Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ll-xn!husc6!hao!noao!mcdsun!nud!anasaz!john
From: john@anasaz.UUCP (John Moore)
Newsgroups: sci.electronics
Subject: Re: Lots more about R-C sinusoidal oscillators
Message-ID: <580@anasaz.UUCP>
Date: 3 Feb 88 16:18:27 GMT
References: <2507@ihlpe.ATT.COM> <971@neoucom.UUCP> <418@pasteur.Berkeley.Edu> <1198@eneevax.UUCP>
Reply-To: john@anasaz.UUCP (John Moore)
Organization: Anasazi Inc, Phoenix AZ
Lines: 24

In article <1198@eneevax.UUCP> noise@eneevax.umd.edu.UUCP (Johnson Noise) writes:
>In article <418@pasteur.Berkeley.Edu> max@eros.UUCP (Max Hauser) writes:
>>
>>The twin-tee, horror of horrors, when you sit down and analyze it,
>>theoretically requires "infinite" amplifier gain to oscillate, since
>	You seem to suggest that the T network exhibits infinite Q
>requiring infinite gain in order to sustain stable oscillations.  This
>is of course theoretically true, but not realistic. All passive tuned
>circuits exhibit finite Q due to resistances in inductors or leakages
Not true in this case!
	The twin-T is not a resonant circuit. "Q" in this case is not
the point - stop-band attenuation is. The twin-T
is a bridging device, and the stop-band attenuation is only limitted
by how well matched the component values are. In effect, the
twin-T consists of two equal-gain phase shift networks with opposite
phase shift, which results in cancellation of the signal
at the frequency where the phase shifts are just right. At that point,
the only signal passing (assuming values are tweaked right), is
that passed by leakage outside of the twin-T. I have used twin-Tee's to
achieve attenuation well in excess of 80dB at 60Hz.
-- 
John Moore (NJ7E)   hao!noao!mcdsun!nud!anasaz!john
(602) 870-3330 (day or evening)
The opinions expressed here are obviously not mine, so they must be
someone else's.