On Mon,6/20/2016 5:32 PM, Hans Hammarquist via TowerTalk wrote:
OK, this is how I am doing it:
1) My antenna tuner is isolated from ground. 2) the coax from the tuner to the
radio is passing a choke. This render a balanced feed to the antenna feeder. I
hope that clears that up a little. The technique was presented at a seminar at
Boxboro some years ago.
Don't believe everything you hear or read. Always question the
qualifications and education of who's talking/writing.
So, answeres:
1) I have a 250 feet wire, fed 1/3 from one end in the air. Call it a Windom if
you like.
2) The feed line is attached directly to the antenna.
3) The choke is (technically) at the ground end of the feed line.
"Technically?" It IS at the transmitter end of the feedline.
4) The feed line is connected to the ground isolated antenna tuner. The
isolation contribute to equal, balanced current in the feeder.
That's Alice In Wonderland. Balance is determined by the impedances in
the circuit -- ALL of the impedances. The antenna is unbalanced, so
current on the feedline will be unbalanced.
5) The choke is on the 50 ohm side of the tuner.
And exactly what is that choke? I think I've heard you say that it's a
coil of coax. That is NOT an effective common mode choke, for reasons
noted in the slide show I referenced.
6) Yes, as the tuner is "acting" balanced.
Again, Alice in Wonderland. The tuner itself may be balanced, but the
rest of the antenna circuit is NOT balanced, so the feedline is NOT
balanced, and it carries common mode current!
The tuner is, in reality unbalanced but as it doesn't have a return path to
ground the high Z is by all means balanced.
A coil of coax does NOT provide a high impedance to ground. It is an
inductor, with stray capacitance.
7) The transceiver end of the coax has the shield grounded (to the shack
shield. The shack shield is connected to the tower.)
I don't know if I explained it clearly but the tuner is "floating" from ground
as the transceiver side is connected to the choke. That way the antenna side is balanced.
The tuner is homebuilt. It consist of a tuned circuit that is tapped for proper
SWR. I have several of them. Each one covers about 3 - 1 in frequency. I am
using four to cover 160 - 10 meter.
My question and interest is to get a CM choke next to the antenna so I can
reduce the radiation from the feeder.
As I've repeated several times, it is not practical to choke the antenna
you have described. That's why no one who knows how chokes work has made
a suggestion.
73, Jim K9YC
Hans - N2JFS
-----Original Message-----
From: Edward McCann <edwmccann@yahoo.com>
To: Hans Hammarquist <hanslg@aol.com>; towertalk <towertalk@contesting.com>
Cc: edward mccann <edwmccann@aol.com>
Sent: Mon, Jun 20, 2016 12:32 am
Subject: Re: [TowerTalk] Fwd: Fwd: OWAs or Fans?
Hans:
Your initial inquiry asked about CM choke for open (and ladder line, I presume)
feeder.
I passed on K9YC's counsel on the topic.
Your latest message has me a bit confused:
"I have a setup with the tuner isolated from ground and a CCM chock made of 50' of coax
wound around a 4" PVC pipe. The chock is fairly wide band by NOT having an even pitch on
the winding. The choke insure that there is no CM current entering the shack."
So, for clarity:
1. What antenna is in the air?
2. Is it fed with open wire feedline?
3. Where is your CM choke in the line?
4. From antenna, at you CM Choke, do you connect one side of open wire to coax
center conductor and other to ground?
5. Coming out of CM Choke, are you back to open wire feedline to tuner?
6. Is this open feedline hooked into balanced terminals of tuner?
7. Antenna side seems isolated from ground at tuner. But what about output side
of tuner? Now coax, right, and transceiver chassis ( and therefore shield of
coax) is now grounded. It is this not the case?
PS-what tuner are you using?
Thanks for clarification on this most interesting topic, i.e. A CM Choke for
open feeder.
73,
Ed McCann
AG6CX
Are you using an open wire feed?
Sent from my iPhone
On Jun 16, 2016, at 3:04 PM, Hans Hammarquist via TowerTalk
<towertalk@contesting.com> wrote:
I am very fortuned not being surrounded by noise. Next door neighbor is 1000
feet away with no TV or any other RFI source and next neighbor is 1/2 mile
away. Wonder if I can make a CM choke for an open feeder. Any idea?
Hans - N2JFS
-----Original Message-----
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk <towertalk@contesting.com>
Sent: Thu, Jun 16, 2016 1:19 pm
Subject: Re: [TowerTalk] Fwd: OWAs or Fans?
On Thu,6/16/2016 7:26 AM, Hans Hammarquist via TowerTalk wrote:
Open wire feeders are simple to use if you know to address a few things
The thing that it is NOT POSSIBLE to address is choking the feedline at
the feedpoint (that is, where it junctions the dipole). This makes the
antenna inherently noisy in most parts of the real world. Off-center-fed
antennas like Windoms are even worse in that regard.
This doesn't mean that they don't radiate -- that's NOT the issue.
There's nothing wrong with these antennas in concept, only that we as
hams are surrounded by RF noise sources.
73, Jim K9YC
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