Bob, try it without the balun. In most cases, a balun isn't needed except
to reduce TVI-type problems.

Also, if you're looking for multi-band performance, consider trimming about
30 feet off the antenna - 102 to about 120 feet tends to be more tunable.
You might also consider changing over from coax to twin lead, if you can
work the logistics...

73,
Mike KI6PR
El Rancho R.F., CA

"Bob" wrote
Hi
We have put together a dipole, each leg is 66 feet. We put a 1:1 balun and
it is running about 60 feet of 50 ohm coax. Presently it is about half way
up the tower it is intended for so we could check the SWR before getting
it
up to the highest point. Presently each leg has some lags and dips, no
major
bends but it is just hanging there, over some bushes and the entire thing
is
over top of the house, and not touching anything but is very close to some
steel guy wires (uninsulated).
Now we can only tune this down to a useable SWR on the 80m band. On all
other bands we cannot tune it down to a safe operating range. We are using
a
good antenna tuner but cannot get anything useable except for 80m. Here we
are able to tune the SWR right down.

Questions???
Would we be better without that balun?

Is the fact that the dipole is still too low and close to the guy wires (
but not touching) our problem?

Any suggestions please??

Thank you.
Bob

Mikey wrote:
Also, if you're looking for multi-band performance, consider trimming about
30 feet off the antenna - 102 to about 120 feet tends to be more tunable.
You might also consider changing over from coax to twin lead, if you can
work the logistics...

Mike, unless Bob does both, trim to 102 ft *AND* use twin-lead, That is
very bad advice. A coax-fed 102 ft. dipole is resonant on 4.59 MHz
which is not inside any ham band. It will be a terrible performer
on all HF ham bands except 20m where it will have an SWR about 3:1.
--
73, Cecil, W5DXP



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Bob wrote:

Hi
We have put together a dipole, each leg is 66 feet. We put a 1:1 balun and
it is running about 60 feet of 50 ohm coax. Presently it is about half way
up the tower it is intended for so we could check the SWR before getting it
up to the highest point. Presently each leg has some lags and dips, no major
bends but it is just hanging there, over some bushes and the entire thing is
over top of the house, and not touching anything but is very close to some
steel guy wires (uninsulated).
Now we can only tune this down to a useable SWR on the 80m band. On all
other bands we cannot tune it down to a safe operating range. We are using a
good antenna tuner but cannot get anything useable except for 80m. Here we
are able to tune the SWR right down.

Questions???
Would we be better without that balun?

The antenna is a non-resonant length on most of the other HF bands. You
cannot afford the SWR power loss when feeding it with coax on any band except
80m. Take a look on my web page how I solved the all-HF-band problem using
essentially the same type of dipole. You need to feed such an antenna with
twinlead, window-line, ladder-line, or open-wire line. That moves the balun
to the hamshack. 100 ft. of ladder-line is close to optimum.

Is the fact that the dipole is still too low and close to the guy wires (
but not touching) our problem?

That may be part of your problem but not the biggest part.
--
73, Cecil, http://www.qsl.net/w5dxp



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In article , "Bob"
writes:

We have put together a dipole, each leg is 66 feet. We put a 1:1 balun and
it is running about 60 feet of 50 ohm coax. Presently it is about half way
up the tower it is intended for so we could check the SWR before getting it
up to the highest point. Presently each leg has some lags and dips, no major
bends but it is just hanging there, over some bushes and the entire thing is
over top of the house, and not touching anything but is very close to some
steel guy wires (uninsulated).

What you have is the classic dipole for 80 meters.

Now we can only tune this down to a useable SWR on the 80m band. On all
other bands we cannot tune it down to a safe operating range. We are using a
good antenna tuner but cannot get anything useable except for 80m. Here we
are able to tune the SWR right down.

That is normal behavior.

Questions???
Would we be better without that balun?

No.

Is the fact that the dipole is still too low and close to the guy wires (
but not touching) our problem?

No.

Any suggestions please??

The problem is this:

The antenna you describe is approximately:

one half-wavelength long on 80 meters

two half-wavelengths long on 40 meters

four half-wavelengths long on 20 meters

six half-wavelengths long on 15 meters

etc.

Such a center-fed dipole antenna has a feed point impedance that is fairly
"low" (that is, under about 100 ohms) on frequencies where it is an *odd*
number of half-wavelengths. On frequencies where it is an *even* number of half
wavelengths, the feed point impedance is very high - greater than 1000 ohms.

The 1:1 balun and 50 ohm coax you are using are low-impedance devices, so they
work fine on 80 meters. But on the other bands, they do not work with the high
impedance of the antenna. A tuner at the shack end of the coax cannot make up
for the enormous mismatch at the antenna end. Even if it could, the loss in the
coax from being operated at such a high SWR would make such a system very
inefficient.

There are several possible solutions:

1) Use a different transmission line (high impedance balanced line) and
eliminate the balun. This requires a balanced antenna tuner and the mechanical
difficulties of using non-coax transmission lines

2) Use a different sort of dipole that is an odd number of half-wavelengths on
the desired bands. One form of this dipole is the "trap dipole", in which tuned
circuits (traps) electrically alter the effective antenna length.

A really good information source is W4RNL's (Cebik) website. Goole on his name
or call to find it.

73 de Jim, N2EY

Hi all

I have it back up without the balun, and still have to use the coax for now.
I am able to tune it now on all bands but I am sure there is a lot of power
loss from the tuner. I grounded out all devices in the shack but still
receiving a lot of RF interferrence on tv, computer, and home alarm.
Thanks for all the advice, really appreciate it.






"N2EY" wrote in message
...
In article , "Bob"
writes:

We have put together a dipole, each leg is 66 feet. We put a 1:1 balun
and
it is running about 60 feet of 50 ohm coax. Presently it is about half
way
up the tower it is intended for so we could check the SWR before getting
it
up to the highest point. Presently each leg has some lags and dips, no
major
bends but it is just hanging there, over some bushes and the entire thing
is
over top of the house, and not touching anything but is very close to
some
steel guy wires (uninsulated).

What you have is the classic dipole for 80 meters.

Now we can only tune this down to a useable SWR on the 80m band. On all
other bands we cannot tune it down to a safe operating range. We are
using a
good antenna tuner but cannot get anything useable except for 80m. Here
we
are able to tune the SWR right down.

That is normal behavior.

Questions???
Would we be better without that balun?

No.

Is the fact that the dipole is still too low and close to the guy wires (
but not touching) our problem?

No.

Any suggestions please??

The problem is this:

The antenna you describe is approximately:

one half-wavelength long on 80 meters

two half-wavelengths long on 40 meters

four half-wavelengths long on 20 meters

six half-wavelengths long on 15 meters

etc.

Such a center-fed dipole antenna has a feed point impedance that is fairly
"low" (that is, under about 100 ohms) on frequencies where it is an *odd*
number of half-wavelengths. On frequencies where it is an *even* number of
half
wavelengths, the feed point impedance is very high - greater than 1000
ohms.

The 1:1 balun and 50 ohm coax you are using are low-impedance devices, so
they
work fine on 80 meters. But on the other bands, they do not work with the
high
impedance of the antenna. A tuner at the shack end of the coax cannot make
up
for the enormous mismatch at the antenna end. Even if it could, the loss
in the
coax from being operated at such a high SWR would make such a system very
inefficient.

There are several possible solutions:

1) Use a different transmission line (high impedance balanced line) and
eliminate the balun. This requires a balanced antenna tuner and the
mechanical
difficulties of using non-coax transmission lines

2) Use a different sort of dipole that is an odd number of
half-wavelengths on
the desired bands. One form of this dipole is the "trap dipole", in which
tuned
circuits (traps) electrically alter the effective antenna length.

A really good information source is W4RNL's (Cebik) website. Goole on his
name
or call to find it.

73 de Jim, N2EY

On Sun, 11 Apr 2004 13:27:04 -0400, "Bob" wrote:

Hi all

I have it back up without the balun, and still have to use the coax for now.
I am able to tune it now on all bands but I am sure there is a lot of power
loss from the tuner. I grounded out all devices in the shack but still
receiving a lot of RF interferrence on tv, computer, and home alarm.
Thanks for all the advice, really appreciate it.

Hi Bob,

Unfortunately you have proven that the BalUn was very effective in
doing what it is designed to do - prevent all the problems you have
now inherited from those who blamed your coax.

Mikes suggestion was the best - fix the antenna. The golden rule of
consulting is to give the customer advice they can perform. You are
limited to coax and they all had twin lead answers. Mike's suggestion
of making multiple dipoles AKA fan dipole is the simplest and quickest
(just make sure that you drop the ends away from each run by one to
two feet - the fan).

73's
Richard Clark, KB7QHC

Mikes suggestion was the best - fix the antenna. The golden rule of
consulting is to give the customer advice they can perform. You are
limited to coax and they all had twin lead answers. Mike's suggestion
of making multiple dipoles AKA fan dipole is the simplest and quickest
(just make sure that you drop the ends away from each run by one to
two feet - the fan).

This is the approach that I'm taking,
6 and 20m dipoles up now with balun, and more as I have time/inclination.

Me, I like the antenna to do the radiating, not the feedline.

Dave VanHorn wrote:
Me, I like the antenna to do the radiating, not the feedline.

Not a problem with a balanced antenna and a current
balanced feedline.
--
73, Cecil, W5DXP



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"Richard Clark" wrote in message
...
On Sun, 11 Apr 2004 13:27:04 -0400, "Bob" wrote:

Hi all

I have it back up without the balun, and still have to use the coax for
now.
I am able to tune it now on all bands but I am sure there is a lot of
power
loss from the tuner. I grounded out all devices in the shack but still
receiving a lot of RF interferrence on tv, computer, and home alarm.
Thanks for all the advice, really appreciate it.

Hi Bob,

Unfortunately you have proven that the BalUn was very effective in
doing what it is designed to do - prevent all the problems you have
now inherited from those who blamed your coax.

Mikes suggestion was the best - fix the antenna. The golden rule of
consulting is to give the customer advice they can perform. You are
limited to coax and they all had twin lead answers. Mike's suggestion
of making multiple dipoles AKA fan dipole is the simplest and quickest
(just make sure that you drop the ends away from each run by one to
two feet - the fan).

73's
Richard Clark, KB7QHC

Actually the first to suggest the multiple-dipole approach was Steve KI5YG,
and that should indeed work extremely well, bearing in mind that the lowest
dipole should still maintain an angle from leg-to-leg of greater than 120
degrees, if possible. I use just one "fan" under the main resonant frequency
(around 60 meters), and it is also resonant at the tuned length of the
"fan", or second dipole as well. Using the tuner works very well up to the
required 15mhz range that my particular station requires. "Very well" to me
means that bareback testing is receivable from a station in Caracas,
Venezuela, which is over 2,000nm away.

Jack
Va Beach