Need help ...........

[Pd0hni]

Hello all,
I recently purchased a Motorola two-way radio, Motorola TETRA MTP850s.
It is now possible to connect an external antenna at the back.
But I can't figure out what kind of plug should go in there.
Who knows ? ? all I know is that it needs a female plug. (se photo )
Kind regards,

Jan / Pd0hni

[SkyVision]

Hi Jan

Motorola don't make things easy, that rear connector is for a craddle or this antenna adapter: GMLM5099 -75 Euros
I have a junk MTP850 in the shed, I'll check tomorrow
Try a short piece of 086 hardline chopped off flush with an SMA, round off the shield like the picture
Use some copper foil or brass shim soldered in place to build up if it's too thin

A modified phone patch lead like a TS9 butchered to fit might work too
Good luck

Cheers Roger VK5YYY

gmln5099-motorola-1800x1800-80.jpg (59.91 KiB) Viewed 1383 times

[Pd0hni]

Hi Roger,

Thank you for your response.
I would really appreciate it if you would check if you have anything in the shed.
It's so strange that there is no information at all about it.
Can't even find anything in the service manual?
And I can't find anything about the antenna adapter: GMLM5099 either.
If you have something I can use, just send me a private message

Kind regards Jan / Pd0hni

[SkyVision]

Hi Jan

A 5mm brass screw is a snug interference fit (the antenna thread is 5mm that's how I found that out)
I drilled a 2.2mm hole through the head of a short 5mm screw (drill through the antenna stud if you don't have a screw)
Bevel the thread slightly, then screw in till it mates with the "earth" outer
You can measure around 12 ohms to the right hand battery terminal

Allow around 1mm of the inner of a short lenght of .086 hardline or semiflex to protrude (trim the shield and dialelectric 1mm)
Push the coax through the hole and when it mates there is a small amount of spring pressure
(There maybe a switch underneath to swap from the antenna to the dock socket)
With the spring depressed mark the coax position against the screw, remove and solder

You should be able to measure 0 ohms to the right battery terminal
For some reason motorola handhelds always have the antenna at Ground (0 Volts) does anyone know why?
Maybe to keep us out grrrr.
Motorola is so expensive, anything to hack their stuff is always a pleasure, have fun on your Tetra adventures

Cheers Roger VK5YYY

drill 2.2mm hole in 5mm screw

DSCN1017.JPG (536.64 KiB) Viewed 1221 times

insert 086 into hole and solder

DSCN1019.JPG (844.05 KiB) Viewed 1221 times

[Pd0hni]

Hi Roger,

Thanks for your reply.
I'll definitely work on this.
I have also found a company in Germany that sells the complete cable.
But I was shocked by the price: 80.00 euros + shipping costs.
So I'm going to try your way first. Hi

Kind regards: Jan / pd0hni

[Pd0hni]

Hello Roger,

I've been a bit lucky.
People had heard through the repeater that I was looking for the antenna adapter cable.
The story spread quickly and I was emailed by an amateur offering one for sale.
All in all I am now provided, and it works perfectly.
Thank you for your input, I will save the information and pass it on if necessary.

Kind regards Jan / Pd0hni