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Re: [CQ-Contest] Coax Stubs for SO2R

To: k9yc@arrl.net
Subject: Re: [CQ-Contest] Coax Stubs for SO2R
From: Steve NR4M <steve@nr4m.com>
Reply-to: steve@nr4m.com
Date: Tue, 26 Jul 2016 18:17:11 -0400
List-post: <cq-contest@contesting.com">mailto:cq-contest@contesting.com>
Jim,

Been following this thread since it started (this time) several days ago. I have lots of interest in it as I have a multi multi station here in VA. I have built coaxial stubs in the past using my AIM 4170, FSJ4 heliax, and K2TR's data as a good place to start. I think after screwing with them for years, I've gotten pretty good at putting the nulls where I want them. And, they seem to work, but no real data on how well they work. My 40m 3rd harmonic on 15 is about S-5 and I can get withing a couple of KC, or so. It's just not much of a problem any longer.

Been quite interested in your suggestions on how to place them for maximum attenuation of the undesired RF. I, like many, I guess, have installed them at the output of the amplifier, because that would be a 50 ohm point in a properly tuned amp. But, now I see that it's more important to know what the impedance of the harmonics is on your band of choice.

What got me up and moving on this is your comment in a previous post today about it being the second harmonic that's important. I have been building stubs, per N2TR, that covered multiple bands, without really focusing on a particular stations 2nd harmonic.

I pulled the coax off the stub set on the back of my 20 meter amp, connected a Rig Exper AA54, and started looking up my coax toward the antenna. On 10 meters, I saw R101 -J14.6 and on 15 (for the heck of it) I saw R112 j-36.

Following your instructions in your pdf on locating the stubs, I am just about where I need to be. If I added .44 feet of Coax, it would be right on the voltage peak.

Do these numbers above look as they should?  I was expecting higher R.
--

73 de Steve, NR4M

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