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Dean,
I have set up for hard IFR with two Comm antennas mounted in accordance with advice from Gary Lane at Lancair. The second one is placed aft of the baggage bulkhead just a few inches ahead of the stock position of the pitch servo, on the centerline -- about where the builder's manual shows the TCAD antenna (Ch 27, p.18). I painted the bottom of the airplane with copper paint (Electrodag), from the firewall aft to a point underneath the rudder bellcrank, and the full width of the fuselage, from left to right wing root, as a ground plane and then covered it with primer except where the antennas mount. At each antenna, the ground plane is exposed and I provided an Av-DEC squishy conductive gasket, cut to the size of the antenna base -- as a sealant and to insure a good grounding. Finally, I ran a single ground wire, that I just frayed out and stuck between the transponder ant gasket and the ground plane, up to the aft ground block. This was an attempt to cure a problem with the transponder (that turned out to be the transponder itself) but it eliminated a significant amount of background static that was present on the comms radios.
Results are excellent in the first 70 hours of flying including a 1-hour hard IFR practice flight with plenty of rain and cross-countries from Dallas to Oregon, Kansas City, and New Mexico.
Charley Brown
Legacy #299 N550KC
1. Building a thick pad of flox with 2-BID carbon fiber over it on the fuselage centerline just behind the baggage bulkhead.
2. Mounting nutplates. You can see the copper ground plane up forward, I hadn't planned on a second antenna but later extended the ground plane about 2 feet aft of the second comm antenna.
3. Ground plane visible through the outer primer coat.
On Dec 30, 2011, at 11:07 AM, Dean Whiting wrote:
I was looking for some advice about communication antennas. The legacy is setup to have one com antenna. We want a capable IFR airplane and I am hesitant to have one antenna with a diplexer (or is it duplexer, I've seen it both ways) as a possible single point of failure. Is this the method that most people are using? If you mounted a 2nd com antenna, where did you place it? I searched the archives and found someone else who asked the same question but I couldn't find the answer. Any other input or advice on the subject would be appreciated.
Dean Whiting
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