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Eric[_6_]

wrote:
In alt.engineering.electrical Eric wrote:

| I can attest to vhf/uhf content in lightning strikes. I worked for a
| communications outfit. We owned and maintained a number of comm sites
| with towers and antennas. One strike on an antenna destroyed the LDF rf
| cable all the way to the polyphaser at the bottom of the tower. It had
| blowouts at about 1 foot intervals all down it's length suggesting a
| 1/2 wave of about 1 foot or approx 460 mhz. That's one hell of a lot of
| energy at that frequency..

Apparently you had some kind of resonance involved. Maybe the antenna itself
can cause that. Or the output tank circuit in the transmitter. Once you have
the resonance to narrowband the energy, it would only take a reflection back
up the line and you turn a propogating surge into standing waves.

Pretty much what we determined. Also in another thread I stressed that
the rise time by itself does not determine frequency content. One needs
to know the rate of change, or slew rate, to determine that. A
lightning pulse may have a rise time of 1.2 microseconds but in that
short time the current can rise to thousands of amps, generating a large
amount of vhf,uhf energy.
Eric