[CQ-Contest] Coax Stubs for SO2R

[Mike Smith VE9AA]

OMG Bill-really? Well...I am not using the 10m stub. Let's forget that one for just a moment.
I have a 1/4WL 7MHz shorted stub (roughly 23' or so and tweaked/measured vy carefully on my AA-230pro) on my 40m transmitter, hoping it will null the 40M (7MHz) harmonics I hear on the 20m receiver.

Do I have this all backwards?

Oh dear...........

If that's true, I need to go back to school.

Mike, Coreen & Corey
Keswick Ridge, NB


-----Original Message-----
From: Bill Hider [mailto:n3rr at erols.com] 
Sent: September 8, 2015 7:54 PM
To: 'Mike Smith VE9AA'; towertalk at contesting.com; cq-contest at contesting.com
Subject: RE: [CQ-Contest] Coax Stubs for SO2R

MIKE!!

Just to verify, you are putting a  1/4 wavelength 20m Shorted stub and a 1/4 wavelength 10m Shorted stub  in parallel with the coax line at your transmitter while you are transmitting on 40 m, correct?

If that is correct.....
A 1/4 wave length SHORTED stub will look like an OPEN to the 20m and 10m harmonic of your transmitted signal and DO NOTING to the harmonic transmitted signal!!
That is exactly what you are seeing, is it not?
You need an 1/4 wavelength 20M OPEN stub and a 1/4 wavelength 10m OPEN  stub which will short out the 20m and 10m signals as they leave your transmitter.
The 10m and 20m stubs should be located several feet apart on your transmit line as an isolator between them.
I would try one stub at a time to be sure it performs as an open stub should  before you combine them on the transmit coax.

Bill N3RR

-----Original Message-----
From: CQ-Contest [mailto:cq-contest-bounces at contesting.com] On Behalf Of Mike Smith VE9AA
Sent: Tuesday, September 08, 2015 5:14 PM
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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