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Re: [CQ-Contest] Coax Stubs for SO2R

To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] Coax Stubs for SO2R
From: Jim Brown <k9yc@audiosystemsgroup.com>
Reply-to: k9yc@arrl.net
Date: Sun, 4 Oct 2015 23:57:28 -0700
List-post: <cq-contest@contesting.com">mailto:cq-contest@contesting.com>
On Sun,10/4/2015 2:59 PM, Jeff AC0C wrote:
That's a great way to start. Especially as the solar cycle fades and 10/15 are not open. Then in the day, you run 40/20, and in the night you run 80/40.

Yes, but there's a LOT more to it if you want to maximize the effectiveness of the stubs. It can matter a LOT (20-30 dB) where along the line stubs are placed, both with respect to the antenna and to the power amp.
See my piece in NCJ one issue back, or download it from my website.

For our CQP expedition, I made up double stub packs for the 40M and 80M CW stations only. Each pack was two stubs cut to kill the second harmonic, with a quarter wave (at the harmonic) connecting them. I didn't have time to optimize their placement, but using two stubs insures that you'll get at least 25-30 dB, and with optimized placement, another 25-30 dB.

Stubs are less important on SSB because the likely operating frequencies are not directly harmonically related, whereas the harmonic of 3525 hits 7050, and 7025 hits 14050.

73, Jim K9YC


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