At Feshiebridge, Scotland, AIUI they developed telemetry for
indicating glider airspeed to the winch driver, and it was said to
work very well. IIRC, it did not send an airspeed number in knots, but
rather an indication of too slow, a bit slow, OK, a bit fast, or too
fast (or something like that) which is what the winch driver really
needs to know, they believed. The unit in the glider was calibrated
for the glider type.

It needs somebody with first hand experience of it to tell more, and I
don’t know if it has been kept going.

Chris N.