Frank Dresser wrote:

Am I reading the nifty formulae wrong? It looks to me like he's deriving
the distortion of a diode detector from the modulation index only. My sense
of these things says that a 50% modulated signal at a tenth of a volt is
going to have much more distortion than a 50% modulated signal at 10 volts.

Frank Dresser

Very few radios drive the detector with anything near 10V.
The R390 and R392 have the highest diode drive voltages I have
seen and I think they are less then about 3V.

Most modern, IE "solid state", receivers I have measured have less
1V. All that I have seen that use discrete diode detectors as oppossed
to ICs, have farily high AF gain stages.

I didn't post this as an attemp to claim that "Synchronous detectors"
are a hoax,
but to offer another viewpoint that is backed up by what appears to be
valid
engineering to me.

ASCII text is not my choice for this arcane topic because of the great
difficulty
in expressing meaningfull equations.

This is merely another tool to be used in trying to receceive fading
signals.
His filters work much better then I expected. I found that by forward
biasing
the detector in my R2000 I got a much cleaner, ie lower distortion,
signal.
This was difficult to manage over very modest temperature changes.
A full wave "improved AM detector" gave even better results.
http://www.amwindow.org/tech/htm/alowdisdet.htm
A synch detector in an outboard detector gave even better results.

But the simple improved AM detector with a 4000Hz LP filter is a pretty
close
match to the synch detector at 1/100 the effort.

The above link goes into the math, this link starts with simpler math
and may
help the none engineers enter the fray.
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part9/page2.html
Another unusual but good detector can be seen at:
http://www.pan-tex.net/usr/r/receivers/elrpicamdetect.htm
Tom Holden's Synch detector group has a link to a very detailed math
examination of "detection". I lost the link to that paper so you will
have to ask
Tom or join his group.

And please note Mr. Lankford is not merely slapping a 4000Hz LP AF
filter
in the audio chain, he is offset tunning, with good narrow IF fitlers,
to eliminate
one sideband.

Terry