[TowerTalk] Coax Stubs for SO2R
n0tt1 at juno.com
n0tt1 at juno.com
Wed Sep 9 22:04:33 EDT 2015
Mike et al....
To add to the collective knowledge about stubs, there
was an article in QST years ago called (I think) "The BOA - a
constrictor for unwanted radiation". :D)
Just FWIW.
73,
Charlie, N0TT
On Wed, 9 Sep 2015 19:48:47 -0300 "Mike Smith VE9AA" <ve9aa at nbnet.nb.ca>
writes:
> 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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