[CQ-Contest] Coax Stubs for SO2R

[Dave Hachadorian]

Mike,

I guess the problem that you are seeing is that when radio A 
transmits on 40, you can hear interference on 20 and 15, around 
the harmonic frequencies?

I suspect that radio B is being overloaded by the 40 meter 
fundamental energy, and is generating the harmonics and possibly 
wideband interference internally, in the receiver.

In that case, you need stubs on the radio B antenna to pass 20 
and reject 40, and to pass 15 and reject 40.  To test this 
hypothesis, take one of the 23' shorted stubs that you already 
made for 40,  convert it to a 23' open stub, and connect it to 
radio B on 20 meters.  See if the 20 meter interference is 
lessened when you transmit on 40.  A 23' open stub rejects 40 and 
15 and passes 20 and 10.

Are you using bandpass filters?  A stub by itself may not provide 
sufficient isolation, especially since both of your antennas 
cover all bands.

Dave Hachadorian, K6LL
Big Bear Lake, CA


-----Original Message----- 
From: Mike Smith VE9AA
Sent: Monday, September 7, 2015 6:07 PM
To: cq-contest at contesting.com
Subject: [CQ-Contest] Coax Stubs for SO2R

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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