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

Thu Sep 10 10:36:22 EDT 2015

part of the problem is that different people use different types of stubs for different purposes.

for instance you can use an open 1/2 wave stub as a band pass filter the same as a shorted 1/4 wave stub, the harmonic behavior would be different though...  an open 1/2 wave stub would pass the 2nd harmonic, but a shorted 1/4 wave stub would reject the 2nd harmonic.   now if you go to sub harmonics (say on 20m you want to block front end overload from 40m) the open 1/2 wave stub would reject the 40m fundamental, but the shorted 1/4 wave wouldn't be as good as it would be too short to properly reject 40m.

there are lots of possible combinations... k2tr did a good job of minimizing the number of stubs needed for a 6 band HF contest station in his design here:  http://www.k1ttt.net/technote/k2trstub.html   I have been using these for years and measured them with a vna and they really do work.  but as has been pointed out there are limitations to them if the harmonics are not being generated by the radio or if there are other paths between the radios.

also note, stubs are not the best way to protect one receiver from another transmitter... their rejection is limited, 20-30db is about as good as you will get based on my analysis and testing... see the discussions at: http://www.k1ttt.net/technote/techref.html#filters  I highly recommend using lumped filters also, they have better rejection and passband characteristics, especially for rejecting fundamentals from another radio.

Sep 10, 2015 10:00:58 AM, jpklemola at gmail.com wrote:

Seems like people who have never done any of this are ahring their views.
That is good. People want to share and be in the group.

In case you have a problem like should 40m quarter wave resonator's other
end be shorted or open, you will notice that very quickly after connecting
the resonator in the system.

Once you get over the fundamental basics, you will get into the wild world
of un-intentional RF rectifyiing.
I still suggest reading Dave's book. It is online.

73,
Jukka OH6LI

2015-09-10 1:48 GMT+03:00 Mike Smith VE9AA :

> 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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