[VHFcontesting] 6m Array Switching

[Fred Lass]

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 at 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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