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From: asd@cbnewsj.att.com (Adam S. Denton)
Newsgroups: sci.electronics
Subject: Re: Weirdness Electronics
Message-ID: <1990Oct31.233529.25251@cbnewsj.att.com>
Date: 31 Oct 90 23:35:29 GMT
Organization: AT&T Bell Laboratories, Middletown, NJ
Lines: 38

In article <1883@gorn.santa-cruz.ca.us>, (C. Elliot Friday UMN ) writes:
> [talking about weird electronics with bizarre and obviously-false claims]

A long time ago ('82?) in Radio-Electronics, there was a construction article
to build a "gravity-wave" detector!  This simple circuit, the author
claimed, detected `gravity waves' which travel throughout the universe
instantaneously (much faster than the the speed of light)!!

The circuit was simply a 1458 dual op-amp with a large (.22uF) capacitor
across the inputs, together with a few biasing resistors.  By charting
the output voltage vs. time, you would notice that the output voltage
did, in fact, move up and down very slowly, seemingly chaotically.
The author claimed that his circuit output a particular voltage peak
at the same time some solar phenomena was measured from the sun.

Apparantly the author had never heard of flicker noise (aka 1/f noise).
His circuit operated the op amp with open loop (very high!) gain.
The output voltage was produced by the input noise voltages and noise
currents of the op-amp's input transistors, resulting in very high
low-frequency content random output noise.  The big .22uF capacitor filtered
out miscellaneous noise and ambient 60Hz hum, etc.  The author even claimed
his circuit produced best "results" if one used a cheap (741 or 1458)
op-amp and not a more-expensive (i.e. FET input) op-amp.  Gee whiz,
naturally a low-noise op-amp will give much less noise output voltage!
R-E actually ran this article, and the author was actually paid for this!!

Imagine my surprise when in a few months, R-E ran another article
by the same author with his same dual-op-amp circuit being used
as a (drum roll please...) RADAR DETECTOR!  You tuned the circuit
by modifying the lengths of the leads on the .22uF capacitor!
Yes, did you know the common 741 had a gain-bandwidth product
in the GHz range????

I guess after that the author stopped fiddling around with op-amps
and went to work on Cold Fusion...

Adam Denton
asd@mtqua.att.com