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 in message
...
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?

The balun is basically what is limiting your multi-band
operation. At crazy impedances the balun
prevents the shield of the coax from assisting in absorbing
some of the mismatch. Others have pointed out that the
optimum situation is to feed your antenna with balanced line...
if you must use coax, and you must have multi-band operation,
then use an antenna tuner without a balun upstairs. RG58
doesn't work nearly as good as RG8... I couldn't make my
inverted vee (resonant at 3750kHz) work 15m until I switched
over to RG8. You should avoid legal-limit operation on the
higher bands with this setup, unless you like burnt coax.

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.

Yes, the good antenna tuner is the key. Get one
with a built-in balun, so you can try balanced feedline
when you get a chance. It really is hotter, both listening
and transmitting.

You should only climb once, put up a yardarm, rope,
and pulley, and then you can play to your heart's content.
Mounting a wire antenna permanently is pure hubris,
beware!
__
Steve
KI5YG
..

Bob wrote:
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

The 1:1 balun isn't effecting the match on the other bands. If you
remove it, there probably wouldn't be much difference at all.

You could maybe put traps on the antenna so that it will be able to
resonate on multiple bands.

Another option would be to make multiple dipoles for the other bands.
The impedance mismatch will make the signal tend to go down the dipole
that corresponds to the desired band. Think of that sort of dipole as a
fan so to speak. If you go this route, You'll want to trim the lowest
band first, then work your way up in frequency for the other parts of
the dipole.

But all of these options are a good deal more work than the ladder line
method. But if you won't or can't use ladder line due to your
circumstances, I'd try the fan dipole.

- Mike KB3EIA -

Cecil Moore wrote:

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.

Fer sure! I love my ladder line, and it's foibles are worth putting up
with IMO.

- Mike KB3EIA -

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