"RJ" wrote:
Years ago ( when I was a young SWL )
my radio antenna was protected with a "lightning arrester".
As I remember it, it was a glass "brick" with three terminals;
ANT; GND; and RCVR
It was filled with neon, so it'd glow with electrical discharge.
I'd like to add lightning protection to my new antenna,
but I'm having a heckova time finding "lightning arresters".
At best, I see listings for "surge protectors".......
and, as I understand it, these are a one-time protection,
which counts on burning out a "mov-diode" for the first strike.
( as for subsequent strikes ???? )
Any sources ?
rj
Yikes! An on-topic post! What to do, what to do... :-)
While power line spike supressors do use MOVs, I don't think
you'll find them used in RF applications. They aren't one-shot
(unless you take a direct strike), but they do degrade over time
from each strike, eventually shorting out.
As for the term "lightning arrestor," it was just a case of a more
appropriate name being taken. Most surge protectors/spike supressors
cannot handle a direct strike. HOWEVER, THERE ARE EXCEPTIONS!
The best known and most commonly available of these are from
PolyPhaser corporation. The next most available to the SWL are from
I.C.E. (Industrial Communications Engineering).
The Polyphaser model I'd recommend for SWLing or low power
transmitting is IS-B50LU-C0 or IS-50LU-C0. (The "B" version is a
thru-hole bulkhead mount; the other is a flange mount.)
This next sentence is very important, so read it until you can see it
on your eyelids at night: A SUPRESSOR WILL DO NOTHING IF IT IS
INSTALLED IMPROPERLY!
What does that mean? Well, the best way to deal with lightning
strikes is to create what is called a "ground window" -- basically a
sheet of copper or other conductive metal -- to which all lines to
your "protected" gear must pass through supressors on that sheet. Use
120 VAC to power your radio? There must be a good supressor on that
ground window for it. Use a computer? Either protect it or run the
data line from the radio through a supressor. Protecting the computer
but connecting by cable/phone-line/etc. to the internet? Put a
supressor on that line.
Again, an important sentence: Even one wire -- an extension line, a
phone line, whatever -- bypassing that ground window renders it
useless.
Now, not to be too obvious, but the ground window needs to be
grounded! I'm not talking about an 18AWG wire to a 3 foot RS
ground rod, I'm talking multiple ground rods spaced twice their
length apart, connected with copper *strap*.
Now, "doing it right" can be expensive, but it's cheaper than the
damage to your radio. You can also do it a step at a time. For
example, you may want to put together a suppressor and a ground
window and a single ground rod. That will protect you from a lot
of near misses but not a direct strike. Get more ground rods in --
3 or so, bond them all to a single point, bond the house ground to
that (it's the law!) and shoot for a good powerline supressor or
alternate means of powering your radios, like gel-cells.
You can get the supressors direct from Polyphaser, I think, or from
Hutton Electronics, Electro-Comm, Cable-X-Perts, or Ham Radio Outlet.
You can get a catalog from Polyphaser and get an idea on what they
provide.
There is a myth about lightning that nothing can save your gear from a
direct strike. That is blatantly untrue: Cell towers and radio/TV
towers get hit all the time, and if they are properly installed, they
stay up through a strike. But the attention to detail required is
substantial. As an example, running a coax down a tower then at the
8 foot level running it into a building is a disaster waiting to
happen; running the coax down to the base of the tower, bonding the
shielding to the tower leg at the base, then back up the wall of the
building to run in is safe.
hope some of this rambling helps...
Eric
--
Eric F. Richards,
"Nature abhors a vacuum tube." -- J. R. Pierce, Bell Labs, c. 1940