[CQ-Contest] Coax Stubs for SO2R

[Mike Smith VE9AA]

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