[time-nuts] Aerial coax downlead placement

[Gerhard Hoffmann]

Am 05.07.19 um 23:26 schrieb Poul-Henning Kamp:
> --------
> In message <28F942E8-B61D-4FA5-929D-923184828FC1 at n1k.org>, Bob kb8tq writes:
>
>> Energy flow is indeed inside the cable if things are set up and operating correctly.
> Please note in this context that *nothing* about lightning strikes
> works the way you would assume it does.

A friend of mine got his ham radio station pulverized by a lightning

hit in the garden. He had written his PHD thesis on the breakdown

mechanism when charge powers its way through gases.

I call that an a posteriori field research addendum. ;-)

> Cables run inside steel tubes protect the steel tube from lightning
> current because copper is a better conductor than steel - in
> particular when the leading flank is measured in kV/uS and the
> current in kA.
>
> Likewise, a 90 degree bend or a loop on the cable is a huge
> inductance to get all that high frequency energy through, so
> lightning tend to jump from bends and loops, to less inductive
> paths if possible
>
> Be careful with EMI/EMC clam-on ferrites, they can explode in
> lightning strikes.

Then I look upon my pole as a 2 meter long clamp-on ferrite.

That 7 mm Aircell cable won't conduct much better than the pole,

and the outside of the pole will look quite, eh, attractive, given that

king size common mode choke.

And then, at the 90° cable corner to my lab, the lightning bolt may 
continue

downwards through earth on its highway to hell..


cheers, Gerhard

(Unix V6  on 1 of the 5 PDP 11/40E that ever existed)