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,
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
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.
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