On Thu, 29 Apr 2010 12:11:10 -0400, Dick Green WC1M wrote:
>While I'm a big believer in suppressors, the units on the market are
>designed for coax connections to radios and rotor cable connections to
>simple rotor controllers. But I don't believe that MOV-based devices are
>adequate for some of today's new solid-state devices like SteppIR
>controllers, advanced rotor controllers and advanced stack controllers.
Thanks for your detailed account. As to MOVs and other similar protection
devices. These are SHUNT MODE devices -- that is, they operate by
attempting to short out the lightning event, usually to "ground." In
addition to any issues with the protectors themselves, that "ground" itself
is a major part of the lightning damage problem.
The reasons are simple. First, lighting is not DC, it is a monster IMPULSE,
and any impulse has infinite harmonics. IEEE working groups have shown that
the ENERGY in lightning is broadly centered around 1 MHz, with strong
components several octaves (2:1 frequency ratio) above and below. In other
words, it's 100 kHz to 10 MHz.
Second, "ground" is not a single point, nor is the earth an ideal
conductor, and our connections to it have both resistance and inductance,
at at all frequencies above about 10kHz, inductance dominates the
Third, equipment is interconnected. So we have "grounded" towers,
"grounded" shacks, "grounded" telephone and CATV wires, and "grounded"
power entry, usually "grounded" at different points. These points SHOULD be
bonded together (short fat wires), but often they are not. So when a
lightning event hits, current tries to go to the earth in all of them, and
thanks to their impedance (mostly inductance), the voltage at every piece
of equipment rises to a DIFFERENT HIGH voltage. Another reason for the
DIFFERENCE is that any given strike couples more into one circuit than
another based on proximity.
Thus -- the single most important element of lightning protection is the
bonding together of all of their equipment grounds. The second most
important element is to avoid shunt mode protection and use SERIES mode
when possible. Series mode suppressors are only made for AC power. The only
mfrs I know of are SurgeX and Brick Wall. They aren't cheap, but those of
us working in pro audio learned about them at least 15 years ago and use
When we MUST use shunt mode protectors (rotor controllers, SteppIR, coax),
it is CRUCIAL that they be bonded to a very low impedance ground, AND that
ground is bonded to all other grounds in your home, AND to all of the
A major exception to the advice against shunt mode protection is at the
power service entrance -- whole house protectors use big shunt mode
devices, and they ARE a good thing IF properly installed with good bonding
of all grounds.
Jim Brown K9YC
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