[CQ-Contest] Stubs - 40 & 15 meters

[Zivney, Terry]

That's what happens when you don't have the reference in front of you   

W2VJN's Type 4 stubs (page 34) - keeps 21 MHz out of 7MHz - 
1/4 wave 21 MHz open ended and 1/2 wave 21MHz shorted teed -
this puts shorts on 21MHz while resonant (low loss) on 7Mhz.


                           open
                              |
                              |
tx _____________|_______________  ant
                              |
                              |
                              |
                         short


W2VJN's Type 5 stubs (page 36) - nulls 7 MHz passes 21MHz -
a) 1/4 wave 21Mhz teed off of transmission line - the other end of the
1/4wave stub is teed again; this second tee has  b) 1/4 wave 21MHz
open-ended stub as well as c) 0.41 wave 21MHz (0.1365 7MHz)
open ended stub

 tx      __________________   ant
                |
                |   a
                |____________      c
                |
                |     b
                |


Terry Zivney, N4TZ



________________________________________
From: Tom W8JI [w8ji at w8ji.com]
Sent: Friday, July 20, 2012 5:32 PM
To: Zivney, Terry; cq-contest at 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