[Topband: Lightning Arrestor]

[Tom Rauch]

> 1.  A 5kV LA functions at 10-20 times the required sustaining voltage
> necessary for an amateur 1/4-wave vertical antenna system operating at
> maximum legal power and assuming a base impedance of 50+/-j0 Ohms. 
> For example, the peak voltage to ground at the base of such a system
> is approximately 300 volts, while the lowest available

I think you are using RMS voltage. The nominal peak voltage is 
actually 1.414 times the RMS voltage you gave above, plus we 
need margin for tolerances and transients. Many rigs overshoot on 
the initial envelope rise, and we have to allow for firing tolerances 
and occasional SWR problems. 

I normally spec 1200 volt nominal peak voltage devices for 50 ohm 
1.5kW rated protection devices that are rated at 2:1 VSWR. 

The very last thing we want is a unneeded arc, which can destroy 
tank components like switches and other parts!  

> It is generally considered poor engineering practice to utilize a
> device designed and tested for a specific application in another
> application far removed in operational parameters without first
> conducting extensive analysis and controlled laboratory testing of the
> device under the expected operational paranmeters.  This becomes
> especially critical where the device is "expected" to provide a
> measured degree of protection for equipment and human life!

The real protection comes from disconnecting your equipment 
when not in use, and proper grounding and wiring.

I bend my three copper pipes used as "ground rods" over near the 
tower legs to form a gap at each leg. I don't even use gas-
discharge tubes, and very few MOV's and other devices.  

The only reason I have a base gap is to protect the tuning and 
switching components in the doghouse at the tower base.

I leave all my cables connected, and just depend on proper 
grounding and routing to protect stuff. The transmitting antenna 
lines are opened with RCS-8 relays, and all of the receiving 
antennas and control lines remain connected. Of course the safest 
thing is to unhook and unplug.  

73, Tom W8JI
W8JI@contesting.com 


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