Top Antenna Question with Rearward Performance

[Jono]

I fly gliders and tow planes, we often find that a glider on tow (behind and just lower/higher) can be hard to hear on the radio.

I believe it is simply because of the radiation pattern of the antennas.

It sounds like the champ was in a similar position?

[LSaupe]

Yep, Champ problem was between 4:00 and 8:00 when at, or slightly below, my altitude.

[Dusty]

AM or PM

[jmodguy]

The antennas we use are typically vertically polarized 1/4 wave monopole "whip" style antennas that put out an omni directional radiation pattern. The radiation pattern typically resembles a doughnut (mmmmmm)
Omni directional means basically "every direction" around the antenna. In a perfect world the transmit and receive antennas are perfectly parallel to each other. Any offset in the alignment of the 2 antennas results in a signal loss. The closer they get to 90 degrees to each other, the greater the signal loss.
Ground planes are important for antennas. The antennas we use are ground plane or monopole antennas that are basically half of a di-pole antenna. The active part of the antenna is the whip you see, and the ground part you don't see is the "ground plane".
Here is a website to peruse at your leisure...
http://electronicdesign.com/wireless...-plane-antenna
Here is a site that can help you figure the minimum size of your ground plane. Ground planes should NOT BE ROUND. Ground planes do not have to be thick. Aluminum foil will work as long as you can make a good bonded connection to the antenna base.
http://www.buxcomm.com/ground_plane_calculator.htm

[SkySteve]

Does it matter if the antenna is straight up or at an angle?

[jmodguy]

Not really. The losses start getting bad the closer you get to perpendicular. the antenna will still work, but will be degraded somewhat (lot's o' math). The typical "swept" antennas used on aircraft are not a factor.

[SkySteve]

Thanks, Jeff.