[Elecraft] Automatic lightning protection for radios, .... an off the wall idea

[hb9cvq at hispeed.ch]

Yes, Jim,  but:  "It's also the kind of destructive failure that the use of
MOV surge protectors can CAUSE".

MOV can be used even in AC power applications (50/60Hz) , but only if the
potential thermal run away effect ( drawing more leakage current after
energy absorption/exposure or by aging ) is controlled by a series connected
high impedance (no-fire mode)  spark gap. What is however critical under
non-fire RF conditions (MOV -ZnO has big nF capacitance and is a
semiconductor) is the nonlinear diode effect. This can lead to RF
rectification (harmonics, emission issue)  before the firing level is
reached.

73 Andy HB9CVQ


-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
Behalf Of Jim Brown
Sent: Montag, 18. Januar 2021 19:16
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Automatic lightning protection for radios, .... an
off the wall idea

On 1/18/2021 9:09 AM, Bill Frantz wrote:
> While serious lightning protection for structures and other robust 
> things must be done outside the building, I have heard reports of K3S 
> USB chips being fried from currents induced in the USB cable attached 
> to the radio, with the suggestion of disconnecting the cable to 
> protect the chip. I don't see how to do this disconnect outside the
building.

Right. That is the kind of failure that proper grounding and bonding are
able to protect against. It's also the kind of destructive failure that the
use of MOV surge protectors can CAUSE.

> When I consider a direct strike on my shack's lighting rods, I see 
> massive currents flowing down the thick aluminum cables from the rods 
> to the grounding system. I see these currents inducing currents in any 
> wires in the house, including the USB cable. The lightning rods are 
> the first level of protection, but may not be enough to protect 
> sensitive electronic equipment. Remember, when we work on these 
> radios, we have a grounding wrist strap and a conductive mat on the work
surface etc.

That's another thing the proper grounding and bonding protect against. 
But lightning induces current not only on that external wiring, but also
wiring within the building. IEEE studies show that up to 3kV can be induced
on internal wiring by a strike!

73, Jim K9YC
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