No audio or won't transmit: common codeplug mistakes

Category: CodeplugDifficulty: ★★☆~9 min

You built a channel by the book, loaded the codeplug into your radio, pressed PTT — and got silence in return. Or the opposite: the radio transmits, the hotspot receives, but the other party can't hear you. DMR differs from analog in that here any one of five or six channel parameters, off by a single value, kills the link. This article is a structured checklist: why there's no receive, why there's no transmit, and how to verify each item in a couple of minutes.

Block 1: no receive — the radio stays silent

Mistake 1. Wrong Color Code

Color Code (CC) is the equivalent of the CTCSS sub-tone in analog systems. The radio only receives a signal if the CC in the channel matches the CC of the hotspot or repeater. The typical value for a DMRhub hotspot is CC 1. Check the Color Code field in the channel settings and compare it with what's shown in your dashboard or in the Pi-Star/WPSD settings.

Quick checkOpen the DMRhub dashboard and look at your hotspot's settings. The Color Code is listed there. The very same value must be set in every digital channel of the radio.

Mistake 2. Wrong timeslot (TS1 instead of TS2)

A hotspot is a simplex device. Most hotspots use timeslot TS2 for user channels. If you set TS1 in the channel, the radio will "listen" to an empty slot — silence. For all channels tied to a personal hotspot, set Time Slot 2.

A repeater is differentOn a real repeater TS1 and TS2 are split across different talkgroups. Check with the repeater administrator which slot the group you need uses.

Mistake 3. The talkgroup isn't in the RX Group List

The RX Group List is the list of talkgroups the radio listens to on a given channel. If the group people are calling you on hasn't been added to that channel's RX list, the radio stays silent even when a signal arrives. Verification steps:

  1. Open the channel with no audio in your CPS.
  2. Check the RX Group List field — which list the channel is tied to.
  3. Open that list and make sure the talkgroup you need is in it.
  4. If the list is empty or unassigned, add the TG.

The RX Group List and the Contact field are exactly the first places to look when you have receive problems.

Mistake 4. Promiscuous / Digital Monitor disabled (OpenGD77)

OpenGD77 has a Digital Monitor mode (a.k.a. promiscuous): the radio listens to all digital signals on the channel, ignoring the TG filter. If you're testing and want to confirm the signal is getting through at all, enable it via the radio's quick menu (the SK2 + # buttons on the GD-77). In normal operation Digital Monitor is best left off — otherwise the radio will open up on other people's traffic.

TYT and AnyToneOn TYT and AnyTone firmware the same option is called Monitor or Promiscuous and is available through the menu or the monitor button.

Block 2: the radio won't transmit, or transmits but nobody hears you

Mistake 5. Your own DMR ID isn't set

The DMR ID is your unique identifier in the network — the equivalent of a callsign, only numeric. Without it the radio technically transmits, but the server doesn't know who's calling and may ignore the transmission. In the DMRhub dashboard you're issued a private ID from the 10000000+ block.

Enter it in the CPS under General Settings → Radio ID (in some CPS it's "CCS7 ID" or "DMR ID"). If you took someone else's codeplug, be sure to change the ID to your own, otherwise you'll appear in the network under another operator's callsign.

ImportantIf you work through a hotspot and the ID in the radio doesn't match the ID in the hotspot settings, the hotspot may reject the transmission or pass it into the network on behalf of a different subscriber. Verify that they match.

Mistake 6. Wrong Admit Criteria

The Admit Criteria field determines when the radio allows itself to start transmitting:

If Color Code Free is set on a hotspot where "something is always hanging" in the slot (for example, Pi-Star sends sync bits), the radio will wait forever and never get on the air. For a personal hotspot, set Always or Channel Free.

Mistake 7. RX and TX frequencies swapped

A hotspot operates in simplex: the radio transmits and receives on one and the same frequency. But some CPS offer separate RX and TX fields by default, and they sometimes get mixed up or left different. The result: the radio transmits on one frequency while the hotspot "listens" on another — no link.

Check that the RX Frequency field and the TX Frequency field in the hotspot channel are identical. The same value must also match what's entered in the Pi-Star/WPSD/RadioStar settings in the "Radio Frequency" field.

Example for a hotspot:
RX Frequency: 438.800 000
TX Frequency: 438.800 000   ← the same value

Mistake 8. Wrong Contact (TX contact)

The Contact (or TX Contact) field in the channel determines which talkgroup your voice goes to. If this field holds a group the hotspot doesn't serve, or one that isn't activated in the network settings, subscribers won't hear you even if the signal technically passes through. Make sure the contact points to an existing TG from your network.

Summary checklist before you call for help

If there's no link, work through this list from top to bottom:

  1. Does the channel's Color Code match the CC of the hotspot/repeater?
  2. Timeslot: TS2 for a hotspot, check with the administrator for a repeater?
  3. Is the talkgroup you need added to this channel's RX Group List?
  4. Are the channel's RX and TX frequencies identical (hotspot simplex)?
  5. Is your DMR ID from the DMRhub dashboard entered in General Settings?
  6. Admit Criteria = Always or Channel Free (not Color Code Free)?
  7. Does the TX Contact point to a real, active TG of your network?
Process of eliminationThe fastest way to diagnose is to enable Digital Monitor (promiscuous) on the radio and press PTT on the hotspot or ask someone to come up on the group. If the signal is audible in monitor mode but not in normal operation, the problem is in the RX Group List or the timeslot. If it isn't audible even in monitor mode, the problem is the frequency or the Color Code.

Why a ready-made DMRhub codeplug rules out most of these mistakes

Configuring all these parameters by hand for every channel is tedious, and a single typo breaks everything. That's exactly why a ready-made codeplug for your radio is available in the DMRhub dashboard: frequencies, Color Code, timeslots, RX groups and contacts are already set up for the network. All you have to do is enter your own DMR ID and load the file into the radio.

Contact lists with the current TGs and network operators are exported separately — in formats for OpenGD77, AnyTone, TYT and other popular radios.

Built a channel from the dashboard parameters but still no link?

Grab a ready-made DMRhub codeplug — it already contains the correct Color Code, timeslots, RX groups and contacts for our network. Most of the mistakes in this article are simply impossible in it. All that's left is to fill in your own DMR ID.

Ready-made DMRhub codeplug Download contact lists
Codeplug from scratchThe logic of channels, zones and RX groups Hotspot channel by handHow to enter the parameters step by step Color CodeWhat it is and why it matters MMDVM frequency calibrationIf the signal arrives but with errors

Sources

  1. Programming a DMR radio codeplug: admit criteria, RX group, color code — jeffreykopcak.com
  2. OpenGD77 User Guide: Digital Monitor, TG list, promiscuous mode — github.com/LibreDMR/OpenGD77_UserGuide
  3. DMR Notes and Tricks (BRARA): common hotspot and simplex configuration mistakes — brara.org
  4. Codeplug Programming Guide (BRARA): build order, RX groups, contacts — brara.org (PDF)