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Old December 11th 03, 05:47 PM
K7JEB
 
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"Mohd Nazry Bin Mustapa":
Anyone know how to make a simple lightning arrester
(Homebrew) that really work in case of lightning.


"David Robbins":
the most basic one is a spark gap. these have been
used since the first days of long telegraph lines.
just position two sharp pointed metal pieces a small
distance apart, connect one side to the cable and the
other to a good ground. you want the distance as small
as possible, but wide enough so your normal transmission
power doesn't create an arc.


The usual practice for radio antennas is to place
a series capacitor downstream (towards the radio
set) from the spark gap to dispense with the DC
and low-frequency components of the lightning strike.

In crude, fixed-pitch ASCII art, it would look like
this:
| |
Antenna ---------+--------| |----------- To Radio
| | |
SPARK V Blocking
GAP ^ Capacitor
|
Ground ---------+----------------------

The size of the capacitor is a compromise between not
disrupting the RF circuitry and coupling the low-frequecy
energy from the strike into the radio. Making the
capacitor reactance in the order of a few ohms at the
lowest operating frequency generally should work for
50-ohm coax.

Jim, K7JEB, Glendale, AZ