As part of an experiment we have to build 4 antennas with quite wide beamwidth suitable for satellite signal reception with no mechanical tracking mechanism.
Quadrifilar helix are one of the best candidates for this particular job. So far so good. We started building the antennas for the 433 MHz band, just to discover that it is very difficult to make them to have the same characteristics. Especially in this band, tiny offsets from the “proper” values affect greatly the performance of the antenna. Also due to the size of the antenna, it was quite difficult to put support tubes, leading to mis-alignment due to inconsistent wire bending.
So I decided to make a 3D model using Freecad that would need, “just to put the fucking wire”. The result is relatively good, especially in terms of repeatability. Below are some photos:
The Freecad project is already up https://gitlab.com/surligas/qfh-antenna
It is far from ready, but you can download the stl files for the 433 MHz version. For the mast, I am using a Φ16 electrologist tube, a quite common diameter.
All necessary dimensions and information were retrieved from mainly from https://www.jcoppens.com/ant/qfh/calc.en.php and http://orbanmicrowave.com/wp-content/uploads/2015/03/TheBasicsofQuadrifilarHelixAntennas.pdf
I will post SWR and impedance when I have access to the VNA.