Com and Transponder antenna location RV-9A

rv9aviator · #1 01-18-2010, 06:03 AM

I would like to mount the antenna for my Transponder right behind the firewall in the center and the com antenna right in front of the wing spar in the center as well. This way the coax for both would be in the center under the removable cover. What issues if any will I have doing this. Will the coax's be too close to each other? They will be only 2-3 inches apart. This would keep the wiring contained in the forward area. Thanks in advance.

RickWoodall · #2 01-18-2010, 06:10 AM

Hi Jim. Most builders seem to put one near each gear tower on the A's. They are supposed to be several feet apart, and when I was doing my research it seemed up close to the towers was a good call and what most suggested and works well. It is easy to put in a backing plate, easy to install and no issue to service, inspect or replace connections down the road if needed.

tc1234c · #3 01-18-2010, 06:36 AM

I don't think you have to worry about the distance between co-axial cables. It is the spacing between antenna you have to keep. As said by Rick many people put transponder antenna under the gear tower. You can run the cable down the side. At that location it is easy to replace (the stub antenna is very easy to break) the antenna. Think about it, behind the firewall at the center location is not good. Each time you remove the pins for the lower cowl, you risk breaking the antenna.

This is how I did mine. Under the gear tower is the stub transponder antenna. At the center is a home made COM2 antenna, back under the pilot seat is COM1, near the left gear tower is a home made APRS antenna.

apkp777 · #4 01-18-2010, 06:55 AM

I put my transponder antenna just fwd of the center blkd (spar) on the right hand side. That gives me 30" from the transponder to the antenna. Garmin suggests 36". I am sure it will be okay. Garmin also recommends 36" between antennas. I had planned to put my comm antenna on the left side fwd of the blkd also, however it'll will only be about 28" from the transponder. I had previously been told somewhere I can't remember that 18" between antennas is the sufficient. I am currently looking for some documentation on that.

Camillo · #5 01-18-2010, 07:23 AM

Jim, transponder right behind the firewall in the center is not a good idea. It will be exactly aft in the middle of the tail exhaust pipes.

I installed mine (RAMI shark fin antenna: no problems for maintenance, since it has 2 connection with the skin and the coax connection) between the pilot pedals, just beside the longeron and now that I installed lower cowl and exhaust I am scratching my head if that is the ideal installation. It would have been better if it was 4'' apart on the left, so to clear more the aft exhaust tail pipe. I am not worried very much about heat (I will add a heat shield on the pipe) but about signal shadow.

My last idea - untile next ;-) - is to use such antenna for DME and installing the other identical antenna under the belly, under the baggage compartment.

In my case I have problems to install everything in the rear, because I have 1 COMM, 1 ADF, 1 XNDR, 1 DME under the belly and the latters should stay 6' apart one from the other, XNDR antenna 3' from receiver, COMM from ADF (if I well recall) 3' and so on...

On the other side, I saw a few airplanes with a XNDR installation like mine (between pedals) and they did not report issues. Maybe, you can try to locate it slightly on the left, behind of the left pilot pedal ot on its left. Double check if it is necessary to have a 12'X12' square flat surface. I can't remember now.

Hope this helps (and hope someone also clarifies the situation to me).
Camillo

rv9aviator · #6 01-18-2010, 08:00 AM

Thanks for the input. I didn't find any information on Garmins site to see what size plate I need for the Transponder antenna if anything more than just a doubler. Close to the gear towers won't be a problem either as they will still be in front of the spar. Thanks

USCANAM · #7 01-18-2010, 03:51 PM

On our 9A, we have one com antenna on top,and one on the bottom.
The top one goes to our more powerful G530, and the bent whip bottom one goes to our KY97. You can see it mounted in a line right below the top one.
Transponder is a blade type mounted on the right side bottom right behind the firewall. Never a problem

Regards
Jack

rv9aviator · #8 01-18-2010, 04:07 PM

Man, what a gorgeous airplane!

USCANAM · #9 01-18-2010, 04:21 PM

Quote:

Originally Posted by rv9aviator

Man, what a gorgeous airplane!

Thanks Jim
Amazing what 7 weeks full time painting will accomplish. Stopped counting at $2K for materials
4 days just to do the masking.There are matching stripes on the bottom of the wings and H.S. Those were fun???
Regards
Jack

ron sterba · #10 01-20-2010, 11:57 AM

Get a hold of Jim at VAL avionics in Salem Oregon airport.1-800-255-1511 He helped me. They have a 1" high com that he demo-ed at our EAA chapter meeting last year.WoW cool unit. the case is milled from a solid piece of alumium. you'll like the price too! Jim Wright. I have a set of your pedals polished with 3 levels of grit compound and painted Black in between the horizontal lines in the casting! Great looking. Ron in Oregon