Stub combos are very easy to model in Elsie. I like using that because I
don't have to remember what the various combos are.
The Elsie coax is "ideal" and as such it will show really huge attenuation
notches. Real stubs are going to be in the low to mid 20's. But otherwise,
the plots from Elsie looks similar to what the VNA measures for the real
thing.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Tom W8JI
Sent: Friday, July 20, 2012 4:32 PM
To: Zivney, Terry ; cq-contest@contesting.com
Subject: Re: [CQ-Contest] Stubs - 40 & 15 meters
> Pretty simple - see W2VJN's book on stubs "Managing Interstation
> Interference"
>
> My copy is not at hand here, but as I recall it involves a quarter
> wavelength of
> coax at 40m, but 'tapped' up 1/4 wavelength from the shorted end on 15m.
> That is, use a Tee connector; on one side of the tee is a 1/4 wavelength
> shorted
> stub on 15 and on the other side of the tee is an open ended 1/2 wave stub
> on 15.
>
> But, check the book for more details. I tried it back when I did a book
> review of
> it for NCJ and it worked FB.
Thinking about that logically, it appears it would still pass 40 meters to
me.
The reactance of a 30 degree shorted stub is the same but opposite sign as a
60 degree open stub. The result would be a parallel resonant circuit on 40,
which would also appear as an open on 15 meters.
I don't see how that would reject 40 at all.
I have ran the stub impedances to get exact values, but off the top of my
head I can't see why that would null 40. It should pass both 15 and 40.
73 Tom
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