[CQ-Contest] Coax Stubs for SO2R

[Gerry Hull]

Hey Mike,

Some great replies to you so far...

One other comment I have:  You cut the subs based on frequency and velocity
factor...

I was recounted a story recently about a well-known contester who had his
stubs in place for SO2R for (many) years.  He thought they were great
(though their was still some interference between bands).  He had done
exactly what you had done -- calculation, physical measurement and cut.  A
visitor to his shack recently brought over his vector impedance analyzer.
It turns out the stubs were providing < 1.5 dB of attenuation.  After
trimming the stubs, he got the wanted attenuation to > 25 dB!

The moral of the story is: beg, buy, borrow or steal an antenna analyzer,
or even a noise bridge.

73, Gerry W1VE


On Mon, Sep 7, 2015 at 9:07 PM, Mike Smith VE9AA <ve9aa at nbnet.nb.ca> wrote:

> This is about coax stubs.
>
>
>
> Sent this earlier to "Towertalk" then I thought perhaps it was better
> suited
> to contesting.
>
>
>
> Reposting, with some edits:
>
>
>
> I've seen the K2TR stubs, K1TTT page and have recently bought the FB book
> by
> W2VJN
>
> Today, for a change, I had a little spare time so built 2 stubs, but lets
> just concentrate on one.
>
> It was supposed to be for the 40m transmitter (Radio A).
>
> I will add  Radio A (transmitter) is using a multiband vertical.
>
> Radio B (receiver) is attached to a multiband horizontal dipole (ZS6BKW) in
> case it makes any difference in my question.
>
> I see a signal of roughly S9 or S9+ 20/40 on the receiver (varies per band
> &
> harmonic)
>
>
>
> I roughed out the length, attached a T and a 2nd antenna switch (a la VA2UP
> method) (which I'll only use for stubs), trimmed it with my AA-230pro
>
> and when it's inline (parallel to my primary antenna switch) I see no
> difference at all on 20m or 15m on my 2nd receiver when the stub is in or
> out of line
>
> NONE.  Like, not even a titch ESP hopeful. (hi)
>
>
>
> I presume this is a type 1 stub (shorted 1/4WL type, x velocity factor)
>
>
>
> Thinking I had done something wonky, I made another stub from different
> coax..same result.
>
> Later I made one up for 20m - same result. No change whatsoever in the
> received signal harmonic(s) on the receiver.
>
>
>
> Anyone been down this road?
>
>
>
> Too close to rig?
>
>
>
> Interaction from my T and 2nd antenna switch?  Gremlins? Wrong method using
> the AA-230 pro maybe?  I am close to that 23' mark on the 40m one.
>
>
>
> de Mike (SO2R hopeful) VE9AA
>
>
>
>
>
> Mike, Coreen & Corey
>
> Keswick Ridge, NB
>
>
>
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