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Garmin GTR 20 + GMA 245 + GTN 650Xi TX Interlock

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Carlosanlley

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Hi Guys:

I'm in the final fase of the avionic installation in my RV8; and regarding comm radios I'm using a GTR20 and a GTN650Xi managed by a GMA 245.

My question is about Transmitter Interlock, I see that the GTR20 has the pinout for TX Interlock but GTN650 does not; doing some research in VAF I came across a post mentioning this:

"The uniqueness of this new interlock feature is the radio will now detect another radio transmitting and via software will reduce the GTN comm"

GTN650 Transmit Interlock or Lack Thereof

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...
vansairforce.net vansairforce.net

So, based on my setup, will both comm radios will have the ability to detect the other transmitting radio? does the GTR20 have this feature also? If any of you guys have had a similar setup, I would love to hear some comments on how you got it working.

Carlos S.
 
The GTR20 has intlk in and out, you need to tap off the GTN mic key line and use it for the GTR20 intlk in because there is no intlk out on the 650.
 
Last edited:
So disclaimer- I’m the “Amateur” in EAB. I have gtn designated as comm1. GTR as comm2.

On the GMA 245, on connector 2401 pin 12 “Com 1 Mic Key Out” pinned to the GTR connector 2001 Pin 5 Tx Interlock In.

In note 11 on the GTR interconnect drawings: “
11. IF TWO COM RADIOS ARE INSTALLED THIS INPUT AND OUTPUT CONNECTS TO THE OTHER COM RADIO. *TRANSMIT INTERLOCK IN TO
*TRANSMIT INTERLOCK OUT AND *TRANSMIT INTERLOCK OUT TO *TRANSMIT INTERLOCK IN. *DENOTES AN ACTIVE LOW SIGNAL.”

Ok so to simply answer your question, you’ll want to wire the gtr interlock in to the GMA interlock out. That will “protect” or desense the gtr20 when com1 transmits. That’s my amateur understanding… maybe more to it.
 
Pdp7427 said:
In addition to what I wrote below, I also have this pin wired. From the position above to the gtr at 2001-4.
Click to expand...

Look at figure 24-2.4 in the G3’s install manual AW. I believe this is what guided my specific pinout that is now enshrined in my excel document with every pin labeled.
 
Walt said:
Yes but for some reason they only provided the intlk IN, there is no inlk OUT on the 650/750 unless that is something new.
Click to expand...
I took the com1 mic key out(2401 pin 12) at the GMA audio panel to the gtr 20 (com2) interlock in (pin 5). Not sure that was correct but seems to make sense? I’m no Original Poster just trying to help by explaining what I thought at one point during wiring…!
 
Walt said:
Yes but for some reason they only provided the intlk IN, there is no inlk OUT on the 650/750
Click to expand...
Yes, that seems correct - they want you to connect the GTN's interlock input to the PTT of the other radio. (I'm looking at the audio panel interconnect diagram, B-14 in 190-01007-C0 rev 11)
 
For what im understanding, it should be as simple as this two connections:

1. GMA 245 Pin 12 of P2401 "com 1 mic key out" ----> GTR 20 (com2) Pin 5 of P2001 "tx interlock in"
2. GMA 245 Pin 30 of P2401 "com 2 mic key out" ----> GTN 650 (com1) Pin 9 of P1003

Am I right?
 
Carlosanlley said:
For what im understanding, it should be as simple as this two connections:

1. GMA 245 Pin 12 of P2401 "com 1 mic key out" ----> GTR 20 (com2) Pin 5 of P2001 "tx interlock in"
2. GMA 245 Pin 30 of P2401 "com 2 mic key out" ----> GTN 650 (com1) Pin 9 of P1003

Am I right?
Click to expand...
Yes, an alternative to item 2 is GTR20 pin 4 to GTN pin 9.
 
Walt said:
Yes, an alternative to item 2 is GTR20 pin 4 to GTN pin 9.
Click to expand...
Now we’re just confusing things. See post 2. You know, no discussion needed… /sarc

Point here is, there’s more than one way to skin a cat. And we learn from discussion, not all of us are pros in this business and I’m sorry if I muddied things up earlier but your own reply is case in point— more than one correct way to do something. There are pros and cons to different implementations and discussion is worthwhile. Helping new builders learn, possibly identify mistakes before closing up their panel, and sharing experiences I believe is useful. I’ll go away and build now.
 
Since there’s lots of muddy waters I’ll churn it some more.

I’ve never seen a GTN exhibit a bleed over issue. The GTN series architecture is pretty damn good at working with other units in the system, with no interlock pinout.

The GTR is a great basic radio without some of the enhanced features of a GTN and can easily have bleed over issues when installed with older comms - KX155’s, 430’s and the like. The GTR has a sensitivity range that will receive TX from other comms in the aircraft (bleed over) if the antennas are too close and the interlock isn’t wired up.

Caveat on the interlock. This feature does not “block” or lock out reception when used. What it does is momentarily cranks the squelch to 100% for the duration of the TX.
So, if you have an issue with bleed over and you think it’s something is wrong, it may simply be that 100% squelch isn’t enough. None of this should be an issue with a GTN.

Comm Antennas are required to be minimum 6’ apart from each other. I know there’s a million Cessnas with two comm antennas on the cockpit but Garmin will tell you it’s not acceptable if you have a bleed over issue.

In my case of the worst bleed over cases of an old com bleeding onto a new GTR with TX interlock active, installing a bottom (belly) com antenna always solved the issue.
 
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