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[AMPS] Why build high level AM?

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Subject: [AMPS] Why build high level AM?
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Date: Fri, 13 Jul 2001 17:47:07 EDT
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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