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

[Bill Frantz]

I've been thinking about some kind of automatic lightning 
protection for radios, specifically ones like the K3 and K4. The 
idea is that when you turn the radio off, all the things that 
are subject to damage are protected by disconnecting them from 
the external world and shorting their inputs to ground.

This approach probably wouldn't protect against a direct hit to 
one of the wires coming into the radio, which are most likely on 
the antenna input and the power from a solar system. But I 
understand that the most significant part of the problem is 
voltage spikes introduced when the external wires act as 
antennas and pick up nearby lightning strikes.

I'm not a hardware engineer, so I'm going to assume that relays 
are used in this device. Some of the things I see this device 
doing are:

USB connection: Elecraft tells us that blown USB chips are one 
of the more common forms of lightning damage in the K3. There 
are 4 wires in the USB interface, two of which carry power from 
the external world. The relay(s) would float the USB wires and 
ground the connections to the internal USB chip. Since power 
from the external world is present when the radio is off, we 
can't ground the power leads, although we can ground the power 
input to the radio's USB chip.

Note that currently a computer attached to the K3 can see its 
USB chip, even when the radio is turned off. This change would 
mean that the computer would no longer see the radio over USB, 
which might have annoying software effects.

A similar thing could happen to the antenna inputs.

Key/Paddle, microphone, headphones, RS232, etc. would be treated 
the same way.

The AUXbus would be treated similarly, but anything that can be 
turned on via the AUXbus would need special handling.

The 12V power input is needed to turn the radio on with the 
power button. I don't know how often radios are damaged through 
their 12V power input. This input may not need protection. 
Otherwise, the relay that protects power and the switch to the 
radio could be the only things powered when the radio is off. If 
it can't be protected, it could be made easily field replaceable.

It would be neat if there's enough room inside a K4 to put this 
kind of protection "under the covers".

73 Bill AE6JV

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