Sure am enjoying all the 4sqr talk and some very nice posts on wire arrays.
I'd like to inquire if anyone has real time experience or would simply like
to wax poetic on the following wire arrays. One for 40M and the other for
80M.
80M - I have room to erect a two element vertical array at EU with up to 1/4
wavelenght spacing between elements. Endeavoring to keep things simple, I
searched for spacings and feeds that would allow for an approximate 50 ohm
match and produce a cardioid or endfire figure-8 pattern. Page11-25 of
ON4UNs book (2nd edition, ISBN 0-87259-466-1) seems to have just the ticket.
The array is two 1/4 wavelenght verticals spaced 1/8 wavelength apart and
fed with 157 degree lines and a switchable 29 degree line to provide the 135
degree phase shift between elements. Feed impedance is Z=47+j0.9 and you get
a nice cardioid switchable in two directions. Looks great on paper and would
fit just swell between two big 'ol trees on my lot - has anyone tried this
array and/or the Christman feed method?
For 40M - I'm considering the five sloper array which is shown on page 6-30
of the latest ARRL antenna book (18th Edition). This array is simply five
1/2 wave dipoles spaced around a tower in a sloper configuration. A five
position switch allows selection of any single element, and the unused
elements appear as reflectors. Claimed gain is about 4db over a single
sloper and 20 db F/B. Curious how folks think this array will do compared to
the ubiquitous shorty 40 at 75 feet and perhaps against the K8UR type array.
I could probably do a 4sq, but being on a budget, and given the cost of the
coupler and other parts for a 4sq, I will probably just opt for an XM-240 if
I can't get it done with wires. I am thinking that a remote switch and some
wire is not a bad way to go though. The slopers would hang off either a 75
foot tower, or perhaps from a high support rope slung between trees.
Cheers,
Mark Curran
KI7WX/4
ki7wx@aol.com
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|