Multi wavelength antenna
 

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

Multi wavelength antenna
 

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.

Multi wavelength antenna
 

Multi wavelength antenna
 

Multi wavelength antenna
 

Would it increase 'performance' or just cause problems? Probably
both. The performance increase may or may not be present when
compared to what you're using now. Problems? You can bet on it.
Mechanical ones mostly. What conductor will you use that will hold up
it's own weight at 480 or 900 + feet? And since there will be 'sag'
no matter what you use, will the end points be high enough to keep
from 'clothes-lining' yourself on the antenna? Certainly not
impossible to put up such an antenna, but not exactly as simple as it
sounds.
- 'Doc

Do it! See what happens.

Multi wavelength antenna
 

On Sep 2, 8:47*am, wrote:
Would it increase 'performance' or just cause problems? *Probably
both. *The performance increase may or may not be present when
compared to what you're using now. *Problems? *You can bet on it.
Mechanical ones mostly. *What conductor will you use that will hold up
it's own weight at 480 or 900 + feet? *And since there will be 'sag'
no matter what you use, will the end points be high enough to keep
from 'clothes-lining' yourself on the antenna? *Certainly not
impossible to put up such an antenna, but not exactly as simple as it
sounds.
*- 'Doc

Do it! *See what happens.

For that length, I imagine you would need multiple supports along
the way to deal with the sag. Of course, you could use real light
gauge
wire to reduce the tension needed to sag, but then the first real
storm that comes along and it will be most likely toast and he will
have to do it over again.
Unless there is a real need for the directive gain, I'd tend to avoid
the
real long wires.. Can be more trouble than they are worth, considering
I can use a yagi and be able to steer the thing at will. With a wire,
you are stuck with one or two directions, depending if terminated or
not.
I've considered running long wires as a beverage receiving antenna,
and even it can be prone to damage after a while with all the trees
whipping in storms, etc.
But at least the usual beverage is low to the ground, and fairly easy
to install and repair if needed.
Long wires can be interesting, but I would not want them as an
"everyday" antenna. I'd always have the standard dipoles, etc for
everyday use. I might play with a long wire, but it would be an
"extra"
antenna used more as an experiment.
Being there is no real efficiency advantage to using extended dipoles,
the only reason to really consider one is if you want some gain in
certain directions. Being that there will be directions where the
gain is less, and you can't control the pattern, any advantages
would be totally up to the user and who they work.
It would generally be a disadvantage to me on the lower bands.
I want to be as loud as possible in all directions.. :)
I have used a few extended double zepps with good results, but
that's only .64 wave per leg. Or about 150 feet +- per leg of the
dipole. "about 300 feet total". Anything longer than that, and the
pattern becomes more X shaped, and the gain is no longer
broadside to the wire.
Anyway, to make a long story short, I would not use extended
dipoles if it were me building "everyday" use antennas.
I'd stick with the standard dipoles, etc, and leave the long wire
stuff as "experimental or DX" antennas. With that much room,
seems to me he could have both.