When we received a parabolic reflector 'on loan' from a local cellphone
company, some thinking was in order. We were planning several other
antennas of this type for weather satellite tracking, so some time
to gather information was needed.
As a helix is easy to construct, and very tolerant of size errors, it's an excellent plaything.
According to literature, the minimum number of turns for a helix is between 3 and 5. Only after 3 turns, acceptable circularity is realized. Still, with the f/d ratio of the available reflector, we needed near 3 turns to illuminate it efficiently. So maybe this solution is a bit of a compromise.
Here's a page with images of a 3-turn helix
that was constructed for reception in the 1690 MHz Wefax band
(geostationary weather satelliteslike GOES).
These images are not photographs but generated with a raytracing
programa (pov-ray).
| Documentation and links |
| (c) John Coppens ON6JC/LW3HAZ |