[amsat-bb] L band gear

[Greg D]

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