[amsat-bb] Re: HELIX REFLECTOR?

[Edward R Cole]

At 04:51 PM 6/3/2010, Pete Norris, K1HZU wrote:
>Hi All:
>I am rebuilding a 440 MHZ Helix that I built several years ago . It 
>worked very well, but I would like to reduce the size of the 
>reflector to a more manageable size than I had before. The only 
>reference to reflector size I can find is, "minimum 20" ". I may be 
>looking in the wrong places. I would appreciate it, if someone would 
>steer me in the right direction.
>Thanks,
>Pete, K1HZU
>
>
>
>
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You might be interested in the Helical Beam that Mike Cook designed 
in 1996 for reception of the Mars Global Surveyor (MGS).  He used a 
10.66 inch diameter loop Reflector.  His antenna was designed for 
437.1 MHz so you will want to adjust size to your operating 
frequency.  If you doubt the performance of this antenna, mike 
detected MGS at 10 Million km from earth.  MGS signal output is 
approx. 1w EIRP.
http://af9y.com/helix.htm

I made an 18-turn version of Mike's helix, but did not have my 432 
converter completed in time to receive MGS.  I used a 15-inch 
aluminum pizza pan for my reflector.  In general one uses a 0.5 to 
0.6 wavelength reflector (diameter) (13.6-16.3 inch at 440-MHz)  (Not 
withstanding W1GHZ's findings in his Antenna Book)



73, Ed - KL7UW, WD2XSH/45
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BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
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