Just to close the loop on a few details.
For the wingtip antenna you have two choices, buy the Archer product or build. If you build, you must have a way to tune the antenna, such as this:
https://www.gigaparts.com/mfj-259d-...CYWXbLeLy0HnL7BaDog5gy3BBNft1ecRoCGk4QAvD_BwE
I suggest however even if you buy, you should use this or similar antenna analyzer to verify operation - of all your antennas. This is a perfect shared tool for builders or an EAA chapter.
If you build, use the nice diagram on page 13-16 of the AeroElectric publication as a model. From that however you can achieve better performance by optimizing all the space you have in the wingtip. This translates to holding the “triangle” constant, extending the arm from the end rip do that the antenna reaches all the way into the wingtip, then shortening the trailing arm inside the wingtip about the same amount as you extended it from the rib. Make this last piece a couple of inches long so you have material to trim as you tune it. Same for the gama match - make it a little bigger to allow for tuning. When you tune, you trim the end of the trailing piece to achieve the desired resonant frequency. After that you trim the gama match to achieve the best impedance match. This is an iterative process that sounds harder than it is.
Side notes
- As with any bent whip type antenna the majority of the “work” is done by the first third or so (the high current part). This is a driving reason to extend this part as far into the wingtip as possible. The rest is there to bring the antenna into resonance.
- LOC and GS signals are relatively strong. If you tune the antenna for VOR frequencies LOC and GS reception range will be way beyond practical use.
- While if I could put the airplane on an instrumented test stand I suspect I could measure aspect dependency on signal strength (the same for any antenna). I suggest that my extending the antenna way out into the wingtip aids in my not experiencing any aspect “shadowing”.
Attached photo shows how I mount my antennas:
Note three things:
- I do not run the Nav/Strobe wire along the antenna arm as I’ve seen on some Archer installs. I can only assume the Archer instructions have this for those installs that “must” do so.
- I move the antenna back a bit - keeps NAV/Strobe RFI down.
- I mount the antenna on the rib, not the wingtip. The wingtip just slides over it. Not shown in the photo is a piece of 1/4” split plastic wire conduit (Harbor Freight) along the outside edge of the antenna. The outside edge nestles into the wingtip - this little piece of plastic keeps it from moving.
Carl