Richard wrote:
> >
> >
> >Richard wrote:
> >
> >>
> >> ? I use a Hertz antenna (end-fed multi half-wave; high feed-Z). Equal
> >> currents flow into the antenna and the antenna tuner ground. The lead to
> >> the ground system is 5' of two-inch wide copper strap (c. 200nH of
> >> inductance). Thus, there is an RF voltage drop across the tuner ground
> >> lead. If the tuner ground is connected to the radio ground, the radio
> >> becomes hot with RF. I installed a coaxial choke balun to prevent RF
> >> from going back to the radio.
> >
> >If you got an 18 kA lightning strike the voltage on the ground at your tuner
> >would rise to around 18 kV due to the impedance of the 5 foot ground lead.
> >That is assuming you had a perfect ground at the other end of the strap.
> >
> ? 18kV is a semi-reasonable assumption,Gary . However, an 18kVpulse of
> c.100kHz RF on the tuner case should not be a problem since the antenna
> tuner is isolated from the amplifier with a 30uH, air-core coaxial
> choke-unun. Also. the Hertz antenna has a 300k-ohm shunt resistor to
> ground to bleed off static-charge build-up during thunderstorms.
>
> cheers
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
> www.vcnet.com/measures.
> end
You may or may not be all right. Being that lightning is a constant current
source it is going to develop it's strike current no matter how high it has to
raise the voltage to get to the strike current. 30 uH will still want to pass
about a 15th the strike current. That would be around 1.2 kA through your choke.
Then the other problem is that it is a big coil setting there that will also be
charged by induced current from the ground strap, tuner etc. Much more so than
if
it was just a straight piece of coax.
You are doomed. :>)
73
Gary K4FMX
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