Homebrew dipole help please?
 

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

"Bob" wrote in message
...
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?

If you want multi-band operation, then yes, you have to
forget the balun, or put multiple dipoles on the output lugs.
__
Steve
KI5YG
..

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?

Bob, the antenna as you describe it is pretty much *for* 80 meters. If
you want to tune the thing on multiple bands, and I'm assuming that you
want it for the Ham frequencies, you will want to replace the coax and
balun with ladder line, and use a tuner to match the impedence with your
radio.

- Mike KB3EIA -

Hi Steven

Thank you for your response to my problem.

Any suggestion? What you say is that I would be better off without that 1:1
balun? Yes, now I have it at 66feet each leg for a total of 132 feet but now
it is not at the best height but kinda sagging and lopping where it is but
off the ground and about 2 feet above the roof and other obstacles. I also
have it presently close to steel guy wires and the tower itself. What would
be my problem then here now? You believe it is my balun? I was hoping to get
this up there and then leave it. All this climbing is difficult. Do you
believe that once I get it up there, with the coax, with the dipole, no
balun, do you think that would allow me better results with a good antenna
tuner? Any advice is greatly appreciated.

Thank you
BOb







" Stephen Cowell" wrote in message
m...

"Bob" wrote in message
...
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?

If you want multi-band operation, then yes, you have to
forget the balun, or put multiple dipoles on the output lugs.
__
Steve
KI5YG
.

Hi, Thank you for your response. I do not have ladder line and only have the
coax basically. Is it acceptable for good results to simply use the coax and
then split it out to each direction of the copper wire? And not use the 1:1
balun? I was hoping to simply get the dipole in the air and leave it and
simply tune it at the transmitter to acceptable SWR and go from there. Now I
only get good SWR on the 80meters because of the length it is cut at. I was
hoping also to use the dipole with the tuner on 10, 15, 20 and 40. Is this
possible? The tuner is good and I know I will lose the power to the tuner
but would still get to use the other bands when needed.
Any more advice is greatly appreciated.
thanks
Bob






"Mike Coslo" wrote in message
...


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?

Bob, the antenna as you describe it is pretty much *for* 80 meters. If
you want to tune the thing on multiple bands, and I'm assuming that you
want it for the Ham frequencies, you will want to replace the coax and
balun with ladder line, and use a tuner to match the impedence with your
radio.

- Mike KB3EIA -

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

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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Bob wrote:

Hi Steven

Thank you for your response to my problem.

Any suggestion? What you say is that I would be better off without that 1:1
balun? Yes, now I have it at 66feet each leg for a total of 132 feet but now
it is not at the best height but kinda sagging and lopping where it is but
off the ground and about 2 feet above the roof and other obstacles. I also
have it presently close to steel guy wires and the tower itself. What would
be my problem then here now?

The problem is the coax.

You believe it is my balun? I was hoping to get
this up there and then leave it. All this climbing is difficult. Do you
believe that once I get it up there, with the coax, with the dipole, no
balun, do you think that would allow me better results with a good antenna
tuner? Any advice is greatly appreciated.

Feeding your dipole with ladder-line moves all the matching problems to the
hamshack where you don't have to climb anything to solve them. Try the following
configuration and get back to us on any remaining problems.

XMTR--tuner--1:1 balun/choke--100 ft. 450 ohm ladder-line---132 ft. dipole

This configuration will allow multi-band operation on most of the HF ham
bands. The problems you will have with a couple of bands are solvable.
--
73, Cecil, W5DXP



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Bob wrote:
Hi, Thank you for your response. I do not have ladder line and only have the
coax basically.

The coax *IS* the problem. If you don't like to climb, you are going to
have to replace the coax with something like 450 ohm ladder-line. 100
ft. of such ladder-line costs about $17.

One other possible solution is to install an autotuner at the antenna
feedpoint but that is a pain to do.
--
73, Cecil, 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