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Antennae Coax

Blizzard

Active Member
Just finished the mounting brackets for two AV-17 Comm antennas under the rear seats. Planning on using all Garmin avionics. Where are most people putting their GTR 20 comm radios. Just looking at which direction to run the coax from the antennae before I install the rear seat and baggage floors. Forward or aft?

Thanks
 
Be aware that Garmin has a dual comm antenna isolation distance recommendation of 6’ IIRC, to prevent feedback while transmitting.
 
Be aware that Garmin has a dual comm antenna isolation distance recommendation of 6’ IIRC, to prevent feedback while transmitting.

And they will as I noted in a GTN-650 (Comm #1) and a GTR-200 (Comm #2) RV-14 install. The GTN-650 was not affected when transmitting on the GTR-200 but the the GTN-650 bled over to the GTR-200. This made the GTR-200 about useless to monitor other frequencies as you had to keep it’s volume turned down. Garmin does have a connection to “desensitized” the GTR-200 when transmitting on the GTN-650 but I consider this a just bandaid fix. This connection will eliminate the pilot and co-pilots operating split mode. Decide if this is important to you or not.

I note that the same panel running the GTN-650 as Comm #1 and the Dynon radio as Comm #2 had no issues at all.

Carl
 
GTR-20 Location

J Where are most people putting their GTR 20 comm radios.

I don't know where most people are mounting theirs, but on my RV-10 I mounted mine the the underside of an avionics tray attached to the back side of my panel, ahead of the sub-panel. Afraid I don't have a photo of it there, but it makes it easily accessible.

Cheers,
 
3 steps forward......2 steps back......ughhhhh. After reading the distance requirements for the different antenna that might be used on the RV-10, I've determined that half the antenna's will probably need to be flying in formation at a reasonable distance from me. Since there are a lot of RV-10's out there flying with G3X systems; dual comms, transponder, nav, gps, ILS/LOC I don't really want to re-invent the wheel. If there's a map somewhere showing where all these antenna's are located...and work, it would be greatly appreciated. Thanks.
(I had hair when I started this build)
 
My 2c, put a Comdat (GPS/Com) antenna on top and 2nd com on the bottom.
If you go with both coms on the bottom just hookup the interlock between com1 and 2 and it'll be fine, just keep them as far apart as practical.
I like to keep audio wires as short as possible, so com's go up front where the audio panel lives.

Interlocks are not "band-aid" fixes, this method of controlling receiver overload has been around forever and is widely used whenever dual transmitters/receivers that share a common freq. are installed in close proximity to each other.
 
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I'm doing this right now. Stick a COM antenna on the top of the tailcone, and then stick another one under the fuselage so it pokes through from the tunnel.

Then you should just need a place to put the transponder antenna, which I'm putting underneath the tailcone, and a NAV antenna which will go in the wingtip. Finally, two GPS antennas will go in the overhead console separated by the minimums required in the install manual and staggered left to right.

This should meet all separation requirements. I'm planning on mounting the GTR-20 in a shelf in the tailcone so it has a short coax run to the COM antenna, same for the GTN which will hookup to the COM antenna in the tunnel.
 
I'm doing this right now. Stick a COM antenna on the top of the tailcone, and then stick another one under the fuselage so it pokes through from the tunnel.

Then you should just need a place to put the transponder antenna, which I'm putting underneath the tailcone, and a NAV antenna which will go in the wingtip. Finally, two GPS antennas will go in the overhead console separated by the minimums required in the install manual and staggered left to right.

This should meet all separation requirements. I'm planning on mounting the GTR-20 in a shelf in the tailcone so it has a short coax run to the COM antenna, same for the GTN which will hookup to the COM antenna in the tunnel.

Putting the xpdr in the back is fine, this is where the coax needs to be kept to minimum length as the losses at xpdr freq's are quite high (6' cable max length is the 'norm').

As for the com, coax's losses are much less so a longer cable is not that big of a deal, on the other hand having audio wires (mic/hdph) going all the way to the back is asking for noise trouble in the radios/intercom.
 
This works

My 2c, put a Comdat (GPS/Com) antenna on top and 2nd com on the bottom.

As Walt says, the Comdat on top, comm only antenna on the bottom will work. On our RV-7A - we hooked #2 comm (and GTN-650 GPS) to the Comdat - for receiving ATIS/AWOS and the #1 comm is on the bottom antenna. Works well for us and we have duplicated this setup on our RV-10. Cat whiskers for VOR/ILS at the tail.
 
I have a number of antennae on my RV10. I have two GPS on top. One is just a GPS, the other a combo GPS/XM.

My nav antenna is in my wingtip.

My (2) COM antennae are behind the rear bulkhead on the bottom of the plane - basically one on either side of the battery tray.

My transponder antenna is on the belly in my tunnel, under the flap motor.

Lastly my ELT antenna is on the top of the empennage, about 18” forward of the vertical stabilizer.

I have a GTN650 and then my panel mounted radio right under it.

I have zero issues with anything after 1 year and 160 hours.
 
Interlock?

Walt - what is the interlock that you speak of? I don’t have one and have both antennae on the bottom side by side.
 
Echo, what GPS pucks are you planning for the overhead console? The 650 and XM pucks won't fit in my Aerosport overhead console.
 
Com Antenna location

I have both bent whip COM antennae mounted on the underside of the fuselage in the rear seat bays as the OP indicated. Transmit interlock active. Zero problems in over 500hrs and no speed-robbing spikey things on the topsides :p
Gotta watch out for the antennae poking you in the eye when cleaning the belly or otherwise working under the plane tho...
 
Just me

Walt - what is the interlock that you speak of? I don’t have one and have both antennae on the bottom side by side.

I have a Garmin gnc255 and GTR20 comm radios. Only the GTR 20 has an interlock. The interlock connects from the mike kek on one radio to the interlock input on the second radio. I think it turns off the reciever when the first radio is broadcasting.
 
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