[CQ-Contest] [TowerTalk] Coax Stubs for SO2R

Tue Sep 8 18:57:09 EDT 2015

So if that is true Peter, what do I put on the 40m station to prevent 7MHz
harmonics from appearing on 20m?
Maybe I am thinking about this all the wrong way. I love to learn new things
but I cannot believe I can't get my head around this.
I thought 1/4WL shorted stubs prevented the 1rst (and 2nd) harmonics from
being transmitted (well, down 20-30dB anyways)

By the way, I do not have a way to put a stub "on a receiver only".

There are no receive only ports on my radios (A=IC-7410 & B=IC-746)

Mike, Coreen & Corey
Keswick Ridge, NB

-----Original Message-----
From: Peter Voelpel [mailto:dj7ww at t-online.de] 
Sent: September 8, 2015 7:51 PM
To: 'Mike Smith VE9AA'
Subject: RE: [TowerTalk] [CQ-Contest] Coax Stubs for SO2R

Hi Mike, 

The effect of the shorted stub at the 40m station (A) will be seen only when
you use the other station (B) to transmit on 20m or 10m.

To see attenuation of the 40m signal on 20m the open stub must be at the 20m
station (B) while the 40m station (A) is transmitting.

73
Peter

-----Original Message-----
From: Mike Smith VE9AA [mailto:ve9aa at nbnet.nb.ca]
Sent: Mittwoch, 9. September 2015 00:34
To: 'Peter Voelpel'; towertalk at contesting.com; cq-contest at contesting.com
Subject: RE: [TowerTalk] [CQ-Contest] Coax Stubs for SO2R

OK, hi, just saw your email now. They crossed coming across the Atlantic ;-)

Mike, Coreen & Corey
Keswick Ridge, NB

-----Original Message-----
From: Peter Voelpel [mailto:dj7ww at t-online.de]
Sent: September 8, 2015 7:28 PM
To: 'Peter Voelpel'; 'Mike Smith VE9AA'; towertalk at contesting.com;
cq-contest at contesting.com
Subject: RE: [TowerTalk] [CQ-Contest] Coax Stubs for SO2R

Sorry it has to be the other way round, open stub at the 20m station,
shorted stub at the 40m station, I mixed it up while writing.

73
Peter

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Peter
Voelpel
Sent: Mittwoch, 9. September 2015 00:22
To: 'Mike Smith VE9AA'; towertalk at contesting.com; cq-contest at contesting.com
Subject: Re: [TowerTalk] [CQ-Contest] Coax Stubs for SO2R

That shorted stub cut for 20m has to be installed on the 20m station
(station B) to suppress 40 and 15 there.
On the 40m station (station A)you will need an open stub cut for 20m to
suppress 20 and 10m interference.

Both stubs will be around 23 feet long when made from RG213,

73
Peter

-----Original Message-----
From: CQ-Contest [mailto:cq-contest-bounces at contesting.com] On Behalf Of
Mike Smith VE9AA
Sent: Dienstag, 8. September 2015 23:14
To: towertalk at contesting.com; cq-contest at contesting.com
Subject: Re: [CQ-Contest] Coax Stubs for SO2R

Thanks for the many replies so far.  So today after I got home from work I
tried just running radio A @ about 1w on 7.000MHZ and saw S9 on 20m and s1
on 10m.

No change switching stub in or out, so I took Jim's(K9YC) suggestion and
moved the stub farther away from the transceiver.  I made up 3 random length
patch cables and so have the stub roughly either:

10-12', 15'-17, 20'-22, 25'-27 away from the transmitter (Radio A). (rough
guesstimates)  ( a 1/4wl, accounting for VF would be in the 23'-27' range)

No perceptible change whatsoever at any point in the line no matter where I
put the stub.  Just the slightest SWR change when I put it in line.  Almost
cannot detect it.

I am going nuts.

It's either something in the shack or something outside rectifying (I
guess?)  but these are pretty low power levels. (usually 100w, but also at
1w !)

Radio A (transmitter in the scenario) is hooked to an amp (not turned on in
close to a year), an antenna switch, a tuner/wattmeter (used on
straightthrough function only, just for it's wattmeter/SWR function.)

Radio B (receiver in this scenario) is hooked to its own power supply and
coax straight outside to a multiband dipole some 100' from the Radio's A's
various antennas. No SWR meters, switches or anything.

They share a 4" hole in the wall in the garage where they exit to the
outside, where the RG8 or LMR400 coax;'s could be close to one another.

They share 120VAC  in the shack (but different power supplies)

I have two additional (perhaps important?) questions.  Should any of these
harmonics between any bands sound pure and "clean", like a real CW signal?
Mine all sound low/muffly, wide, growly, like they have buzzing/humming AC
riding on top of them.

Additionally, the AA-230pro's manual says to make the 1/4WL stub with the
end of the coax OPEN.  . . . .but then for the purposes of these tests, I am
using the stubs shorted.

Maybe I have a ground loop somewhere and there is feedback or an isolation
problem on the shacks's 120VAC line?

Mike

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