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

Wed Sep 9 00:24:40 EDT 2015

Hi Mike, 

That "growly" signals you're hearing are harmonics of your transmitted 
signal generated by unintentional radiators, especially switching power 
supplies. This type of RFI -- sometimes called "flooding" -- is caused 
by solid state devices flooded by intense RF fields (your transmitted signal) 
in which they were not intended to operate. The unintentional radiator 
produces harmonics of your transmitted signal mixed with the AC power 
line or digital signals that are normally present in the unintentional radiator. 

Common unintentional radiators of harmonics of your transmitted 
signal include many of the newer compact "wall wort" DC power supplies 
and susceptible power supplies in devices such as antenna rotators. 
The control box for the Ham series and T2X rotator is a well known 
source of re-radiated "growly" harmonics. Smart phone chargers are 
among the most common unintentional radiators of your harmonics in 
your home and neighborhood. 

As you rotate your transmitting and receiving antennas you will notice 
a considerable variation in the signal strength of the "growly" harmonics 
you've observed. Its likely that your harmonics will be free of "growly" 
signals in some directions. 

73 
Frank 
W3LPL 

----- Original Message -----

From: "Mike Smith VE9AA" <ve9aa at nbnet.nb.ca> 
To: "Bill Hider" <n3rr at erols.com>, towertalk at contesting.com, cq-contest at contesting.com 
Sent: Wednesday, September 9, 2015 12:05:20 AM 
Subject: Re: [CQ-Contest] Coax Stubs for SO2R 

Hi Bill & many others, Kimo, Dave, Jim, Peter, Gary, Gerry....I've forgotten a few. 

You are all very helpful and I am trying to wrap my head around this. 

I think I have to start from scratch and remove everything from in line from the transmitter. \ 

I did measure with the T in line and also the coax switches (I say switches as one is a coax switch, and one is Teed off to potentially just switch stubs) 
Tonight I took all that switching out of line and no change. (knowing full well my stub is no longer perfectly resonant as I lost perhaps 4" of extra line when I removed the T and the stub-switch, but I still should've been in the ballpark) 
No change. 

I can't help but wonder by what some of you are saying that I am getting rectification or bleedthrough inside the shack itself somehow. 

I don't have time tonight to try anything more. Been at it ~4 hours and have other stuff to do now. 

Wednesday or Thursday I am going to connect the transmitter directly to the antenna (remove amps, switches, tuners, etc. and try again.) (my receiver, or radio B in my SO2R setup is already direct to a multiband dipole) 

On harmonics...should they sound more or less pure, or no? (or is that like a "how long is a piece of string" type of question ?) 
Mind are pretty much bang on frequency but real growly....not pure at all. (either on the IC-7410 or IC-746)...... 

One time I recorded VE9HF some 8-10kms away running QRO on 14MHz and his 10m harmonic was a pure signal. He even had some callers on 10m ! 

Dit dit & tnx agn. Very much appreciate the great help ! 

Mike VE9AA ;-D 

Mike, Coreen & Corey 
Keswick Ridge, NB 

-----Original Message----- 
From: Bill Hider [mailto:n3rr at erols.com] 
Sent: September 8, 2015 8:52 PM 
To: 'Mike Smith VE9AA'; towertalk at contesting.com; cq-contest at contesting.com 
Subject: RE: [CQ-Contest] Coax Stubs for SO2R 

OK, Mike, 

I misunderstood you originally, as you can see from my most previous email, I tried to verify what I thought you said. 
The assumption I made was wrong. You are right. 

Moving forward: 
Yes, your 40m 1/4 WL shorted stub on your 40m transmitter should attenuate the 20m transmitted signal. 
UNLESS, you are not receiving the harmonic from the antenna you are transmitting on! 
OR, there may be a problem with the T connector or coax line. 

Also, the harmonic may be getting to the rx from inside your shack and not from the antenna. 

Is the stub attached to the xmit coax with a T connector? Verify it's tight or just replace the T connector & test again. 
If you still hear the harmonic, replace the T connector with a dummy load. Don't change anything else and test it again. 

If you still hear the harmonic, it's being radiated to the receiver before the dummy load. 

If you don't hear the harmonic, one other thing you could try: 
Listen on 20m using the radio you were just transmitting on 40. 
Make sure the 1/4 WL 40M shorted stub is attached to the T connector properly. 
Attach a 20 m antenna to this radio via the antenna port of the T connector. 
Listen and determine if you can hear signals on20m. Do not transmit. 
If you don't hear any 20m signals or band noise this time of night, the stub may be working. 
Remove the stub from the T connector and see if 20m comes back to life - noise increases. 
If it does, the stub works, the other T connector may have problems. 
Lots to test now... 

Let us know your test results. 

Bill 

-----Original Message----- 
From: Mike Smith VE9AA [mailto:ve9aa at nbnet.nb.ca] 
Sent: Tuesday, September 08, 2015 7:01 PM 
To: 'Bill Hider'; towertalk at contesting.com; cq-contest at contesting.com 
Subject: RE: [CQ-Contest] Coax Stubs for SO2R 

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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