Basic strategy

Tom Horne wrote:
On Sep 28, 10:20 am, "Rick" wrote:
How does one protect against these without breaking the bank doing so ?
Go on Mousers web site and look at gas tubes made by Littelfuse. Go to
Littelfuses web site from the link on Mousers site and check out the specs
on gas tubes. Compare them to the specs on your $50-70 commercial lightning
arrestor.
Then note that what's in that little casting box is two coax connectors, one
capacitor and one $2-3 gas tube and you have the answer to your question.
Myth revealed.

Rick K2XT

Rick or anyone else for that matter.

Can anyone suggest a strategy for reasonably safe operation of a
station when lightning is actually present in the area. The stations
located at the weather service offices are used to receive real time
weather reports from AROs. If they go off the air during lightning
events the whole network becomes useless to the weather service.
Television and radio stations continue to operate even after direct
strikes to their antennas so it must be possible to provide protection
that does not involve shutting down when lightning is present. Can
anyone draw me a written sketch of how that gets done so that I can
make a more knowledgeable decision on whether or not to try to
replicate the technique.

--
Tom Horne

Hi Tom. In general, remember that all lightning strike issues, from cloud to
ground or .. ground to cloud, depending on how things develop focus on on
thing. The radio wave which is produced by the affair is trying to distribute
itself over the surface of the earth in the area of the strike point.

Recall that radio waves travel over the surface of the conductor involved.
Thus, for example, the tower, pole, tree, building or whatever is the strike
point is a conductor, good or bad, which is going to be used to carry the wave
to the surface of the earth at that point. Then the wave expects to travel
outward on the surface of the earth away from the focal point of the conductor
until the energy of the wave is used up.

OK, think this way. A more or less usual lower frequency tower for an AM
station in the 500-1650Khz band is actually built so that the metal tower is
directly grounded at the earth surface. At the 1Mhz point, the tower height
for a quarter wave tower is around 250 feet high. Actually, at the bottom of
the tower there is usually a metal plate that spreads out over the surface of
the earth that is tied to the tower bottom, (Legs?). As well, for transmitter
antenna purposes, there are also a more or less standard 120 copper wires that
go out like spokes in a wagon wheel at or just below the surface of the earth
there too.

That means, very much surely, any lightning strike which hits that tower has a
WONDERFUL way to go to the surface of the earth, then spread out over the
surface away from the tower. The trick at this point is to keep the lightning
strike from going on into the radio station from there. On a quarter wave
length high tower, the conventional way to couple the transmitter to the tower
is at the base to move out a little way from the tower, go up a little way with
a separate wire, then couple the feed line to the tower via what is called a
shunt feed system. It typically has a capacitor in series with the coaxial
cable center conductor. And .. in all cases, the cable that goes back to the
station will be close to or .. even in some cases under the surface of the
earth for that run.

The lightning protector will be out at the tower and will arc or flash the
lightning bolt that might go down the feed line to the station so that it
shorts the feed line for that split second for SURE to the earth and that
collection of the metal plates and radial wires that make SURE the strike out
over the surface of the earth and NOT back toward the station. As well, there
is usually another lightning protector which does a similar job back where the
feed line goes into the station as well.

Using this technique, sure for a split second the station signal is shorted to
ground when the strike is there. But it does NOT affect the station.

Now .. fast forward to VHF TV, FM stations and HF shortwave stations. For
towers for FM or TV stations, they may be MUCH higher, But the feed lines for
the antenna or antennas on them are brought down the tower to GROUND level.
There they are also put through lightning protector devices that do the same
stunt of shunting the strike to the EARTH at the bottom of the tower. Then,
the feed lines are send back to the station at, again, a same low level which
protects them from carrying in the strike back to the station, as above.

Variations of this sort of design are also present in on-building antenna
systems that are done right to protect the equipment from strikes. One way or
another the design ALWAYS should provide a VERY GOOD electrical path from the
antenna to the earth, that is designed to have enough metal SURFACE to get the
hit down to the earth without burning the conductor up. And again, this
travels on the SURFACE of the wire, metal strip, pole or whatever.

Bottom line. You always create a really good metal surface conductor that
shunts things to the earth. And connect the feed line(s) for the antenna so
that they are isolated from this good path to ground by bonding the shielding
to the earth bound system, while providing a lightning protector to guarantee
that the hit will pop to the ground bound side on a hit, while positioning the
feed line so that it is a much less attractive path for the hit to go in to
take down the equipment at or in the building.

There are other things that are also of importance to a radio operation for
protection from power line connected strikes, as well as overhead phone line
strikes and copper wire cable system connections too. But, in general, the
same details as above are in place for them too.

My HF site gets hit at least two or three times directly every year. I operate
right through thunderstorms, whatever in contests and have for decades now on
40 and 80 meter CW. With additional protection for the equipment this site is
up 24X7 and hasn't lost a single radio, computer, modem, or ANYTHING for over
30 years now, though I also know enough to use isolation transformers and
linear power supply computer systems, plus very carefully planned relay rack RF
ground and surge protection techniques that do *NOT* use switching power supply
CD voltage operations for computers and so on.


W5WQN

--


-- Sleep well; OS2's still awake!

Mike Luther

Tom Horne wrote:
Can anyone suggest a strategy for reasonably safe operation of a
station when lightning is actually present in the area. The stations
located at the weather service offices are used to receive real time
weather reports from AROs. If they go off the air during lightning
events the whole network becomes useless to the weather service.
Television and radio stations continue to operate even after direct
strikes to their antennas so it must be possible to provide protection
that does not involve shutting down when lightning is present. Can
anyone draw me a written sketch of how that gets done so that I can
make a more knowledgeable decision on whether or not to try to
replicate the technique.

Got to polyphaser's web site, read their white papers and contact them.
Between them and Trans-Tector (they recently merged), they do antennas and
power lines for things like air traffic control centers.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

"Tom Horne" wrote
...
On Sep 28, 10:20 am, "Rick" wrote:
How does one protect against these without breaking the bank doing so ?

Go on Mousers web site and look at gas tubes made by Littelfuse. Go to
Littelfuses web site from the link on Mousers site and check out the specs
on gas tubes. Compare them to the specs on your $50-70 commercial
lightning
arrestor.
Then note that what's in that little casting box is two coax connectors,
one
capacitor and one $2-3 gas tube and you have the answer to your question.
Myth revealed.

Rick K2XT

Rick or anyone else for that matter.

Can anyone suggest a strategy for reasonably safe operation of a
station when lightning is actually present in the area. The stations
located at the weather service offices are used to receive real time
weather reports from AROs. If they go off the air during lightning
events the whole network becomes useless to the weather service.
Television and radio stations continue to operate even after direct
strikes to their antennas so it must be possible to provide protection
that does not involve shutting down when lightning is present. Can
anyone draw me a written sketch of how that gets done so that I can
make a more knowledgeable decision on whether or not to try to
replicate the technique.

Here are the two ways.

1. Provocation of lightning strikes, or
2. Eliminating of lightning strikes.

The instalation are the same only "tipping" is different. The blunt
provocate and the sharp eliminate.
Which is better I do not know.
S*