Hi Paul,
Multi op contest stations are a challenge, and much fun for some in many
ways. You should take notes each time you do it, and document the problems
as they occur, so you can go back to them at a later date and have some clue
as to what the circumstances were. It does not happen overnight. Some
problems require more than one person to solve. That can be a problem. Our
group had work parties on weekends where a number of us got together and
worked out gear problems as well as work on the towers or antennas. As we
get older and go thru many of these it is getting harder and harder to
motivate the troops :-)
I was in PA at N3NGE for the January contest. He has a slick station
with good engineering much in evidence. RFI is minimal, but there is some
monor de sensing on the higherbands (1296) and he is slowly pecking away at
the problems over five years later from his first multi effort. It is a
pleasure to operate such a station with little interstation QRM. His biggest
problem is cellsite QRM on 900 MHz!
In a portable situation, I guess some minor contests can be the impetus
to get the vehicle out and work over the problems as the contest progresses.
I know that I have used the June Contest as a warmup for our big effort in
September. We have fun and solve a few problems along the way.
Dave K1WHS
----- Original Message -----
From: "paul rollinson" <ke1li@sbcglobal.net>
To: <vhfcontesting@contesting.com>
Sent: Monday, January 26, 2009 9:51 PM
Subject: Re: [VHFcontesting] Multi-op interferance on IF freqs
Thanks to all for the suggestions. Limited time and budgets mean we will
have to make a list of solutions, proximity of antennas to each other being
the easiest and cheapest.
Running a portable set-up is much more difficult. We didn't have the luxury
of setting up testing and tweeking before the contest. We hope to be able to
do more of that before the next go at it.
73,
Paul, KE1LI
________________________________
From: David Olean <k1whs@metrocast.net>
To: paul rollinson <ke1li@sbcglobal.net>; vhfcontesting@contesting.com
Sent: Monday, January 26, 2009 4:20:11 PM
Subject: Re: [VHFcontesting] Multi-op interferance on IF freqs
Hello Paul,
I always try to use a minimum of power at the IF frequency, whether it be
28, or 144 MHz. 1 milliwatts causes less trouble than 10 watts. After that,
you need to shift the IF on the MWs away from 144 MHz. It is also a great
idea to get the 144 antenna as far away from the microwaves as is possible.
When I had the 5/10 GHz rig on the same tower as the 144 antenna it was a
bummer. Even with hardline IF lines, the 144 QRM was too much. Besides
physically moving 144 away, the change to 145 or another IF helps a lot. We
are using 145 and 147 MHz to keep IFs separated between stations. Face it, a
KW on 144 can get into almost any IF cable on the same frequency. Most coax
has about 95-100 dB shielding. 1500 watts is + 61.8 dBm, so any leakage
could be very loud anywhere near a 144.100 MHz microwave IF!!
Finally, you must invest in suitable filters to keep the QRO bottom four
from hitting the higher bands. 3 X 432 bothers 1296. 4 X 222 bothers 903
etc. Putting stubs on the preamps will help as well. Good grounding of IF
lines will help. We use 3/8" heliax for 144 MHz IF lines running up to tower
mtd boxes. High power filters can be a problem. There is a good 144 MHz
filter using teflon board caps that handles 1500 watts OK. I made a third
harmonic 432 filter to protect 1296. It was double stub teflon coax
construction. I got over 100 dB notch at 1296.3 MHz. I use a big surplus
filter on the 222 amp as well. I found it on eBay!
Lastly, you will still need input filtering on your receivers on all the
bands. They protect frontends from huge amounts of power that sneaks down
your feedline when running a KW a few feet away from your antenna. When you
get it all working, operating a multi op station gets to be fun.
Dave K1WHS
----- Original Message -----
From: "paul rollinson" <ke1li@sbcglobal.net>
To: <vhfcontesting@contesting.com>
Sent: Monday, January 26, 2009 1:29 PM
Subject: [VHFcontesting] Multi-op interferance on IF freqs
> 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
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting@contesting.com
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