Talkgroups – and pick a colour, any colour ..

We’re often asked what a talkgroup is, and what all the rest of the jargon is all about, after all, you’re on the right frequency – you should hear stuff right ?  – Wrong !

In FM simplex  it’s easy to exchange audio,  you just TX and you will hear the audio coming out of your receiver, it’s very simple, but we can and do use CTCSS too, this is really handy, as you don’t get the FM squelch ‘chuffing’ or suddenly opening and disturbing you when you have the squelch set finely or local noise unmutes the receiver.

Most of us will undoubtedly remember the 1750hz toneburst used to access repeaters, which some older amateur repeaters still use,  which was needed back then, as carrier-access repeaters were generally regarded as a bad thing..  imagine an interfering noise source local to the repeater on it’s input frequency, holding the repeater open.. staying open for hours on end, just relaying noise, and all that entails,  thank goodness for  CTCSS too.

CTCSS also added the ability to have multiple groups of users all on the same frequency, all using different CTCSS tones, and all with Groups of users being able to hear only each other in the same group , while other groups using different CTCSS tones on the same frequency, only heard their users.. and so on,  this of course, also works on repeaters, used to most noticeably on the ‘community repeater’.

In DMR, the three most confusing terms that new users come across are Talkgroups,  slots, (or timeslots), and colour codes. the word ‘Talkgroup‘ comes from the crazy world of trunking or Trunked radio systems, where we in the UK are most familiar with MPT type trunking channels as the constantly transmitting ‘control channel’ often heard in the commercial PMR segments  of the VHF and UHF bands

As for colour codes – i would say just think of them as a DMR version of CTCSS.  and Timeslots – well in simple terms, DMR has two to choose from, each is it’s own seperate RF channel, and mostly slots only matters when using a DMR repeater.  They can be used to good effect on simplex too, but for now, slots can be thought of as just a ‘repeater slot’   TETRA has 4 timeslots, and some French system, which was called Detranet i think, has three –  but importantly they’re all TDMA  (more of which, in another article coming later)

So,  lets consider setting up a rig’s codeplug so that we can access our local DMR repeater, we know the frequency, we know the colour code and all we need to know now, is the talkgroup ID  It’s a number,  which we give a descriptive  name to like ‘UK Wide‘  or  ‘Local TG9‘ or whatever,  it doesn’t really matter exactly *what* they’re named in your radio, as long as the Talkgroup ID Number is correct, and what you’ve named it UK Wide or something similar which makes sense, like on the DMR-MARC  talkgroups.

At present some British DMR repeaters are not on the DMR MARC  network, but most do plan to be. also, every DMR repeater should somewhere publically list all used Talkgroups and slots, and maybe other settings for your codeplug, like we do on here or list setp info on the GB7MB web entry.

Talkgroups are just ‘virtual channels’ and you can have many different Talkgroups on a single frequency,  and  like CTCSS  – each different talkgroup only hears calls from the same talkgroup number (ID) programmed in the transmitter.  you can not transmit on talkgroup 9 and pick it up on a rig programmed only to receive talkgroup 1.On the DMR-MARC network there are many Talkgroups in use around the world, and there is a list of used Talkgroups HERE   – no DMR-MARC repeater carries them *all* and most here in the UK use about a half dozen talkgroups, or variations thereof.
Below is a condensed list of Talkgroups commonly used on most UK DMR-MARC repeaters

  •   Talkgroup ID number 1:    slot 1:
    Worldwide,  all-language calling Talkgroup, used only if you are calling worldwide, QSY to up to the most local Talkgroup you can. QSO’s on here, if allowed, must be short.
  •   Talkgroup ID number 2:    slot 1:
    European-wide  multi-language Talkgroup,  also on , this Talkgroup can be used for QSOs presently, as always, it is recommended to change to a more local Talkgroup whenever possible.
  •   Talkgroup ID number 8:   slot 2:
    used for roaming between neighbouring repeaters, Your rig, if correctly configured, will automatically switch to the next strongest repeater as it comes into range whilst you are mobile – something like a mobile phone does when physically moving between ‘cells’ of differing strengths
  •  Talkgroup ID number 9:   slot 2
    Local calls,    This is used for QSO’s between users on the same local repeater, this talkgroup is not routed across to other repeaters, and is more like a standard repeater.

    (NB TG 9 is most used for simplex DMR in the UK also, but you can use any, and any colour code) 

  •  Talkgroup ID number 13:    slot 1
    Worldwide, This is for International English language QSOs only.
  •  Talkgroup ID number 235:   slot 1 (was slot 2)
    UK only,   calls on this Talkgroup are for QSOs between UK Amateurs Nationwide, where TG8, TG9 or simplex would not work.

Every repeater can carry their own mix of talkgroups as per the repeater groups wishes or requirements, so do not necessarily expect these talkgroups to always be available all of the time, the network is growing and adjustments are being made accordingly to accommodate more users, provide more facilities, solving issues and to be more efficient.
There is much more to DMR of course than this basic introduction, and there is more to talkgroups too, like the All-Calls Talkgroup and private calling, to name just a couple, but I’ll leave you to discover those for now…


All work, text and images © GB7MB

An audio pre-amp for wired headset use with the Motorola DM4000 series. by ‘Mot Orious’

This is a very useful article penned by Mot Orious  here at GB7MB – i only posted it  !

The circuit presented below is a simple op-amp based pre-amp to provide the necessary gain to enable a two terminal electret microphone to be used with the rear microphone input on the Motorola DM4000 series transceivers.
The circuit can easily be constructed on a small piece of 0.1″ Veroboard or similar.
For vehicle use the 12V supply is ideally obtained from the switched auxiliary output, maybe tapped off the cigar lighter socket etc. Screened cable should be used between the headset and the input to the pre-amp. The output is taken via screened cable to the rear accessory connector on the DM4000 series transceiver. PTT is also routed to the same accessory connector.


The pin-out of the DM4000 series accessory connector is shown below. This is the view looking towards the back of the set, pin 2 is top left, pin 25 bottom right.




by ‘Mot Orious

 All work, text and images © GB7MB

A USB programming lead for the Motorola DM4000 series of mobile transceivers. by ‘Mot Orious’

This is another very useful article penned by Mr. Mot Orious  here at GB7MB – i only posted it.

The USB programming lead for the DM4000 series is an expensive item if bought from Motorola. However construction of a home made version is not complex.

You will need

1. An old, good quality USB lead
2. An accessory plug, Moto part No. PMLN5072A.
3. Ideally a crimp tool to suite, however a soldering iron and needle nose pliers will suffice.

Cut the USB cable to the required length removing the socket end. Remove approximately 35mm of outer jacket from the cable taking care not to damage any inner insulation or the bare earth wire within the cable.

USB cables normally have the following standard colour code
D+       =     Green
D-        =     White
+5V      =    Red
Gnd     =    Black

Check yours just to be sure !


Note the bare (shield) wire is also crimped together with the ground wire.

A note about pin insertion. The pins used in the accessory connector must be inserted with the correct orientation. As can be seen from the image below, the pins have a locking protrusion. The pins are inserted so the protrusion is pointing down for the bottom row and pointing up for the top row. This ensures the pins lock into the shell and enables the pin removal tool to function correctly. The pin removal tool is inserted into the lower or upper slot adjacent to the respective connection pin.



By  Mot Orious
 All work, text and images © GB7MB

A beginners guide to using the MotoTrbo CPS

Its a fine and long standing tradition amongst Radio Amateurs to convert old military or commercial (PMR or Land Mobile) equipment to get onto the Amateur radio bands, but technology moves on and its time Amateur Radio did too. You’ve bought a DMR transceiver, so lets get the set programmed up.

While not always immediately obvious how to set up a channel  if you’re new to any radio programming software and you’ll be wanting to get started, here we’ll show you a quick and easy way to get started, with screen-grabs and some basic facts.

First things first – select Expert mode, like pictured below, and now save your codeplug – dont write it back to your radio, save it to your PC.  do not forget this step, because If you make an error one day, you may need to revert back to an earlier codeplug, in fact, we suggest that you save most codeplugs’ you make, provided you name and date them – as they take virtually no space up on your PC.
Click on the thumbnails to get full pic / screenshots

expert mode

And before we begin, a few factoids.

1:) You can not swap or use the codeplugs, software or leads on or between Motorola and non Motorola sets.
2:) Do not ask us for Mototrbo software.
3:) Motorola DPxxx program leads are expensive because they have a ‘chip’ in them.
4:) You cant do Dstar or Yaesu digital on them.
5:) Only the Motorola MotoTrbo SL4000 portable has no FM (as far as i’m aware)
6:) Note difference’s between TDMA and FDMA – TDMA is a pulsed system unlike less efficient FDMA Yaesu/D*star
7:) A codeplug is the program data from the radio, most commonly seen, saved as files on your PC
8:) High power DM4600 codeplugs can not be written into standard 25w DM4600 codeplugs
9:) There are likely mistakes in codeplugs, its up to you to check them before use, we will not be held responsible.
10:) There are a few different approaches to programming them, i prefer simplicity.

That said, lets get ‘programming’

Lets create a simplex DMR channel. As you can see the radio ID is already filled in – yours will start with 235 – instead of just 007 here, in the box – just above the Motorola graphic sign. (you can change that too if you get the right size)


For a simplex DMR frequency you need three bits of info, frequency, colour code and numeric talkgroup ID, and for a repeater you obviously need the TX/RX frequencies   **and the slot number used for each talkgroup**

Around Morecambe Bay we use 430.3125 DMR simplex, talkgroup 9, and colour code 1, so lets use that.
First, set up the ‘Digital Contact’ like in the screen-grab below –
first we are going to define which talkgroup (group call) to TX on.

So, in the left-hand side pane, pictured below, navigate to Contacts / Digital – and right click on ‘Digital’ and add a ‘Group call‘ – it will probably be named ‘Call 1’ which will be wrong for most channels, so always rename these to something meaningful – i named this ‘Talkgroup 9’

Then across at the top of the right-hand pane, change the number in ‘Call ID’ to whatever talkgroup ID number you need. in this case, ‘ 9 ‘ it should then look like ours pictured below when you’re done..




Next we need to define which talkgroup(s) to receive on – so, it’s talkgroup 9 again, Yes, you’ve already defined it, but as you can receive up to 16  – you’ll need to specify just which ones in a list, of course we’ll only need to add our single talkgroup – so navigate to RX Group Lists / Digital / and right-click on ‘Digital’ and add  ‘RX Group List’
Strictly speaking, you don’t really need to specify *any* RX grouplist in the RX field, in which case the default TX talkgroup will be used for RX if set to ‘none’



see the ‘Talkgroup 9’ you’ve just made in ‘available’ ?  – so now click  ADD so it appears in ‘Members’  then rename it to ‘Talkgroup 9’  then in the left-hand pane rename ‘List 1’ to ‘Talkgroup 9’ like below ..


Now its time to add some frequencies !
In a new or existing zone,  right-click the zone you want the new channel in and select ‘add Digital channel’ and rename it to whatever you want the channel display on the radio to say. here ours below are automatically named  ‘Channel 1’ ‘Channel 2’ – the square icon represents a digital channel, the other means analogue FM.

and of course, rename the channel to   430.3125 DMR – or whatever you want to appear on the radio display. Select the channel you’ve defined and fill the channel info like pictured in on the right-hand pane in the screen-grab below


So after the frequencies are in, and you’ve set the colour code above, and the slot (if it its repeater) select your newly made ‘talkgroup 9’ in both the RX section’s ‘Grouplist’ drop-down, (arrowed) and again over in the TX section, in the  ‘contact name’ dropdown. Make sure your transmit timeout is something a bit longer than the default 60 seconds and make sure all the ‘Emergency’ stuff is unticked too, as i need to do in this example here below. again arrowed


You have now made a digital channel for your MotoTrbo set. You can either write it into your MotoTrbo set or carry on programming your set up. The DM4600 codeplug on this site can be downloaded and some of its bits dragged and dropped into your codeplug, but beware, if you drag ‘n’ drop digital channels from another open codeplug in to your codeplug, you will need to set up talkgroups and RX group lists separately, and name them exactly the same too, which is very tedious. You might want to do this too..

And finally – a lot of people new to DMR can’t tell when the person they are listening to has stopped transmitting.  so, back up in ‘General Settings’ click ‘channel free indication tone‘ and it you really hate the ‘chirp’ everytime you press the PTT,  choose  ‘Talk permit tone‘ to ‘None‘ in the drop-down.

All work, text and images © GB7MB