Hi Bob,

It takes about 100 volts for the neon tube to strike. The back to back
diodes in the receiver antenna input should protect against this. The
duration of a lightning strike is so brief that insufficient heat will be
generated to destroy the diodes.
BUT
The neon or any spark gap protection device cannot protect against a direct
lightning strike, only a near miss.

Shorting the coax centre to the braid may not be good electrical practice
but will provide sufficient protection for all practical purposes against
static build up and lightning strikes within around 100 yards from your
antenna.

When at sea in the merchant navy a similar system did withstand a direct hit
while I was in the radio room. The whole room lit up with a blue glow and
there was a terrific crash from the antenna switching box as the strike
arced to the ground through the ship's superstructure. Probably helped to
have 20,000 tons of steel in contact with the ocean!

The receiver (Marconi Apollo - wadley loop tuning and digital frequency
readout on nixie tubes) blanked for about 5 seconds and then came back.
Marconi know how to build stuff in those days. :-)

Any protection is better than nothing, a spark gap (old automobile spark
plug) or small neon tube, a couple of back to back diodes and a 5 megohm or
higher resistor across the diodes to provide a static discharge path will do
the job for pennies.

Regards

Mike G0ULI

"Robert11" wrote in message
...
Hi,

Saw a picture somewhere of an in-line lightning protector for a HF radio
receive only antenna.
Coax style.
Apparently has the typical gas tube, and when activated shorts the center
conductor to the braid.

Was wondering a bit about this.

I seem to remember in the old days, there was always a third tap on these
sort of things that you ran a solid ground to, e.g., a water pipe.

Does merely shorting to the braid provide "good" protection ?

Any thoughts would be appreciated.

Also want to ask: what about voltage surges of a few hundred volts or so
induced on an antenna lead from a nearby lightning strike perhaps
.
The levels way below what would trip a gas tube I would imagine, but still
more than enough to ruin a front end of a receiver.

How does one protect against these without breaking the bank doing so ?

Thanks,
Bob