Telamon wrote:

Congratulations for the continuation of one of the most retarded
threads I've yet read. Never heard of biasing a diode or being unable
to understand doing so is pretty pathetic. Electronics does not get any
simpler than this.

John understands this stuff extremely well: I've argued detector issues
with him on rec.antiques.radio+phono in the past. John obviously doesn't
believe Patrick really understands what he's advocating.

Biased diode envelope detectors are *not* simple: I've used them for
x-ray spectroscopy with scintillation counters, and they are tricky
beasts. A biased diode is far from an ideal switch: its dynamic
resistance varies with instantaneous signal level, making the circuit
bandwidth vary rapidly. The mathematics of this are rather difficult.

I also think an emphasis on detector distortion under idealized test
conditions misses the real issues. The most annoying distortion on AM
signals doesn't come from the detector. Multipath, steep IF skirts, and
AGC all distort the modulation envelope. Perfect reproduction of such
distorted envelopes yields bad sound. I suspect that the great sound of
the old tube diode detectors actually results from their poor
reproduction of these sorts of envelope distortion (but this is a
difficult hypothesis to test).

In any case, my 1934 Stromberg-Carlson 58-T, with its weak AGC, poor
skirt selectivity, and a classic diode detector has the best sound of
any of my AM radios, both to my ears and my wife's. One receiver it
beats is my Drake R-8, which uses a very low distortion (active full
wave rectifier) envelope detector. Of course, the R-8 is a much better
DX machine, but that's a different issue.

-jpd