Avionics Work on my NXCub

[Neal]

Good catch. I had REV 6 I got from some link, I found REV 13 on the Garmin site. Here are updated images. I see now that I should be able to find a reference on the unit for the dip switches and on/off direction.

 

[Neal]

All of my dip switches are oriented down towards the ground when the unit is mounted. That would seem to be all are in the OFF position. So I think mine is set correctly by toggling the 3rd dip switch back from the USB port side of the unit being the front. All good now...

 

[Cactus Charlie]

Where did you find that drawing showing the DIP switch label. I cannot find it in my rev 13.

 

[Neal]

It’s in the GMA 245 installation manual.

 

[Cactus Charlie]

Ok. Found it on page 2-18 of rev 13. A search for DIP does not find it.

 

[Neal]

I want to think that muting other radios during transmit is a good thing and should be the default. I can't remember in my A-10 life where we had 3 radios if I ever heard someone talking on a different radio while transmitting.

Our cubs are notorious for poor grounds and I'm guessing the ground planes on these two antennas aren't ideal or grounded in any good way. So transmitting on one may cause feedback to the other which I think is what is happening. Muting the other radio during transmit is a way to omit that feedback noise. We'll see as I test with this during normal use vs in hangar test.

 

[lrobichaux]

All … so sorry I’ve been tardy in responding to all the above. First, the detailed instructions provided by CC was developed from my emails to Pete. Upon request, Pete sent me detailed, readable wiring schematics for the IFR panel in my plane. Very helpful. I’m sure he will send to anyone who requests.

When I first recognized this problem, I received advice from my local avionics shop to flip the #3 DIP switch on the remote audio panel. Doing so helped the issue, but Pete said CC recommended ALSo installing the interlock they designed. Took me a few weeks to get the plane into the shop to have this done. Took me until today to properly test the results. I can confidently report the following.

1) Flipping the DIP switch without completing the interlock procedure helped significantly. If that would have been all that I did, it would have been fine.

2) Taking next step and installing the interlock cleared up all remaining minor static. It’s now very clear.

3) At @Cactus Charlie ‘s suggestion, today I tested both MIC1 and MIC2, each time when simultaneously monitoring both COM1 / COM2. Tested the forgoing both from both the pilot and passenger positions. All four tests were clear, consistent and free of static.

4) I also recorded the inbound transmissions using my handheld radio from 50 yards away. Again, clear, consistent and free of static.

I think the additional clarity attained from the completing the interlock procedure was worth the 2 days in the avionics shop.

Hope this helps.

 

[Cactus Charlie]

Thanks for the report. Good to hear the mod worked for you.

 

[Neal]

Thanks for the follow up @lrobichaux - but is the #3 dip switch still toggled ON? It would be interesting to toggle this back OFF and test. It seems with it ON it's going to MUTE any ability to monitor the other radio while transmitting, not sure why I'd want that, but I'm curious how the interlock works without this muting.

Glad you have successful results and thanks for sharing so others can learn from this.

 

[Neal]

Also, per what @Cactus Charlie mentioned about the GNC 355 not having the interlock, I assume this change only affects MIC1/COM1 active and COM2 in monitor mode? How does the interlock affect MIC2/COM2 with COM1 in monitor?

 

[ve6yeq]

There are two different kinds of “interlocks” being discussed here:

1. Audio mute to prevent you from hearing other transmissions while talking which can confuse some people if they are not practiced at multiple simultaneous conversations. This is controlled with DIP switches on both the GMA-245R and for Bluetooth audio on the headset controller.
2. RF Pre-amp interlocks which prevent the large amount of RF energy from one transmitter overloading or even permanently damaging the very sensitive RF pre-amps by powering it down.

In my Carbon Cub EX-3 with GNC-355A and GTR-20 using the default antennas, I can definitely hear the RF pre-amp on the edge of overload so after this discussion, I will look at adding the necessary wires to disable the pre-amps when one is transmitting. I already have my Lightspeed ANR mounted in the helmet set to mute and I think I might try it with the GMA-245R as well.

 

[lrobichaux]

@ve6yeq please let us know if you get better results after installing the interlock. Mine seems to work great now.

 

[Cactus Charlie]

I was very surprised that this mod worked when wired as documented. I had expressed my doubt about this mod several times.

A day before I heard the report I had emailed Pete at CC saying basically that I did not understand the mod as drawn and asked if there was a pin numbering error. I asked if pin 12 was the intended GMA pin.

Pete replied late Monday - "That is a preliminary sketch and indeed there was a pin number mixup with the GNC 355. The upcoming service document will have the correct pin number there, pin 12."

Pin 12 is "COM 1 MIC KEY* OUT". That connection would pull COM 2 "TX Interlock In" to ground and de-sense the receiver when COM 1 was keyed.

 

[Neal]

Definitely going to wait for them to move this out of BETA. Thanks for the info.

 

[lrobichaux]

@Neal ... Hey - I've been messaging with @Cactus Charlie on the COM issue, and I'm concerned that Pete / CC may now think that the COM1 / COM2 monitoring issue is resolved (based on my feedback to CC / Pete ... as I am the "beta" test he referred to) when @Cactus Charlie is convinced it's not. I wanna send an email to Pete and copy all of us to make sure that everyone is working off the same information. Can you DM me your email address so I can loop you in? I have @Cactus Charlie 's email address.