Com Antenna location aft of baggage bkhd?

avi8tor50 · #1 03-23-2007, 06:31 AM

Anyone know of any problem mounting the com antenna just aft of the baggage bulkhead?
Also, I thought I read somewhere that Garmin 327 transponder requires a distance of 3 ft from the panel unit to the transponder antenna-is that true?

Peter K
9A QB

Steve · #2 03-23-2007, 06:41 AM

There is a suggestion that an antenna not be placed near any other vertical object that may shadow or block the signal, like gear legs.

Steve Fabiszak

Mel · #3 03-23-2007, 07:01 AM

Shouldn't be a problem with the com ant aft of the baggage bulkhead. Don't know about the 3' distance from the ant to the GTX-327. Normally 18" is enough. I have my com antennas just forward of the main spar and the transponder ant aft of the baggage bulkhead.

vlittle · #4 03-23-2007, 07:59 AM

Peter, I mounted my Comm antenna aft of the bulkhead, with a floor doubler and stiffener.

The Transponder antenna was mounted on the opposite side, with no doubler. The 327 cable length restriction is approximiately 10 feet or 3 meters, and depends on the type of cable used. RG-400 is the best.

RV7Guy · #5 03-23-2007, 09:02 AM

Trying to work smarter not harder, I mounted the comm antenna just in front of the spar in outer most bay of the fuselage. The Transponder antenna (Garmin 330S) mirrored on the other side. This provides a short run for the coax, and the nearly 3' desired, (but not completely necessary) separation. A little more difficult with the "A" model.

I occasionally confirm everything is working great with my neighbor who is a Tracon controller at Phx Sky Harbor. He is building a 7A and put the antennas in the same location.

No issues in 200 hours.

az_gila · #6 03-23-2007, 10:35 AM

Yes... the 3 ft. direct distance from unit to antenna is in the Garmin TSO'd Installation Manual.

If in doubt, read the manual.....

It might be an issue with the electrical screening of the unit itself... it's not a wire length distance.

The Manual also calls out different coax types for differing lengths... IIRC RG-400 was good to 9 ft or so... but check the manual!!

gil in Tucson

az_gila · #7 03-23-2007, 10:41 AM

Quote:

Originally Posted by RV7Guy

....
This provides a short run for the coax, and the nearly 3' desired, (but not completely necessary) separation.
.....

Darwin... the Manufacturer differs with your assessment on this, and the Transponder System is one of the few items on our Experimentals that has to be TSO'd - or a proven equivalent. Your TRACON test does not meet a test to the full compliance with the TSO requirements....

gil in Tucson

RV7Guy · #8 03-23-2007, 12:48 PM

Quote:

Originally Posted by az_gila

Darwin... the Manufacturer differs with your assessment on this, and the Transponder System is one of the few items on our Experimentals that has to be TSO'd - or a proven equivalent. Your TRACON test does not meet a test to the full compliance with the TSO requirements....

gil in Tucson

Well, Gil as typical of virtually everything I post you seem to disagree with it. My point is that if can't get EXACTLY 3 feet or MORE it is not going to affect the operation of the transponder or Comm.

Mine is 31.5" of separation. So I'm apparently not in compliance so why don't you turn me into Feds. I consulted with Garmin and they said this spread is fine. As Mel pointed out 18" will give you a functional spread.

Regarding checking with Tracon, it is nice to have a "friendly" give you confirmation that everything is reading as it should.

More time in the shop and less on the computer and you'll be flying before Van's comes out with the flying saucer kit.

Mel · #9 03-23-2007, 01:54 PM

WAIT!!! Back up. I never said that 18" separation was sufficient. What I said was that the distance between the transponder and transponder antenna, 18" usually enough to prevent feed back into the transponder.
My rule of thumb on antenna separation is: "Nothing should be closer to an antenna than the length of the antenna." i.e., a 24" long antenna should be at least 24" away from another antenna. Even this is not precise, but it is a fair rule of thumb.
Your 31" of separation should be OK in my opinion.

RV7Guy · #10 03-23-2007, 02:37 PM

[quote=Mel] Normally 18" is enough. QUOTE]

Hi Mel,

Just repeating your quote. Not trying to dispute what you said.