chas wrote:
> Feeling sorry for those poor souls who moved out of the wrong side of
> the track neighborhoods and left their towers and antenna farms to go
> live in gated communities where they are trying to figure out how to
> put up a 20' piece of wire.... invisible wire is the question here.
>
>
> what is the minimum size or guage of insulated wire which can be used
> hooked up to a kilowatt amplifier?
>
> I live in a barrio (now, 20 yrs ago.. whole different thing) so I have
> either a king cobra or a dx-cc 12ga with grey insulation, etc.
>
> so I have NO problem running my SB-220 flat out thru the things.
>
> but what about 26guage wire? actually, that Cobra is three pieces of
> 26ga zipped together, 70ft on a leg suspended from a 35' center.
> it works just fine and seems to have great bandwidth.
>
> just curious. I know that some loops are made from magnetic speaker
> wire and are used for both RX and TX.
>
> anyone have an answer or a source?
>
how much loss are you willing to tolerate. A kilowatt into 50 ohms is
1000=I^2*50 -> I = sqrt(1000/50)=sqrt(20), about 4.5 Amps (RMS).
30 ga wire is 0.1 ohm/ft, a 40m dipole is 66 ft of wire (although the
current is only 4.5A at the feedpoint).. But.. at the feetpoint, you're
going to be dissipating 2W/ft. in free air, that probably won't melt
your AWG30.
Go to AWG24 (twice the diameter, 0.025 ohms/ft) and you're down to
0.5W/ft. Say the power dissipation goes down linearly (it doesn't but I
can do this one in my head), so the average dissipation is half, or
0.25W/ft. *66ft is about 16-17W total dissipation in the antenna.. not
a huge fraction of your kilowatt.
Something to think about is the human visual acuity. You can resolve
about 1 arc minute (1/60th degree), so something that is significantly
smaller is invisible. That's about 1 part in 3500.. that is if you're
3500 inches (285 ft) away, something 1 inch wide is just resolvable. For
a more practical distance, say, 50 ft, scale it. Something smaller than
0.15 inches probably will be hard to see. (easier when working metric..
1mm diameter, 3.5 m away) 1mm is AWG18, AWG24 is about 0.5 mm diameter
(closest wire gauges)
It's a bit tricky, because a wire is small in one dimension visually,
but long in the other, but the reality is.. a 24AWG wire is very hard to
see from 50-60 ft away.
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