[amsat-bb] Helical Antenna for 2-meters
Edward R Cole
kl7uw at acsalaska.net
Wed Feb 8 00:23:27 UTC 2017
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.
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
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