Works fine. Attenuation depth depends on the shield & conductor resistance.
RG11/6 tends to have a bit more resistance so the attenuation null is not as
deep. But you should get at least 23 dB out of even the worst coax.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: K3RAG LB3RE Brobakken
Sent: Wednesday, July 27, 2016 9:23 AM
To: cq-contest
Subject: [CQ-Contest] Coax Stubs for SO2R
Hello
Have anyone tried RG11 75ohm or cheap RG6 CATV cable for stubs???
Need something for our scout club JOTA LA6JAM
73 LB3RE Rag
onsdag, 27 juli 2016, 00:17a.m. +02:00 from Steve NR4M steve@nr4m.com :
Jim,
Been following this thread since it started (this time) several days
ago. I have lots of interest in it as I have a multi multi station here
in VA.
I have built coaxial stubs in the past using my AIM 4170, FSJ4 heliax,
and K2TR's data as a good place to start. I think after screwing with
them for years, I've gotten pretty good at putting the nulls where I
want them. And, they seem to work, but no real data on how well they
work. My 40m 3rd harmonic on 15 is about S-5 and I can get withing a
couple of KC, or so. It's just not much of a problem any longer.
Been quite interested in your suggestions on how to place them for
maximum attenuation of the undesired RF. I, like many, I guess, have
installed them at the output of the amplifier, because that would be a
50 ohm point in a properly tuned amp. But, now I see that it's more
important to know what the impedance of the harmonics is on your band of
choice.
What got me up and moving on this is your comment in a previous post
today about it being the second harmonic that's important. I have been
building stubs, per N2TR, that covered multiple bands, without really
focusing on a particular stations 2nd harmonic.
I pulled the coax off the stub set on the back of my 20 meter amp,
connected a Rig Exper AA54, and started looking up my coax toward the
antenna.
On 10 meters, I saw R101 -J14.6 and on 15 (for the heck of it) I saw
R112 j-36.
Following your instructions in your pdf on locating the stubs, I am just
about where I need to be. If I added .44 feet of Coax, it would be
right on the voltage peak.
Do these numbers above look as they should? I was expecting higher R.
--
73 de Steve, NR4M
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