Article View: sci.electronics
Article #20581Re: Dial tone generation
From: Isaac S Wingfield
Date: Mon, 30 Jan 1989 01:59
Date: Mon, 30 Jan 1989 01:59
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1199 bytes
"Precision dial tone", I think, refers to the fact that, pre-DTMF, the dial tone generator was just that: a rotating machine! With the advent of DTMF, it became necessary to control the harmonic content of the dial tone so it didn't gimp up the DTMF decoder; hence "precision". If you think about the DTMF frequencies, and the precision dial tone, none of the possible harmonics from any of those could be mistaken for an instance of any other tone. BTW, on the precision dial tone: the frequencies are 350 and 440 Hz, with amplitudes chosen so that the lower produces 100% double sideband modulation of the upper. The signals are actually just summed, but if you look with a 'scope, that's what you'll see. Isaac isw@cup.portal.com
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arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!unmvax!ncar!ames!amdcad!sun!pitstop!sundc!seismo!uunet!portal!cup.portal.com!ISWReferences:
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!unmvax!ncar!ames!amdcad!sun!pitstop!sundc!seismo!uunet!portal!cup.portal.com!ISW From: ISW@cup.portal.com (Isaac S Wingfield) Newsgroups: sci.electronics Subject: Re: Dial tone generation Message-ID: <14094@cup.portal.com> Date: 30 Jan 89 01:59:35 GMT References: <349@serene.UUCP> Distribution: usa Organization: The Portal System (TM) Lines: 16