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A look at and repair of a Motorola DP4800 with an SMA aerial socket.



I have a love / hate relationship with the Motorola DP4800, It’s a great HT for Amateur use, if a bit high teir compared to the usual (and perhaps even better suited) Chinese sets that seem to dominate the Amateur DMR airwaves, The DP4800 and the rest of the DP4000 series unfortunately have a design problem, namely that you can’t connect an outside aerial or a coax fed one. This is a huge fail for me, although the latest DP4800e versions can be ordered with SMA, it’s adds even more money on to the cost of an already expensive set.  When our GB7MB repeater was on-air a year or two back, my previous DP4801 was the normal ‘stud mount’ aerial connection, and thus limited in aerial connectivity,  and sadly, GB7MB was a pretty poor signal indoors at my QTH, and so the HTs aerial limitations were an insurmountable issue, and rendered the DP4801 useles here.

So, fast forward, with local Lurkio-in-Chief, Dave G6CRVs GB7MP repeater just a mile away coming on air, i reconsidered again a DP4800, the signal was way better here than GB7MB, and  i already had the external mic and an old charger, so i thought a cheap DP4600 would serve as a DMR HT.

A used DP4600 was found on Ebay, but it refused programming totally, so had to return it. The seller was adamant it worked and said he would not accept a return, and got snotty. he must have got confused as he accepted a return the day after but i had already started a Paypal claim as the seller was refusing any refund, Paypal took three weeks to process the refund however. i was really not impressed with Paypal, and i will likely be not requiring their services again.
A DP4800 appeared online,  it was cheap and had no accessories, it was only a few dollars more than the DP4600 that Paypal had refunded too, so it was purchased, and for a good knocked down price too, to make it a better buy.

During a swap of aerials however, the HTs’ SMA unscrewed itself, i was using a SMA to BNC adaptor and noticed the SMA itself was unscrewing itself out of the set, this was bad news, but there was nothing i could do, so i had to carry on until it all had fully unscrewed and then i could go in and inspect the damage and hopefully repair it.
Upon closer inspection the SMA looked to have had a fair bit of use, as indeed had the radio, but not excessively so, the outer threads of the SMA did have some unexpected tight spots, so a tiny pinhead of light oil was applied to the threads which made the ‘mechanics’ much smoother, only thing was a thin wire has snapped off the bottom of the SMA.

I will order another nicer silver SMA when i find one, but it won’t be one of these gold-coloured chinese ‘turkey foil special’ either, like the SMA that is unfortunately presently fitted, it will be a quality one instead, and a minute dab of threadlock will be applied too.

In regards to Motorola’s decision to NOT fit a SMA, If i were cynical, i’d say it seems Motorola have deliberately made the set and the whole DP4000 series compromised, with no option to add a coaxial or external aerial.. This is discussed on some of the serious and professional radio comms forums, and i think the argument holds water too.
Sure, there is a MS147 Hirose RF socket on the HT’s PCB – if you slide off the small back cover above the battery.. but you can’t just go and buy a normal MS147 cable or adaptor, plug it in and get going using an external aerial, that would be far too easy. No.
The standard, ‘off the shelf’ MS147’s don’t fit, so you have to buy the special Motorola one, which is longer, and reaches deeper into the secret trap door ‘hidden’ in these sets, down on the HT’s main PCB, doing so will disable the HTs set top aerial connection when it plugs into the HT’s internal ‘RF port’  I wish China would make a few hundred of these elongated MS147s, i think most Motorola using Amateurs would buy one.

So Motorola would have you buy the (over 100 uk pounds) to stump up and buy this rip-off MS147, and once you’ve quite recovered from that,  Motorola then expect you to buy another rip-off in the shape a clip which holds the already grossly overpriced Motorola RF adaptor that you’ve just bought, into the set solidly, and, here is the funniest bit, the clip costs around 100 uk pounds as well.  Hilarious.

I can only assume that Motorola hired the Guy who priced up Apple’s $999 monitor stand (a bit of polished metal) – over to Motorola HQ to dream up a suitably ridiculous price for their Moto MS147 adaptor,  both are things that even Hans Christian Anderson would reject as a fairy tale.   Thanks Motorola.

A company such as Motorola, itself employing radio amateurs…  are all too well aware of Amateurs buying it’s gear, but what appears to be corporate arrogance or paranoia ensures Motorola continue to be curiously hostile to the Amateur community, even though some hobbyists have contacted Motorola to help them with bugs they’ve not fixed, only later to have these fixes implemented in firmware updates by Motorola. Talk about having ones cake and eating it..

Motorola’s literature suggest that the MS147 is actually an ‘RF test point’ for measuring and aligning the set, most digital Motorola HTs I have seen that have no ‘proper’  external antenna connection either, seen seem to have either an adaptor similar to the Hirose MS147

Here is a MS147 lead :
The cheap BNC to MS147 lead above is about a fiver, which would be good value if it were it to enable you to use your DP4800 at home, or in the car, as i say, bit it’s too short and needs to be something like half the length again to fit in the DP4800, some people say they have found MS147 extensions, but i’ve spent months looking, and i still haven’t found the extension yet, not in the UK anyhow, neither have i seen or read about such a thing anywhere else either.
I’ve messaged Chinese RF suppliers and the nearest i got was a longer MS147 connector on AliExpress, but it was crimp-on only, and it was for that crappy 2mm, or 3mm wide coax the Chinese seem to love so much, so not much use to me, and no other sellers really seemed to understood what i was actually asking for, so I’m going to say good luck with your search.

Some home made BNC  adaptors, made by mechanically savvy Amateurs  *are* available on Facebook groups and elsewhere for the DP4800, but I’m quite skeptical, as they provide no answers when asked simple questions about the general ‘how it works’ and $40 from California could likely turn into ÂŁ60 or ÂŁ70 wasted by the time it’s arrived.

The SMA mod seems pretty easy if you have a good microscope & eyes and fine SMD or suchlike soldering gear and skills.
i thought I’d take a couple of photo’s and think and ponder how the mod was actually done.

I wasn’t overly thrilled to have to be messing with the HT, but i did enjoy the whole orangeness of the gasket however, so that kind of helped, as i think orange is a calming colour, that is until you come to reassemble the HT…

So, with PCB removed, i inspected the MS147 and aeriel socket and tried to figure out how they’d done it. They had taped over the MS147 socket, not with kapton tape or anything, but with what looked like masking tape, or some other fibrous tape.

The frame and chassis we see would normally be ‘hot’  – so they cut a track or two and isolated the frame, and then jumpered a short link to the GND of the set to the frame

The top end of the tuning coil has a wire soldered to it and that is soldered directly on to the centre pin of the SMA socket, and that seems about it. The photo’s aren’t great i know, but they looked much sharper on the phones screen.
I know it’s not Louis Rossmann quality PCB detail. Sorry 🙂


You can perhaps see in the photo below a little more clearly, above the top of the coil what looks like a piece of track was removed or perhaps a SMD component like a small cap. I haven’t checked the circuit diagram  – i don’t have one.

You can see to the left of the coil (which is the top)  a missing SMD or portion of track.

It looks like a simple enough mod to do, I’m not 100% sure how to isolate the frame and which track(s) to cut or whatever, though the PCB would make it pretty obvious if you had a good magnifier and set of eyes.

I’d fancied a BNC really, but the frame is already threaded nicely for a SMA, and BNC would be a mess and wouldn’t fit.

I wouldn’t want to mod a brand new DP4800, but this DP4800 was cheap enough, so i’ve only relatively few qualms about having to fix the SMA, although i’m not set up for SMD or anything remotely fiddly, this was pretty simple to repair, but damn fiddly, but interesting to note. i just wish i had a suitable magnifier and tinier soldering iron, this was at the extreme limit of what i could do with the basic low tech gear i have.

-Hax-

Decode TETRA as easy as FM on SDR Sharp

No, really.. It’s simpler now to listen to unencrypted (clear) Tetra on SDR Sharp than it is to listen to FM

DSD isn’t needed, because it doesn’t support Tetra, and i thought one of the unpleasant bits of getting SDR Sharp set up – was having to ‘send’ the audio output from SDR Sharp – with a ‘virtual cable’ over into DSD or DSD PLus, both of which work well, but The UI of the DMR decoders is pretty messy and unintuitive, with several separate windows springing open it’s and a mess of separate windows opening up.
You don’t need anything except the file I’ve zipped up for you here, an aerial and an RTL-SDR Dongle – and of course, a Tetra signal.
I have zipped up a working SD Sharp folder ready with the Tetra Decoder already built in. Here is the link below.
it will ask you for a password, type in   MBARS

Download

To use, just unzip it to anywhere on your C: drive.  It contains all you need. You may need to run Zadig if you do not have SDRsharp another SDR installed already. instructions below.



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) though it 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.


Preparing SDR sharp for Tetra decoding.

Once you have selected the correct USB device and have SDR sharp running, you can test it out on normal analogue transmissions and, once you are happy, It’s time to go and search out some unencrypted Tetra.

Firstly, set SDR Sharp up, you can either be in Wide FM or Normal Narrow mode – all you need to know is that whatever FM mode you choose, set the filter width to 25khz. i use NFM and zoom in, and drag the passband out wider that way, but you can use the Wide FM or the option in the Radio menu, it’s more precise, but it’s not too critical, unless you go too narrow.

Now in the Audio tab, make sure that the’ filter audio ‘ button is NOT checked. then go to the Tetra Demodulator panel and select the first option, Demodulator and if you are looking for `DMO Tetra, you must tick the DMO checkbox to it’s right also.
Also, underneath the config button.. click & select the Voice tickbox and click AUTO.
These are your 4 Tetra timeslots, so they need to be set at AUTO unless you are interested in monitoring just one particular slot. If you are listening to a Tetra base station, or DMO just leave it to AUTO

When you have found a valid Tetra frequency, the red text “Received’  will appear  – along with any errors, like in weak signal areas or mistuning.

DMO tickbix

In the UK, there is clear Tetra above 420mhz, some pirate activity around 420.125 mhz where non techs and non Hams set up, as many codeplugs on the UK secondhand market come with some DMO frequencies here. This is illegal but is often referred to as DMO 1 and so on for other channels. Up to and above 460mhz too you may find Tetra, and often hiding in between the usual DMR, FM and carriers – tune carefully,, if you find a valid Tetra signal – a TMO one, get to recognise the harsh high pitched nasty sound of a TMO transmission the Tetra panel will display ‘”Received’ in red font and for more info you can click the Net Info button and serch through there and see the cell info and all kinds of lovely tech info, and whether there is encryption.
You want to see ‘Air Encryption = 0’  towards the bottom of the info cell panel, though there are other Group call panes too, once you do hear things.

What You want to see – .

You will see what talkgroups are being used also in the Groups and more detailed info in the Calls tab too.
Of course current cell  refers to the Tetra base station that you are currently tuned to, and as Tetra is Trunked, Neighbour cell is, as the name suggests, the next cell on the Trunking system. With another USB SDR receiver, and a little plugin called Tetra Trunk Tracker will enable you to follow calls from site to site. I didn’t include Tetra Trunk Tracker because it’s at an early stage of development sill, and not simple to set up and get working.

There is no DMR or other digital voice decoding in this build of SDR sharp. just the Tetra plugin. When youclick the Tetra decode button ON the volume slider on SDR Sharp should have a cross through as Tetra mutes it, to use FM again, uncheck the Tetra demodulator tick box, and you can then slide the SDR Sharp volume slider back up.

We use Tetra around Morecambe, on 430.3125   GSSI 10 (talkgroup)  we think the 430.000 Tetra frequency is a bit of a poor choice as you will still be radiating outside of the Amateur band. That’s why we use 430.3125 locally and It’s only a 5 minute job getting most commonly available Motorola Tetra gear on to 70cms anyway, and most Tetra sets are the 380mhz to 430mhz band only, not the preferred 410-470 mhz but the 380-430mhz band sets are perfectly fine a few mhz up from 430.000 anyway.

This is just a basic How To on how to hear non encrypted Terra. It’s up to you to get scanning the airwaves and discover things in places you wouldn’t normally expect.