Re: Lightning Arrestor & Protection Of Receiver ?
- From: "w_tom" <w_tom1@xxxxxxx>
- Date: 19 Jan 2006 07:38:05 -0800
Have you never static shocked a radio antenna? Why was that radio
not damaged by up to 18,000 volts? Radios have internal protection
which is why those 10,000+ volts did not damage. Parameters are
voltage ... and time.
Reason why a well earthed protection 'system' protect electronics
even from direct strikes includes internal electronics protection, fast
response of all protectors, and how well a protection system is
earthed. With properly earthed protection, then protection internal to
electronics is not overwhelmed; damage does not occur.
Disconnecting without earthing is not a best protection method. Ham
radio operators in the early days would disconnect an antenna lead, put
that connector inside a mason jar, and still suffer damage. When that
antenna lead was earthed, then damage stopped. Disconnecting - trying
to stop a destructive transient - works when the transient has a better
path to earth. Most essential is to provide a better path to earth.
Disconnecting would only enhance a good protection system. But
disconnecting without a non-destructive path to earth has been
demonstrated not sufficient. Idea is to keep protection inside that
electronics from not being overwhelmed even by a direct lightning
strike.
What was more than sufficient to protect telephone switching stations
- connected to overhead wires everywhere in town? Gas discharge tubes.
We have since obsoleted that technology (depending on other
parameters) twice over. But response of a gas discharge tube is not
'too slow'. Too often, people will blame 'slow GDT' for damage when
they failed to confirm the most critical component in a protection
system - earth ground and connections to that earthing 'system'.
Robert11 wrote:
> Very interesting comments on my question of a few days ago re lightning
> arrestors.
> Thank you all for trying to educate me on this subject; really find it
> confusing.
> Thread is a bit buried by now, so thought I'd start another one.
>
> I fully understand that the best approach is to (also) just disconnect
> everything.
>
> But if not around, here's what I don't understand and concerns me.
>
> Assuming a "nearby" strike, and a subsequent emp pulse that's picked up by a
> receive only antenna wire strung outside:
>
> No matter how quickly an arrestor's gas tube fires, and diverts the pulse to
> a good RF ground, the fact that it takes
> a few hundred volt threshold to fire makes "any" gas tube type of arrestor
> almost worthless re the protection of a receiver whose front end certainly
> won't take a few hundred volts, even for u-seconds, probably.
> ...
.
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- Lightning Arrestor & Protection Of Receiver ?
- From: Robert11
- Lightning Arrestor & Protection Of Receiver ?
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