Home |
Search |
Today's Posts |
#8
|
|||
|
|||
A Top Band 1/4 wave vertical?
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 |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Which is better: 5/8 wave vertical or J pole? | Antenna | |||
20m 1/4 wave portable vertical | Antenna | |||
New program - 1/2-wave vertical | Antenna | |||
5/8 wave 6m vertical | Antenna | |||
1/4 wave vertical vs. loaded vertical | Antenna |