[time-nuts] GPS Antenna and Lightning (Bruce Hunter)
Javier Herrero
jherrero at hvsistemas.es
Sat Sep 26 22:16:41 UTC 2009
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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--
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Javier Herrero EMAIL: jherrero at hvsistemas.com
HV Sistemas S.L. PHONE: +34 949 336 806
Los Charcones, 17A FAX: +34 949 336 792
19170 El Casar - Guadalajara - Spain WEB: http://www.hvsistemas.com
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