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[aprssig] Multiple Radio Desense

Robert Bruninga bruninga at usna.edu
Mon Mar 14 23:24:45 UTC 2005

Last week, I asked 3 AMSAT volunteers (OE1DMB, N6IZW,
and ZL3RX to take some radio measurements for FM desense 
just to see if we were in the ballpark for multiple radio 
operations at one site.  This data will be useful for you  at 
FieldDay and your EOC or other operations where multiple 
radios will be used.  (APRS everywhere!)

At separations of 100' between antennas:

2 meters:             (the spread is worst-to-best radios)
25 KHz separation blocks at  1 mw to 100 mw
600KHz separation blocks at  about 100 mw to 1 W

25 KHz separation blocks at 30 to 80 mW
1 MHz separation blocks at  2 to 5 Watts

Thus, at two meters, even at lowest power levels you
are going to get desense and even blockage with any
pair of radios on 2 meters.  SO plan accordingly with
better antenna separation and beams if needed.  For
APRS events, I use a 2m beam at the end of a 150'
piece of RG-58 pointed at the digi.  THe lossy coax
and beam still work for APRS but do not desense the
other 2m voice ops at the same site.

At 70cm, with a little thought, you can operate dual 
voice radios simultaneously easier...

de WB4APR, Bob

>>> "Robert Bruninga" <bruninga at usna.edu> 3/11/05 12:16:30 PM >>>
>>> "Robert Bruninga" <bruninga at usna.edu> 3/10/05 12:12:12 PM >>>
>We need a volunteer ...[to assess radio desense when 
>two radios are operating in close proximity (say 100') 
>and on the same band]...

Thanks AMSAT!  I got many responses and three have already
produced good data.  I am assembling it now and will post 
the results.  Generally it only takes a few 10's of milliwatts to
desnse one radio with another on an adjacent channel
(25 KHz away).  At 100 KHz, it is on the order of 100 mw
and for the normal 2m split of 600 KHz it is on the order
of a watt.  And of course some radios are better than others.

Thanks to  ZL3RX,  N6IZW,  OE1DMB 
and also PE1RAH and Gerry

More later.
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