My Wooden Airplane
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8/15/2013 - 8/25/2013

Transponder Antenna

I considered making my own transponder antenna, but decided I don't have the equipment to tune and test it, and commercial ones are cheap enough (mine was only about $17), so that's what I did. The most difficult part of installing the transponder antenna turned out to be deciding where to mount it. The transponder instructions said to mount the antenna at least 3 feet from the transponder itself, but if you're using RG-400 coax (which I was), the maximum length of coax could only be about 6 feet or so. Becaude of the way I was routing the coax, there was no way to mount the antenna while staying within those constraints. Three feet from the transponder would put the antenna directly between the landing gear legs, which I felt would end up shielding the antenna too much, so I moved it back about a foot, so that it was directly under the bulkhead that separated the baggage compartment from the cockpit. Unfortunately, that meant the coax had to be about 9 feet long. Theoretically, I could have done it with RG-304 coax, but that stuff is hard to find, expensive, and hard to work with because it's twice as thick as RG-400. I ended up reading a post on an internet discussion group where a knowledgeable person (I think it was Bob Nuckolls) said while RG-400 might not be ideal, it wouldn't be that bad, either, so that is what I went with.

Total Time: 2.5 hrs.