[TowerTalk] Capacitors To Tune 160 Vertical

[Dubovsky, George]

Except that Jim did exactly what he said he did: he ran a qualitative
power-handling test of some capacitors he had on hand. He apparently
instrumented only one value, RF power on the source end, and he "pumped"
that through the capacitors. He reported a qualitative measurement of
their power-handling capability - they got warm. He probably doesn't
know exactly what the current was, but we can infer that the Z and
system Q were low because he had previously described the sort of
antenna he was trying to match. Semantics, pedantics - he certainly
described the experiment well enough for this old RF engineer to
understand ;-)

73,

geo - n4ua

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Martin Ewing - AA6E
> Sent: Thursday, November 29, 2007 3:57 PM
> To: Tower Talk List
> Subject: Re: [TowerTalk] Capacitors To Tune 160 Vertical
> 
> Let me jump in with a pet peeve.  I know Jim knows better, but there
are
> few components that know or care how much power is "pumped through"
> them, although people often speak as if they did.
> 
> Capacitors, inductors, coax, switches, and what-have-you have voltage
> and current ratings, but not "power" -- unless referred to a specific
> impedance.  They would have power _dissipation_ ratings, but that's a
> different number.
> 
> In this case, it's the capacitor's current rating that is in question.
> Your 1 kW is 4.5 A @ 50 ohms, but it might be 3.2 A @ 100 ohms, or
> whatever.  Same idea applies to voltage ratings.  A corollary: A
> component (switch, ferrite, etc) that handles 1 kW into 50 ohms (VSWR
> 1.0) may not handle 1 kW with VSWR 2.0.
> 
> Sorry to interrupt the proceedings with such pedantics!
> 
> 73 Martin AA6E
> 
> Jim Brown wrote:
> > ...  I began with two .0047 400V dipped micas in
> > series, and pumped 1 kW through them for a few minutes. They got
> > warm, as one would suspect, but no sign of overheating.
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> 
> 
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