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