Lightning Arrester
 

Anyone know how to make a simple lightning arrester (Homebrew) that really
work in case of lightning.

Hang up "STOP" sign.

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Anyone know how to make a simple lightning arrester (Homebrew) that really
work in case of lightning.

"Mohd Nazry Bin Mustapa" wrote in message
...
Anyone know how to make a simple lightning arrester (Homebrew) that really
work in case of lightning.


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.

NOTE: a lightning arrester WILL NOT WORK if you don't have a good ground.
IT IS NOT A REPLACEMENT FOR A GOOD GROUND SYSTEM! All a lightning arrester
does is limit the voltage difference between signal carrying wires and the
nearby ground it is connected to, you must properly connect all grounds
together to get any benefit from any kind of lightning arrester.

David Robbins wrote:
SNIP

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.
SNIP

Remember, there is still a significant voltage across the spark gap
before it ignites and during conduction. A 1/16 inch, or a 1.5 mm, gap
will sustain ~1000 volts before igniting and support several hundreds of
volts during conduction.

The best solution, disconnect all antennas when not in use.

DD, W1MCE

"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

| |
Antenna ---------+--------| |----------- To Radio
| | |
SPARK V Blocking
GAP ^ Capacitor
|
Ground ---------+----------------------

PS: The breakdown voltage of the capacitor should be
10 times that of the spark gap. For a 1KV spark gap,
that would give 10 KV.

JEB

There's no such thing. It's going to be a bit of work and money to do
anything effective.
"Mohd Nazry Bin Mustapa" wrote in message
...
Anyone know how to make a simple lightning arrester (Homebrew) that really
work in case of lightning.

K7JEB wrote:

| |
Antenna ---------+--------| |----------- To Radio
| | |
SPARK V Blocking
GAP ^ Capacitor
|
Ground ---------+----------------------

PS: The breakdown voltage of the capacitor should be
10 times that of the spark gap. For a 1KV spark gap,
that would give 10 KV.

JEB

2uF at 10kV, quite a capacitor. That would be 6 ohms or so on
topband. As I understand it, there is nothing that can work if
a direct lightening strike occurs. We are talking megavolts and
thousands of amps. Way beyond anything an amateur could build.
The best we can hope for is to dissipate charge build up on the
aerial and ensure that there is no more than a kilovolt or so at
the input to the rig caused by the (field) effects of a nearby
strike. A spark gap that can conduct a lightening strike would
be the size of a small truck.

The only way to make sure you have a working station after a
lightening strike on your aerials is to take out good insurance.

vy 73

Andy, M1EBV

Mohd Nazry Mustapa wrote:
"Anyone know how to make a simple lightning arrester (Homebrew) that
really work in case of lightning?"

I`ve found shorted (folded) antennas are less susceptible to lightning
overload than are open-circuit antennas.

A folded VHF monopole fed by coax and well grounded at the tower top is
nearly immune to lightning.

Coax, inside, rejects common-mode propagation of lightning energy. Coax,
outside, needs good grounding to make a good path around (bypass for)
protected equipment.

The equipment needs direct low-impedance grounding so that most surge
energy is dropped across the coax, not the equipment.
Coils of extra coax may be used to raise the impedance of the outside of
the coax.

Equipment is still vulnerable to excess differential voltage on the
power wires. Perhaps, excess common-mode voltage too. Manufacturers make
brute-force L-C pi-network low-pass filters for each power wire
connected to the equipment. These can be homebrewed if desired. They are
important in delaying the surge on the power source lines to give time
for the arresters time to spark across, giving protection to the
equipment. Arresters need to be fast acting and placed to protect
line-to-line and line to ground. These low-pass filters and arrestors
are suitable for power and control wires, not for antenna wires in most
cases. I`ve used lots of gas tubes on audio and control lines but never
on a coax cable where I believe they are superfluous.

I`ve used tower lighting RF chokes for the inductor in the low-pass
powerline filters to get the needed current carrying capability, and
various breakdown devices on the input and outpur of the filter. MOV`s
work well. They are fast and cheap but may require replacement at times.

Power lines are susceptible to dangerous surges. Filters reduce the
bandwidth of energy that must be handled by the suppressor, just as the
folded antenna or short-circuit 1/4-wave stub across an antenna limits
the bandwidth of lightning energy that it has to accept.

Lightning and other related surges are just enormous noises. They can be
suppressed with the same techniques used with weaker noise. The
equipment must be sturdy to endure a lightning strike. Arresters may be
compared to sturdy noise clippers.

Best regards, Richard Harrison, KB5WZI

Effective lightning protection can be done in the amatuer station for a
reasonable cost. Most though, don't do so.
"Andy Cowley" wrote in message
...

As I understand it, there is nothing that can work if
a direct lightening strike occurs.