Tony, The normal way is to use a spark gap set to 1/16 for 100 watts or more
depending on your power level. It should never arc over during transmit.
The spark gap is grounded to a GOOD outside ground. There are also gas
discharge tubes that can be fitted to open wire line, but cost more. The old
military command sets used a NE2 (neon bulb) on their receiver inputs. Use
at least one 8 foot ground rod and preferable 3 set about 8 feet apart and
connected with ground rod clamps (or better yet with cadweld at about $5 a
connection - but it is permanent) using with #4 Bare Copper wire if your
soil is neutral or alkaline or #2 aluminum wire if it is really acid soil in
which case the ground rods should be galvanized instead of copper finish.
The water pipe ground is not necessarily a good ground and is certainly a
high impedance ground to lightning.
I have set and watched the spark gap arc almost continuously during a storm
on antennas that were only 30 feet high on open wire line not connected to a
grounded balun (which is what you will have when the knife switch is open).
Have also watched a 2 meter beam corona almost continuously off of the tips
during a storm, so the problem is very real. If the tuner uses a grounded
center tap primary on the balun, that is a good secondary ground but should
not be used as your primary protection. I would still use a ceramic knife
switch on the rig side of the spark gap and open it up during storms. By
the way, the telephone line takes out the most equipment, followed by the
power line, followed by your antennas system. I have had the front end of
my receiver blown (FET) without even knowing anything was happening.
It doesn't take much to cause a problem. Lightning took a direct hit on our
house when I was about 15 and a ham. It hit the TV antenna that was on the
house, vaporized the small aluminum ground wire from the outside knife
switch that disconnected it from the TV, picked up a #14 wire that was being
used as a trellis, followed it for 30 feet, knocked a 12 inch diameter hole
in the house and knocked off the kitchen cabinet, went to the kitchen sink
drain and melted all of the lead out of over 70 feet of cast iron drain
pipe. My equipment was in another room and was not hurt in any way. It was
all tube type, though.
[mailto:email@example.com]On Behalf Of Tony Casciato, AI9X
Sent: Friday, August 02, 2002 11:05 PM
Subject: [Towertalk] Proper way to ground open-wire feeders
I have been enjoying this list, especially recently with all the text about
grounding. My question is about how anyone is grounding 450-ohm line as it
enters the house. My antenna is only up about 30 feet, so maybe not a big
lightning risk, but I am concerned just the same. I did have the line coming
in a basement window, then a small knife switch with one side connected to
the cold water pipe - I was uneasy about bringing lightning inside for that.
1) Manually disconnect outside the basement window, then connect both wires
to a ground rod about 4' away.
2) Leave connected all the time, since the tuner's balun is grounding the
line to the house ground.
3) Leave connected, but put some sort of ICE or spark-gap device outside
connected to ground rod.
4) Replace the 30' high doublet with better antennas (Sigma vertical clones)
and use coax.
5) Go back to the knife switch and cold-water pipe ground inside.
Again, since the tuner does ground the line, is it worth worrying about at
all? If I put a seperate ground rod outside, doesn't a strike propagate to
the house wiring grounds (which the radios' are connected to for RF)? Is
that a ground loop then?
Sorry for the bandwidth, but I have been fussing over this for a while. I
like using open-wire especially for a small city lot and multi-band
operation. I don't have a lot of space or finances, so simple antennas are
used for now. I am always thinking of better approaches, and might this year
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