[TowerTalk] Conductive Concrete and Grounding

[K8RI on Tower Talk]

>> Although lightning is DC (static electricity) is does tend
> to "ring" with a
>> strike consisting of both positive and negative current
> flow.
>
> Even when flowing in one direction a waveform can contain
> multiple high frequency components and act just like AC.
> Lightning can never be treated like DC.

I agree.  The fast rise time creates a wide range of frequencies.  The 
amplitude does drop off rapidly with frequency, but I believe it is still 
strong at 1 MHz and can be heard up into the microwave range.
Like any wave with fast rise and fall times there is a lot of power outside 
the primary range if memory serves.


>
>> The latest, or at least one of the latest theories is the
> super strikes are
>> a downward current flow receiving power from sprites which
> cover a wide
>> area.  Strangely enough these are a higher percent of cold
> weather
>> lightening than that associated with warm, or hot weather.
>
> That's when it hit here. During an ice storm.
>
>> Supposedly the regular strikes of a strength that can be
> managed, while the
>> super strikes are a tad beyond our abilities at present.
>> So, taking precautions should mitigate damage from the
> lesser strikes, but
>> with the super strikes you can only hope for the best.
>
> Not true. I had a strike that hit my 300 ft tower. It melted
> the shield on 7/8th inch heliax and melted the telephone
> wires from the street to the house. It did not damage my

I do think the majority of damage comes from either the power or telephone 
lines and not the antenna system.

> modems or anything else inside any building, including a
> GAsFET preamp on a repeater that was on that 7/8th inch
> cable AND I don't have a single Polyphaser or other
> lightning protection device on any feedline.

I had one hit on the old tower that blew off all the water proofing and even 
removed the plating from every connector at the top of the tower.  It left 
the repeater antenna looking like an exploded cigar, but did nothing to the 
old TH-3.  It did take out the front end on one 2-meter receiver and blew 
out the 7/8" heliax about 30 feet below the top of the tower.  It didn't 
hurt the old repeater.

That tower only had about 8, 8' ground rods and roughly 150 to 200 feet of 
bare #2 for a grounding system.  It was also at the back of the garage which 
meant the ground system was not symmetrical with nothing to the East.  Then 
again, it was a painted tower which would have had fairly high resistance 
between sections.

I some times wonder if the added insurance of the poly phasers is worth the 
effort.

Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com