[TowerTalk] crosstalk between beams on a common boom (such as c31xr)

[Pete Smith]

I am about to try an SO2R approach for the high bands that involves 
splitting my tribander stack and feeding the bottom one with the second 
radio while the first radio continues to use the top one.  According to 
W2VJN's book you need 45 dB of isolation (at 1500 watts transmitter power) 
to be comfortable about not damaging the receiving radio, and much more 
than that to have good receiver behavior.  My assumption is that even 
30-foot spacing will not be sufficient to give 45 dB, and therefore I need 
bandpass filtering, at a minimum.  I also plan to run passive limiters in 
both receive antenna lines just in case I screw up - it could get expensive 
otherwise.

If my assumption is correct about 30-foot spacing, imagine the difficulty 
that a C-31XR would present.  My hat's off to 5B4AGC (I think) for making 
it work.

73, Pete N4ZR



At 12:47 AM 3/19/2005, David Hachadorian wrote:


>----- Original Message -----
>From: "Al Williams" <alwilliams at olywa.net>
>To: <towertalk at contesting.com>
>Sent: Friday, March 18, 2005 10:11 PM
>Subject: [TowerTalk] crosstalk between beams on a common boom
>(such as c31xr)
>
>
> > For example, transmitting on a 20 meter beam while listening on
> > a 15 meter beam.
> >
> > How great is the risk of damaging the front end of a receiver
> > listening on one beam while transmitting on a second beam
> > when both are close spaced?
>
>How far apart are those elements on the multi-feed C31XR, just a
>couple of feet? If you don't do everything just right, you will
>blow the Rx every time. I would suggest dedicated sets of stubs
>on the three feedlines, in addition to the BPF's. That's what
>Natan, formerly of Force 12, recommended when I talked with him
>about this subject. There is a 5B4 doing this with a C31XR, and I
>remember him writing about it. It took a fair amount of work for
>him to get overload under control, but he is doing it
>successfully, at high power.
>
>
>Dave Hachadorian, K6LL
>Yuma, AZ
>
>
>
>
>
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