On 7 Nov 2005 14:00:56 -0800, "SpamHog" wrote:

I am very tempted to use either a toroid or a couple of ferrite rods
with 1:1 windings made of... spark plug wire?! The stuff takes 30kV
pulses without even blinking, If I use non-resistive type, an
appropriate container, and keep it all dry, breakdown voltage between
incoming and outgoing coax could exceed 50kV. A low-ohm, low-Z
grounding could help ensure that it's not easily exceeded.

The real question is the grounding impedance.

You might even be able to measure the grounding resistance at DC or
50/60 Hz, but measuring the grounding impedance at a few hundred kHz
might be a bit problematic. Assuming the direct lightning hit is about
10-30 kA, a grounding impedance of only 1 ohm would create a potential
difference of 10-30 kV.

I do not know your mains wiring practises, but assuming that a
separate mains grounding electrode is used for each house, the
grounding impedance should be measured between the antenna ground and
house ground. If not, the grounding impedance should be measured
against some distant point.

Assuming that the house has a separate grounding electrode and your
antenna will get a hit, which is conducted to ground. Due to the
finite ground resistance, the house grounding electrode will move to
an elevated potential (several kV) compared to the surrounding (mains
neutral, telephone and CATV).

Thus, I think that the 50 kV isolation between your antenna and
receiver is more than enough and I would guess that more damage would
be caused due to the mains neutral, telephone and CATV connections to
your equipment.

Paul OH3LWR