The easy way to see if you have "holes" or voids in your antenna pattern is
to get some goodly distance away from a constant transmitter source (atis or
awos) where the received signal has some noise in it. THen put the airplane
in a SLIGHT bank (say, half standard rate) and see if there are any deep
nulls in the pattern. Deep meaning that the signal disappears completely.
THen cut the distance in half (6 dB) and see if the null is still there.
Half again (another 6 dB) and try again. Most metal aircraft have 15-20 dB
nulls in quite a few spots in the pattern, but more than 18 dB (half, then
half, then half again) calls for some investigation.

Jim




"COLIN LAMB" wrote in message
k.net...
If the antenna is mounted on the top of your metal aircraft, you could be
shielding the transmissions below you, while having good coverage
horizontally.

Colin