Zach Metzinger via AMSAT-BB wrote:
On 05/14/20 13:41, Greg D wrote:
You'll also need an antenna. Surprised that's not been mentioned in this drift into homebrewing...
Before I got my 30 element Beam at a swap meet, I was using a homemade 17 turn Helix. It was easy to make, and worked quite well. I would not say that the beam was any better, especially since the helix is circularly polarized. I still have it, and may swap it back into service some day.
Yep! Plenty of designs out there, should one want to build vs buy:
https://vk1sotaon23cm.wordpress.com/23-cm-antennas/
One of these cheap, perhaps-not-perfect-but-good-enough VNAs would help tune it up:
https://www.tindie.com/products/hcxqsgroup/nanovna-v2/
(I have the v1, which is good up to ~900 MHz, and have been pleased with it.)
--- Zach N0ZGO
Wow, love some of those designs. Quite creative.
My helix was pretty basic. It ended up being 17 turns because that's where I ran out of wire :) I didn't (still don't) have any equipment to tune it up, so just depended on the helix being inherently pretty forgiving to make it all work. I forget the exact dimensions, but the idea was to mark the wire every "x" millimeters, then twist and stretch the turns to space them every "y" millimeters. I can't find my reference to "x" and "y", but I expect x is one wavelength at the target frequency, and y has something to do with the speed of light and the velocity factor of the winding, with the idea that the rotating wavefront basically screws itself onto the helix winding. There are a number of "helix calculator" sites where the dimensions can be generated.
http://home.wavecable.com/~ko6th/IMG_0138.JPG
Fun project.
Greg KO6TH