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Date: Mon, 5 Nov 2007 12:26:01 +0000
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: CLASS D E
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Its not difficult to measure RF voltage at this frequency.  A scope
calibration at DC will extrapolate accurately.  Then you can measure I
using a current transformer / resistor.  Getting within a few percent
shouldn't tax any abilities provided you can calibrate a scope at DC.

The mistake I made the time I "saw" 105% efficiency was, I seem to
recall, due to forgetting the 4/pi factor when filtering the
fundamental component out of a square wave - all old history now.

Efficiency in class D/E amplifiers falls when the match is not purely
resistive, and the devices are forced to switch at other than the zero
crossing point of the current waveform.

Andy  G4JNT
www.scrbg.org/g4jnt



On 05/11/2007, hamilton mal <g3kev.ham@virgin.net> wrote:
> Hi all
> Tnx to all for the information, but some of the figures do not work out. How
> are the % figures measured.
> One simple method is to calculate the DC input PWR in watts (I x V) then
> using an RF current meter calculate the PWR out (Isq x R) let R be the norm
> 50 ohm D/load. Compare the two figures and calculate the Eff %
> 73 de Mal/G3KEV
>
>
>
>