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