MGL Avionics User Forum

I have dual V16 radios fitted to my jabiru, comm 1 using the standard antenna in the vertical stab. Comm 2 is connected to an underbelly com antenna.

When I have both comms on no 2 always breaks squelch when I transmit on comm 1. Makes no difference what freqs are being used.

Any ideas anyone.

Simply, COM 2 is getting interference from COM 1's antenna. This is exaggerated when the antennas are positioned so that one is perfectly on top of the other in many cases.

To get rid of this, hook up the TX Interlock between the two radios. When one radio is transmitting, the other will be unable to receive, but it will solve this.

Adam

Thanks Adam,

For some reason I incorrectly believed the tx interlock was to stop simultaneous transmissions, makes sense that it would be as you describe. Will connect it up.


Mike

The interlock didn't fix the issue, next step is to try and shield the antennas from each other.

It is definitely an RF issue so I'm thinking it is one antenns overpowering the other.

I'll try with foil and then make a more permanent solution of it works.



Mike

The TX interlock does not mute the receiver - just prevents the inactive radio from activating the PTT.

However, since everything is software defined in this thing - if nobody can think of a good reason why the receiver should not be muted in this case - that would be easy to do.

A nearby TX antenna can indeed couple an awful lot of RF energy into a tuned RX antenna close by - typical squelch on a radio would perhaps typically be set at -95dbm or so since the V16 is pretty sensitive as far as modern radios go. On the other hand we are looking at +40dbm or so on the TX antenna - that's a whopping 135dbm difference (factor 1:5.000.000 approximately if all energy coupled - in reality it may be just 100th of that - but that is still huge - Even the very best channel filter will be overwhelmed) and worse, the front end driven into saturation.

So let me know your opinions - I can easily add something here.

That's a definite yes from me, I can't listen to a second radio while I'm transmitting anyway.

Mike

Just got down to hacking away in the V16 code - looks like this is actually already in.
RX is suppressed when the TX interlock input is active...
This is by means of switching off the actual receiver chip input amp.

If something is still getting though it must be really strong - I can add another "kill" in the actual DSP code that processes the I/Q signals. Will do that. Lets see if that makes a difference.

Thanks rainier

I tried it with a handheld as well, when transmitting within about 8 inches of the antenna it breaks squelch as well.

If you remove the antenna lead from the second comm nothing breaks through on the second comm.

Mike

Tasmag wrote: ↑Wed Feb 17, 2021 11:11 pm Thanks rainier

I tried it with a handheld as well, when transmitting within about 8 inches of the antenna it breaks squelch as well.

If you remove the antenna lead from the second comm nothing breaks through on the second comm.

Mike

Looking further - if the TX interlock is pulled low - even the DSP processing of RX freezes. So all of that is already in.

Please do not do that with a handheld - you can easily fry the receiver if you do this. That is way too much power at the RX input.

I'm going to add a forced audio mute if the TX interlock is pulled low. Then nothing comes out.

Thanks Rainer,

Looking forward to trying out the revised firmware (and I won't be playing with the handheld anymore)

Mike