[CQ-Contest] Coax Stubs for SO2R
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
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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