There is defiantly a phase angle, as I can measure it on my scope.
The problem with plasma is it exhibits a negative resistance as the plasma
begins to ionize, and this happens on every cycle. The characteristics, from
cold to hot do change. Also there is no current flow untill the strike
voltage or energy is reached.
What I am battling with is measuring the impedance of my oscillator finals,
before the directional coupler can be dimensioned properly. Then once that
is done, how do I relate the observed voltage and current wave forms, with
phase angle to true power, and SWR, as I would want to optimize the matching
at some point, to maximize power transfer. Fortunatly the wave form looks
like a sine wave, with very little distortion.
I take it the bomb calorimeter is just a gummy load in a jar of water, with
lots of thermal isolation, agitation and a temp. readout. If so I am stuck
on the resistance to use for my dummy load, also you don't want to have
around 2000vp-p running anywhere near water! Also this may give me an
indication of the power the oscillator puts out, it may be good to calibrate
the directional coupler.
I basically want to fairly accurately +-1% measure the power going into the
plasma tube, this will be made up of heat, and rf energy.
Roger
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: <rblain@iafrica.com>; <amps@contesting.com>; "Radio WC6W"
<wc6w@juno.com>
Sent: Saturday, April 06, 2002 2:49 PM
Subject: Re: [Amps] Directional coupler design
> > Since you have an essentially resistive, albeit wandering, load you
> > might just use an old (thermocouple style) RF ammeter to calculate
> > your power output. I'm assuming that the plasma tube exhibits a
> > fairly constant voltage drop when ionized.
>
> Most plasma tubes I've seen have reactance, and even if they
> somehow don't have significant reactance there will be reactance
> added from the mismatch in interconnecting leads.
>
> That means you'd have to measure phase angle.
>
> A directional coupler would be more accurate by far, exceeded only
> by thermal measurements of load power.
> 73, Tom W8JI
> W8JI@contesting.com
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