Pat Barthelow wrote:
> When deciding on the reliability factor in your antenna construction,
> especially when running high power, or with modern solid state
> finals, I wonder what the probability of expensive damage is if an
> antenna connector, or adapter has a "hard" failure, i.e. an open or
> short circuit/flashover, etc. I have experienced few TX failures
> through the years, due to SWR faults caused by various antenna system
> faults. With a high power tube amp, I have heard of fatal damage
> inflicted to tubes, or to bandswitches, or output network components.
> On the other hand, I guess we can be lucky, and sometimes survive an
> antenna fault without damage to QRO active or passive path. If the
> probability is high of expensive damage caused by antenna faults,
> perhaps it is worthwhile to achieve higher reliability by using
> higher quality and care with connector components.
> Also, I often wondered that it might be a good widget to have a
> "trip relay" in an inline meter accessory to quickly, but not
> instantaneously remove TX power under fault SWR occurances. I know
> Bird, has such in the commercial market. Is damage inflicted to the
> TX RF chain components by an antenna fault, usually quicker than a
> relay could remove/reduce RF power?
For tubes, you get a bit more tolerance of off-nominal than with
semiconductors (more mass to melt, mostly)..
Many amplifiers have protection circuitry for just the reason you
describe. Then it can be tailored to the damage propensity of the
amplifier. For instance, automatic power reduction with excessive
collector current or voltage on solid state amplifiers. In the
microwave area, circulators/isolators are often used.
As to whether a retrofit would be effective.. it probably depends on the
amp and the kinds of failures.
And this brings up an interesting system design question.. do you spend
some limited resource (i.e. cash) on better connectors or on protecting
against connector failure. It's not an obvious trade: One likes to
minimize failures, but the protection circuit also protects against
other things: Antennas getting broken in the wind, for instance
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