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

On Mon, 20 Apr 2015 20:36:48 +0100, Ian Jackson
wrote:
(...)

Today, we had Chen Dubin, owner of Santa Cruz Drones, gave a
presentation and a demonstration of his drones at the FLUG (Felton
Linux Users Group) meeting:
http://www.santacruzdrones.net/#content_area
Of course, I mentioned the idea of using a tethered drone aerostat to
support a wire antenna and asked how long the motors would last before
overheating. His drones have rather large motors, which he says would
last for days. He also mentioned that the military is already using
such tethered drones to hoist antennas. For example:
http://www.skysapience.com
http://www.droneaviationcorp.com/tethered-drone.html
https://www.google.com/search?q=tethered+drone&oe=utf-8
https://www.google.com/search?q=tethered+drones&tbm=isch

I also asked if he has tried any of his drones near the local AM
transmitter antennas (KSCO). It seems he lives nearby, hangs around
the station, and has not seen any problems. So, it should work at 160
meters. (The control links are usually 2.4GHz. Video is either 900
MHz or 5 GHz).

Since the main limitation of a tethered drone is weight lifting
ability, doubling the wire length and hoisting a 1/2 wave antenna is
easy. A half wave antenna does not need a ground plane, and might
work better than a 1/4 wave. End fed 1/2 wave antennas:
http://www.aa5tb.com/efha.html
http://www.vk2zay.net/article/115
http://pages.suddenlink.net/wa5bdu/efhw.htm
http://www.w8ji.com/2end-fed_1_2_wave_matching_system_end%20feed.htm



Drivel:
Kite and balloon lifting antennas for 160 meters:
http://www.qsl.net/g4vgo/
http://www.qsl.net/g4vgo/Kites.htm


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558