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Old September 20th 04, 01:19 AM
Reg Edwards
 
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"Bill Turner" wrote
The voltage at the ends of a half wave dipole can reach thousands of
volts even with relatively low power. Trees have been set on fire with
as low as 100 watts. Be careful!

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Hi Bill,

A half-wave dipole is a resonant tuned circuit.

A 40 meter dipole using 14-gauge wire has a Q of about 11.

At 100 watts there is 85 volts at the feedpoint.

The voltage between the ends of the antenna is 85 times Q which equals 956
volts.

Therefore, the voltage between one end of the antenna and ground is only 478
volts.

And this falls to a much lower value when the end of the wire is in contact
with anything by virtue of the very high antenna impedance of around 1500
ohms.

Furthermore, the antenna is immediately detuned when it comes into contact
with anything and Tx power falls.

From where do you get your "thousands of volts" - the old wive's monthly
magazines?

There are far more Californian forest fires caused by arsonists than 100
watt transmitters. Fortunately, it doesn't seem to have a bad effect on the
quality of the wine.
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Reg, G4FGQ