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

[Jim Brown]

On 1/18/2021 11:53 AM, hb9cvq at hispeed.ch wrote:
> 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.

There's FAR more to it that these issues. The problems include 1) where 
they dump the current when they short out a strike; 2) accumulation of 
discharge current over time degrades their performance, causing them to 
fail shorted or open; and 3) they can start a fire! When an MOV shorts 
the strike to the equipment ground ("green wire") it raises the chassis 
potential of connected equipment; when that equipment is connected to 
other equipment by "low voltage" wiring (audio or video cables, Ethernet 
or other computer cables) to equipment plugged into different outlets 
(or even a different MOV device), the potential difference between the 
two pieces of gear is likely to fry I/O circuitry.

Many years ago, we in the world of pro audio learned this, with 
equipment for large audio (that sometimes included video systems) spread 
out over wide areas. As long ago as the '90s, very well-educated EEs 
recounted stories of computers in their design offices networked by 
wired Ethernet being fried by lightning induced on the Ethernet cables 
and computers with MOV surge protectors. No intentional antennas 
involved (not hams).

All of this is a great reason for using WiFi rather than wired Ethernet 
unless the added latency of WiFi cannot be tolerated (remote operation, 
for example). I dumped the use of wired Ethernet a couple of years 
before moving from Chicago in 2006. Decent WiFi hardware provides plenty 
of bandwidth for my uses, including streaming audio and hi-res streamed 
compressed video.

73, Jim K9YC