Regarding tuning capacitors . It is worth remembering that for best operation in a resonant circuit the tuning cap. needs to have a low loss / high D , so the cap. needs to be kept perfectly shiny clean . Any dust forming on the capacitor plates would attract moisture which is the enemy of RF. I have several high quality level meters and the tuning capacitors are mounted in sealed enclosures . The repair manual for the HP 606 B signal generator states, if the output fails , the first thing to do is to blow air gently between the plates of the tuning capacitor . So obviously to remove dust . Perhaps some form of dust proof enclosure for a mag. loop tuning cap. might help to keep the performance up for longer periods of time .
I am wondering about the possibility of making a tuning cap with two sets of fixed plates as it were , but with one set of plates mounted on a moving insulated frame such as teflon , so as to allow one set of plates to mesh with the other . The moving gang would have one more plate than the fixed gang . The moving gang would possibly connect to one end of the loop via a section of thin copper strap suitably pre- formed to allow for lateral movement of the tuning motion . The other possibility would be to hard mount the gang sections to the ends of the loop and allow the loop to flex slightly during the tuning motion as the plates move to and fro . Might be able to use teflon sheet for some of the support structure A capacitor made this way might be more efficient than some of the other more traditional methods . Bad luck about the "Gastite" it would have made a beaut Trombone capacitor .
I am toying with doing a PCB to drive a stepper for the antenna remote control.
It will be an Arduino Nano and a stepper driver like the A4988 modules commonly in 3D printers.
Only one input will be needed to set the home position then the steps are counted to keep track of the capacitor setting.
RS485 drivers for balanced comms and the cable will be an "Ethernet" 4 pair for power and comms.
Or would folk want a home input, a max limit input and an encoder input?
Comments are gratefully received.
There is a handy hole in the back yard where the previous owners had removed a rotary close line.
This is a length of heliax that was in my shed.
Still to do is make some spacers for the sides, add a tuning capacitor and drive loop.
This antenna "design" was just the size of the roll. It will be interesting to see if it works, and on what bands.