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Second com aerial

H

Handclutch

Well Known Member
Patron
Has anybody fitted a second com? if so, where did you put the aerial? I replaced the original radio that had dual monitoring with a Garmin 420. I am happy with the upgrade but it is handy to be able to monitor a second frequency. My plan is to fit one of the small radios that go into a 2" hole and may set it up only to receive. Panel space is fine but finding a location for the antenna with good accessibility might be a challenge.

Jack
 
I added a second com and mounted the antenna about 2 ft aft of the ADAHRS box. I added two F-1283C stiffeners and a 6x8 doubler under the antenna. The antenna is a RAMI AV-10. Running another coax cable may be an issue, I have four in the tunnel (Com1, Com2, GPS, Nav), with the ADS-B mounted behind the baggage bulkhead.

John Salak
RV-12 N896HS

2ufyrfb.jpg
 
I put my second comm antenna on the top of the fuselage half way between the vertical stab and the aft canopy edge. I use a stand alone Microair 760 as my backup.
 
Might have a solution

Thanks for the installation photo. Midway on the fuse between the baggage bulkhead and vertical stabiliser, either top or bottom, is the obvious place but getting in there (aircraft bought flying) is beyond me. However, I've identified a spot immediately behind the rear window, above the lap joint and F1232A might work. The connector and coax would be inside F1232A (barely visible) and could be fed through a hole in the bulkhead, down behind and then underneath the baggage compartment through to the tunnel. The mounting surface is far from ideal with the joint and rivet heads but might be doable with some dense foam rubber as a gasket, or sealed with silicon or similar. Immediately adjacent would be much better from a mounting point of view (flat surface) but would put the aerial slightly off the centre line and angled just off the vertical. Not ideal aesthetically but wouldn't affect function and I think I would get used to it.


Jack
 
Speaking as an old electronics and ham radio guy I would have to say that location is not a good idea, IMHO. Vertical antennas need a good electrical ground plane to operate at peak efficiency, and mounted where you describe you would only have sort of a half ground plane. And, being so close to the cockpit with only the plexiglass in between I would be concerned about RF causing interference with other avionics when you transmit.

Suggest you find a helper that is small and agile and install the antenna farther back in the tailcone.
 
I agree with John. In the spot you suggest the radiation pattern will be skewed forward.

I've posted before on the inspection ports I installed on the belly of the fuselage. I was able to install the antenna with rivnuts and route the coax with only those ports for access.

I wish Vans would consider adding some ports into the design.
 
Which airframe? If it's a -7 tipup, don't forget that there's a hefty aluminum U-channel running from the back of the back glass, forward to the roll bar. That would very effectively make the 4th leg of a 4 leg ground plane.

Charlie
 
Yes, after posting I thought about the ground plane issue and realised it wasn't the best idea I've had this year. I had a good look at the aeroplane today and now feel confident I can reach through the baggage bulkhead to locate an aerial on the underside, far enough back from the existing installation. Thanks also for the suggestion about using rivnuts. That would certainly make it easier with only the coax to be attached from inside.

Jack
 
RFSchaller said:
Charlie,

Since it's on the RV-12 forum I assume it's an RV-12.

Rich
Click to expand...

Well, I'm certainly observant... Sorry; totally missed it. I've been clicking on threads from "today's posts", not paying attention to their source. Or reading the poster's signature line, apparently.

On mounting mechanics: Does Van not recommend a skin doubler at antenna mount positions on the -12? On the faster models, it's recommended.

On rivnuts: I've never met one I didn't eventually replace. Might be ok on something like an antenna, that will effectively never be removed after installation.
 
Charlie! Put down the mouse and enjoy your RV! I hit the 160 KT ground speed club today with the help of a 47 KT tailwind in northern AZ. The return trip at 59 KTS GS gave me ample time to contemplate the deeper meaning of life and the vastness of the universe! Thank God for my iPod!
 
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