A design for a wire antenna length changing unit
Antenna tuners are kind of annoying. I'd like to achieve natural resonance by always having the right length of dipole flying. The following is a rough design for a unit that can ride along the length of a dipole wire antenna and coil up its ends as the frequency requires.
The power + comms line would be a two-conductor cable. With the device the farthest from feedpoint as possible, all the power + comms cable would be rolled up on the right spool. As it goes inwards, coiling up the antenna wire, it unrolls the power + comms cable. Due to layering on the spools the turns ratios of the two spools would not be equal, so a potentiometer at the swivel joint would control the error by varying the position of the power + comms spool to keep the angle of the joint constant.
A shaft encoder in the antenna spindle can communicate distance down to the control room. If integrated with some smart control electronics, quick tuning would be possible.
Two units like this would need to ride the dipole in sync with each other. I'm not yet clear on how to achieve a perfect electrical balance between the two dipole halves, but a balun at the feedpoint would help mitigate the impact of any small imbalance.