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kalee20 · 5th Dec 2017, 12:15 am

The circuit Synchrodyne put up is not a peak envelope detector, though. It's an average (positive) responding thing.

The emitter of Q811 is loaded by a resistor, unbypassed to RF, with then an RF filter to give the audio output. If there had been a capacitor across the 2.2k emitter resistor, this would have charged up to the RF peaks, giving about 3 times as much voltage (actually π times as much)..

There is also an AC/DC load ratio issue here, because the emitter resistor of 2.2k is bypassed from an AC point of view by the load on the AF output. More extreme is the AGC filter following the 47k resistor, which will effectively take the emitter positive a tiny amount, so at approaching 100% modulation there will be appreciable distortion at the modulation troughs.

5th Dec 2017, 12:15 am	#38
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Infinite Impedance detectors. The circuit Synchrodyne put up is not a peak envelope detector, though. It's an average (positive) responding thing. The emitter of Q811 is loaded by a resistor, unbypassed to RF, with then an RF filter to give the audio output. If there had been a capacitor across the 2.2k emitter resistor, this would have charged up to the RF peaks, giving about 3 times as much voltage (actually π times as much).. There is also an AC/DC load ratio issue here, because the emitter resistor of 2.2k is bypassed from an AC point of view by the load on the AF output. More extreme is the AGC filter following the 47k resistor, which will effectively take the emitter positive a tiny amount, so at approaching 100% modulation there will be appreciable distortion at the modulation troughs.