----- Original Message -----
From: "John D'Ausilio" <jdausilio@gmail.com>
To: "paul rollinson" <ke1li@sbcglobal.net>
Cc: vhfcontesting@contesting.com
Sent: Monday, January 26, 2009 8:38:18 AM GMT -05:00 US/Canada Eastern
Subject: Re: [VHFcontesting] Multi-op interferance on IF freqs
Now here is a very interesting subject. This past contest when out for the
first time in a long while as a rover, I experienced this issue somewhat with
my partner, but only on 903. After building up K8GP for the last 10 years, I
found that you can not maintian the same IF frequency for transverters, even at
10m for 6 - 432. For my rover, 1296 and up all use a 146 MHz IF and I had no
interference at all except for some harmonic trash just due to close proximetry
of the antennas. On 903, I hadn't moved my transverter to 146 yet and
interference was very bad.
At K8GP, I had to move even the 10m IF's to keep folks from hearing our own IF
signals. Since we used TS850's on all bands and they were all set for all band
tx. I ordered special crystals for the DEM transverters and moved them around
to avoid this issue. 6m stayed at 28 = 50, 2m went to 26 = 144, 222 = 27 and
432 = 25 (using DEM's standard 28 = 437 crystal). For 903 and 1296, I moved the
IF's to 147. Using a 2m intermediate IF transverter with 26 = 144, this moved
my tuning range to around 29 MHz. For 2304 and above we used a 146 IF and the
2m intermediate transverter was 26 = 144 which meant the tuning range was
around 28 MHz. There was some issues with the 6m IF being heard on the
microwave station but since we now use K3's for 6m natively, that issue has
gone away.
In most cases with a rover, I would suspect it's just close proximetry of all
the antennas. My 2m station running 350w was only 6 feet away from the 903 and
up stack of antennas, it hard to fight that!
Terry
I'm considering moving all my microwave IFs to 145Mhz to solve this
problem in the Jitney (which is a 2-op rover) ..
de w1rt/john
On Mon, Jan 26, 2009 at 8:29 AM, paul rollinson <ke1li@sbcglobal.net> wrote:
> Good morning all,
>
> During the last contest we expanded the bands we worked up to 10G from the
> bottom 4. This created a huge problem.
>
> We had to shut down the 2, 220, and 432 stations to use the upper bands due
> to interference from the lower, high power stations on the IF rigs for the
> transverters. 6M had little effect but we only had 100W running. Murphy
> reduced our power level.
>
> I speculate that a common patch panel and close proximity of the antennas may
> be the culprit but I'm looking for other opinions and potential solutions.
> Especially from the big multi-ops that run legal limit on 2 and 432 which we
> use for IF's.
>
> June is coming and I'd like to start clearing this problem asap. We always
> run out of time.
>
> 73 and thanks for the input,
>
> Paul, KE1LI
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>
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