According to my ARRL Antenna Handbook, the Windom Antenna was described
by Loren Windom in QST in 1929.

The design is a horizontal half wave (ie single band) fed by a vertical
single wire feedline attached just off centre (~14%). Explanations go
that this approximately matches the feedline Zo (which is quite high)
with the horizontal wire. It is single wire (ie ultimately unbalanced)
feedline and therefore radiates. The Antenna is fed between the source
end of the feedline and ground, and the load impedance should be
somewhere in the many hundreds of ohms. The feedline carries an
appreciable net current.

More recently, the Off Centre Fed (OCF) Dipole design emerged,
principally as a multi-band antenna. The OCF Dipole is a horizontal wire
with a coaxial feed and coupling transformer (often called a balun)
attached offset from the centre of the dipole. The feedpoint excursions
at a half wave length and harmonic frequencies are much lower than centre
feeding, and may be operated as a multiband antenna with reasonable
efficiency, though it probably really needs an ATU at the tx end of the
coax. The OCF dipole feedline does have current flowing on the outer of
the outer conductor, at least as a result of the assymetric coupling to
the dipole legs, and to some extent because the ineffectiveness of
practical coupling transformers to isolate the feedline ends from the
differing voltages on each dipole leg. The feedline carries an
appreciable net current.

Then along came the Carolina Windom, which appears to be a OCF dipole
with a proprietary (ie secret, undescribed) coupling transformer, a
vertical coax section (feedline and radiator) and a proprietary (remember
the meaning) "isolator" located at a given distance along the coax to
prevent the current flowing on the outer of the outer of the coax from
flowing further towards the transmitter. The isolater would appear to be
a ferrite choke and it would introduce a series impedance (reactance and
resistance) to current on the coax, so influencing the establishment of
the standing wave pattern on the outer of the outer of the coax. You
might naively think that this isolator prevents current flowing into the
shack, but that is unlikely.

In all these cases, there is an expectation that the feedline carries a
net radiating current, and it seems to me, that if you don't want to
bring that into the shack, you need to design an appropriate solution.

In the case of the true Windom, it seems the easiest solution is to end
the single wire feedline outside the shack and place a matching unit
connecting to ground and the single wire feedline at that point, and
transforming the load to something suitable to coax or balanced feedline
to the shack.

In the case of the OCF Dipole and the Carolina Windom, shunting the
current on the outer of the outer to ground outside the shack is a
potential solution. Series chokes might help, but the magnitude of the
choking impedance is limited, and their effectiveness could be improved
greatly by a low impedance shunt to ground.

Comments?

Owen

PS: In todays paranoid world where rules in many jurisdictions restrict
the maximum permitted exposure to electromagnetic radiation, antennas
such as these with radiating elements that are close to areas accessible
by people are a safety challenge.

Owen Duffy wrote:
According to my ARRL Antenna Handbook, the Windom Antenna was described
by Loren Windom in QST in 1929.

The design is a horizontal half wave (ie single band) fed by a vertical
single wire feedline attached just off centre (~14%). Explanations go
that this approximately matches the feedline Zo (which is quite high)
with the horizontal wire. It is single wire (ie ultimately unbalanced)
feedline and therefore radiates. The Antenna is fed between the source
end of the feedline and ground, and the load impedance should be
somewhere in the many hundreds of ohms. The feedline carries an
appreciable net current.

More recently, the Off Centre Fed (OCF) Dipole design emerged,
...

EXCELLENT page on OCF construction:

http://www.radioelectronicschool.net.../ocfdipole.pdf

Will take a bit to load up in adobe reader (is a BIG file) on slow 56K
dialup connection.

JS
--
http://assemblywizard.tekcities.com

John Smith I wrote in news:esfki4$k29$1
@nnrp.linuxfan.it:

Owen Duffy wrote:
EXCELLENT page on OCF construction:

http://www.radioelectronicschool.net.../ocfdipole.pdf


Yes, a good article. But Ron doesn't really address the common mode current
issue, and routing common mode current into the shack.

Seems like an excuse to give him a ring, we haven't talked in a while.

Owen

Owen Duffy wrote:

...
Yes, a good article. But Ron doesn't really address the common mode current
issue, and routing common mode current into the shack.

Seems like an excuse to give him a ring, we haven't talked in a while.

Owen

Yes, for that any good page on voltage\current baluns or hybrid baluns
will bring one up to speed. For example, a page which provides more
than you want to know:

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12661

--
http://assemblywizard.tekcities.com

John Smith I wrote in
:

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12661

Hmmm, content hijackers.

John Smith I wrote:
Owen Duffy wrote:

...
Yes, a good article. But Ron doesn't really address the common mode
current issue, and routing common mode current into the shack.

Seems like an excuse to give him a ring, we haven't talked in a while.

Owen

Yes, for that any good page on voltage\current baluns or hybrid baluns
will bring one up to speed. For example, a page which provides more
than you want to know:

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12661


Practical example of winding a guanella type balun ... (good detail in
picture depicting green/white wires)

http://www.n0ss.net/qrp_4-1_guanella-type_balun.pdf

JS
--
http://assemblywizard.tekcities.com

John Smith I wrote in news:esg31b$n0a$1
@nnrp.linuxfan.it:

John Smith I wrote:
Practical example of winding a guanella type balun ... (good detail in
picture depicting green/white wires)

http://www.n0ss.net/qrp_4-1_guanella-type_balun.pdf

Notwithstanding all the focus on current baluns, a current balun does not
(by itself) prevent common mode current on an OCF Dipole feedline. The
feedline has assymetric mutual coupling to the dipole and can not be
expected in any configuration of significant length to be balanced wrt the
dipole over a wide frequency range.

Owen

I tried a real Windom on 20 meters. Used the ARRL antenna book
formula. Ran a single wire feedline to the random wire terminal of an
old Murch transmatch. Had a 1/4 wave elevated counterpoise attached to
the ground terminal of the tuner. I couldn't match the thing to my
little QRP rig to save my soul. Lots of RF and buzzing sounds.

Ended up turning it into a standard dipole.

bob
k5qwg

On Sun, 04 Mar 2007 22:07:30 GMT, Owen Duffy wrote:


According to my ARRL Antenna Handbook, the Windom Antenna was described
by Loren Windom in QST in 1929.

The design is a horizontal half wave (ie single band) fed by a vertical
single wire feedline attached just off centre (~14%). Explanations go
that this approximately matches the feedline Zo (which is quite high)
with the horizontal wire. It is single wire (ie ultimately unbalanced)
feedline and therefore radiates. The Antenna is fed between the source
end of the feedline and ground, and the load impedance should be
somewhere in the many hundreds of ohms. The feedline carries an
appreciable net current.

More recently, the Off Centre Fed (OCF) Dipole design emerged,
principally as a multi-band antenna. The OCF Dipole is a horizontal wire
with a coaxial feed and coupling transformer (often called a balun)
attached offset from the centre of the dipole. The feedpoint excursions
at a half wave length and harmonic frequencies are much lower than centre
feeding, and may be operated as a multiband antenna with reasonable
efficiency, though it probably really needs an ATU at the tx end of the
coax. The OCF dipole feedline does have current flowing on the outer of
the outer conductor, at least as a result of the assymetric coupling to
the dipole legs, and to some extent because the ineffectiveness of
practical coupling transformers to isolate the feedline ends from the
differing voltages on each dipole leg. The feedline carries an
appreciable net current.

Then along came the Carolina Windom, which appears to be a OCF dipole
with a proprietary (ie secret, undescribed) coupling transformer, a
vertical coax section (feedline and radiator) and a proprietary (remember
the meaning) "isolator" located at a given distance along the coax to
prevent the current flowing on the outer of the outer of the coax from
flowing further towards the transmitter. The isolater would appear to be
a ferrite choke and it would introduce a series impedance (reactance and
resistance) to current on the coax, so influencing the establishment of
the standing wave pattern on the outer of the outer of the coax. You
might naively think that this isolator prevents current flowing into the
shack, but that is unlikely.

In all these cases, there is an expectation that the feedline carries a
net radiating current, and it seems to me, that if you don't want to
bring that into the shack, you need to design an appropriate solution.

In the case of the true Windom, it seems the easiest solution is to end
the single wire feedline outside the shack and place a matching unit
connecting to ground and the single wire feedline at that point, and
transforming the load to something suitable to coax or balanced feedline
to the shack.

In the case of the OCF Dipole and the Carolina Windom, shunting the
current on the outer of the outer to ground outside the shack is a
potential solution. Series chokes might help, but the magnitude of the
choking impedance is limited, and their effectiveness could be improved
greatly by a low impedance shunt to ground.

Comments?

Owen

PS: In todays paranoid world where rules in many jurisdictions restrict
the maximum permitted exposure to electromagnetic radiation, antennas
such as these with radiating elements that are close to areas accessible
by people are a safety challenge.

On Mar 4, 4:07 pm, Owen Duffy wrote:
According to my ARRL Antenna Handbook, the Windom Antenna was described
by Loren Windom in QST in 1929.


I can't stand windoms myself... A poor design overall.. Bout par for
1929
technology..
I compared a dipole to one of those "carolina windoms" one time using
a
A/B switch.. It was ugly.. The dipole thrashed it. The windom setup
had
way too much loss. Mostly in the perverted mess of a feedline/tuner I
suspect.
But.... It doesn't bother me if anyone else wants to use them. IE:
field day,
etc. I like having an unfair advantage... All those windoms strung
across
the country on field day just help me get a better score...
Ughhhmm, maybe I should keep my mouth shut...
Yea.. Forget what I said. The windoms are great antennas.
A very efficient antenna system, and everyone should use one. If you
don't
use a windom at field day, you ain't really living.. Those funky fed
tuner/choke
G5RV's also have a special place in my heart.
Greatest antenna I've ever used.. :/ Grrrrr... I still remember
losing about
3 mm of tooth length due to excessive grinding when using a "funky
fed" G5RV
on 80m at field day a few years ago..
MK

wrote in
oups.com:

On Mar 4, 4:07 pm, Owen Duffy wrote:
According to my ARRL Antenna Handbook, the Windom Antenna was
described by Loren Windom in QST in 1929.


I can't stand windoms myself... A poor design overall.. Bout par for
1929
technology..
I compared a dipole to one of those "carolina windoms" one time using
a
A/B switch.. It was ugly.. The dipole thrashed it. The windom setup
had
way too much loss. Mostly in the perverted mess of a feedline/tuner I
suspect.
But.... It doesn't bother me if anyone else wants to use them. IE:
field day,
etc. I like having an unfair advantage... All those windoms strung
across
the country on field day just help me get a better score...
Ughhhmm, maybe I should keep my mouth shut...
Yea.. Forget what I said. The windoms are great antennas.
A very efficient antenna system, and everyone should use one. If you
don't
use a windom at field day, you ain't really living.. Those funky fed
tuner/choke
G5RV's also have a special place in my heart.
Greatest antenna I've ever used.. :/ Grrrrr... I still remember
losing about
3 mm of tooth length due to excessive grinding when using a "funky
fed" G5RV
on 80m at field day a few years ago..
MK



We have used OFC dipoles here for a few years at field day. They fill a
very specific set of needs for us. 1) They are simple to put up
2) The feed line coming from one end of the dipole is shorter than from
center feed dipoles in our setup. 3) OFC dipoles offer an impedance at
the end of the coax that is within the range of the tuners built into
our radios on the bands that are important to field day. This simplifies
our setup and operation. 4) They work as well as an antenna of that
physical length on any one frequency would no mater how it’s feed.

The radiation pattern from an OFC is set by the length of the wire not
where RF is feed in/out of the antenna. In our setup open wire line and
tuners would be a pain in the butt, and an operational inconvenience
that gains us nothing. Fan dipoles or separate dipoles are hard to setup
and or tune and would perform no better for us. The antennas we use were
built by myself and use a 4:1 current balun which minimize feed line
radiation. On 80/40/20m we can easily match the antenna with the built
in tuners so the SWR must be under 3:1. OFC dipoles don’t work well on
15m but with the current sun spot cycle not a problem. We see no
indication of common mode current problems, so we don’t worry about it,
we just operate and have fun.

John W3JXP