Normally, there should be no degradation of an active device with aging.
Contamination of semiconductors was solved long ago, and the processes are
pretty reliable now; look at all the successes of long duration space missions
to Mars, Jupiter, etc.
Barring a plastic problem allowing some abnormal condition, in spite of
passivating layers, etc., my belief is most likely any change of operating
character of the active devices comes from either operation on the limits of
thermal rating, or from static build up on antennas left connected to a
receiver when not in use. It never hurts to reduce the operating temperature
within reason, inside the radio, for longer life of all components.
My concern is that everyone have a positive disconnect, and maybe with more
spacing than an antenna switch, to avoid static arc over from wind or nearby
thunderstorms. These could affect the antenna and then cause rig problems
later on. One way around the static build up is to bridge the feed with a
high value carbon resistor such as 100,000 ohms which will take almost no
power while transmitting but will equalize the voltage gradients due to static
on the halves of the antenna. A way we used in the tube days, was to shunt a
bare 65 volt arc over NE-2 neon lamp across the receiver end of dipole
feedlines. It would flash when thunderstorms were still 5 miles away!
However 65 volt rating would not protect most semiconductors used today.
Zener diodes or silicon diodes used in shunt to ground might act as AM
detectors I fear, so I have not used them. Positive disconnection, and moving
the coax away from the operating table is my SOP in between on the air
sessions.
Same is done with AC power, unplugging power supplies to the rigs.
---Stuart K5KVH
rohre@arlut.utexas.edu
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