transponder antenna.

[dhall_polo]

I've read all the threads on this, but still have a question.

Installed (2) comant bent whips where most comant go, under the belly just behind the spar in the outboard ribs. This puts them 37" apart. Good.

Now, where to put the Transponder Antenna. I've seen a number of places where most people install the transponder antenna. Near the firewall or inbetween the bent whips. To me, both those locations have issues. Comant says 36" from other antenna, so between violates that. And near the firewall seems too close to exhaust.

An good location seems to be just aft the baggage compartment near on the passenger side of the vertical support. It's >>36" from other antenna and a safe distance from the exhaust. Also very serviceable.

Has anyone used that location, or can you think of any issues?

Thanks,

Don Hall
reserved N517DG
finishing and beyond
http://rv7.donka.net

 

[DGlaeser]

Sounds OK

That location will be just fine. The location isn't super critical. I have mine right between the 2 COMM antennas (which are behind the spar as you described). I'm not flying yet, but my son, who is, has his in the same location and everything works great.

BTW- I had to do a double-take when I saw your identification. My airplane is N751DG

 

[Mel]

An good location seems to be just aft the baggage compartment near on the passenger side of the vertical support. It's >>36" from other antenna and a safe distance from the exhaust. Also very serviceable.
Has anyone used that location, or can you think of any issues?
[/url]

That's exactly where mine has been for 15 years. No problems at all.

 

[Bryan Wood]

Just a thought... Ask yourself, do I want pulsed microwave literally between my legs for hundreds or thousands of hours? Only you can answer that for you. Just my two cents.

 

[az_gila]

Shields and plastic....

Just a thought... Ask yourself, do I want pulsed microwave literally between my legs for hundreds or thousands of hours? Only you can answer that for you. Just my two cents.

Ahh... but that is why we are building metal planes with an integral RF shield, and not plastic planes that microwaves can pass through....

gil A

 

[Bryan Wood]

Ahh... but that is why we are building metal planes with an integral RF shield, and not plastic planes that microwaves can pass through....

gil A

Yes. But... Bad BNC connections at the antenna are not that uncommon. I've fixed a lot of them on spam cans and most of them were done by avionics shops. This can allow stray rf on the pilot side of the shield, or can it?

 

[RickWoodall]

So....

Planning on installing bent whip and trans stubby in the next couple weeks. Not trying to get into a frying the guys debate....but...where is the best place to put ONE comm, and trans on the belly? I understand the spacing, and wanting to be short runs...so....planning doing my bnc properly, can you tell me your suggestion? You are suggesting that under the seat could leak rf and not be the wisest choice. Alternatives that are simple short runs...pics would be great.

 

[Mel]

Yes. But... Bad BNC connections at the antenna are not that uncommon. I've fixed a lot of them on spam cans and most of them were done by avionics shops. This can allow stray rf on the pilot side of the shield, or can it?

If it is under the seat pan or behind the baggage bulkhead, you have one more layer of shielding.
Also even though the pulse is around 200 watts, it is of such short duration that the actually radiated energy is very small.

 

[AltonD]

I looked at Checkoway's website and put mine in the same place, just forward of the spar, right side. It is away from com one, my primary com.
I wanted to put it in the baggage area or even behind the tunnel cover, but. . . after checking the install manual, with RG400, the coax run would have been too long.

Max. Length Insertion loss ECS Type MIL-C-17 Type RG Type
____________(dB/100ft)
6' 1.3" 8.0 M17/128-RG400 RG-400

 

[Kenny Gene]

Garmin 327

I have the small inexpensive rod with round tip antenna with a new garmin 327 and I have had approach lose or not make contact depending on my altitude, above 5,500 usually no problem. I have had a ground test or check's done with strong signal, so it must be a location or antenna issue. My transponder antenna is located on the passenger side just about 12" behind the seat. To me it's a bummer not to have radar contact with the first Ident from approach, so I was thinking of ADDING another antenna at a different location and splitting the coax?? Any thoughts?? 108 hours on 7A, first flight 9-7-07.

 

[Mel]

"A" Model?

If you are flying an "A" model, the landing gear could be shadowing your antenna in that location.
Relocate the antenna. Do not add another one.

 

[vlittle]

I have the small inexpensive rod with round tip antenna with a new garmin 327 and I have had approach lose or not make contact depending on my altitude, above 5,500 usually no problem. I have had a ground test or check's done with strong signal, so it must be a location or antenna issue. My transponder antenna is located on the passenger side just about 12" behind the seat. To me it's a bummer not to have radar contact with the first Ident from approach, so I was thinking of ADDING another antenna at a different location and splitting the coax?? Any thoughts?? 108 hours on 7A, first flight 9-7-07.

Can't have 2 antennas, just won't work. Your location may be shadowed by the gear legs or steps. Consider rewiring to a different location, say behind the baggage bulkhead.

V

 

[dhall_polo]

OK, good one, check on cable length.

Found a good thread on this.
http://www.vansairforce.com/community/archive/index.php?t-8446.html

Paraphrasing the other thread on Garmon xpdr (what I have):

There is a 1.5 db at 1.09 GHz (much tighter than above) total loss (includes connectors) requirement for the cable.
Therefore: RG-400 ==> maximum length of 8.8 ft.
RG-304 ==> 12.5 ft max.
RG-393 ==> 17 ft. maximum. - these numbers directly from the installation manual.

**I will check my install guide and not trust this thread entirely, but I'm leaning on baggage compartment install with longer coax run. I'll measure that distance before committing with the drill...

 

[Kenny Gene]

327

Yes Mel, it is a 7A, so tomorrow I'll measure my RG400 cable length or do what I was coming to the conclusion of and that was to re-locate the antenna. I'm not nuts about tearing the interior out,,, again,,, but it is frustrating when approach don't have you on radar, which may keep you out of controlled airspace.
Thanks everyone for your replies.

 

[AltonD]

The numbers I posted were from a Garmin 327 install manual.

I used a piece of 6 ft #20 gage wire to see just how much of a run it was. I didn't make it. I wanted to put mine behind the baggage bulkhead as well.