Chris:
>Modern RF Fets are pretty robust devices and have an MTBF a couple
orders of
magnitude better than thermionic devices, provided the junction/channel
temperature is kept to a sensible level, and the breakdown voltage and
dissipation limits of the device are observed. Monitoring the drain
currents, heatsink temperature and load VSWR is really all that is required.
A $2 microcontroller could be used to automate the monitoring/trip
functions......
I am troubled by this opinion. When I study the hardware to the R&S box
I see evidence of great attention to details that I sense are associated
with longevity of the devices. I am also told that many high power RF
solid state devices have a definite life cycle. The issues are as I see
it survival in the keying ON/OFF mode, some issues of linearity and
instability below, at, and above the operating frequency. My sense is
that we need some serious development of protection for open or short
antenna feedlines or relays, even to the extent of a momentary test
every time one goes into transmit mode. I suspect that we need some
rather serous protection efforts as well as a way to understand what the
protection system did when it protects the devices.
If protection and management was simple we would already have it in
place. Since we have no available systems I must assume that the task
is far beyond trivial.
My one dread with my own station is a very close lightning strike, but then
that would be a serious problem with many tube PAs. Fortunately we don't get
big electrical storms in this part of the world too often. I try to remember
to keep the
transmitters disconnected from the antennas at times when I think we might
get one.
Broadcast stations, solid state, work right through repeated lightning
hits on the operating tower - they survive amazngly well. From what I
have seen when a working transmitter does get a hit there is a real mess
- not often but when it does it is expensive. I sense that for amateur
radio this is really no reason, other than for repeater service, to have
problems of this type.
Larry
VA3LK
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