[TowerTalk] Beam comparisons and costs

[K7GCO@aol.com]

In a message dated 28.04.00 04:00:50 Pacific Daylight Time, 
John_L_Pantaloni@icpmech.navy.mil writes:
<< Hi,
 I'm looking at the antenna mart quad but relatively poor f/b has me thinking 
 twice.  I understand you have a fix for that using a variable capacitor. 
What is 
 involved in executing this? Does Antenna Mart supply the parts?
         Thanks John KB3EAY
  >>
No one does what I have described yet.  The idea is to make the Reflector 
slight longer than normal and add a series Xc in it with an insulated shaft 
going to the mast driven by a selsyn.  Certain spacings of a 2 element quad 
can give well over a 50 dB F/B null in the rear.  It's a critical length of 
the reflector.  Would you beleive this null is so deep it creates a 
"Reception Black Hole" in the rear?  Therefore to always obtain it anywhere 
in the band you need a variable Xc.  It will also allow one to tune for max 
gain anywhere in the band but the DE Z is much lower.  I'm building a 6 band 
2 element tapered quad with 6 variable Xc's all ganged together on the same 
insulated shaft driven by a selsyn.  This will take the proper selection of 
components and good mechanical support techniques.  I have platforms on my 
towers for easy access to the DE's and lower test towers.  K7GCO  

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