On Sep 1, 4:31*pm, wrote:
I have a lot of space available for antenna installation and i am
wondering if installing a 4 or 8 wavelength antenna would provide
increased performance or problems. *For instance, instead of a 120 ft
dipole for 3900 khz *a 480 ft or 960 ft.

*I would be installing across a valley so ends would be about 25-30 ft
off the ground and the center would be about 80-90 ft off the ground.

Thanks

Wouldn't help efficiency, but would alter the pattern. Being you may
well
need a matching device, I don't see much point unless you want gain in
certain directions.
You would want to model the antenna on the various bands to see
how the pattern would look.
On the higher bands, you might be better off feeding as a longwire
rather than a dipole if you wanted gain.
But beware of static buildup, etc.. Ground the wire out when not in
use, and consider a gas tube or whatever. A friend of mine ran a
longwire years ago when he was a novice. You could often draw a
good sized arc to ground if conditions were right.
Anytime you get gain in certain directions, you lose gain in some
other directions. So on 75m, I generally prefer as omnidirectional
an antenna as possible, while maximizing system efficiency.
But I'm usually talking to more than one at a time, in various
directions. I want to avoid nulls. I just use coax fed dipoles on
75m.
A turnstile, if I'm feeling fancy. That's what I've had for that band
here at
the house for the last few years. I started using those back in the
80's, and it's still about my favorite antenna for 75m NVIS type
stuff.
BTW, if you did decide to string out a lot of wire, you might also
consider a flat loop. Again, you would want to model it for all the
bands
to get an idea what it would do.