[Fourlanders] adjusting takeoff angle

[Paul Yeager, ABR(R), REALTOR(R)]

Ron WW8RR points out that our high-gain stacked beams are likely striking the ionosphere quite some distance away, due to their low takeoff angle.  Ron further suggests that this is causing us to miss closer in stations that we might be able to work, if could arrange a higher takeoff angle.  (Ron - please let me know if I have misstated something here)
   
  I see two obvious ways to change the takeoff angle.
   
  1) Mount anntenna(s) on an az-el rotator.  This seems pretty simple, but when one considers the details, it becomes a bit complex mechanically.  How does one mount a horizontally-polarized yagi on an az-el rotator?  The only way I can see is to mount it on a rather long "boom", rotated by the elevation rotator.  The boom needs to be rather long to avoid interaction between the antenna and the tower/rotator, and may need to be fiberglass or other non-conductive material to avoid degrading the performance of the antenna.   This will also place quite a side load on the rotator and tower, unless the boom is extended to the side opposite the rotator with a counterweight.
   
  Alternatively, we  might extend the antenna's boom, then add a right angle to the rotator.  This increases the load on the elevation rotator considerably, unless a counterweight is added.
   
  See what I mean about mechanical complexity?
   
  2) Using a similar antenna arrangement to the one we used for the contest, adjust takeoff angle by adjusting the phase between the two antennas.  Mechanically, this is no more complex than the current arrangement.  Electrically, it's quite more complex.  Not rocket science, but certainly more complex than a single feedline running to a splitter feeding both antennas.
   
  We could do something as simple as selecting upper/lower/both yagis, or get more complex and switch sections of feedline in and out to actually change the phase.  Two switchable sections of feedline would give us 4 choices of takeoff angle - in-phase pluse three different phase delays.
   
  Anyone have any idea how to model phase vs. takeoff angle for out pair of yagis?  Speaking of modeling...  how about takeoff angle vs. "skip distance"?
   
  I suggest that we test the concept using a lightweight 6m yagi, like the 4 element Comet I have, mounted on an az-el rotator, either during the September contest or at some time between now and then.  This would give us an idea of whether or not the concept is viable, and what sort of adjustments to takeoff angle are necessary.  Once the concept is validated, we could construct a "phasing system" to use with our pair of yagis.
   
  So... what do y'all think?
   
  73 de W4SKI


Paul Yeager, ABR®, REALTOR®/Broker
Accredited Buyer Representative
Mountain Fever Real Estate
828 400 9442 (cell)
828 926 2545
888 926 2545
828 926 3860 (fax)
paul at mtnlist.com
www.mtnlist.com

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