GTN650 Transmit Interlock or Lack Thereof

Brantel · #1 03-20-2013, 03:05 PM

UPDATE: See post #7, Garmin has created a MOD to bring this feature to the GTN series....

This only applies to dual COM installations.....

One thing to understand about the GTN650 is that it does not have a COM interlock feature like the GNS series had.

I used that feature back when I had a 430W installed. The purpose of it is to interlock with the other COM radio and when either radio xmt, the opposite radio's receiver is disabled or it runs at a reduced sensitivity.

This feature prevented feedback from one radio to the other when the antennas were located close together like they are when people mount em both on the belly.

I was unable to do this with my new panel since I went to a GTN650 and I get crosstalk on the two radios. Good news for me is that the GMA240 has a feature that can be enabled to mute the opposite radio when xmting. This prevents the feedback squeal in your ears....

My antennas are on the belly...

Not sure why Garmin's certified engineers removed this interlock but they did....

BigglesRV7A · #2 03-20-2013, 03:46 PM

Thanks for your post Brantel,

I am looking at removing my 495 and AirGizmo to install both the GTN650 and 240 that you mention above. I intend to still use my SL30 as a second radio so good to know the 240 will work here with the GTN shortfall. Any other gotchas worth mentioning. I have to install a second VHF antennae so will keep this in mind.

Cheers,

Brantel · #3 03-20-2013, 03:57 PM

Just make sure to install the jumper in the GMA240's harness that enables the feature to mute the non xmitting radio's audio.

Page 2-5 in the install manual:
MUTE ON COM TX: This input configures the audio panel to mute all selected radios (COM, NAV, AUX) except the mic selected COM (COM selected for transmission) when a PTT key is activated for COM transmit.

More details in the manual on where and how to wire it...

The GTN650 is an amazing device. You will love it!

Airzen · #4 03-21-2013, 04:02 PM

Thanks Brian for sharing your insight about the problem!

Just wondering:

1) Did you hear cross-talks over the radios all the time? Or did they occur only in a particular configuration (e.g. listening on both radios)?

2) While you were able to solve it via GMA 240, what are the options for folks who dont have that audio panel? Any thoughts on that? I suspect many RV-8s (and 6,7,9 too) have belly mounted antennas so they'll suffer from the same problem.

Thank you again for the details on this problem.

Ashish

Brantel · #5 03-21-2013, 05:14 PM

Quote:

Originally Posted by Airzen

Thanks Brian for sharing your insight about the problem!

Just wondering:

1) Did you hear cross-talks over the radios all the time? Or did they occur only in a particular configuration (e.g. listening on both radios)?

2) While you were able to solve it via GMA 240, what are the options for folks who dont have that audio panel? Any thoughts on that? I suspect many RV-8s (and 6,7,9 too) have belly mounted antennas so they'll suffer from the same problem.

Thank you again for the details on this problem.

Ashish

When I originally installed my 430W prior to the current panel, I did not hook up the interlocks and had issues when one radio would bleed over on the other anytime the channels were close enough together. I solved the issue back then by installing the interlock wires.

On question #1, I never heard anything with the current new panel because I anticipated the issue and used the GMA240's feature from the beginning. I can tell you however that the RX lights up on the non Xmitting radio when the channels are close enough together so I know there is some crosstalk going on strong enough to open the squelch.

On question #2, Keep the non xmitting radio deselected on the audio panel will do it if you have an audio panel, if you don't, turn down the volume on the non xmitting radio. Switches are also an option for no audio panel...One could have a switch that selected COM1 AUDIO/BOTH/COM2 AUDIO or something like that. The other thing you can do is put one antenna on bottom and one on top or put em out on the wings to get em far enough apart.

Airzen · #6 03-21-2013, 05:26 PM

Great info. Thanks for the reply.

In fact I did experience similar thing in C172 euqipped with 430W (i.e. feedback/cross talk when frequencies were close together).

Ashish

TrekLawler · #7 04-02-2013, 11:05 AM

Good Afternoon everyone,
My name is Trek Lawler and I'm the Supervisor of the Aviation Field Service Engineering team for Garmin International based out of Olathe, Kansas. As you know we have a couple of our G3Xperts that comment on the forum and I do some lurking however try and leave the Sport Aviation side to these experts. However this thread caught my attention as this is part of my support team and I wanted to get with everyone to explain this and the features of the GTN series of radios.
Yes, at the initial release of the GTN series of radios there was in fact no process for providing a transmit interlock, early on in the release of the product line we discovered this in fact will be a necessity and quickly started working on this. As of March 2013 we have in fact incorporated this feature in all production GTN series units. The uniqueness of this new interlock feature is the radio will now detect another radio transmitting and via software will reduce the GTN comm. radio receiver sense so that the noise or crosstalk is disabled. This does require a hardware change in the GTN series radios however can be added to any fielded units that may be installed already. This will be identified as mod 2 on the unit. Should you desire to have this mod installed on a unit please get with your local Garmin dealer and have them contact us to coordinate getting this scheduled.
As I indicated I do lurk from time to time on the forum however if there is any questions please feel free to drop me a note and I will be glad to assist you.

Best Regards,

Mike S · #8 04-02-2013, 12:08 PM

Trek, welcome aboard the good ship VAF

Good to have you here.

Brantel · #9 04-02-2013, 12:40 PM

Trek,

Thanks for the very open and honest reply to this thread. It is another example of how Garmin is experiencing a paradigm shift within its organization! Sounds like the unique solution used to bring this feature to the GTN series will be a real winner since no wiring mods are required. Most of all thanks for listening to and informing the customers!

I have one technical question for you....Is there any risk for damage to a GTN unit that does not have this MOD implemented when it is used in an installation/environment that is conducive to crosstalk similar to the types of interference that this MOD is intended to prevent?

TrekLawler · #10 04-02-2013, 01:31 PM

Quote:

Originally Posted by Brantel

I have one technical question for you....Is there any risk for damage to a GTN unit that does not have this MOD implemented when it is used in an installation/environment that is conducive to crosstalk similar to the types of interference that this MOD is intended to prevent?

Hello Brantel,
Thank you everyone for the warm greeting, one of our senior RF engineers was able to supply me with some very good data regarding this.

"There is no risk of damage to any circuits in the radios front end only the annoying squelch popping.

As both versions of the GTN stand today, with and without MOD 2, non mod 2 receivers can take up to 1 watt of on channel RF applied directly to the receiver front end while those with the TX interlock mod have been tested with more than 5 watts directly applied on frequency and neither models were damaged."

Obviously depending on your comm units on board and the proximity of the antennas will dictate how much RF energy is being absorbed however the GTN units are a very robust design and I've yet to see a problem with them in the two years they've been on the market.

Hope this helps, let me know if there is any other questions,