[CQ-Contest] Stubs - 40 & 15 meters

Tom W8JI w8ji at w8ji.com
Fri Jul 20 14:32:23 PDT 2012

> 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 

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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