Henry Kolesnik wrote:
QST March 2004 page 34, upper left hand corner mentions that at 100 watts
the voltage at the base of an 8 foot mobile whip could exceed 1000 volts and
arc over a CB-ball. Can anyone plase show me the math?

Assuming that an 8 ft. whip plus autotuner may be 0.5% efficient on 75m,
1/2 watt is reaching the 0.5-j2000 ohm feedpoint impedance predicted by
EZNEC. To get 1/2 watt into the 0.5 ohms requires a voltage of 0.5 volts
across the 0.5 ohms. It follows that the voltage across the -j2000 ohms
will be about 4000 times the voltage across the 0.5 ohms. So 4000 times
0.5 equals 2000 volts. That's obviously a ballpark figure but should
"show you the math".

On a damp morning at a 75m mobile shootout on the beach in CA, my 11 ft.
whip plus SGC-230 autotuner actually did arc across the antenna mount.

Question is: Why would anyone in their right mind tolerate 2000 volts
while radiating a measly 1/2 watt from a 100 watt transmitter?

Incidentally, that 11 ft. whip plus SGC-230 autotuner was a pretty
good mobile antenna system for 20m-10m.
--
73, Cecil http://www.qsl.net/w5dxp



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