In message , Jeff Liebermann
writes
On 19 Apr 2015 10:45:10 GMT, Rob wrote:

But do you want a radio controlled gadget with 4 electric motors at
the top end of your vertical?

A drone would work, but does not have enough battery capacity to be
able to keep the antenna in place for more than about 10-20 mins.
Longer would require seperate power wires, which would interfere with
the radiation pattern.

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.

16AWG wire does indeed seem a bit overkill (at least for the sort of
powers that UK amateurs are allowed to run). Something much thinner and
lighter would do (eg PVC covered multistrand flex).

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).

If there's any danger of the pull of the copter snapping the wires, it
could be restrained with (say) thin woven nylon cord.

However, how would the intricate control circuitry in the copter cope
with the very high level of RF signal?








--
Ian

On Sun, 19 Apr 2015 20:00:49 +0100, Ian Jackson
wrote:

In message , Jeff Liebermann
writes
On 19 Apr 2015 10:45:10 GMT, Rob wrote:

But do you want a radio controlled gadget with 4 electric motors at
the top end of your vertical?

A drone would work, but does not have enough battery capacity to be
able to keep the antenna in place for more than about 10-20 mins.
Longer would require seperate power wires, which would interfere with
the radiation pattern.

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.

16AWG wire does indeed seem a bit overkill (at least for the sort of
powers that UK amateurs are allowed to run). Something much thinner and
lighter would do (eg PVC covered multistrand flex).

Yep 16AWG is a bit heavy. I have one of these:
http://rotorconcept.com/Discovery.asp
which will allegedly lift 1 lb (0.45 kg) for 10-15 mins. My guess is
more like 300 grams for about 10 minutes including landing time.
Trying to land with a dead battery is a really bad idea.

http://www.engineersedge.com/copper_wire.htm
Eyeballing the above chart, if I limit the lifting weight to about 300
grams, the largest wire gauge for 40 meters of wire would be roughly
18AWG leaving a little slack for an insulating line.

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.

If there's any danger of the pull of the copter snapping the wires, it
could be restrained with (say) thin woven nylon cord.

Hardly. If something goes wrong, I want the quadcopter to break the
connection and fly freely away, not get dragged into the ground by
some bird attacking the wire antenna. I would probably add some thin
fishing line as both an insulator, and as a safety feature, at the
point of attachment.

However, how would the intricate control circuitry in the copter cope
with the very high level of RF signal?

Dunno. I've never tried it near a BCB transmitting station. My
guess(tm) is that it will be ok. I haven't had it long enough to see
how it will deal with strong RF areas. I plan to use it for tower
inspections, which will certainly require substantial RF
compatibility. We'll see.

--
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 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
--
Ian

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

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