Pete Smith wrote:
>
> It's lightning season again around here, and ...
>
> Polyphaser and ICE make much of the ability of their line protectors,
> properly installed, to protect against lightning hits even if the lines
> remain connected throughout the event.
[snip]
> Fine so far. But if the base of the tower is well grounded (multiple rods
> and radials, properly connected to the tower base), but it's several
> hundred feet from the tower base to the house, I question whether it's
> really possible to keep that ground and the house ground at the same
> potential, with any reasonably-sized conductor between them. Moreover, my
> shack is on the second floor, which would make it very hard to have a good
> low-impedance ground connection at the bulkhead.
[snip]
In the early 80's I spent an entire summer installing lightning
protection on mountain top repeaters and remote bases. For the coax we
used Polyphaser protectors, on the AC (where we had any) we used
Motorola branded secondary surge arrestors, and across the DC supplies
we used Transtector silicon avalanche diodes (SADs). We made sure that
each site had a single point ground and installed DC grounded antennas
where we had the non-grounded variety. On a wireline tone-controlled
remote base, I installed back-to-back SADs across the telco dry pair,
and between one side of the pair and ground--four SADs in all.
Several sites presented difficulties similar to Pete's. In some cases
our equipment was a long way from a decent ground. In other cases there
were other users present, who did not have a comprehensive lightning
protection program, with installations guaranteed to conduct any strike
into the common equipment room.
In these cases I chose to create a mini protected environment within our
equipment cabinet as much as possible. Battery chargers and batteries
were moved inside the radio cabinet. Secondary RF and AC entry panels
and protectors were installed directly on the cabinet. VHF duplexors
which were too big to fit inside the cabinet, were mounted and bonded
directly to the side with the coax run directly back inside the
cabinet. A single heavy ground wire was run back to the nearest
building ground. In essence, we created a site within a site.
Our idea was to protect our equipment if a strike came into the building
riding someone else's wiring. We knew that the strike could create
differences of potentials of thousands of volts between the equipment
cabinets. Our hope was to keep it as low as possible within the
confines of our own equipment cabinet--hopefully preventing any damage.
It seems to have worked. After completing the program our lightning
losses dropped dramatically. Of the post installation strikes while I
was still around, I can only recall three that impacted operation. One
took out the first RF amp FET (only) on a Radio Specialties repeater.
One damaged a Polyphaser protector itself, reducing its site's coverage
area--although the radio was undamaged. And lightning came in through
the telephone lines (ignoring the 110 foot tower) at our site with the
tone-controlled remote base. There was no damage to the radio but the
telco pair was literally vaporized off of the wall right up to the point
where I had installed the four SADs. All the other users in the
building were down with extensive radio damage.
73
Malcolm KR4HP
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