[CQ-Contest] Coax Stubs for SO2R

Wed Sep 9 18:48:47 EDT 2015

Hi Guys n Gals, 

I have been getting lots of help, but every other private email (it seems) I am getting is conflicting.
Can I go back to basics and just ask this please:

Do I put a 1/4wl SHORTED stub on my 40m transmitter to knock down the harmonics appearing on 20m?  

Do I have that logic correct that I want a 1/4wl SHORTED stub on the transmit band to knock down the first harmonic on the next higher band?
(forget about receivers for a moment)

This is roughly 23' or whatever in length.  I've made up so many chunks of coax in the last few days
out of different stuff (RG-213, LMR-400) I am going bugeyed, hi!

Once I get this figured out, I can move onto other bands/combos, double stubs etc.

The rigs are: IC-7410 & IC-746...no "receive only" ports.

TNX

Mike VE9AA

Mike, Coreen & Corey
Keswick Ridge, NB

-----Original Message-----
From: Mike Smith VE9AA [mailto:ve9aa at nbnet.nb.ca] 
Sent: September 9, 2015 5:29 PM
To: 'towertalk at contesting.com'; 'cq-contest at contesting.com'
Subject: RE: [CQ-Contest] Coax Stubs for SO2R

So, vy late last night, just before bed, I had Radio A straight to the HF9V (multiband) vertical and Radio B straight to the ZS6BKW multiband horizontal dipole.
I spliced in the T and the stub on radio A.....

Yup, you guessed it.

No change. It was like the stub wasn't even there.  Still S9 on radio B.

I fell asleep with the W2VJN 'managing interference' book on top of me.

HI !

I almost to the point of putting the radios on batteries out in the yard or something else to rule out everything in the shack and the 120vac feed.

Mike VE9AA

Mike, Coreen & Corey
Keswick Ridge, NB

-----Original Message-----
From: Mike Smith VE9AA [mailto:ve9aa at nbnet.nb.ca] 
Sent: September 8, 2015 9:05 PM
To: 'Bill Hider'; 'towertalk at contesting.com'; 'cq-contest at contesting.com'
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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No virus found in this message.
Checked by AVG - www.avg.com
Version: 2015.0.6125 / Virus Database: 4409/10599 - Release Date: 09/08/15