On 11/3/17 9:58 AM, Jeff wrote:
>> In one of the Polyphaser documents they talk about the rise time and
>> length of a strike duration. Forget the details but the conclusion
>> was that rods further out than about 50' would not be effective
>> because the strike would be over before the outlying rods came into play.
>>
>> If that's true then it seems there is an implied maximum density of
>> the field based on the 50' maximum radius for rods and the 2x rod
>> length spacing.
>Its a bit more complex than that..
>you've got what's really a weird sort of transmission line, so while the pulse
>from the lightning stroke at one end of your 50 foot line is >done, the wave
>is still propagating out. I guess 50 ft, if the propagation velocity is 0.1c,
>is about 1/2 microsecond, which is getting >towards the rise time, but not the
>fall time, of the lightning impulse.
Not only is it very slow propagation, but it is very lossy propagation as there
are streamers and corona and all sorts of other ugly things going on
underground along a radial. When I measured the velocity along a buried radial
at the lab I worked at I got about .5c, but it is not an easy measurement to
make and will vary with soil conditions. Our recommendation to utilities
ground hv lines was also about 50' for radials.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
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