RadioBanter - View Single Post

April 27th 04, 06:07 AM

In article ,
(Mark Keith) wrote:

Angela & Gary wrote in message
...
I would like to consider this for 20m dxing. Anyone done this/seen it
published anywhere or otherwise have suggestions?? Thanks.

Gary

Sure, it's quite common. How many do you have in mind? Two? More? You
can feed as broadside or endfire arrays. Sometimes both, for a
multiband setup. In general, the maximum gain with a broadside array
is with the spacing at appx 5/8 wave. In general, an endfire array
will have maximum gain with about an 1/8 wave spacing. But you can use
other spacings with good results. Of course, if you have a way to
change phasing, IE: adjusting feedline lengths, L/C phasing box, etc,
you can steer the pattern. You can get many details in the ARRL
antenna handbook. Also plots of the various patterns with changes in
phasing. I've paired up verticals and ran them as broadside arrays on
the higher bands, but as endfire arrays on lower bands. Once ran a
pair of elevated 5/8 ground planes on 10m, and crudely steered by
changing coax lengths. Worked quite well for what I needed. I used
them as a broadside array on 10m, but I used them as an endfire array
on 30m. The "maximum" gain you can get from a pair of verticals is as
a broadside array. It's peak is slightly more than the peak maximum
gain of an endfire array. But the endfire gets fairly close, and can
be handy sometimes being the spacing is less. 1/4 wave is a common
spacing. Two verticals 1/4 wave apart, and fed 90 degrees out of phase
gives a nice fat unidirectional pattern, and can easily be reversed.
As I said, the possibilities of spacing/feed combinations could fill
three pages of text I bet...:/ The ARRL antenna book covers it in good
detail, and also the best ways to feed. There are other useful books
also of course, but just that one will do the trick, and covers most
other ant related topics. MK

Mark, thanks for the info. I was thinking of perhaps placing 3 vertical
dipoles at the apices of an equilateral triangle. What I need to
research is optimum spacing in such an arrangement (quarter perhaps?)
and details on putting together a nifty steering circuit. I must admit
that I forgot 'bout the venerable ARRL antenna book. I perused the
handbook last nite and came up dry. I will try to hit our local lib
this wkend to ferret out the details. Thanks again.

Gary