Topband: RIG PROTECTION FROM BEVERAGES

[Tom W8JI]

> 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