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Old 4th Dec 2017, 8:13 am   #35
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: Infinite Impedance detectors.

The attachment shows the AM demodulator that was used in the McKay Dymek series of HF receivers of the late 1970s:

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Name:	McKay Dymek DR33C AM Demodulator.jpg
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To me, it looks like the bipolar transistor version of the infinite impedance demodulator. In this case AGC bias was taken from the emitter and thence to the AGC DC amplifier. In the solid-state realm, AGC was less of a problem than with valves in that with transistors and ICs, AGC voltages were relatively easily inverted, offset one way or another and amplified as required for application to RF and IF amplifier stages.

But McKay Dymek described the demodulator differently, saying in its product literature: “Class D AM envelope detection is used giving much lower distortion levels than the conventional AM diode detector”.

That seems to be just a fancy description for the infinite impedance demodulator, or am I missing something in that schematic that makes it radically different to the point of justifying a new name?


Cheers,
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