[Fwd: LF: Kites]
Tue, 09 Jun 1998 10:29:28 -0400
Peter Martinez wrote:
> >From Peter Martinez G3PLX Kendal Cumbria.
> To answer Mike's question about the relative merits of line plus wire
> or wire line, my experience is that trying to have the kite tethered by
> a nylon line from one point on the ground and drop the antenna wire
> vertically to the feedpoint, is too difficult to manage operating
> single-handed. It can be done, but the object of the exercise is to
> play with radios not with kites! Furthermore, if the kite sinks a bit,
> the antenna wire can drop to the ground, going badly off-tune,
> get hooked around things on the ground, and then when the kite
> rises again, it snatches the copper wire tight again with a sickening
> twang. So I have until today operated with only one anchor-point.
> However, I have not been able to find wire strong enough to use as a
> single line. Copper is just not strong enough. Steel wire, although it
> is strong enough and it's resistance (40 ohms for 100m) is low
> enough (It only needs to be lowish compared with the TOTAL
> coil+ground losses), it's stiff and almost impossible to reel in and
> out without kinking and breaking. Electric fence wire looked
> promising, being polypropylene with embedded wire strands, but the
> wire is stainless steel, and 100m of it has a resistance of 700 ohms!
> So until today I have used nylon line and copper wire, on separate
> winders but both anchored at the feedpoint. I put up with the fact
> that the copper is not vertical and indeed the bottom end is often
> about 45 degrees to the horizontal, curving up in a catenary to the
> kite, while the nylon line which is carrying the tension, is straight up
> at 60 degrees. Its still a lot of work to launch and recover
> single-handed, and gives my signal some QSB as the kite moves
> What changed today was that I had the idea of fitting a pulley at the
> kite, fastening the nylon and the copper in series and winding the
> lot, copper first, onto one winder. I pass the end of the nylon through
> the pulley so that I start off with a double length of nylon. This is
> easier to launch in a light wind since the kite only has to lift the light
> nylon and not the heavy copper when it is close to the ground where
> the windspeed is lower. I then secure the free end of the nylon to a
> point on the ground about 400ft upwind of the feedpoint and unreel
> first the remaining nylon and then, with the kite pulling stronger than
> near the ground, the heavier copper follows it up.
> The pulley means that the copper is always in tension and can be
> set nominally vertical. If the kite sinks, copper is drawn through the
> pulley giving me an inverted-L with the vertical section tilted slightly
> downwind. When the kite rises nylon is drawn through the pulley
> giving me a vertical tilted slightly upwind. The capacitance should be
> fairly constant.
> Using this technique I should be able to operate with northerly
> winds, so you should hear me on more often.
> My kite design is still available as a .DOC file if anyone else would
> like a copy.