If the arc starts, then it could continue at much lower voltage and your
description is finally correct and could serve also to describe also what
happened inside some failed antenna traps. The practical point is that a
voltage arc doesn't easily start using a device that can't deliver more than
1500W RMS, and this because of the device used.
Of course, if a transmitter has a spike at full power (i.e. because of a
slow ALC attack) and the following PA is potentially capable to deliver much
more than 1.5 Kw peak (i.e. a 3CX3000 and an oil cap filter, vacuum load
capacitor and also a vacuum relay to antenna), then such kind of troubles
you described are quite possible and the weak point could be a connector
(more often a trap, if any).
In any case, there's not a big difference between N and PL in terms of
isolation while there is with mechanical and weatherproofing factors that
may quicly decrease the theorical UHF ratings, expecially when outdoors.
It would be better to choose a more appropriate connector if one knows to
own a PA with an high peak power capability than trusting in UHF connectors.
In terms of pure voltage, a BNC joint would be better because male and
female connections have a also a dielectric in between the inner and outer
contacts with no flat surfaces where dirt or moisture can accumulate and
worsen things (carbon tracks).
----- Original Message -----
From: "Tom Rauch" <firstname.lastname@example.org>
To: "Guy Olinger" <email@example.com>; "TowerTalk"
<firstname.lastname@example.org>; "Maurizio Panicara" <email@example.com>
Sent: Wednesday, April 04, 2001 11:21 PM
Subject: Re: [TowerTalk] Connectors
> A low energy pulse of excessive voltage can cause much damage
> when it is followed by sustained normal power. It also can cause
> accumulated damage as it slowly (if the arc is not sustained long)
> carbon tracks any dielectric.
> This is one of the most common failure modes in high power
> > in favour of UHF connector was the current, now it seem has been
> > "moved" to voltage rating. As well as the load capacitor in a PI
> It is both. Current is a duty cycle failure, where time is long. Arcing
> can wipe out a component in a fraction of a second. The arc by
> itself is NOT the problem, it is the current that flows through the
> plasma and the heat that is the problem.
> When you look at either result, you can not tell which caused the
> problem. All you see is a toasted connector.
> > thank, the capacitors of low pass in PA output or the antenna relay,
> > the connector of a 1500 W PA doesn't require to withstand thousand
> > kilovolts.
> They indeed do, if you do not want field failures.
> 73, Tom W8JI
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