[fasilpereira]

Hi,

I'm in the process of wiring a GMA240 to a GTR200 as a COM2.

While checking both installation manuals, I've found a difference on the twisted shielded cables wiring. (Ref GTR200 Fig D-4 vs GMA240 Fig B-1).

The GMA240 setup only uses 2 shielded pairs for Audio and MIC interconnect while the GTR200 setup uses an additional unshielded wire for the MIC key. Check attached image.

The GTR200 Fig D-4 is specific to GTR200 to GMA240 interconnect and I'm thinking on goint this route. But I would like to understand why the GMA240 manual proposes a completely different setup.

Thanks,

Fabricio

 

[BobTurner]

Use the GTR diagram.
The only difference is that the top diagram has no dedicated mic ground connection. In older radios this was not uncommon - the mic ground was the same as the airframe ground, and the ground return would find a way between the two boxes. More modern radios float the audio grounds, to try to reduce noise. Whether you run the PTT line inside a shielded cable or not, should not, in principle, make any difference - it’s just a dc signal. But noise can be hard to diagnose. If it was me, I’d shield it, just to be sure.

 

[fasilpereira]

Bob,

Thanks for the explanation.

Would you use a single conductor shielded wire for the PTT or change one of the lines to a 3 conductor? I’m considering the last option.

Thanks,

Fabricio

 

[BobTurner]

I’d just use whichever cabling I had on hand. But if I had both single and 3 wire, I’d use the 3 wire - less work.

 

[fasilpereira]

Thanks Bob!

Fabricio