Lightning arrestors
 

On 8/15/2011 4:46 PM, Owen Duffy wrote:
Jim wrote in
:

...
Most UL listed wall wart power supplies these days can hold off
several thousand volts between inside and outside (that's the so
called "hi pot" test rating).

That may be so at DC or 60 Hz, but it may be relatively transparent to
the spectral components of lightning discharge current, components that
may me significant to 100MHz or more.


yes.. although for the most part, if you're looking at the transient
from a "spark gap arrested lightning impulse" you probably don't have
quite that spectrum.


There is no simple broadband equivalent circuit of the power
transformer, but at 100MHz, it might look more like some series
capacitance of the order of 100pF from primary to secondary for common
mode excitation... and that may well allow damaging currents to flow
(without insulation breakdown or permanent damage to the transformer),
whether driven from the coax shield, the power line, or more likely,
both.

Could be.

Standler's book on transient protection comments that several studies
have shown that most modern consumer electronics can tolerate standard
transient impulses (both the 1 us and 6 us rise time variety) of several
kV. The not so halcyon ESD days of TTL gates connected directly to the
device connector pins are long gone.




Just another factor that makes design of bullet proof solutions so
challenging.

Owen

Lightning arrestors
 

On Aug 12, 5:23*am, DrYattz wrote:
Having but recently returned to the world of shortwave radio, I'm
trying to be better informed about technical and safety issues than I
was as a kid. *Now a homeowner with a mortgage and a homeowner's
insurance policy, I'm worried about lightning protection. *I'm
receiving only, not transmitting. I have a ground rod just outside the
window where the antenna wire enters, and I intend to disconnect the
antenna outside the house when I'm not using the shortwave. *But I
want to be extra careful!

So I'm considering some options. *Which make sense to you seasoned
hams? *Do any of these leave me open to my homeowner's insurance being
voided if I get a direct hit by lightning?

Choice of device seems to be what you're concentrating on but I don't
think the brand name of any device will figure into the solution at
the insurance and electrical code level.

Correct bonding of the equipment ground/RF ground to the house ground
at the entrance panel is the key for any of this. See e.g. W8JI's
webpages.

Tim.