In message , Jeff Liebermann
writes
On Mon, 20 Apr 2015 08:14:29 +0100, Ian Jackson
wrote:




Would you need a power extractor at the top end? The whole copter could
simply ride on the RF voltage, ie a bit like a bird perched on a
high-voltage power line (assuming that the copter electronics were
happy). Even if you had zero-weight power extraction chokes etc, I doubt
if it would make much difference

Good point. That should work, but I would feel better if the
quadcopter were not at RF potential.

Because the copter is at the very end of the antenna (a very high
impedance point) there is essentially no RF current flow into it. You
would need extremely high inductance RF chokes to get any significant RF
voltage drop across them.

I don't want to find out that it
doesn't work when I key the transmitter when the quadcopter is 40
meters in the air. There's also a small chance that some of the
wiring in the quadcopter will pickup RF from the antenna independent
of the power/antenna wiring, which might cause some havoc. Different
problem, where more RF chokes might be needed. I guess I could just
fly it around an AM BCB transmitting antenna and see what breaks. The
only problem is that the local AM transmitting antennas are surrounded
by water.

The important thing is that the twin wires comprising the antenna be
both at the same RF voltage. They need to well capacitively coupled to
each other at the TX end and at the top end. As long as you can ensure
that all the parts of the copter and its circuitry are leaping up and
down at the same RF voltage, it shouldn't suffer any interference.

However..................













--
Ian