I posted this to the Force12Talk reflector this morning but it occurs to me
it might be of interest here too. FWIW
Bob, 5B4AGN
----- Original Message -----
From: "Bob Henderson" <bob@cytanet.com.cy>
To: <Force12Talk@qth.com>
Sent: Friday, October 01, 2004 7:05 AM
Subject: C31XR in SO2R
> Just in case anyone is contemplating SO2R using tri-fed C31XR(s) I thought
I
> would share my experience with you.
>
> I run a limited SO2R setup here as I only have one crank-up tower so all
of
> my antennas have to hang off that. I'm using a single tri-fed C31XR , a
> cushcraft XM240 above it and offset 90 degrees, a delta loop for 80m and I
> shunt feed the whole caboodle for 160m. In the world of contesting this
is
> not an overly impressive arrangement but if you want to see it anyway, you
> can find pics at www.5b4agn.net under the "Station" category.
>
> I had a few early hiccups with this setup but it works very well now. A
> fundamental limitation is that all yagis rotate together so there is no
> independent directional control for run and mult radios. That's not too
> much of a problem for me though because 99% of my world is at 320 degrees!
>
> With this kind of setup where antennas are so close together (with the
C31XR
> we are talking 3 driven elements only inches apart) it is important to use
> adequate filtering. I have stubs hanging across my feeders to 160/80/40 &
> 20m antennas and both radios have multiband Dunestars between tranceiver
and
> amp. I currently run two Ten Tec Orions, having replaced my FT1kMPs in my
> SO2R setup. One Orion drives an Alpha 87A and the other an Acom 1000.
>
> I measured the return power fed back via the coaxes of the two undriven
> C31XR interlaced yagis to scope the danger from use of this arrangement.
> This is what I found:
>
> 20m driven then 15m -32db and 10m -40db
> 15m driven then 20m -12db and 10m -25db
> 10m driven then 20m -16db and 15m -32db
>
> The above data shows just how important the stubs and band pass filters
are.
> If you were doing the above without these and running 1.5kW on 15m whilst
> listening on 20m you would pour a full 100W into the front end of your 20m
> receiver and would instantly be in deepest doodoo land! We're only
allowed
> 400W here so my risk is less but still real enough.
>
> I've used this arrangement for 2 years now with an FT1kMP and an FT1kMP
MkV
> Field. It has worked very well though I found I could sense modulation of
> the noise floor in the second tranceiver when transmitting with the first
> and I couldn't work within 10 kHz of my second harmonic. Changing to the
> two Orions provided a significant improvement in that now I can detect no
> noise floor modulation and I can work readily only 1 kHz away from my 2nd
> harmonic.
>
> Maybe someone will find this interesting or useful so FWIW.
>
> Bob, 5B4AGN, P3F
>
> Bob Henderson, 5B4AGN, P3F
> Giolou, Pafos, Cyprus
> Email: bob@cytanet.com.cy
> http://www.5b4agn.net
>
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