RE: [amsat-bb] Minimizing de-sense on Arrow and other closely spaced antennas

["Howard Long" <howard@xxxxxxxxxxxxxx>]

Hello Bill

> I just picked up a used FT-530, but for mobile/portable, I also have the
> Alinco twins (DR-135, DR-435) available, so the answer is "both". :-)

I'm not personally au fait with the FT-530, but I checked out the ARRL
review (they reviewed five full duplex HT's in March 1994). Although they
didn't specifically talk about full duplex, they did mention the cross band
repeater function and unlike at least one other model, there was no hint of
any problem in desense.

It is of course somewhat of a weak hypothesis for me to suggest from this
that this radio will be great for FM satellite full duplex operation. Other
owners of this radio are far better qualified than me to comment!

With a dual band HT and Arrow working through a duplexer I can't see there's
much you can do unless you want to take the radio apart.

If you have two separate radios, a neat solution is to use half a 2m/70cm
duplexer to do some pretty heavy filtering. Indeed, this would let you find
out whether it's the harmonic or the front-end being desensed. BTW, there's
a school of thought which says to be on the safe side, terminate the unused
port with a 50 ohm resistor or dummy load, otherwise the filter
characteristics might be a bit off.

73 Howard G6LVB


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