I have an off center fed dipole that was made by Antennas and More. I am
very aware of the hype surrounding the overblown claims for such antennas
and their inherent problems. (radiating feed lines, etc. ) What I was not
ware of is the problems with getting basic information about the antenna
from the "manufacturer." What I have is a 132 foot off center fed dipole
they refer to as the Windom HSQ. What I am trying to decipher is what
type of balun they are using. In their literature they refer to a 1 to 1.
This can not be. From the location of their balun which is about 48 feet
from one end, I am guessing that they are trying for the illusive 200 ohm
impedance point for 80 meters and that the balun may be a 2:1. This
company does NOT return any calls. I was trying to figure if I could cut
this antenna down to a 40 meter version, which might be possible with a 2:1
balun, but not a 4:1. Anyone have any experience with this type of
antenna?
Thanks.


Charlie KD7HU

"W5DXP" wrote in message
...
Charles Wittnam wrote:

I have an off center fed dipole that was made by Antennas and More. I
am
very aware of the hype surrounding the overblown claims for such
antennas
and their inherent problems. (radiating feed lines, etc. ) What I was
not
ware of is the problems with getting basic information about the antenna
from the "manufacturer." What I have is a 132 foot off center fed
dipole
they refer to as the Windom HSQ. What I am trying to decipher is what
type of balun they are using. In their literature they refer to a 1 to
1.
This can not be. From the location of their balun which is about 48
feet
from one end, I am guessing that they are trying for the illusive 200
ohm
impedance point for 80 meters and that the balun may be a 2:1. This
company does NOT return any calls. I was trying to figure if I could cut
this antenna down to a 40 meter version, which might be possible with a
2:1
balun, but not a 4:1. Anyone have any experience with this type of
antenna?

The balun is probably a 4:1 and the antenna should work pretty well on
40m with an antenna tuner without any cutting. Borrow an MFJ-259B and
see where it is resonant.
--
73, Cecil, W5DXP

I am trying to salvage the situation before going to
war with Antennas and More with my credit card company. They shipped the
wrong antenna to me and have NOT answered numerous calls or emails. I was
looking for a 40 meter OCF dipole and they sent me a 80 meter OCF, which
was not what I ordered because of space limitations.
If I could cut the thing down to use on 40 meters then I can save the
inevitable hassle of dealing with this outfit and going to war with them via
my credit card company.. However, my understanding is that a lot of the
commercial builders of the OCF dipoles use a 2/1 balun for their 40 meter
antennas since they are trying to match a different impedance spot on the
shorter antenna., hence it is not necessarily the case that you can just cut
them down. Any thoughts?


KD7HU


"W5DXP" wrote in message
...
Charles Wittnam wrote:

I have an off center fed dipole that was made by Antennas and More. I
am
very aware of the hype surrounding the overblown claims for such
antennas
and their inherent problems. (radiating feed lines, etc. ) What I was
not
ware of is the problems with getting basic information about the antenna
from the "manufacturer." What I have is a 132 foot off center fed
dipole
they refer to as the Windom HSQ. What I am trying to decipher is what
type of balun they are using. In their literature they refer to a 1 to
1.
This can not be. From the location of their balun which is about 48
feet
from one end, I am guessing that they are trying for the illusive 200
ohm
impedance point for 80 meters and that the balun may be a 2:1. This
company does NOT return any calls. I was trying to figure if I could cut
this antenna down to a 40 meter version, which might be possible with a
2:1
balun, but not a 4:1. Anyone have any experience with this type of
antenna?

The balun is probably a 4:1 and the antenna should work pretty well on
40m with an antenna tuner without any cutting. Borrow an MFJ-259B and
see where it is resonant.
--
73, Cecil, W5DXP

On Fri, 29 Aug 2003 21:37:00 GMT, "Charles Wittnam"
wrote:

I am trying to salvage the situation before going to
war with Antennas and More with my credit card company. They shipped the
wrong antenna to me and have NOT answered numerous calls or emails. I was
looking for a 40 meter OCF dipole and they sent me a 80 meter OCF, which
was not what I ordered because of space limitations.
If I could cut the thing down to use on 40 meters then I can save the
inevitable hassle of dealing with this outfit and going to war with them via
my credit card company.. However, my understanding is that a lot of the
commercial builders of the OCF dipoles use a 2/1 balun for their 40 meter
antennas since they are trying to match a different impedance spot on the
shorter antenna., hence it is not necessarily the case that you can just cut
them down. Any thoughts?


KD7HU


Why not just scale the antenna? That's is to say, in your case, reduce
the length of the wires by a factor of ½.

Danny, K6MHE

One thing that as always bothered me is that antenna is not balanced
with that lop-sided feed. Further-the-more that assumed 300-Ohm
impedance has a pretty hefty reactive component. As baluns like
resistive loads I would question just how well the balun works under
that condition?

I too have modeled the antenna and agree that the claims made
regarding feedline's radiation contributing to a strong vertical
component is over stated to say the least.

Good luck with your cut and try.

73
Danny, K6MHE



On Sat, 30 Aug 2003 02:02:46 GMT, "Charles Wittnam"
wrote:


That is probably what I am going to do. I became a
little more anxious after I read L.B. Cebik's articles on OCF dipole
antennas, "From the Ground Up." Things are a little bit more complicated
than I thought. Most baluns used in OCFs are 4/1. I have have included a
graph from his article .First of all, the calculations used to design OCFs
are supposed to estimate the 300 ohm impedance point. These are always a
rough estimate since as you get further from the center of the antenna it
goes up exponentially. When you factor in nearby objects, your radiating
feedline, and antenna height the calculated 300 ohm point can be in a
different area altogther. A 50% error in impedance result with a 5%
shift in the 300 ohm point, which on a 40 meter OCF would be about three
feet. More recently some of the 40meter OCF builders ( I think the 40
meter "Carolina Windom" would be an example), have tried to hit the
flatter part of the curve by using a different offset calculation. Instead
of D3/L=.167 for the 300 ohm point they used D1/L=.38 and D2/L= .62 for
a 100ohm point. They are using a 2:1 balun. In the inclosed info that came
with the antenna it says it is using a 1:1 balun which I sincerely doubt.
So I measured my antenna and the offset is closer to the second formula,
than the first so I was confused.. If I cut it up and it did not work well
and I knew what the balun was I would know which part of the curve ( and
the antenna) to head for! . So you can understand my intial reluctance to
act. Perhaps this is being overly cautious. You get that way when you are
given a "1:1" balun placed in the position where you would put 2:1 in an
antenna that usually uses a 4:1 AND the company does not answer questions
about their product.

I would highly recommend Cebik's article series on OCF antennas, in
which he debunks a lot of their claims, especially the "vertical radiator"
aspect of the feedline and the "yagi" performance. He basically argues
that these claims are being backed up by overly simplified assumptions about
the antenna being plugged into antenna modeling programs. He believes they
are no different than dipoles really. For my purposes I wanted an antenna
system with an offset feed because I can hide the feedline coax easier
given my available tree locations. (and keep the XYL happier...) This
antenna has a black balun and black insulated flexible wire which really
blends in well on my heavily wooded lot. Right now I am trying to salvage
the situation. This is the first time I have run into an amateur supply
company that has behaved so poorly. It was a rude awakening. I may just do
what you suggested. I hope I have the 4 to balun since I have other uses
for it. If the down sizing doesn't work then I will either just swap out
baluns or try a different approach, such as using a parallel feedline and
not using the balun. We will see.





"Dan Richardson" wrote in message
.. .
On Fri, 29 Aug 2003 21:37:00 GMT, "Charles Wittnam"
wrote:

I am trying to salvage the situation before going
to
war with Antennas and More with my credit card company. They shipped the
wrong antenna to me and have NOT answered numerous calls or emails. I
was
looking for a 40 meter OCF dipole and they sent me a 80 meter OCF, which
was not what I ordered because of space limitations.
If I could cut the thing down to use on 40 meters then I can save the
inevitable hassle of dealing with this outfit and going to war with them
via
my credit card company.. However, my understanding is that a lot of the
commercial builders of the OCF dipoles use a 2/1 balun for their 40 meter
antennas since they are trying to match a different impedance spot on the
shorter antenna., hence it is not necessarily the case that you can just
cut
them down. Any thoughts?


KD7HU


Why not just scale the antenna? That's is to say, in your case, reduce
the length of the wires by a factor of ½.

Danny, K6MHE

Charles Wittnam wrote:
However, my understanding is that a lot of the
commercial builders of the OCF dipoles use a 2/1 balun for their 40 meter
antennas since they are trying to match a different impedance spot on the
shorter antenna., hence it is not necessarily the case that you can just cut
them down. Any thoughts?

Antennas are scalable so halve the length of the antenna while keeping the
ratio of short leg to long leg the same. Depending on the design, you may
also have to halve the length of the feedline to exactly duplicate 75m
performance on 40m. Hopefully not since 1/2WL on 3.5MHz is about 1WL on 7.0MHz.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Danny:
I think the you have raised a valid concern about the
balun. This is something I did not fully appreciate before I made my
decision to try this. Cebik makes the same point and suggests if you use
this antenna you might be better off using a parallel feed line with a
tuner, and no balun. I will make the cuts and scale this antenna down
preserving the same ratio of offset. Before I hang this permanently I will
need to get a better feel for its performance and limitations. I may do a
head to head test with another antenna set up and see. I was intrigued by
W5DXP's "completed inverted L", which is a full wave loop variant.
The major benefit of this whole experience for me has been the amount of
research it has instigated. I also have a better understanding of antenna
options. I have come to the following conclusions about commercial
"windoms".( which really are folded OCF dipole antennas).

1. The claims about performance are probably overblown due to:
a. Faulty assumptions about the degree the "vertical
radiation" of the feedline plays in modifying performance.
b. These incorrect assumptions being placed into antenna
simulation programs and printed as truth.
c. Placebo effect: I suspect some of the testimonials
are due to expecting better performance. On some occassions the
improvement may actually be due to hanging these antennas at "recommended
heights". Of course your dipole would do better up there too.
2. The unbalanced feedline makes RF in the shack a common problem since
your "vertical radiator" can be coming into your shack, depending upon
whether you have taken the necessary precautions to prevent this.
3. You are almost always better off making your own antenna.
4. I do NOT recommend dealing with any amateur supply company that
routinely will not return inquiry calls.
5. Read up on OCF dipoles as much as possible before building or buying
one.

I will keep you informed of my
progress. I have truly appreciated the input. I hope this discussion helps
some other hams who are contemplating purchasing commercially made
"Windoms."

Charlie KD7HU


"Dan Richardson" wrote in message
...
One thing that as always bothered me is that antenna is not balanced
with that lop-sided feed. Further-the-more that assumed 300-Ohm
impedance has a pretty hefty reactive component. As baluns like
resistive loads I would question just how well the balun works under
that condition?

I too have modeled the antenna and agree that the claims made
regarding feedline's radiation contributing to a strong vertical
component is over stated to say the least.

Good luck with your cut and try.

73
Danny, K6MHE



On Sat, 30 Aug 2003 02:02:46 GMT, "Charles Wittnam"
wrote:


That is probably what I am going to do. I became a
little more anxious after I read L.B. Cebik's articles on OCF dipole
antennas, "From the Ground Up." Things are a little bit more
complicated
than I thought. Most baluns used in OCFs are 4/1. I have have included a
graph from his article .First of all, the calculations used to design
OCFs
are supposed to estimate the 300 ohm impedance point. These are always
a
rough estimate since as you get further from the center of the antenna
it
goes up exponentially. When you factor in nearby objects, your radiating
feedline, and antenna height the calculated 300 ohm point can be in a
different area altogther. A 50% error in impedance result with a 5%
shift in the 300 ohm point, which on a 40 meter OCF would be about three
feet. More recently some of the 40meter OCF builders ( I think the 40
meter "Carolina Windom" would be an example), have tried to hit the
flatter part of the curve by using a different offset calculation.
Instead
of D3/L=.167 for the 300 ohm point they used D1/L=.38 and D2/L= .62
for
a 100ohm point. They are using a 2:1 balun. In the inclosed info that
came
with the antenna it says it is using a 1:1 balun which I sincerely doubt.
So I measured my antenna and the offset is closer to the second formula,
than the first so I was confused.. If I cut it up and it did not work
well
and I knew what the balun was I would know which part of the curve (
and
the antenna) to head for! . So you can understand my intial reluctance
to
act. Perhaps this is being overly cautious. You get that way when you are
given a "1:1" balun placed in the position where you would put 2:1 in
an
antenna that usually uses a 4:1 AND the company does not answer
questions
about their product.

I would highly recommend Cebik's article series on OCF antennas, in
which he debunks a lot of their claims, especially the "vertical
radiator"
aspect of the feedline and the "yagi" performance. He basically argues
that these claims are being backed up by overly simplified assumptions
about
the antenna being plugged into antenna modeling programs. He believes
they
are no different than dipoles really. For my purposes I wanted an
antenna
system with an offset feed because I can hide the feedline coax easier
given my available tree locations. (and keep the XYL happier...) This
antenna has a black balun and black insulated flexible wire which really
blends in well on my heavily wooded lot. Right now I am trying to
salvage
the situation. This is the first time I have run into an amateur supply
company that has behaved so poorly. It was a rude awakening. I may just
do
what you suggested. I hope I have the 4 to balun since I have other uses
for it. If the down sizing doesn't work then I will either just swap
out
baluns or try a different approach, such as using a parallel feedline
and
not using the balun. We will see.





"Dan Richardson" wrote in message
.. .
On Fri, 29 Aug 2003 21:37:00 GMT, "Charles Wittnam"
wrote:

I am trying to salvage the situation before
going
to
war with Antennas and More with my credit card company. They shipped
the
wrong antenna to me and have NOT answered numerous calls or emails.
I
was
looking for a 40 meter OCF dipole and they sent me a 80 meter OCF,
which
was not what I ordered because of space limitations.
If I could cut the thing down to use on 40 meters then I can save the
inevitable hassle of dealing with this outfit and going to war with
them
via
my credit card company.. However, my understanding is that a lot of
the
commercial builders of the OCF dipoles use a 2/1 balun for their 40
meter
antennas since they are trying to match a different impedance spot on
the
shorter antenna., hence it is not necessarily the case that you can
just
cut
them down. Any thoughts?


KD7HU


Why not just scale the antenna? That's is to say, in your case, reduce
the length of the wires by a factor of ½.

Danny, K6MHE

Jack Belrose, VE2CV did considerable research and experimenting with OCF
dipoles some years ago. Some of his work was published in QST. One of
the conclusions he reached was that it's awfully hard to keep the common
mode RF off the feedline to the shack.

Roy Lewallen, W7EL

Charles Wittnam wrote:
Danny,

I will keep a look out for RF Gremlins. I don't plan to run more than
100 watts. My rig will be the first to let me know since it is a Ten Tec
Jupiter, which I suspect would not like a lot of RF in the shack. You know
if you start randomly switching on the touch lights in all the bedrooms in
your neighborhood while transmitting with your OCF dipole in the evenings
you would probably would give a while new meaning to "interfering with
vertical polarization." You would also become very popular. g

73,
Charlie
KD7HU



"Dan Richardson" wrote in message
...

Charles,

Looks like you've got a good handle on things. I have used an OFC, fed
with ladder line. Nothing particularly outstanding in its performance.
However, as to common mode current: running around 100 watts I
experienced no problems, but when I bumped up the power to about
600-watts all hell broke loose. My computer, the TV, stereo, touch
lights and just about any thing else electronic went wild. And I use a
pretty good single point RF ground system here. So be prepared that
some "strange things" may happen. g

Good luck, nice talking with you.
73,
Danny, K6MHE


On Sat, 30 Aug 2003 16:20:10 GMT, "Charles Wittnam"
wrote:


Danny:
I think the you have raised a valid concern about

the

balun. This is something I did not fully appreciate before I made my
decision to try this. Cebik makes the same point and suggests if you

use

this antenna you might be better off using a parallel feed line with a
tuner, and no balun. I will make the cuts and scale this antenna down
preserving the same ratio of offset. Before I hang this permanently I

will

need to get a better feel for its performance and limitations. I may do

a

head to head test with another antenna set up and see. I was intrigued

by

W5DXP's "completed inverted L", which is a full wave loop variant.
The major benefit of this whole experience for me has been the amount of
research it has instigated. I also have a better understanding of

antenna

options. I have come to the following conclusions about commercial
"windoms".( which really are folded OCF dipole antennas).

1. The claims about performance are probably overblown due to:
a. Faulty assumptions about the degree the "vertical
radiation" of the feedline plays in modifying performance.
b. These incorrect assumptions being placed into antenna
simulation programs and printed as truth.
c. Placebo effect: I suspect some of the testimonials
are due to expecting better performance. On some occassions the
improvement may actually be due to hanging these antennas at "recommended
heights". Of course your dipole would do better up there too.
2. The unbalanced feedline makes RF in the shack a common problem since
your "vertical radiator" can be coming into your shack, depending upon
whether you have taken the necessary precautions to prevent this.
3. You are almost always better off making your own antenna.
4. I do NOT recommend dealing with any amateur supply company that
routinely will not return inquiry calls.
5. Read up on OCF dipoles as much as possible before building or buying
one.

I will keep you informed of my
progress. I have truly appreciated the input. I hope this discussion

helps

some other hams who are contemplating purchasing commercially made
"Windoms."

Charlie KD7HU


"Dan Richardson" wrote in message
...

One thing that as always bothered me is that antenna is not balanced
with that lop-sided feed. Further-the-more that assumed 300-Ohm
impedance has a pretty hefty reactive component. As baluns like
resistive loads I would question just how well the balun works under
that condition?

I too have modeled the antenna and agree that the claims made
regarding feedline's radiation contributing to a strong vertical
component is over stated to say the least.

Good luck with your cut and try.

73
Danny, K6MHE



On Sat, 30 Aug 2003 02:02:46 GMT, "Charles Wittnam"
wrote:


That is probably what I am going to do. I became a
little more anxious after I read L.B. Cebik's articles on OCF dipole
antennas, "From the Ground Up." Things are a little bit more

complicated

than I thought. Most baluns used in OCFs are 4/1. I have have

included a

graph from his article .First of all, the calculations used to design

OCFs

are supposed to estimate the 300 ohm impedance point. These are

always

a

rough estimate since as you get further from the center of the

antenna

it

goes up exponentially. When you factor in nearby objects, your

radiating

feedline, and antenna height the calculated 300 ohm point can be

in a

different area altogther. A 50% error in impedance result with a

5%

shift in the 300 ohm point, which on a 40 meter OCF would be about

three

feet. More recently some of the 40meter OCF builders ( I think the

40

meter "Carolina Windom" would be an example), have tried to hit the
flatter part of the curve by using a different offset calculation.

Instead

of D3/L=.167 for the 300 ohm point they used D1/L=.38 and D2/L=

.62

for

a 100ohm point. They are using a 2:1 balun. In the inclosed info that

came

with the antenna it says it is using a 1:1 balun which I sincerely

doubt.

So I measured my antenna and the offset is closer to the second

formula,

than the first so I was confused.. If I cut it up and it did not work

well

and I knew what the balun was I would know which part of the curve (

and

the antenna) to head for! . So you can understand my intial

reluctance

to

act. Perhaps this is being overly cautious. You get that way when you

are

given a "1:1" balun placed in the position where you would put 2:1

in

an

antenna that usually uses a 4:1 AND the company does not answer

questions

about their product.

I would highly recommend Cebik's article series on OCF antennas,

in

which he debunks a lot of their claims, especially the "vertical

radiator"

aspect of the feedline and the "yagi" performance. He basically

argues

that these claims are being backed up by overly simplified assumptions

about

the antenna being plugged into antenna modeling programs. He believes

they

are no different than dipoles really. For my purposes I wanted an

antenna

system with an offset feed because I can hide the feedline coax

easier

given my available tree locations. (and keep the XYL happier...) This
antenna has a black balun and black insulated flexible wire which

really

blends in well on my heavily wooded lot. Right now I am trying to

salvage

the situation. This is the first time I have run into an amateur

supply

company that has behaved so poorly. It was a rude awakening. I may

just

do

what you suggested. I hope I have the 4 to balun since I have other

uses

for it. If the down sizing doesn't work then I will either just swap

out

baluns or try a different approach, such as using a parallel feedline

and

not using the balun. We will see.





"Dan Richardson" wrote in message
om...

On Fri, 29 Aug 2003 21:37:00 GMT, "Charles Wittnam"
wrote:


I am trying to salvage the situation before

going

to

war with Antennas and More with my credit card company. They

shipped

the

wrong antenna to me and have NOT answered numerous calls or emails.

I

was

looking for a 40 meter OCF dipole and they sent me a 80 meter OCF,

which

was not what I ordered because of space limitations.
If I could cut the thing down to use on 40 meters then I can save

the

inevitable hassle of dealing with this outfit and going to war with

them

via

my credit card company.. However, my understanding is that a lot

of

the

commercial builders of the OCF dipoles use a 2/1 balun for their 40

meter

antennas since they are trying to match a different impedance spot

on

the

shorter antenna., hence it is not necessarily the case that you can

just

cut

them down. Any thoughts?


KD7HU



Why not just scale the antenna? That's is to say, in your case,

reduce

the length of the wires by a factor of ½.

Danny, K6MHE

Thanks, Roy. I believe the Belrose articles were in 1994. I know
they are downloadable by ARRL members from the ARRL web site. I just
rejoined and don't have access to them yet. I will have to judge how bad a
problem that will represent with 100 watts. I will undoubtably have to take
precautions with the feedline. I will keep all informed with my experience
unless I die from RF setting my after shave on fire.

Charlie KD7HU


"Roy Lewallen" wrote in message
...
Jack Belrose, VE2CV did considerable research and experimenting with OCF
dipoles some years ago. Some of his work was published in QST. One of
the conclusions he reached was that it's awfully hard to keep the common
mode RF off the feedline to the shack.

Roy Lewallen, W7EL

Charles Wittnam wrote:
Danny,

I will keep a look out for RF Gremlins. I don't plan to run more
than
100 watts. My rig will be the first to let me know since it is a Ten
Tec
Jupiter, which I suspect would not like a lot of RF in the shack. You
know
if you start randomly switching on the touch lights in all the bedrooms
in
your neighborhood while transmitting with your OCF dipole in the
evenings
you would probably would give a while new meaning to "interfering with
vertical polarization." You would also become very popular. g

73,
Charlie
KD7HU



"Dan Richardson" wrote in message
...

Charles,

Looks like you've got a good handle on things. I have used an OFC, fed
with ladder line. Nothing particularly outstanding in its performance.
However, as to common mode current: running around 100 watts I
experienced no problems, but when I bumped up the power to about
600-watts all hell broke loose. My computer, the TV, stereo, touch
lights and just about any thing else electronic went wild. And I use a
pretty good single point RF ground system here. So be prepared that
some "strange things" may happen. g

Good luck, nice talking with you.
73,
Danny, K6MHE


On Sat, 30 Aug 2003 16:20:10 GMT, "Charles Wittnam"
wrote:


Danny:
I think the you have raised a valid concern about

the

balun. This is something I did not fully appreciate before I made my
decision to try this. Cebik makes the same point and suggests if you

use

this antenna you might be better off using a parallel feed line with a
tuner, and no balun. I will make the cuts and scale this antenna down
preserving the same ratio of offset. Before I hang this permanently I

will

need to get a better feel for its performance and limitations. I may
do

a

head to head test with another antenna set up and see. I was
intrigued

by

W5DXP's "completed inverted L", which is a full wave loop variant.
The major benefit of this whole experience for me has been the amount
of
research it has instigated. I also have a better understanding of

antenna

options. I have come to the following conclusions about commercial
"windoms".( which really are folded OCF dipole antennas).

1. The claims about performance are probably overblown due to:
a. Faulty assumptions about the degree the "vertical
radiation" of the feedline plays in modifying performance.
b. These incorrect assumptions being placed into
antenna
simulation programs and printed as truth.
c. Placebo effect: I suspect some of the
testimonials
are due to expecting better performance. On some occassions the
improvement may actually be due to hanging these antennas at
"recommended
heights". Of course your dipole would do better up there too.
2. The unbalanced feedline makes RF in the shack a common problem
since
your "vertical radiator" can be coming into your shack, depending
upon
whether you have taken the necessary precautions to prevent this.
3. You are almost always better off making your own antenna.
4. I do NOT recommend dealing with any amateur supply company that
routinely will not return inquiry calls.
5. Read up on OCF dipoles as much as possible before building or
buying
one.

I will keep you informed of my
progress. I have truly appreciated the input. I hope this discussion

helps

some other hams who are contemplating purchasing commercially made
"Windoms."

Charlie KD7HU


"Dan Richardson" wrote in message
...

One thing that as always bothered me is that antenna is not balanced
with that lop-sided feed. Further-the-more that assumed 300-Ohm
impedance has a pretty hefty reactive component. As baluns like
resistive loads I would question just how well the balun works under
that condition?

I too have modeled the antenna and agree that the claims made
regarding feedline's radiation contributing to a strong vertical
component is over stated to say the least.

Good luck with your cut and try.

73
Danny, K6MHE



On Sat, 30 Aug 2003 02:02:46 GMT, "Charles Wittnam"
wrote:


That is probably what I am going to do. I became a
little more anxious after I read L.B. Cebik's articles on OCF
dipole
antennas, "From the Ground Up." Things are a little bit more

complicated

than I thought. Most baluns used in OCFs are 4/1. I have have

included a

graph from his article .First of all, the calculations used to design

OCFs

are supposed to estimate the 300 ohm impedance point. These are

always

a

rough estimate since as you get further from the center of the

antenna

it

goes up exponentially. When you factor in nearby objects, your

radiating

feedline, and antenna height the calculated 300 ohm point can be

in a

different area altogther. A 50% error in impedance result with a

5%

shift in the 300 ohm point, which on a 40 meter OCF would be about

three

feet. More recently some of the 40meter OCF builders ( I think the

40

meter "Carolina Windom" would be an example), have tried to hit the
flatter part of the curve by using a different offset calculation.

Instead

of D3/L=.167 for the 300 ohm point they used D1/L=.38 and D2/L=

.62

for

a 100ohm point. They are using a 2:1 balun. In the inclosed info that

came

with the antenna it says it is using a 1:1 balun which I sincerely

doubt.

So I measured my antenna and the offset is closer to the second

formula,

than the first so I was confused.. If I cut it up and it did not work

well

and I knew what the balun was I would know which part of the curve
(

and

the antenna) to head for! . So you can understand my intial

reluctance

to

act. Perhaps this is being overly cautious. You get that way when you

are

given a "1:1" balun placed in the position where you would put 2:1

in

an

antenna that usually uses a 4:1 AND the company does not answer

questions

about their product.

I would highly recommend Cebik's article series on OCF antennas,

in

which he debunks a lot of their claims, especially the "vertical

radiator"

aspect of the feedline and the "yagi" performance. He basically

argues

that these claims are being backed up by overly simplified
assumptions

about

the antenna being plugged into antenna modeling programs. He
believes

they

are no different than dipoles really. For my purposes I wanted an

antenna

system with an offset feed because I can hide the feedline coax

easier

given my available tree locations. (and keep the XYL happier...)
This
antenna has a black balun and black insulated flexible wire which

really

blends in well on my heavily wooded lot. Right now I am trying to

salvage

the situation. This is the first time I have run into an amateur

supply

company that has behaved so poorly. It was a rude awakening. I may

just

do

what you suggested. I hope I have the 4 to balun since I have other

uses

for it. If the down sizing doesn't work then I will either just
swap

out

baluns or try a different approach, such as using a parallel
feedline

and

not using the balun. We will see.





"Dan Richardson" wrote in
message
om...

On Fri, 29 Aug 2003 21:37:00 GMT, "Charles Wittnam"
wrote:


I am trying to salvage the situation before

going

to

war with Antennas and More with my credit card company. They

shipped

the

wrong antenna to me and have NOT answered numerous calls or emails.

I

was

looking for a 40 meter OCF dipole and they sent me a 80 meter OCF,

which

was not what I ordered because of space limitations.
If I could cut the thing down to use on 40 meters then I can save

the

inevitable hassle of dealing with this outfit and going to war with

them

via

my credit card company.. However, my understanding is that a lot

of

the

commercial builders of the OCF dipoles use a 2/1 balun for their 40

meter

antennas since they are trying to match a different impedance spot

on

the

shorter antenna., hence it is not necessarily the case that you can

just

cut

them down. Any thoughts?


KD7HU



Why not just scale the antenna? That's is to say, in your case,

reduce

the length of the wires by a factor of ½.

Danny, K6MHE