I made up a template for the transponder antenna to make up the doubler plate. I realized as I was doing this that I never tested the hole pattern I made for the VHF antennas, so I drilled the hole pattern into some scrap to make sure they would all line up and they were perfect. After cutting out the sheet of aluminum I drilled the pilot holes for the transponder doubler. I then marked the location I am thinking of for the transponder, which is just forward of the rear seat just left of center. This location will provide easy access. I do have a concern; the instructions say to keep the transponder antenna 3 feet from other antennas, 3 feet from the transponder unit itself and with the cable (RG400) that I am using, I can’t have a run of cable longer than 8 feet. This really limits where the antenna can be placed. There just is not that much space on the RV-8. Many have mounted the VHF antennas like mine; they say if you can keep the antennas one antenna length apart then they work fine. I need to ask where others have put the transponder antenna. I would prefer to put the transponder antenna further aft but this would make the cable length close to 12 feet. Time for more research, I bet I spend as much time researching issues as I do in the shop working!
The last thing I did is cut the forward flange of the VHF doublers so they now fit under where the wing bolts will go, I will actually drill holes for these tomorrow.
Transponder tempate after holes were drilled
Location is just foward and left of the back seat, there will be a console cover over this area.
This shows all of the antenna locations, VHF front transponder aft.
