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Re: [TowerTalk] Castastrophic Consequences of Connector Failure?

To: Pat Barthelow <>
Subject: Re: [TowerTalk] Castastrophic Consequences of Connector Failure?
From: Jim Lux <>
Date: Wed, 21 May 2008 06:48:51 -0700
List-post: <">>
Pat Barthelow wrote:
> Folks,
> 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

Jim, W6RMK


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