Has anyone put xpndr antenna less than 3 feet from unit?

avee8tor13 · #1 02-08-2009, 08:48 AM

I can muster up about 30 inches from Garmin GTX327 to the antenna but am reluctant after reading posts and Garmin installation. Has anyone mounted their transponder antenna a little closer to their transponder?

Thank you for your response.

Oh, I noticed when measuring from the avionics stack to any location three feet out, there isn't a lot of options other than back down the fuselage. Others evidently have installed the antenna around the fuel filter/pump area in the tunnel (RV-10).

Greg Arehart · #2 02-08-2009, 10:11 AM

I don't know about the 10, but on my 9A, I mounted the transponder antenna in the right forward corner on the bottom of the fuselage, near the fuel tank vent. This meets the 30 inches (barely), and it has worked fine.

greg

Webb · #3 02-08-2009, 10:26 AM

My xponder antenna is about 30 inches away, front right corner near the firewall. Haven't noticed any problems.

With a firewall and hull of metal, the antenna is directly shielded from the transmitter. Shouldn't be a problem. On a glass plane, I would be concerned.

alpinelakespilot2000 · #4 02-08-2009, 12:38 PM

A fair number of builders have put it where Greg mentions, right up by the fuel vent outlet. However, I don't think this technically meets the 30" straight line distance (unless you have the tx on the far left of the panel), but those who have used it by the fuel vent have reported no problems with either the tx itself or reception with the antenna up by the gearleg (on tailwheel versions). Mine is there. We'll see if I have any problems. (FWIW, the above reports are for GTX320A's. Not sure if the 327 would be different.)

aerhed · #5 02-08-2009, 01:34 PM

I tried a BNC union and stuck it right on the back of the rack in my wooden airplane, sounded simple. Pop, pop, pop. Guess who felt simple then?

MauiLvrs · #6 06-09-2009, 12:42 AM

Quote:

Originally Posted by alpinelakespilot2000

...I don't think this technically meets the 30" straight line distance... (FWIW, the above reports are for GTX320A's. Not sure if the 327 would be different.)

The 327 manual say 3 feet.
So... 1.2 Kw can't get through the holes in the front of our microwave window.... Anyone have any ideas how the 200 W from the transponder will make to through 3/16" of solid Al and interfere with the transponder...

Mel · #7 06-09-2009, 06:18 AM

Years ago we had a situation in a Pitts where the antenna was about 6" from the transponder. The very short antenna lead had a standing wave that radiated the signal back into the transponder causing it to "reply" to itself continuously. We installed a longer antenna lead looping it away from the transponder and solved the problem.
Sometimes it's the lead length and not necessarily the direct distance.

Camillo · #8 06-09-2009, 06:48 AM

I also put it in the left corner, between the pedals and besides the fuel vent line. 3 feet seems met. Short cable travel is provided, too. Not flying yet.

See installation photos. Just below the middle of the page:
http://nuke.rv9.it/Finishing35h/tabi...T/Default.aspx

ddurakovich · #9 06-09-2009, 07:59 AM

I'm on the centerline of the bottom skin, 8" aft of the firewall in my -4. I'd guess straight line distance is 24" or so.

However, my coax lead is at least 60", which is usually the critical issue.

An extra 6" at 200 watts is negligible for that total distance. But as Mel said, 6" short of the required coax length can be disastrous!

GTX-327 about 80 hours ago.

RV6_flyer · #10 06-09-2009, 09:16 AM

My transponder antenna is right below my fuel selector. My transponder (KT-76A) is in the panel right above the fuel selector. There is less than 3-feet but there may be about 3-feet of coax.

It has not failed a transponder test for the past 2,230 hobbs hours over the past 11.5-years.