On Mon, 20 Apr 2015 08:14:29 +0100, Ian Jackson
wrote:

In message , Jeff Liebermann
writes
On Sun, 19 Apr 2015 20:00:49 +0100, Ian Jackson
wrote:

With a little ingenuity, there's no reason why you couldn't feed DC
'line power' up the antenna wires (or, more accurately RF up the power
wires).

I'm sure it can be done. I'm not so sure the added weight of the
insulation and isolating chokes at the top will be tolerable. A 1.7
MHz RF choke is not a small or light weight device and this thing will
need two chokes at the top. Also, there's another reason for the
10-15 minute limit. The motors do get rather hot after a flight.
Running them continuously from a tether wire might cause a meltdown.

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. 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.

Incidentally, the biggest quadcopter helistat of them all:
http://en.wikipedia.org/wiki/Piasecki_PA-97
A helium filled ZPG-2W dirigible and 4 old H-34J helicopters
underneath. It was designed to lift 26 tons of logs out of the
forest.
https://www.youtube.com/watch?v=_7jENWKgMPY
Oops.

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

"Jeff Liebermann" wrote in message
...

Weight might be a problem. I'll guess(tm) #16 AWG wire, which weighs
7.82 lbs/1000ft or 11.6 gm/meter. 1/4 wave at 160 meters is 40 meters
so that antenna would weigh:
11.6 gm/meter * 40 = 464 gm
Hmmm... Probably too heavy. By comparison, a GoPro camera body weighs
100 gm. Ok, smaller guage wire or bigger quadcopter.
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Hi
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.
Collector noise in receive could be a problem too.
May be wiring the 4 motors in serial would be a good idea too to minimise
voltage drops and weight.

bilou wrote:

"Jeff Liebermann" wrote in message
...

Weight might be a problem. I'll guess(tm) #16 AWG wire, which weighs
7.82 lbs/1000ft or 11.6 gm/meter. 1/4 wave at 160 meters is 40 meters
so that antenna would weigh:
11.6 gm/meter * 40 = 464 gm
Hmmm... Probably too heavy. By comparison, a GoPro camera body weighs
100 gm. Ok, smaller guage wire or bigger quadcopter.
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Hi
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.

Then all you need is a gear box to get the rotational speed down to where
propellors will work.

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

As control on these things is done through individual motor control, that
isn't going to work.


--
Jim Pennino

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

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 12:31:13 -0700, Jeff Liebermann
wrote:

Marginally related drivel:
"The Promise of Drones for Tower Inspection"
http://online.qmags.com/AGL0415#pg47&mode2

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

On 2015-04-18 08:38:31 +0000, gareth said:

This current interest (and privacy furore) about drones set me thinking,
what an interesting way to elevate a TopBand vertical, but being a temporary
structure, not breaching any planning permission (Brit) or zonal (Yank)
restrictions.

One problem would be the flight time / battery life, so one approach
could be to power the drone through the antenna cable (much as with
mast-head preamps), in which case, being tethered, it would no longer be
a drone!

The power considerations, however, would call for too heavy a cable to
be lifted
aloft, so, taking the cure from the electricity grids, perhaps the solution
would be to power with 1kV AC (say, 10kHz, to reduce the sizes of
aloft transformers) going up a twin feeder, with the top band excitation
driving both of the AC feeder wires in parallel?

(Not too dissimilar in principle from the electicity grid using Pilot Tone
protection)

Gareth G4SDW

PS. By varying the frequency and / or phase of the 1kV AC, the
positioning of the ex-drone woulc be controlled thatway.

How about a tethered helium balloon instead? This way you don't have
to worry about powering the thing. Bell wire will handle 100 watts all
day without turning into smoke.

You could use some SpiderWire kevlar fishing line to make a few tethers
so that the balloon doesn't whip around too fiercely in the wind, and
it would require no power at all.

In message , Oregonian Haruspex
writes



How about a tethered helium balloon instead? This way you don't have
to worry about powering the thing. Bell wire will handle 100 watts all
day without turning into smoke.

Many amateurs would give their right arm for a functioning helium
balloon. It's the sort of thing that most LF band aficionados can only
dream about. It's a lot easier to obtain electricity than helium.




--
Ian

Ian Jackson wrote:
In message , Oregonian Haruspex
writes



How about a tethered helium balloon instead? This way you don't
have to worry about powering the thing. Bell wire will handle 100
watts all day without turning into smoke.

Many amateurs would give their right arm for a functioning helium
balloon. It's the sort of thing that most LF band aficionados can only
dream about. It's a lot easier to obtain electricity than helium.




Then I guess the solution would be an electric balloon! :-)

de Irv VE6BP

On 4/23/2015 3:37 PM, Ian Jackson wrote:
In message , Oregonian Haruspex
writes



How about a tethered helium balloon instead? This way you don't have
to worry about powering the thing. Bell wire will handle 100 watts
all day without turning into smoke.

Many amateurs would give their right arm for a functioning helium
balloon. It's the sort of thing that most LF band aficionados can only
dream about. It's a lot easier to obtain electricity than helium.





Weather balloons can be found for sale all over the web, and in all
sizes and skin thicknesses. They work quite well for hoisting a wire.
I tried it one time with two NWS balloons (about 3 feet in diameter,
IIRC); the only problem was they bounced against each other constantly.
Next time I would arrange them so that one is above the other.

A tank of helium isn't overly expensive, either.

--
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Jerry, AI0K

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