NAV Antenna in Lower Cowl?

[Toobuilder]

Don't laugh - my understanding of antenna theory approaches total ignorance- but if it works in the fiberglass wingtip, why not the glass lower cowl? I've read about the directionality issues with one wingtip, but the lower cowl location looking forward and down seems like its ideal. Seems like there is plenty of real estate for an Archer, foil, or stripped coax type, and the firewall should make for a fine ground plane.

Is this workable?

[BobTurner]

Well, I can think of some potential issues
1. Close to the spark plugs/ignition wires, potential RF noise source.
2. Poor VOR reception if the station is behind you.
3. Antennas designed to use the firewall as a ground plane will tend to work best left-right, not front-back (see #2).
4. The ILS uses AM modulated signals. If you look thru the prop (forward) there may be strange stroboscopic effects, depending on RPM. I recall Cessna at one time had windscreen GS antennas, and they came with that caution.

OTOH, modern receivers are amazingly sensitive, so that almost any antenna will work. Just that some are better. No harm in trying!

[noelf]

Several of us have marker beacon antennas in the lower cowl and they seem to work well. The reasoning for selecting this location was the aircraft would be located close overhead to the transmitting antenna, and the MB transmitter puts out a relatively strong directed signal. Plus there is a strong possibility the true MB transmitters will go away as GPS derived points are implemented.

If you use the foil heat shield inside the lower cowling, it will block the signal from an antenna inside the cowling. My particular implementation solution to this problem was to use the heat shield foil as the MB antenna. Other AC have bonded a wire underneath the fore/aft piano hinge line of the lower cowl. Having the antenna incorporated into the cowling structure also requires that you provide for an antenna wire disconnect so that the cowling can be removed when needed.

Trying to place a com or nav antenna firewall forward is somewhat problematic as the com antenna needs to be vertically polarized and the nav antenna needs to horizontally polarized. And, with the metal firewall, motor mount, and engine mass, I would be concerned with severe signal and directional distortion for our com and nav signals.

[RV6_flyer]

Originally Posted by Toobuilder

Is this workable?

See Bob Turner's response.

The Archer Antenna by design has a very very very very small bind spot. Not following installation instructions will only degrade its performance. The engine above the antenna will decrease nav antenna performance. There is NOTHING around it in the wing tip.

Generally pilots follow directions because the directions work and provide SAFE Good performance.

[aerhed]

If you made a copper strip dipole with the point of the V just below the spinner and the radiator legs going back along the lower sides it should work fine. You would need to provide a balun and I would hard point a BNC connector.

[Steve Melton]

I consistently pick up VORs at 80 nautical miles distance at 9K altitude using the archer antenna in the wingtip using SL-30. ILS approach needles are smooth. Edited: upon further testing, when approaching some ILS from the left and 10 miles out I get a slight hesitation of the vertical needle until I am established. I believe this is because the archer antenna is installed in the right wing tip and some fuselage blocking occurs. When approaching from right I do not have the hesitation.