On Thu, 14 Sep 2000 11:40:37 -0400 "Tom Rauch" <w8ji@contesting.com>
writes:
>
>When you say "class D" what are you doing exactly? What modes
>will the amplifier amplify?
>73, Tom W8JI
>w8ji@contesting.com
>
Hi Tom,
The power amp will be used in all modes essentially amplifying a CW
signal.
The amplifier will be high level Drain modulated by the PWM amp to:
1. Create CW envelopes (and rise/fall timing for all the other
modes)
2. Control the power level in CW, FM, FSK
3. Create AM in the old way
4. Restore the SSB envelope as calculated by the DSP chip
The power amplifier will be driven by a faithful square wave at the
(instantaneous) carrier frequency. The real world Drain waveforms will
likely resemble over driven Class C (at least at the higher frequencies)
by the time all the strays have taken their toll and the switching time
limits of the high power FETs are considered.
There will be some form of harmonic decoupling (yet to be finalized)
of the power transistors from the Pi-net output structure so that some
increase in efficiency over Class C will be realized.
A few Class D references, if you'd like some further background:
Hi Efficiency RF Power Amplifiers. Raab pp 8-29, Ham Radio 10/74
Motorola AR141-- Applying Power MOSFETs in Class D/E RF Power
Amps... 6/85
Hi Efficiency Power Amplifiers... Dierberger et al. pp 28-36, RF
Design 5/95
73,
Marv WC6W
*
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