Several years ago I built a 200 watt all-solid-state Pulse Duration
Modulation (PDM) AM transmitter using a pair of $5 switching Mosfets in the
final Class-E amplifier and one in the class-S modulator. PDM dispenses with
the need for a modulation transformer which is the main bottleneck in a
high-level plate modulated Class-C tube-type AM transmitter. Measured
frequency response with the PDM rig was ruler flat between 50Hz-12KHZ and
distortion measured less than 1% at 100% positive peak modulation. PDM is a
form of high-level series-modulation with efficiency for both the final
amplifier and modulator running over 90%. It is amazing to see the final
amplifier operating at 200 watts carrier output with the heatsink barely
warm. I run the final amp and modulator from a relatively safe 100VDC
regulated power supply. If there is a short or some kind of accident the
power supply simply shuts down. No danger of ozone here! The rig has been
operating reliably for over 5 years now. 73 Todd Roberts WD4NGG .
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