[TowerTalk] what size wire for kilowatt TX ??

[Martin Ewing]

Chas,

A little math shows that 5.5 Amps rms into 50 ohms is 1.5 kW.  My handbook
says the DC "fusing current" of #26 copper is 20 Amps.  RF skin effects
increase the resistance (perhaps by 5X at 10 MHz) and heating (25X).  But
you're not going to have 5.5 Amps continuous.  For SSB, the average power is
going to be much less than 1.5 kW, so you might squeak by, assuming the SWR
isn't too bad.  I wouldn't use insulation.  All in all, #26 wire would be a
poor choice for high power -- but hams have been known to try these things.
Note that the current is normally greatest at the feed point and decreases
toward the ends of a half wave dipole.  So you could taper the wire size
down toward the ends.

It might glow red, melt, or start a fire. If so, use a larger gauge!  Also,
whatever power comes out as heat is not being radiated as RF.

This all assumes you're talking about a full size dipole.  If your antenna
is more like a short whip, the current in the wire is much less, since it is
a high impedance antenna.  Then, your problem is in the antenna
tuner/coupler and ground system, where there could be high losses.

73 Martin AA6E

On Fri, Jan 2, 2009 at 11:04 PM, chas <chasm at texas.net> 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?
>
> thanks
> chas, k5dam
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-- 
Martin Ewing, AA6E
Branford, CT