Hi Bruce,
BC> As long as the antenna are not close to being tuned to the 
BC> same wavelegth they don't interfer. At least before and 
BC> after standing wave checks have led me to believe this. 
I'm not saying that you're totaly wrong about the interference,
but I think that the standing wavecheck is not the correct 
technique to measure possible intererence from other antennas
or objects. The SWR check will ONLY tell you how well the
antenna is matched to the IMPEDANCE of the connecting cable
and equipment.
Imagine yourself sitting in a Farradys cage with your perfectly
matched antenna. You will get perfect readings from the SWR meter
but will still get no reception from the outside world. I suggest
that you check the fieldstrenght from a staionary source, like 
a pager transmitter, and make reference measurements when you add
several other antennas on the your car. Then you will see how much,
or little, interferance you'll get from directing/deflecting adjacent
metallic objects.                                         Ubbe.
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