[Elecraft] Lightening damage

[Gmail - George]

Rich,
Even massive grounding systems do not keep a tower from being hit! It only 
mitigates the damage.

I was CE of a TV station in South Florida with towers of 1,000' a couple at 
500' and several more at 100' to 200'. They all got hit at one time or 
other. Sometimes many times a year.
We used massive grounding systems with the tall towers. The towers we rented 
or on buildings - we had to take what we got. Some were excellent some were 
non-existent.

We operated 24/7 since 1955. We did have redundant equipment. We had two-way 
antennas as high as 900', microwaves from 100' to 950'. Tower cameras as 
well. The ENG receive sites (at 950' & 500') had very sensitive LNAs at 2, 7 
& 13 GHZ. as well as the pan/tilt steering electronics and drive systems. 
When possible we did not put electronics on the tower; because of the surge 
current of a direct strike.
A small (tiny?) strike will have over a thousand amp current surge. If the 
steel tower has a 0.1 ohm resistance, then the top of the tower is 100 volts 
above the bottom. Any electronics at the top that is connected at the bottom 
can have that potential on the equipment case (a DC ground loop  so to 
speak) of 100 volts. Most times it is much higher.

The least affected equipment were the microwave transmitters and receivers 
that used waveguide. The signal up and down the waveguide is transmitted 
rather then conducted.

We felt that the best money we spent to mitigate lightning damage were 
dissipation arrays on all of our towers higher than surrounding structures. 
Over a 10 year period our lightning damage costs were reduced significantly 
over the 10 year period prior to that installation. It seems that 
dissipation arrays are in dispute at this time.
It goes to the old adage - that just because you put out elephant repellent 
and then see no elephants still does not mean the elephant repellant works!

My 40 years experience in South Florida as a Broadcast Engineer has taught 
me that you will find the weakest links in your plant's structure and make 
them less vulnerable but never be completely immune to lightning damage 
unless you eliminate all conductors of electricity. Fiber interconnections 
between studios and towers really helped us reduce the losses.

73
George   AI4VZ

-----Original Message----- 
From: Richard Fjeld
... Certain radio and TV services need to operate 24/7 and can't shut down 
when lightening threatens.  Their grounding methods apparently prevent the 
towers from being hit .