----- Original Message -----
From: "Andy Talbot" <[email protected]>
To: <[email protected]>
Sent: Sunday, November 04, 2007 4:57 PM
Subject: Re: LF: Re: CLASS D and E
> In my 700 Watt direct-from mains transmitter
> http://www.scrbg.org/g4jnt/137tx.pdf
> efficiency came out somewhere between 80 to 90%. As Jim says, its
> difficult to measure accurately At one point, due to measurement
> errors, the calculated efficiency ended up at 105%.
This is what I mean. Now over 100% eff any advance on this figure!!!
>
> Andy G4JNT
>
>
>
> On 04/11/2007, James Moritz <[email protected]> wrote:
> > Dear Mal, LF Group,
> >
> >
> > > Hi all
> > > Class D and E amplifiers are supposed to give around 80/90 %
efficiency.
> > Has
> > > anyone actually achieved these figures. It seems anything above 60% is
> > hard
> > > to arrive at using normal coils/capacitors.
> > >
> > > 73 de Mal/G3KEV
> > >
> >
> > Certainly you should be getting better than 80% for a reasonable class D
or
> > E design at LF or MF. I find about 90% is typical for a "good" design -
it
> > is actually quite hard to get an accurate figure due to the small
difference
> > between DC input and RF output powers.
> >
> > In my designs I have used silver-mica or polypropylene capacitors, which
> > have very low losses at these frequencies. For inductors, I have used
> > air-wound coils and Micrometals -2 mix iron-dust toroid cores - the rule
> > here is if doesen't get excessively hot with the key down, the power
loss is
> > probably ok! For most class D and E designs, which have quite low
loaded-Q
> > tank circuits (<5, say) an inductor Q of 100 or more is probably
adequate
> > and fairly easy to achieve. If you want to use a high loaded-Q tank
circuit,
> > it might be another story...
> >
> > Cheers, Jim Moritz
> > 73 de M0BMU
> >
> >
> >
>
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