[CQ-Contest] Coax Stubs for SO2R

Jim Brown k9yc at audiosystemsgroup.com
Mon Oct 5 02:57:28 EDT 2015

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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