Hey Pete,
As Rob mentioned this technique adds series inductance to the path of
lightning. What is more critical than even the loops is a low impedance
ground from the arrestor in circuit before the loops. If implemented
correctly the combined circuit delays the lightning pulse until the gas
tube establishes its plasma and lowers the voltage on the coax to that
of the tubes firing voltage (plus rise due to current through the
tube). An added benefit of the series inductance is the spreading of
energy over time, limiting the peak voltage seen by the transmitter.
In broadcast installations I have done this with large #31 ferrite cores
on the loops for added inductance as recommended by manufacturers. The
outcome after years in service has been a few destroyed gas tube
cartridges, but no damage to the transmitters.
Cheers & 73,
Howie / WA4PSC
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