[CQ-Contest] [TowerTalk] Coax Stubs for SO2R
David Robbins
k1ttt at arrl.net
Wed Sep 9 19:07:27 EDT 2015
Yes, 1/4 wave (measured on 40m) shorted stub goes on the 40m tx... on 40m a
short at the end of 1/4 wave looks like an open circuit so passes the 40m
signal... but 1/4 wave on 40m is 1/2 wave on 20m or a full wave on 10m, on
those bands the short gets repeated at the connection point so should
reflect the 20m or 10m harmonic.
For quick reference see: http://www.k1ttt.net/technote/k2trstub.html
David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Mike
Smith VE9AA
Sent: Wednesday, September 09, 2015 22:49
To: cq-contest at contesting.com; towertalk at contesting.com
Subject: Re: [TowerTalk] Coax Stubs for SO2R
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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