[time-nuts] GPS Antenna and Lightning (Bruce Hunter)

Brucekareen at aol.com Brucekareen at aol.com
Sat Sep 26 18:53:59 UTC 2009

A 6 to 30 MHz Voice of America receiving site in North Carolina had an  
interesting experience when vacuum-tube antenna RF distribution amplifiers were 
 replaced with solid-state units.  At first, frequent damage occurred to  
the input stages of the solid-state amplifiers, whereas few problems had  
been experienced with the vacuum-tube amplifiers.   The many, large,  rhombic 
antennas were all equipped with spark gaps, gas tube suppressors, and  3AG 
fuses in the balanced, transmission lines at the antenna  feedpoints.  Fuses 
frequently opened during lightning storms.
Interestingly, the manufacturer of the solid-state RF distribution  
amplifiers had also sold some of the units to the US Coast Guard in southern  
Florida.  The Coast Guard found that adding 30 MHz low-pass filters at the  input 
to the amplifiers almost completely stopped the failures.  The VOA  
amplifiers were equipped with similar low-pass filters and the North Carolina  
failures also almost completely stopped.  We were never sure whether the  "fix" 
resulted from eliminating energy above 30 MHz or because the phase shift  of 
the filters "unstacked" the harmonics making up the steep wave front, thus  
reducing the peak voltage.  But it would seem that a suitable band-pass  
filter might significantly reduce the likelihood of a GPS receiver failing 
from  energy induced by a nearby lightning strike.  
Bruce Hunter, KG6OJI

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