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Re: [TowerTalk] Castastrophic Consequences of Connector Failure?

To: Pat Barthelow <>
Subject: Re: [TowerTalk] Castastrophic Consequences of Connector Failure?
From: "Roger (K8RI)" <>
Date: Wed, 21 May 2008 11:16:24 -0400
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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.  
This should be a concern even when using the best of connectors.  Sooner 
or later something in the feed line or antenna *will* fail. In Over the 
last 10 years I've had a number of such failures.  One, N type connector 
shorted in the feed line to a center fed half wave sloper.  The wire 
between one side of a balun and another sloper broke at the balun 
connector. There's no way to gracefully remove the old connector and 
replace it.  Don't know why it broke as there as a loop to take out 
tension.   These were hooked to a tuner and the output of the Alpha 76 
and 756 Pro. I  had water get into a coax  due to an abrasion in the 
jacket.  It was hanging in open space so I don't know what caused the 
abrasion. That one was between a 40 meter, half wave, center fed sloper 
and the Tokyo Hy-Power HL-1.5Kfx. SWR looked ok, but it'd give an 
immediate shutdown due to SWR when much over 500 watts.  I had the bees 
get into the AV640 matching network, which caused high SWR shutdowns of 
the HL-1.5Kfx and ruined about 6 or 8 feet of coax. And finally (as far 
as I can remember "at the moment") the Hygain HDR-300 went past the 
stops, tearing up the rotator loops to the tri-bander and the 7L 6-meter 
>  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. 
I don't know how many times I've heard an arc in either the tuner or 
Alpha.  Never any damage though.
>   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.
That should be a given, but even with the best it's still going to 
happen far more often than expected.
> Also,  I often wondered that it might be a good widget to have a "trip relay" 
> in an inline 
In the old days it was not uncommon to see a "crowbar" using either an 
SCR or relay to short the PS. The though of those shorting the PS always 
bothered me, but they worked fine.
> 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?
Many newer amps, both SS and tube, have protection circuitry built in. 
To home brew it's time consuming and adds noticeably to the expense of 
commercial amps, but is well worth it.


Roger (K8RI)

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