I did so much research on the construction and installation of the
Beverages, I feel really stupid because I didn't think of one possibly
critical aspect (nor did I see it discussed). I have the 75 Ohm coax from
the Beverages connected directly to the receive antenna input on my
FT-5000. If high voltage should get induced by lightning, isn't it going
to fry at least the front end of my receiver?
Most lightning damage is common mode. The key to preventing damage is cable
and power entrance bonding, and perhaps disconnecting between the entrance
panel and the equipment.
I have a lot of stuff up here and links from that page:
http://www.w8ji.com/house_ground_layouts.htm
One side note, an RF choke will do almost nothing at all. Neither will a
series capacitor (dc isolation). The frequency content of lightning energy
is well up into the radio spectrum, so an RF choke looks like a very high
impedance for lightning and a blocking cap looks like a low impedance. I
certainly would not use a high value choke. If I used anything, I would stay
down around 50-100 uH and use a "dam" heavy choke.
How you you provided for this possibility?
At the antenna, the DXE stuff intentionally has close spacing between
washers and the metal cases. This forms a spark gap. The gap works pretty
well for close hits if you ground the case to a separate ground rod from the
signal ground.
Not much helps a direct hit.
In the house, for many years I had nothing at all except grounding feed
throughs. I never disconnected the receiving antennas. But I have long
buried cables, good grounding barriers, and my stuff runs through a
multicoupler system that uses the same preamps DXE sells. The only in-shack
damage I ever had, and I get dozens of local hits a year on my tall towers,
was occasional mica capacitor failure or inductors opening in my BCB notch
filters. These were 300 volt micas and miniature inductors.
Because storms are more violent now, even to the extent of vaporizing
Beverage wires, I recently added low voltage gas discharge tubes in my
multicoupler ahead of the BCI filters.
Lightning is a very good reason to not use inexpensive plastic boxes. I have
many pitted aluminum and stainless boxes, where arcs flashed from the
stainless washers to the case, and the electronics inside stayed good.
Almost all of any failures I have are where a conductor melts. Either a
shield blows open, or an actual antenna wire disappears. I've tried low
voltage gas tubes at the antenna equipment, as well as MOV's on control
lines, and I'd say any improvement is there, but is also what I would call
marginal. There is a HUGE difference between plastic cases and metal,
however. Since I'm a cheap skinflint Ham with limited time like most of us
are, the fact I take the time to bend and use metal (or even use
double-sided copper PC board cases) speaks volumes of my own experience with
damage using different materials and construction methods.
73 Tom
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Topband Reflector
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