On 5 June 2012 01:12, Dave Martindale <dave.martind...@gmail.com> wrote: > I don't think that's correct.
This is a funny topic. No matter where see it discussed, there are people with different views on it. I looked on the edaforum http://www.edaboard.com/forum26.html and found a thread (can't find it now unfortunatey), where someone was adament they needed to be one way (I forget whether both RHCP or RHCP+LHCP), and someone else was adament a colleague nearly lost his job after making that mistake. I think there was about a 50:50 mix of views on the topic I think I might have to make 3 axial mode helical antennas and test this myself. If I wind two in one way, and one in another, it should be possible to determine if the strongest signal is received with them wound the same way, or wound the opposite way. I don't know much about helix antenna design, but I know there are two modes - "normal" and "axial". I have some software able to design either, as well as some complex types. Sticking a frequency of 300 MHz (so lambda is a convenient 1 m), I get: Normal mode: helix diamater 0.05 lambda, helix spacing 0.05 lambda. 1.818 turns (no option to set gain). Axial mode: helix diameter 0.318 lambda, helix spacing 0.222 lambda, 3.341 turns for 10 dBi gain, 6.667 for 13 dBi, 13.302 turns for 16 dBi and 26.541 for 19 dBi and 33.413 turns for 20 dBi. So the diameter of the helix does not tell you much on its own, as there are two different types, one of which has a very different diameter to the other. Note the axial mode helix has a diameter of 0.318 lambda, so a circumference of Pi*0.318 = 1.0 lambda. I think there is some story that when Krauss invented this antenna, he made the first one with a circumference of 1 wavelength, and more by luck than anything else, got it right first time. (Note, this software is designed to create a model for a 3D electromagnetic simulator, so the results are not perfect, and one is expected to tweak the design using the 3D electromagetic simulator). Dave _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.