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KG6BAJ > NWSGRP 25.09.09 03:46l 61 Lines 2096 Bytes #999 (0) @ WW
BID : 11912_N1OES
Read: GUEST
Subj: Re: Lightning Arrestors Question
Path: DB0FHN<DB0MRW<DB0FOR<DB0SIF<HB9EAS<OK0NHD<OK0PHL<OK0PCC<OK0NAG<OK0PPL<
DB0RES<DK0WUE<7M3TJZ<ZL2BAU<N4JOA<N9ZZK<KG6BAJ<KG6BAJ
Sent: 090924/1600Z @:KG6BAJ.#NCA.CA.USA.NOAM #:11912 [Grass Valley] InterGate $
** NEWSGROUP: rec.radio.amateur.antenna
** FROM : Owen Duffy <none@no.where>
"Robert11" <rgsros@xnotme.invalid> wrote in
news:h9ggfl$44o$1@news.eternal-september.org:
> Hi,
>
> Saw a picture somewhere of an in-line lightning protector for a HF
> radio receive only antenna.
> Coax style.
> Apparently has the typical gas tube, and when activated shorts the
> center conductor to the braid.
>
> Was wondering a bit about this.
>
> I seem to remember in the old days, there was always a third tap on
> these sort of things that you ran a solid ground to, e.g., a water
> pipe.
>
> Does merely shorting to the braid provide "good" protection ?
>
> Any thoughts would be appreciated.
>
> Also want to ask: what about voltage surges of a few hundred volts or
> so induced on an antenna lead from a nearby lightning strike perhaps
> .
> The levels way below what would trip a gas tube I would imagine, but
> still more than enough to ruin a front end of a receiver.
There are two issues, the differential impulse, and the common mode
impulse.
The shunt gas discharge tube will fire on the differential impulse
voltage, although relatively slowly, even if it includes a radioactive
isotope to assist ionisation.
More importantly perhaps is that there is likely to be a substantial
common mode current impulse and that will induce a transient voltage
gradient in your grounding system. That transient may cause potential
differences across equipment interfaces generally, possibly sufficient to
damage them. There is also a risk of injury or death to persons.
The type of suppressor you describe does precious little to deal with the
common mode current impulse. The 'third wire' assists shunting common
mode current to ground before entering the equipment room.
>
> How does one protect against these without breaking the bank doing so
> ?
Disconnect antenna conductors when not in use, and do not use them unless
the probability of lighting is low?
Owen
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