[amsat-bb] Helical Antenna for 2-meters

[Edward R Cole]

Just scale the dimensions proportionally (except wire diameter);

ratio = 144/435

I built a 14 turn 437 MHz helical back in 1996 to receive the MGS 
beacon and built a 2.4 GHz 6-turn helical for 33-inch offset dish 
feed for AO-40.  Plenty information in Amsat Archives.  Original 
Kraus-W8JK design is optimistic in gain calculation.
http://www.kl7uw.com/Satellite%20feed.jpg

W9EK had good construction hints in prior publications.

For receive-only do not sweat getting a good SWR.  I used a 1/4 
wavelength long 1/8 inch wide brass strip, run from connector to 
beginning turn of the helix for impedance matching.  Space the point 
of connection to the helix about 3/16 inch above the ground plane 
reflector.  Natural impedance of a helix is 140-ohm.

On air experience with the 432 helix was that a ten element CP 
crossed element yagi is better.  But if you desire CP the helix is a 
natural, though not perfect.

73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
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