Long Explanation

UHF/VHF repeaters receive on one frequency (the repeater’s input) and re-transmit on another frequency (the repeater’s output). Radios normally operate in duplex when using a repeater: they transmit on the repeater input frequency and receive the repeater output frequency (the two frequencies are typically offset by a set split, such as 600 kHz on 2 meters).

The reverse function swaps the usual receive and transmit pair so the radio listens on the repeater’s input frequency instead of the repeater’s output. This lets you hear stations transmitting to the repeater directly (their transmissions go to the repeater input), which is useful if you want to determine whether you can contact that station directly (for a simplex contact) or to hear someone who might be trying to call through a repeater that is down.

Using reverse can also help you assess signal strengths or troubleshoot whether a repeater is working: if you hear the other station on the repeater input but the repeater output is silent, the repeater may be off or not retransmitting.

Memory aids / mnemonics:

• Normally you listen to a repeater’s output. Listening to the repeater’s input is the "reverse" of normal.

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CTCSS stands for Continuous Tone-Coded Squelch System. It uses a sub-audible (below the range of normal speech) tone transmitted along with voice audio to open the squelch of a receiver. Repeaters and receivers programmed to require a particular CTCSS tone will only unmute when that specific tone is present, allowing multiple users to share the same frequency without hearing each other and preventing random noise from activating the repeater.

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A linked repeater network is a network of repeaters where signals received by one repeater are transmitted (repeated) by the other repeaters in the network. Digital repeaters are often linked together; although many are "smart" and may only pass selected traffic, the defining characteristic is that repeaters are connected so that a signal heard at one site can be heard via the other linked sites, making it appear to users as a single, larger coverage area.

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If you can hear a repeater's output but the repeater does not retransmit your transmissions, the most common reasons are that your signal does not meet the repeater's access requirements.

1. Improper transceiver offset — Repeaters normally use one frequency for their transmit (what you hear) and a different frequency for their receive (where you must transmit). If your radio's transmit frequency is not set to the repeater's input frequency (including the correct offset direction and magnitude), the repeater won't receive your signal.

2. Wrong CTCSS tone — Many repeaters require a specific Continuous Tone-Coded Squelch System (subaudible) tone to be transmitted along with your voice. If you do not send the correct subaudible tone, the repeater will ignore your signal.

3. Wrong DCS code — Some repeaters use Digital Code Squelch (a digital squelch code) instead of, or in addition to, CTCSS. If your radio is not sending the matching DCS code, the repeater will not open for your transmission.

If any of these features are in use on the repeater and your radio is not configured to match, the repeater will simply ignore your transmissions.

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If FM audio "drops out" only during the loudest parts of your speech (the voice peaks) the most likely cause is that the audio input to the transmitter is too high — in other words, you are talking too loudly or the microphone is too close to your mouth. Excessive audio levels can overload stages in the transmitter or activate automatic level control/limiting. When that happens the transmitter may clip or compress the peaks, or the limiter may temporarily reduce the audio, so only the peaks are affected while lower-level speech remains audible.

This behavior is different from problems that would affect the entire transmission (for example, being off-frequency or having too much received power at a repeater). The fact that the problem appears only at peaks points to excessive drive at the microphone/transmitter input.

Memory aids:

• Loud voice peaks -> possible transmitter overload or ALC limiting
• Try moving the microphone back or speak more softly to see if the problem stops

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Answer explanation:

Dual-Tone Multi-Frequency (DTMF) signaling sends each key press as two simultaneous audio tones (one from a low-frequency group and one from a high-frequency group). Repeaters commonly accept DTMF sequences for functions such as access control, linking, autopatch, or other keypad-activated commands.

By contrast, Continuous Tone-Coded Squelch System (CTCSS) uses a single, continuous sub-audible tone to gate squelch (so receivers open only for transmissions with the matching tone), and digital or service systems (like D-STAR or GMRS) do not use paired audio tones for keypad-style signaling.

Memory aids:

• DT = Dual Tone (two tones)
• DTMF = Dual Tone Multi-Frequency — each keypad digit is represented by a pair of tones

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A number of different digital radio standards exist such as DMR, D-STAR, and Fusion. They usually implement something called a "talk group" which is described by the DMR-MARC FAQ as follows:

Q. What are Talk Groups?

A. Talk Groups are like different work groups that you communicate with. They are programmed as “channels”. Several can share a Time Slot on a repeater like multiple PL codes can share a community repeater. Each talk group can be isolated from the other, but may get a busy tone if the same time slot is in use by another. Greater efficiency can be achieved by bridge routing and trunking techniques. Each radio can have more than one talk group and may scan or roam based on talk group.

Once a radio has been configured to operate with a particular digital repeater, joining a talk group is accomplished by programming the radio with that group's ID or code so it can listen to or transmit to that group. Digital repeaters are often linked to other repeaters in networks, so the group ID/code tells the repeater network which group you want to use.

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When two stations are transmitting on the same frequency and causing interference, the proper course is for the operators to negotiate among themselves about continued use of that frequency. No amateur radio operator has an absolute right to any portion of the amateur bands; by holding a license you agree to share spectrum and to resolve conflicts cooperatively. Neither being the strongest signal nor having been on the frequency the longest gives a station a preemptive right. Mutual agreement or shifting to another frequency by one of the stations is the appropriate way to eliminate the interference.

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Simplex channels exist in the UHF/VHF band plans so that stations within mutual communications range can communicate without tying up a repeater. That is the primary reason these channels are designated.

Simplex operation uses the same frequency for both transmitting and receiving (no offset), and is useful any time operators want to communicate directly rather than through a repeater — for example when a repeater isn't available or when the stations are close enough for direct contact.

Memory aids:

• Sometimes it's simple(x)r without a repeater.

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Hams use Q codes to convey concise messages. QRM means interference from other stations (man-made interference). QRN indicates natural or atmospheric noise, QTH means location, QSO means a conversation, and QSY means change frequency or channel.

In practical use, if you hear someone say “I’m getting QRM on your signal,” they mean they are hearing interference caused by other transmitters. The distinction is that the “M” in QRM refers to man-made interference, while the “N” in QRN refers to natural static or atmospheric noise.

Memory aids:

• Q - Radio Messy
• sQuiRM – you might squirm in frustration when someone interferes with you
• (Reference: https://www.qsl.net/w5www/qcode.html)

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QSY means to change frequency. It is one of the most commonly used Q codes.

For example:

"Please QSY to 147.34."
"Copy that, this is KD7BBC, QSY to 147.34"

Or

"Shall we QSY to 146.52 simplex?"

Reference: Q code list

Memory aids:

• If you got queaSY about a frequency, you would change to a different one.
• See You at a different frequency.

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On DMR, the digital color code fills a similar role to a CTCSS tone or DCS code on analog FM.

It’s an access code you must program into your DMR radio to match a specific repeater. If your color code doesn’t match the repeater’s, you won’t get in (and probably won't hear it either).

Why the others are wrong:

• It doesn’t set the offset for you — that’s just normal frequency programming.
• It doesn’t identify the CODEC — DMR uses a standard voice codec already.
• It isn’t a status/health code sent by the repeater — it’s part of the access/control scheme.

So: think “color code = DMR access code.”

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The squelch control on a transceiver mutes the receiver audio when no signal is being received.

The receiver portion of the transceiver is very sensitive and provides gain to weak signals. When no signal is present, that gain makes background noise as loud as a normal signal. The squelch control monitors the signal strength detector and mutes the audio until a received signal exceeds the squelch threshold. If the squelch is set too high you may miss weak stations; if set too low you will hear continuous or intermittent "white noise" as the background noise level varies.

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A talkgroup on a DMR system is essentially an identifier (a numeric ID) used to organize radio traffic so members of the group can hear each other without being bothered by other traffic on the same channel. Radios are programmed with the talkgroup IDs they want to monitor; when a user transmits using a given talkgroup ID, only radios set to that ID will open for audio. This lets multiple groups share a repeater time slot or channel while keeping conversations separated.

Additional details: DMR repeaters often use time slots and talkgroup IDs together; several talkgroups can share the same time slot but remain isolated by their IDs. Networks of linked repeaters use the same talkgroup IDs so members of a talkgroup can communicate across a wider area.

Memory aids:

• "A 'talk group' allows a group to talk together (share)."
• Think of a talkgroup as a virtual channel or group ID that lets radios tune to the same conversation without hearing other groups.

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