[TowerTalk] filters as lightning protection

[jimlux]

One technique that may prove useful for lightning protection is suitable 
bandpass filters for the RF lines.  After all, most of the energy in a 
lightning impulse is down in the 1 MHz range. Sure, there's energy out 
quite a ways, but it's probably not enough to cook your front end.

Just speculating here... say you are looking at the higher bands (above 
10MHz).. if you had a good high pass filter that could shunt low 
frequency energy to the ground, that might do quite well.  It would need 
to be designed to take the voltage/current, but a high pass is basically 
series C (easy to get for high voltage standoff) and shunt L (ditto)

say you put in a 50 ohms shunt Z at 1 MHz (which will be 500 ohms at 10 
MHz).. without anything else in the circuit, you've already halved the 
transient voltage at 1 MHz (because each leg will take half the current)

Put a series C in that's say, 500 ohms at 1 MHz.. that will reduce the 
transient voltage by a factor of 10-11 (receiver z is 50 ohms)..

You'd need a matching network at the output to counteract all the stuff 
you've done with the filter, but that's straightforward.


I'm not sure this is any easier or better than a traditional transient 
suppressor, but maybe it's something to think about.