On Mon, 20 Apr 2015 19:16:55 +0200, "bilou" wrote:

I like the idea of using a bifilar antenna with the 2 wires in parallel for
RF and the motors supplied in differential mode.
Good motors for the job could be those used in lowcost Dremel tools
They reach 20000 RPM and work on 220V AC or DC.

Ummm, the Dremel tool probably weighs too much. It would also need a
gearbox to produce counter rotating propellers, to keep the reaction
torque from spinning the motor and winding up the antenna wire. That's
incidentally why quadcopters have two rotors going clockwise, and the
other two going anti-clockwise. That's also why you don't see many 3
rotor devices.

Collector noise in receive could be a problem too.

Not to worry. Collector noise (whatever that is) would probably be
buried under the overwhelming atmospheric noise (mostly lightning) on
1.6 MHz.

May be wiring the 4 motors in serial would be a good idea too to minimise
voltage drops and weight.

I assure you that 4 motors wired in series, parallel, differential, or
a tangled mess, would weigh exactly the same.

However, you're correct that voltage drop would be a problem because
the device really sucks power out of the LiIon battery. My quadcopter
uses a 2200 ma-hr battery for 15 min maximum flying time. Assuming I
drain it completely:
2.2 A-hr / 0.25 hr = 8.8 A drain
The 16AWG wire might handle that, but with about several ohms of
copper loss, most of the energy will go into heating the antenna.
Sorry, but I'm late for a free lunch so let someone else calculate the
resistance of 40 meters of 16AWG wire.

Incidentally, the battery is rated at 25C, which means that it can
theoretically drain at:
2.2 A-hr * 25 = 55 amps
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26472
Yes, you can weld with the battery.

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