Hi Ev;
I have built such a switching system. We use it at W2SZ. I used surplus
coaxial relays similar to Dowkeys. 4 rerlays are needed, one to switch from 4
antennas combined to a pair, one to switch from the lower pair to the upper
pair, and two to switch each pair from the pair T connector (ignore the short
discontinuity) to the matching section. The matching section is 2 quarter
lamda lines of 75 ohm coax with a tee connector in the middle. Improvements in
VSWR bandwidth of such a system were published in July/August 1984 NCJ
My low band stacking switches were all done with open frame relays. Usually I
uase DPDT relays with both contacts in parallel as this is closer to 50 ohms
when mounted in a box. In some cases a 10 pf capacitor was added between relay
contacts to control the impedance. If the relays are small enough the same
trick should work on 6 meters, but I havn't tried it.
Other ULB links:
http://dayton.akorn.net/pipermail/vhfcontesting/2001-July/000050.html
http://lists.contesting.com/archives/html/Towertalk/2002-04/msg00918.html
In order to understand the takeoff angle you should use the program YT. It is
included with the ARRL antenna book. The beauty of YT is that it will match
the proposed antenna heights with the terrain at your location. You'll need a
topo map. If you don't have one, www.topozone.com will work fine.
Good Luck es 73 Fred K2TR
Ev Tupis <w2ev@arrl.net> wrote:Hello everyone,
I am assembling a 4-dipole multi-driven array (horizontal polarized, stacked up
my tower). At first, I was thinking about simply stacking them all 12'
(5/8-wave) apart and feeding them with 3/4-wave 75-ohm harnesses and calling it
quits. However, my thoughts are now wandering and am interested in exploring
the ability to select between:
Upper Two (50' & 38')
Lower Two (26' & 14')
All Four (50', 38', 26' & 14')
with the desire to focus the elevation component of the array to take advantage
of different DX conditions. A couple of questions for those in-the-know...
Has anyone done this (array switching on 6m) with any degree of success?
- How have you accomplished it?
What height does one use to calculate the takeoff angle of each combination?
"Let the tread begin" :)
Ev, W2EV
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