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

[Javier Herrero]

When Yaesu introduced the FT-757GX, it was very prone to damage in the 
input stages, particularly the PIN diode switches in the input filter 
banks. The problem was that the receiver input was isolated from ground 
at DC, and any static build-up in the antenna ended damaging the diodes. 
At that time I was service technician for the Yaesu dealer in Spain, and 
we replaced lots of diodes :) We started adding an inductor between 
receiver input and ground (quite high inductance... I don't remember the 
value), and the problems were a lot less frequent. Not very later, Yaesu 
modified the receiver and emitted a technical note in the same line to 
the modification that we were doing for upgrading older units. But a GPS 
antenna is a different scenario :)

Regards,

Javier

Brucekareen at aol.com escribió:
> 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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Javier Herrero                            EMAIL: jherrero at hvsistemas.com
HV Sistemas S.L.                          PHONE:         +34 949 336 806
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