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
brucekar...@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: jherr...@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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