Buy 300 feet of regular cable. The kind made for 100 foot runs. Do a
quick check on the kitchen table. Measure the voltage at the motor,
note the voltage drop in the cable.
Rig up a transformer in series with the line to the rotor such that it
kicks up the voltage. I did this successfully a while back. Yes it
takes a little effort but works perfectly. As I remember I kicked up
the 24 volts on a CDE rotor to about 30.
The other wires in the cable are used for detecting the position of
the rotor and can tolerate the long run.
The other thing you can do if you have enough scrap romex or other
copper wire is to parallel it with the rotor cable. Not necessary to
have enough to go the entire 300 feet. For example, if you have
enough of say #12 romex cable to go from the shack to the base of the
tower, use it to parrallel the rotor cable and make your measurements.
Use your head, experiment. It is just ohms law we are dealing with
here, not rocket science. Good luck.

Rick K2XT