[CQ-Contest] Coax Stubs for SO2R

[Jukka Klemola]

Jim,
I thought placing double stubs on the TX line is not so critical.
The two band stopping stubs are supposed to be about quarter wave apart; on
the harmonic band; and that should effectively remove the need for extended
optimization.

Also, in my experience, if you get approx 30 or 35dB attenuation using one
stub, you will get more than 45 dB attenuation over the whole band when
measured in a 50 ohm system.

At least my measurements show these results:
-placement not critical for double stub
-attenuation almost doubles in dB compared to one stub

--> I have been building only double stubs nowadays.


73,
Jukka OH6LI

2015-10-05 9:57 GMT+03:00 Jim Brown <k9yc at audiosystemsgroup.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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