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Re: [TowerTalk] 2 Rigs/4 Antennas

To: "K0PYK" <>,"Tower Talk" <>
Subject: Re: [TowerTalk] 2 Rigs/4 Antennas
From: "Jim Lux" <>
Date: Mon, 1 Nov 2004 07:23:30 -0800
List-post: <>
----- Original Message -----
From: "K0PYK" <>
To: "Tower Talk" <>
Sent: Monday, November 01, 2004 6:53 AM
Subject: [TowerTalk] 2 Rigs/4 Antennas

> Tower Talk'ers
> What is the best way to handle 2 rigs and multiple antennas.
> I use one rig for psk and and one for ssb. They are usually connected to 2
different antennas. Lets say 7.070 psk and 20 meter ssb.
> Do I have to be concerned about overloading???
> Tom, K0PYK

Maybe you do, maybe you don't.  A lot depends on how much coupling there is
between the antennas. And, how much front end selectivity there is in your
rig.  And, of course, how much harmonic content there is coming out of your
rig.  -40dBc may sound like decent harmonic suppression, and it is, to the
other end of the HF link, where it's below the noise floor.  However, if
you're radiating 100W (+50 dBm), if the second harmonic is 40dB down, that's
still 10 milliwatts(+10dBm), which is a LOT more than the microwatts your
receiver is used to seeing.

I assume you're not running a kilowatt on the psk rig, which should help.
Have you measured the received signal power on Rig B when Rig A is
transmitting? (Does it pin the S meter?  Does it block received signals or
make them "sound weird" (i.e. are you getting IM in the front end).  The
PSK31 waterfall is a fairly decent diagnostic here.  You can watch the
received signals, and key the SSB rig on and off (CW style, not with voice)
and see if there's a difference.

If you're always on the same bands, then coax stubs might be a cost
effective way to trap out the "other band". You might also think about a
filter to get rid of Tx harmonics.

Another thing springs to mind: you said "usually" connected to 2 different
antennas.  If they're ever connected to the same antenna at the same time
(and if there's any possibility of this occurring in your switching scheme,
it WILL happen someday), you've got a more tricky problem to solve.


See:  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

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