Bob wrote:
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?
My inclination is to believe there's something wrong with your antenna
tuner. Are you certain it isn't in bypass? (of course, that antenna
should be reasonably resonant in the 80m band *without* the tuner, so if
the tuner isn't working at all you may well still have a reasonable SWR
on 80) Can you get your hands on a 50-ohm dummy load? (try to load up
the dummy load through the tuner, it should work on every band)
Can you get the SWR to dip on other bands? (i.e., is it just that the
dips aren't deep enough to give a usable SWR?)
What kind of tuner are you using?
Having it low and close to guy wires will affect the resonances and
efficiency, but with a good tuner you should still be able to tune out
the reactance and get a reasonable match to 50 ohms, at least on *some*
bands if not all.
Do you have access to a SWR analyzer?
FWIW, I've had good luck using 44 feet on one side, 88 feet on the
other, and a 4:1 balun instead of 1:1. That's the same total length.
It gives a decent SWR on every HF band except 160 and 15 meters - and
it's close enough on 15 that the autotuner in my rig will match it.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com