[TowerTalk] Connectors

[Maurizio Panicara]

Istantaneous power of a burst has little to do with RMS power since the duty
cycle is generally irrelevant.
A KW amplifier can generate a peak but the power content of the burst is
well within cthe onnector current capability because of duty cycle and
E=MC2.
The original point 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 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.
PI plate capacitors is highly isolated because working on an impedance that
is 20 to 40 times higher than 50 Ohms, not because of bursts.
The PA load capacitor or the LP filter in a solid state amplifier is
generally less isolated than an N or a PL connector and would fail first.
I agree that from a contester perspective reliability is one of the
important matters and this is the reason why I spent words on N type.
If power is within1500 W the N connector is better under the very most
features of a PL259 whose main "gift" is low price, diffusion and average
performance for amateur use.

73,
Mauri I4JMY


----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "Guy Olinger" <olinger@bellsouth.net>
Cc: "TowerTalk" <towertalk@contesting.com>
Sent: Wednesday, April 04, 2001 7:02 PM
Subject: Re: [TowerTalk] Connectors


> > What is being said here, I'll say it again, operating at 1.5 kW on an
> > N connector, particularly HF, is tight, there's no reserve. If you're
> > a contester, you're baiting Murphy to show up at the worst possible
> > time.
> >
> > You may get away with it. Others have not.
>
> That is very true Guy. There is no headroom at all.
>
> I'm amazed everyone keeps discussing and using RMS voltage,
> which has NOTHING to do with voltage breakdown. It is the peak
> voltage, and not even the repeating peak voltage but the
> ABSOLUTE peak voltage that causes the problem.
>
> You would be amazed at how high that can be with typical
> systems, when all factors are considered. For example, early Icom
> 775DSP's outputed about 300 watts or more on a leading edge
> transient no matter what the actual power was set for.
>
> If you use that radio with an amplifier that drives to 1500 watts with
> 65 watts of drive and set the power control for 65 watts, you can
> count on a spike of up to 350 watts banging the amplifier.
>
> Most 1500 watt amps have the headroom to handle that on pulse,
> and if the tank is loaded heavy enough peak output power during
> the transient can exceed 5000 watts. (This transient is a major
> source of switch and component failures in amplifiers.)
>
> The line must handle the SWR factor+the transient power and we
> must consider PEAK...not RMS.... voltage.
>
> When you strike an arc in the closed connector, the ionized air
> remains in the connector and following voltages, even when much
> lower, will sustain the arc.
>
> I had a radio here (you can guess what one) that, when I watched
> the PO of an AL1500 on a fast storage power meter, reached over
> 5 kW. It not only hammered the heck out of the PA, it stressed
> everything in line. That radio, used with the AL1500, would trigger
> an arc in a KW Johnson matchbox that normally can handle over
> 4kW!
>
> When the Matchbox flashed, the SWR on the line went up to
> almost infinity. You can imagine the connector voltage if I had a
> connector 1/4 wl back from the tuner, where the voltage would be
> maximum.
>
> While that radio was an extreme case, MOST radios today have
> some overshoot on the closure. It is a common problem, not a rare
> event, and it won't show on anything but a fast peak storage
> measurement system....but it will cause arcs and other problems.
>
> That's one reason why you need at least a 2:1 safety factor in
> voltage (not power) over the highest expected PEAK voltage on the
> line. Another is (if you do stuff like I do) you might just grab the
> wrong antenna on occasion.
>
> N connectors have a place, but it is in SWR critical applications or
> at UHF. Anyplace where you want a mechanically tough BNC
> connector is a good place for a N.
>
> 73, Tom W8JI
> W8JI@contesting.com
>



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