrong tone — the repeater requires CTCSS and yours is off or set wrong.
3. Out of range on the uplink — you hear its 50 W from a hilltop; it cannot hear your 5 W from a valley.

That last one is the asymmetry beginners miss. Hearing a repeater tells you nothing about whether it can hear you. A repeater on a mountain with a good antenna is a much better station than your handheld.

Reverse

What is the purpose of the reverse function on a VHF/UHF transceiver?

To listen on a repeater’s input frequency.

Press reverse and you hear what the repeater hears — the other station directly, simplex. Two uses:

• Is the other station workable simplex? If you hear them well on reverse, you can both leave the repeater free.
• Is the repeater actually there? If you hear the same signal with and without reverse, you are hearing them direct, not through the machine.

Tones and signalling

CTCSS — the sub-audible tone transmitted with voice audio to open a repeater’s squelch. Covered fully in the GMRS track, and identical in principle here.

DTMF — signalling that uses two simultaneous audio tones, the same dual-tone system as a telephone keypad. Repeaters use DTMF for control functions: autopatch, linking, turning features on and off.

Squelch exists to mute the receiver audio when a signal is not present. Without it, an FM receiver hisses continuously. Setting it too tight is a common self-inflicted wound: you stop hearing weak stations you could otherwise work.

Audio that drops out on peaks

Which of the following would cause your FM transmission audio to drop out on voice peaks?

You are talking too loudly.

Overdeviation. FM encodes your voice as frequency shift, and the radio limits how far it will shift. Speak too loudly and the peaks are clipped and pushed outside the receiver’s filter — the listener hears distortion, or nothing at all, exactly on the syllables that carry the information.

The fix is not to hold the microphone further away and shout. It is to speak across the microphone at a normal conversational level, a couple of inches away.

Linked repeaters

Which of the following describes a linked repeater network?

A network of repeaters in which signals received by one repeater are transmitted by all the repeaters in the network

A single transmission covers everywhere the network reaches. That is powerful in an emergency and, in ordinary use, a reason for restraint: a casual chat on a linked system occupies a whole region.

Digital voice: DMR

DMR is the digital mode most likely to be on the radios already in a drawer, and its two pieces of jargon are worth getting right.

Talkgroup — an identifier used by DMR to organise radio traffic so that those who want to hear a particular conversation can do so. Think of it as a channel that exists in software rather than in frequency. A single DMR repeater carries many talkgroups; you hear the ones your radio is programmed for.

To join one: program your radio with the group’s ID or code.

Colour code — an access code which must be programmed into a DMR transmitter to access a specific repeater. It is DMR’s equivalent of CTCSS: a number, 0 to 15, that the repeater checks before responding. Wrong colour code, no access, exactly like a wrong tone.

Sharing a frequency

Which of the following applies when two stations transmitting on the same frequency interfere with each other?

The stations should negotiate continued use of the frequency.

Nobody owns a frequency. Not the first station on it, not the one with more power, not the local club. The rule and the etiquette agree: talk about it and work it out. This is also why simplex channels exist in band plans — so stations within range of each other can communicate without tying up a repeater.

Q signals

Borrowed from commercial and maritime practice, and still current on voice:

QRM and QSY are the two the pool asks for. QRM is man-made interference from other stations; QRN is natural noise. The distinction is worth keeping.

Check yourself

1. You hear a repeater clearly but it never responds. Name three causes.
2. A station reports your audio “cuts out when you get excited”. What is happening?
3. What is the difference between a DMR talkgroup and a DMR colour code?