turn your smartphone into a P25 or DMR HT ?

Well, You can certainly do some neat tricks with SDR’s nowadays, clever things like making your Raspberry PI transmit AM/FM/SSB and the (slightly pricey) but very interesting HackRF board. I see Fenton Dynamics have been busy lately, they’ve rebranded now from BriCom, and i completely missed them first time around,   Anyway, this device, which is sort of a set of modular clip-on-goodies for your smartphone can magically turns it into a VHF / UHF P25 / DMR / FM / HT is available, and, not that you can tell, but the photo above is of the 2w VHF iPhone 6 version apparently, well so it says in the blurb, all wrapped up in a  Nextpaq case.

For more info check out their August 2015 Youtube posting HERE  and head over to Fenton Dynamics too, if you have a supported Android or IOS device it may appeal to you .. it does far more than what you’d think, with a dual band module, DMR, and P25 modes, analogue signalling like MDC1200 etc, trunking, GPS, ROIP, SOS, alarms etc, and there’s an SDK kit available for third party developers too, and hopefully the apps that will appear as well. It all seems very modular and well thought out, the clipon goodies even has their own mic and speaker and battery, and it’s all neatly wrapped up in a $99 Nextpaq case – with the actual Dxbm modules beginning at $65 it’s beginning to look mildly Interesting. Watch this video or this earlier video which hopefully gives a better idea of it…

All work, text and images ©GB7MB and @mbars.co.uk

Unencrypted TETRA decode with a £6 RTL dongle.

There seems to be some interest in attemptimg to decode unencrypted TETRA witha a £6 RTL dongle, I will post my own how to perhaps later on when i get time, but all i did was read and do what it says here, and you don’t need me to re-tell you anything more than it says in the linked how-to below really..


doing that is the easy bit – Have Fun 🙂

All work, text and images © GB7MB

North America Mototrbo CPS 12 build 642 bug.

Motorola released a caveat for North American users of CPS_12 build 642..

Motorola issued a ‘Field service bulletin’ because there is a serious issue some users are experiencing where after writing back to the radio using CPS 12 build 642 you lose ability to PTT. not good.
It concerns subscriber units running the 2.4a and 2.4b, CP200d, CM200d, CM300d r01.01.11 and r01.01.20,and xpr 2500 3000, 7000 and 5000 with r02.40.11 and r02.40.20
The EMEA firmware 2.50.04 is said to be ok (so far) as for the CPS, I believe there is a bug fixed version coming soon for NA, and the same for EMEA .. so i hear on the grapevine.

Lets hope the same affliction doesn’t affect EMEA users when moving to MotoTRBO CPSv_12.. it does seem to me at times that the quality normally associated to the Motorola world doesn’t apply to the CPS or firmware, instead bugs are not uncommon in their releases which is a very poor show Moto.. we wish the bitware was as good as the hardware, hopefully public service equipment gets more thorough testing…

If you’ve any CPS 12 bugs to report, feel free to let us know, and once again, especially for Amateurs eager to jump to new CPS or firmware, if the firmware or CPS doesn’t offer any ‘must have’ features, think about why you’re ‘upgrading’ living with buggy firmware can be a pain for Radio Hammies, but could be life or death for commercial users, if you get afflicted you will need to rollback *if you can*, and not everyone has capability to do so either, so if it aint broke… don’t fix it.

All work, text and images © GB7MB

Decoding DMR / P25 with the RTL SDR – an update

Setting up  SDR# (or SDRsharp) for use with an RTL dongle is the easiest and cheapest way of listening to most digital voice modes on the VHF and UHF bands, and you don’t need to know talkgroups, colour codes, slot or anything, so it’s much easier than any other method, and it’s also great for general FM, AM and SSB monitoring too, with sensitivity on par with typical purpose made mobile and portable transceivers, though, for analogue listening, i do think the SSB AGC performance on the SDR side needs some improvement, but that may just be my personal preference, and  on the decoding side, there is no DSTAR audio decode built into DSDPlus ‘out of the box’ (on Windows)  but apart from those very minor issues, it’s a great way to go listening nowadays, and it’s not half as fiddly to set up as it was  earlier, so, as interest in decoding digital voice is still on the increase, it seemed like a good time for a refresh.

You will need:
PC  –
anything from the last several years should be fine,  most of us have PCs that are at least dual core by now, so anything runs Vista (remember that nightmare?)  will do. Windows 10 users may be a little out of luck at the moment, as i believe results can be variable.

Of course, You need an RTL SDR dongle.. this blue MK II one (below) was £6 off a well known auction site, and came with the usual TV remote and the pointless UHF magmount, but hey.. i need  fridge magnet, The SDRs’ coaxial connector is probably going to be an MCX, it was on mine, but some dongles do come with the more traditional TV type Belling-Lee or even other connections, but i prefer BNC. On my previous SDR dongle i removed the whole MCX and fitted a BNC flylead. You can use 2 or 3 extension USB cables to get the receiver up and away from the often ‘RF noisy’ computer gear and possibly save a little bit of cable loss too.
RTL SDR dongles also run well under Linux, Linux driver installation here and Mac OS X Mac OSX driver installation here and an old 2012 GQRX SDR receiver complied for Mac (Thanks Elias) it’s GNU Radio based too. Even Raspberry PI’s and other SBCs can run RTL SDRs too. RTL SDR dongles can even run on Android, with drivers available in the App store, and it can even decode digital voice.

Linux can, of course, run digital voice decoding quite well too, in fact the first DSD decoder program ran on Linux only, not Windows, so to decode on Windows you had to run Cygwin and it seemed a bit fiddly, until DSD was be ported to work on Windows natively. There is a great amount of SDR work going on, not least of all on Linux – check your repo and GIT for goodies, Linux can even decode unencrypted TETRA voice, with GNUradio, so Windows and Mac users are out of luck again with that one, i may do an article on that in the future, if anyone’s interested, but it’s not for the beginner or faint-hearted, but is reasonably straight forward if you’ve compiled  software before on Linux.


The MK II RTL SDR – slightly better spec.


and you may want something like this MCX to BNC lead..


The RTL SDR dongles have recently had a bit of a makeover recently, and are now available as the updated R820T2 tuner, and these do seem to have a slightly better receiver compared to my other 2 or 3 year old SDR, it does seem slightly better too.  The chinese sellers have got a little more wise too, and are often selling these with SDR in the description too, so searching for RTL SDR easily brings results, expect about £6 from Chinese sellers.
Before we start, a brief overview might seem appropriate, as using a PC to tune the bands is still an experimental, but maturing technology, and may take a little getting used to, tuning around on a SDR is quite different, no worse, no better, just different, and besides using your mouse wheel as the VFO, you can buy actual hardware VFO type knobs – on USB leads to control software. Electronic musicians have been quick to adopt real hardware controls for software instruments, and they work well too.

The RF signals come in from your dongle to your PC running the SDR program, then (my badly drawn green cable thingy) signal carries the FM audio into the decoder program (DSD Plus) and then out to your speakers. You will need a software version of one of the green cables i have drawn. Yes.. i know my quick drawing below is rubbish !


You can install it now if you like, but it will want to reboot to take effect. Don’t install the other ‘Banana’ or ‘Voiceemeter’ apps, as they’re far too complicated for what we need.

First things first, Windows drivers often come with dozens of CPU chomping addons and crapware, some soundcard drivers can be over 150Mb download, which, frankly, is ridiculous, and they can install unneeded and unwanted software and sys-tray icons which can, in some cases, be a privacy threat and slow down your PC down. The only reason I am bitching about this, is because some audio drivers, by default, run your computer’s audio through some weird surround sound DSP nonsense automatically, which is no good at all if we want to use the soundcard for something genuinely useful, so it’s worthwhile checking your Windows system tray, and  / or Windows control panel to make sure all DSP and sound effects are turned OFF, these effects can occasionally hamper attempts at decoding digital voice.

Software List:


VB Cable

Airspy SDRsharp receiver  and  here’s the Airspy wiki   (it’s actually quite good)

DSD Plus (digital voice decoder)  and it’s associated homepage  HERE

When you plug in you RTL SDR – Windows will prompt you to install some drivers – don’t bother – but if it does try to download dtivers, let it finish, as you’ll be replacing them in a few minutes anyway.
You’ll may need to install the Microsoft .net framework too, depending on what version of Windows you are using, but you probably have it installed already.

You will have unzipped SDRsharp into a folder then, the file is still called sdrsharp.exe, and you might need to move the whole folder somewhere else, other than the downloads directory where it probably extracted to, You could make a shortcut if you like, to sdrsharp.exe, and also unzip the DSDPlus_xxx.zip you downloaded too, and you could create a shortcut to DSDPlus.exe for convenience. I dragged these two shortcut icons into the start menu for ease of use.

Now it’s time to test it.
start SDRsharp and you should see something like this below:


First thing, check at the top left where it says “Source” and open the drop down menu and select RTL SDR (USB) …. if you dont see RTL SDR listed and the dongle is plugged in, either navigate to the SDRsharp folder and run Zadig  and follow the instructions below, if Zadig,exe is not in your SDRsharp folder already, d/load it here and run it as Administrator, Windows will prompt you for permission.
In the running SDR screenshot above, DSDPlus displays Radio ID, group ID (talkgroup) colour code, and slot.

Running ZADIG (if you need to)
select Options – then List All devices and then from the drop-down, select “Bulk In Interface 0” In the drop down box, choose Bulk-In, Interface (Interface 0) thoughit might also show up as something like  ‘RTL 28320’ or something similar, and that’s ok.
Just make sure that ‘WinUSB’ is selected as the target driver, and then click on ‘Replace Driver’.. you may have to reboot, but next time you start SDRsharp, your RTL SDR should now be in the list of available devices, select it.

Setting it up.

Under the left hand RADIO tab (see the above screenshot) set the mode to NFM, i generally set the filter bandwidth about 12500 for DMR decoding, that’s fine for most normal comms FM listening too, and on NFM i set the steps to 12.5 kc.

These USB devices are cheap and mass produced, the things are not calibrated too accurately, and so we need to fine tune the SDR so they both agree on freq.  (if you’re adventurous and run Linux, try Kalibrate which uses GSM, but it’s really overkill) and you *can* fit a much more accurate crystal.. but i’ll leave that up to you to decide.

Start SDRsharp and click the cog on the SDRsharp toolbar, you will see your device listed, now click both the AGC tickboxes to maximise RF gain, note the frequency correction adjustment there too, we need to find a known signal on air and tune the SDR to the correct freq readout, then, whilst listening, tweak the frequency correction to get it spot on. CW or SSB mode is good as you can more or less find zero beat, as you see, this one is set at +68


Now you’re up and running with SDRsharp, you may want to try to decode digital, check the screenshot, and notice the ‘filter audio’ needs to be unticked for decoding: same for Pocsag etc. squelch off/ open.


also make sure to send the SDR’s audio to the DSDPlus decoder program – select Output to ‘VB Cable input‘ and you should see the ‘scope display on the DSDPlus program jumping about wildly.  If you dont see DSDPlus’ scope displaying activity (even on random FM noise) it could be that audio routing may need one slight tweak, here on my old Windows7 craptop here, i had to go into the control panel, then sounds then check in and output devices as you see below, then it worked. note the audio bargraph level meters reading, your soundcard will probably be named something different.


Get tuning !   if the signals you see are good, but garbled or no audio, they may be using privacy or encryption, or have interference, or it may be data or GPS (LRRP) and all kinds of stuff going back and forwards, still getting problems, check your audio levels, RX bandwidth, make sure your fine tune is correct,  that filter audio is OFF and you are indeed on NFM with no squelch. Remember there is no windows binary widely availble for dstar audio yet (that i have seen) and encryption is used alot.

In case anyone is wondering, clear / unencrypted TETRA isn’t able to be decoded on anything other than Linux at the moment, and it will probably never appear on Windows anyway, On Linux it’s only done with GNURadio as a base, GNUradio companion has the most horrible interface i have ever seen (but it works very well indeed) and there’s not much unencrypted TETRA about anyway, but after all the hours of compiling and patching stuff, it’s a lot of  fun learning about it.

SDR and decoding digital voice can be fascinating, cheap, and lots of fun,  thanks to some really smart people out there, and some really cheap hardware. It offers up a new way of visualising the band and is a crossover of radio experimentation and computer tech, and it’s a developing part of the hacker and radio amateur communities too..  and who knows what direction that may lead to ?   and long may it continue.. Have Fun..

If money’s no object, or if you really must have a VFO knob for your SDR, and let’s face it, most mouse-wheels are pretty crummy for making small or accurate incremental adjustments for any length of time, so you might want to treat yourself to something like the Griffin PowerMate controller .. it’s bluetooth, but it’s still hugely overpriced as it’s little more than a rotary encoder, i wouldn’t mind, but such devices have been around for several years already, and the Chinese manufacturers still haven’t got around to making them for a fiver yet, most you see on Ebay are from Japan or the USA, or if you like the idea, you could always make one…  happy SDRing..


All work, text and images © GB7MB

The Hitchikers Guide to MotoTRBO CPS


To Quote Zaphod Beeblebrox in ” The Hitchikers Guide to The Galaxy  ”
(like i need to put a link to it’s Wikipedia entry)

” It’s the weird colour scheme that freaks me. Every time you try to operate one of these weird black controls,
which are labelled in black on a black background, a small black light lights up black to let you know you’ve done it “

Well, it’s probably not quite as cryptic as the spaceship controls mentioned above, and the MotoTRBO CPS does have a decent help system included with it too, but for some new to the digital voice modes, it can appear somewhat cryptic, and we do occasionally see a codeplug with incorrect settings in.

Adding a new basic FM or digital frequency is simple enough, (see other articles on this site) but we really need to ensure that we are all good neighbours on the repeater and network, and, because we are guests on the network, we must follow the rules and not cause any issues on the system, because they could remove a DMR repeater off the network if this was the case. MotoTRBO sets are not Amateur Radio sets and they’re full of features which most Amateurs may well be unfamiliar with, and incorrect settings here can be problematic or antisocial, so we really do need to check and maybe adjust some of these.

General settings: 
Obviously your DMR MARC ID goes in “Radio ID”  and untick the “Private Calls” box,  Private calls are expressly not allowed on the DMR-MARC Network and not over GB7MB either at any time.

Talk Group Call Hang time adjustments – are not too critical, but probably set it to 1000 or 2000.
sign in/sign out is not used,   Test mode – doesn’t really matter – ARTS is not used either, so you may as well disable the ARTS tones too, the rest are mostly personal preference.
As you can see here, the codeplug i loaded up for this example needs tweaking.

radio disable

One of the most often strange things, especially on DMR repeaters, is that there is no courtesy tone (link to a pdf)  and many find that can be quite unsettling, as there is no noise or squelch tail on MotoTRBO repeaters .. (we at GB7MB are working on it though)  However, your MotoTRBO radio knows this too and the radio can itself generate a ‘beep’ where the FM repeaters ‘k’ tone or pips would normally be, and this is called the ‘channel free indication tone‘ and it’s very handy to have it switched on.

Another one, where a quick tone sounds when you press the PTT button, is called the ‘Talk permit tone‘  and can be set to sound on FM, DMR, both or none. I have this set on none on my mobile, but on my portables, i often have it set to on – on DMR – the reason is that if you sit down with the HT on your belt, it’s all too easy to set the HT into TX accidentally on the side of the chair or whatever, and not know !

You can turn all or some, tones off in the radio’s menu, you dont need a PC hooked up.


Many of that settings are self explanatory,  but before you start looking for help in the CPS, ensure the Help pane is enabled in the View menu and select EXPERT view too. Volume Offset is the tone volume.. ARTS basically, just bleeps the set when a valid transmission is received, and it is not really used on Amateur radio much.

In the Menu
Here in Menu section the you can configure the radio’s menu items and more.

!!   IMPORTANT  !!!
The radio Enable and Disable and it’s associated decode options like remote monitor and Radio Check should all be unticked too, because, however unlikely it may be, you really don’t want to accidentally  STUN, DISABLE or KILL someone else’s (or your own) DMR rig or have your Mic remotely switched on or worse whilst tweaking or experimenting with codeplugs and radios… it has happened, with users monitoring non Amateur systems – and as Amateur radio is full of people experimenting with radios, the possibility of this happening through incorrect programming of DMR channels, or 5 tone and MDC1200 etc. should not be ruled out, so good luck getting ABC123 Taxi’s to un-stun or revive your radio.

You probably only want EDIT and Text messsage Alert ticked in “Contacts” – most are to do with private calls, which are not allowed on GB7MB (or any DMR-MARC repeater)
Scan – One of the great things about MotoTRBO sets is their flexible scanning options, scanlists, (even if they are only 16ch max) which are something i wish All Amateur radio sets should have, I’m sure some may do, but all ticking these scan options enables you to directly add and remove channels from the scanlist on the fly, and that’s done via the rig’s front panel. there are an almost unlimited number of scanlists you can make, and if you have the IMPRESS DTMF Mic  it’s even easier and is much more fun to play with.

Anyway – lets move further down the CPS menu now, and over into the
Channel configuration window
, because there are a few bits in there to check..

udp headerhere we are, in a channel wide pane, now, you won’t have an option board fitted, so this will already be unticked and the others greyed out as above, ‘allow Talk around” is basically TX on the repeater output and that’s not exactly reverse repeater or listen on input as Amateurs sometimes like to use, (so near, yet so far Motorola) so i guess this is personal preference, but generally it’s pretty pointless.

IP site connect is only available on DMR-repeater channels.  Channel Inhibit pretty much stops SCAN from reverting back to this channel, and there’s little point ticking that too.
Compressed UDP Data  header – another one that’s not going to blow the radio off the shack table if you click it, but for other manufacturer (legacy) DMR radios that don’t have this feature, you can untick it to enable a little wider compatibility..    Below ALL EMERGENCY SETTINGS should be OFF !  The MotoTRBO Emergency system is not implemented on DMR-MARC or any British Amateur DMR repeaters that i know of.

In the channel pane, you should set your Emergency System  to NONE and set your rigs  TOT  (Time Out Timer) to something sensible,   300 – 400 seconds is ok on GB7MB at present.  We do ask you to ENABLE TX INTERRUPT on all GB7MB channels, although other DMR repeaters may well not allow this. This enables stuck PTTs to be remotely de-keyed – thus keeping the repeater free from accidental squashed (on TX) mic PTT keys etc.

TX Interuptable frequencies  wants switching off on your DMR radio when using GB7MB at present, until further tests are made by the repeater keepers. Private Call Confirmed should be unticked, and disable data call confirmed too. Please also disable Enhanced Channel Access and CSBK data on GB7MB too please. The keepers are doing tests with these parameters, and so far there appears to be no real benefit, on the contrary, it seems to have a negative call setup time and may actually increase or chances of ‘doubling’

tx interrupt
Hopefully these articles will help demystify some of the less often discussed parameters in the MotoTRBO CPS, and this is intended for all users to check their settings and make sure they are not clogging up the repeater with unwanted data and background services, and with a little bit of luck, help to make life on GB7MB better for everyone, and safer and more fun.
These recommendations may not be applicable on ALL DMR-MARC repeaters, and they may indeed change on GB7MB over time.

All work, text and images © GB7MB

How to update your contact list (Motorola)

It seems there is a little bit of confusion surrounding callsigns not being displayed in the radio’s screen.. here’s a quick ‘how to’ that may help. As for callsigns on the various monitoring websites, don’t worry too much about that for now, because DMR-MARC is doing some big changes to the network, so please be patient.

First thing you should know is that your rig is doing the job of translating the DMR-ID of the person currently transmitting to you, into a callsign and name for your rig’s display. The information to do this is completely held in a database in the radio, and it’s a very simple job to update it.

As more users are coming onto DMR-MARC you may want to update the contact list regularly. The radio can store a maximum of 1000 contacts, so when there are more than 1000 DMR-MARC IDs in the UK – you will have to delete some,  at the time of writing this article there are 968 in the contact list generator that we are going to use.

Some of your radio’s 1000 contact list capacity are taken up by Talkgroup configurations, but for most of us, that’s less than about 10, so at present we can fit all 968 contacts, and all needed Talkgroups into the radio ok.

A Website called TRBO LINK will automatically make you a codeplug (don’t write it into your radio, there are no frequencies in) You simply tick the regions of the world you want adding into your contact list. Here I’m assuming you are in the UK and wish to have all the present contacts displayed .. so here goes.

Go to the Trbo Link contact list generator site here and select the contacts you are interested in, like i did below..
the coloured bar tells you how many contacts you have selected so far..

select contacts on site

then when you have done that, check the number of contacts you have selected –  if you do go over 1000 contacts, notice that it tells you it will truncate the list, also remember that you will still have to lose a few contacts if you get 1000 or more – because a few entries in your rigs database will be used for Talkgroup configuration.

Next: Select the type of rig you have, or the nearest type,  mine is the DM4600 – so i chose DM4601. and click the Generate button. save the file to your PC.

rig type
Okay,  so, the file it gave you is a codeplug, it will be named something random like 98649867509.ctb   although for clarity you might want to rename it something more meaningful like “2015 March 6 contact list only.ctb” that i am using in this example.

Next thing is to fire up the MotoTRBO CPS and read your radio – and save the codeplug you are using–  name this something meaningful too, because if you run into difficulties doing this, you may just want to go back to what you are using now instead, but i doubt you will have any problems, as long as you know how to drag ‘n’ drop in Windows, and select multiple files.
Now in your codeplug, navigate (in the left hand side Explorer type folder-view tree thingy) to the “Contacts”  blue folder, then again into the ‘DIGITAL‘ in there.. That’s where your contacts are stored. You might want to have the CPS sort these by name or type, if you do, right-click and select Sort and choose which option.  The secret here is to delete just the contact names and leave the Talkgroups, which sounds harder than it is, as the CPS already sorts the callsigns. Once you have selected the callsigns only, delete them.  You saved the codeplug before you started right ??

Now as you see,  i’m left with just Talkgroups in there. Yours should look something similar, Your Talkgroups are probably named something else. It doesn’t matter.

old contacts now gone

Now, In the CPS, keep your radio’s codeplug open and now click the ‘Open’ button and open the “2015 March 6 contact list only.ctb” (or whatever you named it when you downloaded it)   – the codeplug that the Contact Generator Website just sent you earlier.
open So now you have 2 codeplugs open in the CPS …  now go to “Window”  up there on the Menu bar and click ‘ TILE” then both codeplugs will be arranged one on top of the other, which makes for easy drag ‘n’ drop operations … Now in both windows, navigate (in the left hand side Explorer type folder-view tree thingy) to ” Contacts / Digital ”

drag new

Now you have your almost empty contact list in your radio’s CPS window, and the codeplug that the website sent you open in another window, both open at the ” Contacts / Digital ” folders.

All you have to do now is select all the full callsign list out of the downloaded codeplug, and drag and drop them onto the blue “Digital” folder of  your radio’s contact list.
– it may take a few seconds to either move,  drag or drop the new contacts into your rigs contact list.

If you’ve been successful you can close the downloaded “2015 March 6 contact list only.ctb” codeplug and you dont have to save it if it asks. but you now only have your codeplug open and you can check it for typo’s and other errors before you write it if you want.

If you want to add a new contact – like your mate’s callsign doesn’t come up on your display, it’s simple enough to add it.  You have the ID number that you want to display a callsign for. To add a contact, go to the ” Digital / Contacts ”  folder, right-click and select “ADD” Private call  – it will appear at the bottom of the digital contact list, likely named ” Call1 ” – right click it to rename it with the callsign you want displayed.  I called mine ‘Hax’ in this example as you see.. Of course, You type the callsign you are adding instead 🙂

make new private
rename it
(Apologies for the quality of the last couple of pics)

Now add the DMAR-MARC ID of the callsign you just added above, this one here 12345678,  is a silly example… dont use that, or don’t make one up,  a proper UK one will start with 235****   235 is the UK’s number.


I untick the ‘ Call receive tone ‘ (the CPS automatically switches this on when you manually add a new digital contact) and  set “Text Message Alert” to “Momentary” too.
Now – once you have checked all this, and it seems ok, it’s time to write it back to your radio. You will want to SAVE this codeplug too, as usual, i strongly suggest naming and dating the codeplug’s filename accordingly.

Have Fun..

All work, text and images © GB7MB

DM4600 audio out – the missing feature..


The DM4600 radios are very good indeed – they do a lot of things and perform well, but here’s one thing that bugs a lot of people … where is the audio out jack ?

Well, of  course, there isn’t one, sorry about that.  remember these are not designed for Amateur radio use, it’s PMR gear, and in the age old spirit of Amateur radio, we adapt these commercial sets to our own use, and adding an line out jack is a simple 10 minute job..  if you already have the parts.

I hope you have studied the great article  HERE by our very own Mot Orious here on MBARS,  about building a little audio preamp for use with these sets too – and you will have noticed the nice selection of pins on the back of the DM4000 and DM3xxx sets.

This little lead gives you fixed volume line-level audio out from the rig, whatever the front panel volume control is set at. That way we don’t have to drill holes in the set and put a 3.5mm socket in line with the speaker to silence the set when used on headphones !
I think this actually gives more control.. we can record or stream it around the house or into other audio equipment, provided they have line inputs. i dont know the actual output impedance from the accessory socket, but i imagine it’s reasonably high, and the fixed output it provides, easily drives some high impedance ear-buds form a mp3 player type device, with enough audio for comfortable listening without the need for one of those cheap in-line headphone amps off Ebay, or just making one with a op-amp.

First thing you need is the accessory connector… it’s pretty easily available, Motorola part number PMLN5072A and they are available on Ebay for £6 or £7 – (just paste that part number into the Ebay search box) or maybe a few pounds more, grab one off your local friendly Motorola dealer. Get the Ebay ones while you can is my suggestion.
Also get a 3.5mm in-line jack socket too… (or whatever plugs into your amp) we used 3.5mm jack because the friend i made the first one for wanted to use headphones, I ended up making one for myself too.


Here are the parts you need..  on the right are the three metal strips you see are the pins, and that small shiny rectangular thing above is the pin removal tool, should you need it, on the left you see the black plastic main shell,  and the 3.5mm socket lead around it.
Total cost around £8.

Prepare the 3.5mm cable – i used 2 of the 3 wires in the lead, as it’s a mono set, i only need one channel, so with a DMM check the tip and sleeve of the socket –  you can’t really get a meter probe into the socket, so as i bought a headphone extension cable, i snipped the unneeded plug end off and plugged that in the socket instead .. with the added bonus that the wire colours will be the same. I tinned the wires and fitted the pins..
tin wiresThen, after nipping the pins up with a pair of small long nose pliers, i heated the pins to reflow the solder that i applied when tinning the wires for added strength.  Now it’s time to decide where to put the pins in the shell,  so i referred to Mot Orious’s pinout HERE and it’s pin 14 and pin 16 we are interested in today..


That’s the two there we’re interested in – above, on Mot Orious’ diagram, Audio Ground and RX audio and below, the same pins as seen looking into the socket at the back of the DM4600

thats these two yellow arrows – this photo is just  looking straight into the back of the DM4600 connector – with the set the right way up. So, Pin 14 is the main RX Audio out pin (signal) and pin 16 is a handy ground right next door.  Note the way the pins are actually numbered here, it’s not the same as the anti-clockwise numbering you find on ICs.. oh deary me no. Instead, the numbering jumps ‘across’ each time, zig-zag like instead.

Pin 1 and the corner pins are numbered already on the socket, but tiny raised black numbers on black doesn’t exactly stand out too well, so lets be doubly sure here, and it doesn’t even hurt just to double check with a scope. which is what i did, this is what FM noise looked like out the back of my VHF DM4600 with the squelch open.

Right .. now we’re cooking, so make sure the signal doesn‘t change on our pin 14 when we turn the main rig’s volume down. Anyway,  you’re now ready to insert the 2 pins into the shell. Choose the pin that is connected to the ‘tip’ and insert that into pin 14 of the shell, making sure that the ‘barb’ on the pin faces upwards, as this will lock the pin into the shell, do the same for pin 16 too, and that the pins are locked into the shell ok, when you are done, leave a little bit of slack cable, and tightly apply the cable tie.

wires in shell

and now your Motorola audio-out lead is done.

finished 1Obviously it’s a very simple job, and is much the same as making the programming cable as Mot Orious detailed here, it’s probably going to be quite handy for some folks, and you can hook it to the car audio system if you like or what have you.


All work, text and images © GB7MB

RSSI, what the hell is that!

I did consider the title ‘where have my μV gone’ but hey here we are. If you are rich/lucky enough to have an Impres microphone for your shiny new Motorola DM4600 or have a DP3600/4600 etc you may have played with the RSSI function. Received signal strength indicator, an S meter to you and me. The information is presented in dBm, that is decibel relative to 1mW.

Why move away from the traditional μV? Well using a dB scale makes a lot of things easier. For example if you know from experience that your rig can receive a DMR signal with no artifacts at -122dBm but you nearest repeater hovers around the -127dBm mark what aerial gain do you need to receive the repeater? Easy -122-(-127) = 5 so a 5dB gain aerial will sort things out.

Using similar thinking RSSI function can be used to find good spots to access repeaters, check filter tuning and look for noise sources around the shack. The resolution of the RSSI display is much better that a traditional S meter, and way better than that silly green mobile phone signal indicator.

All work, text and images © GB7MB


Channels not used on GB7MB

Hi folks ..   I Hope you’re all doing okay now after we had a tiny reshuffle on GB7MB.
Here’s a few channels that i see in various codeplugs occasionally, but they can be safely deleted now.
They may be named slightly different in your codeplug though.. but they are generally named something similar.
You probably don’t have these channels programmed in, (a good thing)  but if you do – its prob best to delete them.

UK wide 235 on slot 2  –  this needs to go. It’s not used.
North America – Tg 3 (either slot)  this needs to go too..
Worldwide English on slot 2 – this needs to go also.


You should only have:

Talkgroup slot commonly called / named in CPS
Talkgroup 1 slot 1 Worldwide calling & very short QSOs
Talkgroup 2 slot 1 inter – European QSO
Talkgroup 9 slot 1 Local channel (secondary, backup used for local QSOs only if s2 in use)
Talkgroup 13 slot 1 WW English,   English Worldwide,   Eng WW,   WW Eng 13
Talkgroup 235 slot 1 UK Wide     UK Wide 235



and slot 2 talkgroups: below:



Talkgroup 8 slot 2 Roaming (Northwest UK with HM, PN LP and NM)
Talkgroup 9 slot 2 Local QSO channel (Main)


This little move around is to free up slot 2 and move the non-local stuff over to slot 1, helping to stop users getting the busy signal when they TX sometimes..  You may still get the busy signal occasionally, but its either just the repeater giving its callsign.. on FM  (yes, it does this)  or its us testing roaming, which is not fully implemented on GB7MB  yet.
There will be an article about roaming on TG8 on here, when it is enabled and tested.


All work, text and images © GB7MB

IMPORTANT: poss firmware bug MotoTRBO 2.4 – random reboots in scan mode

It’s becoming apparent that there may be a firmware bug in MotoTRBO firmware 2.4 for Gen2 radios (DM4xx DP4xxx series) Obviously it will not show itself on all sets for all users, nor in the exact same way.

The error seems to show up as random reboots while the set is in scan mode – also unusual random flickering of the green RX LED is noticed too – suggestions that it may be connected to a mixed mode scan are still being tested by a number of UK Amateurs.     For what it’s worth, I would personally suggest if you notice these random reboots to perhaps comment on this site or on the UK Digital Amateurs Facebook Group or perhaps on the DMR Digital Mobile Radio page by Don VA3XPR or here on the excellent site and all-round place of knowledge a recent thread about it on the P25 forums 


%d bloggers like this: