Yo! TONY:
Sunday September 29 1996 14:52, TONY SZABLOWSKI wrote to BILL CHEEK:
 -> JB>> I'm toying with the idea of mounting two outdoor antennas on the
 ->> same JB> mast, one above the other. Other than the fact that the
 ->> upper antenna JB> will have a greater range is there any reason why
 ->> this is not a good
 ->  JB>> idea?
 BC>> They will interact with each other.  Keep them as far apart as you
 BC>> can
 TS> Bill, would one interact with the other if only one was being used?(eg.,
 TS> one tansceiver turned on while scanner on other antenna is off)
"Use" has nothing to do with it.
Are you familiar at all with how directional beam antennas are designed and 
constructed?  In general, the principle is one driven (used) element and two 
or more parasitic or nearby elements.
And so it is that any two antennas in close proximity with each other WILL 
interact to produce some effect, typically undesirable.  Antennas in the same 
horizontal plane (side by side) will "skew" the radiation patterns to favor 
some directions at the expense of others.  Antennas in the same vertical 
lane
(over & under) will pull the horizontal radiation pattern up and down to 
result in reduce performance out to the horizons.
Antennas within  1 wavelength of each other WILL affect each other. Between 1 
and 3 wavelengths, the effects are less.....perhaps tolerable by the 
scannist, and beyond 3 wavelengths, there is no measurable effect.
I wrote an article for a coming issue of Monitoring Times that explains this 
in more detail and describes how one might take advantage of the effect.
Bill Cheek | Internet: bcheek@cts.com | Compu$erve: 74107,1176
Windows 95 Juggernaut Team | Microsoft MVP
--- Hertzian Mail+
---------------