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[TowerTalk] station to station interference

To: "Towertalk@contesting.com" <Towertalk@contesting.com>
Subject: [TowerTalk] station to station interference
From: Steve NR4M <steve@nr4m.com>
Reply-to: steve@nr4m.com
Date: Tue, 27 Sep 2016 20:17:48 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Hello all,

I'm good at some things and not so much, at others and I have problems thinking 'outside of the box', so looking for ideas.

Have a multi mult here in central VA, which seems to work well.

With the RTTY contest a continual problem came to the forefront again.

I am getting rather annoying interference between stations. What was specifically pointed out to me this weekend was 20 was clobbering 15, but it's usually 40 clobbering 20, 15 and 10. I'm guessing it's about 20 to 30 db of wide 'hash' coming from 20, covering all of 15.

My antennas are all resonant antennas and typically 400 to 500 ft from the shack on multiple towers. 40 is probably 500 feet from 20, which is about 150 feet from 15. All mono band antennas and the shack is generally on the back side of them. I have low power band pass filters after the rig and before the amp and coaxial stub filters after the amp. And, based upon K9YC's narrative on placing stubs, they're pretty close to optimum placement. But, don't think it's harmonically related, as I've transmitted on 40 while looking at 20 and 15 meter spectrum on my Flex Maestro and what I see looks very acceptable. No 'whole band' crap and my second is only about 500 hz wide as my 400 hz cw filter totally covers it on the spectrum display and it's not real strong. This was with 1000 watts out on 40 meters. The 3rd on 15 is about the same. 20m is looking like a -120dbflex and 15 about the same. Local noise floor about -135 to -140dbflex (dbflex = I don't know their reference...)

It doesn't look like I can reproduce the problem when it suits me. It only seems to rear it's 'ugly head' during a contest, when multiple transmitters are going. But, even at that, the other day the only one that was actually transmitting was 20 and it was eating up 15.

Any guidance on what I should be looking for would be of great help.

--
73 de Steve, NR4M

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