Path: utzoo!attcan!uunet!crdgw1!rpi!zaphod.mps.ohio-state.edu!ncar!umigw!mthvax!wb8foz
From: wb8foz@mthvax.cs.miami.edu (David Lesher)
Newsgroups: sci.electronics
Subject: Re: Ring signal generation (was DTMF Decoder IC)
Keywords: resonance
Message-ID: <1990Oct13.002920.10628@mthvax.cs.miami.edu>
Date: 13 Oct 90 00:29:20 GMT
References: <14793@mentor.cc.purdue.edu> <27114b84-483.1sci.electronics-1@vpnet.chi.il.us> <14913@mentor.cc.purdue.edu> <9770@uhccux.uhcc.Hawaii.Edu> <1990Oct10.151422.6001@zoo.toronto.edu> <2876@jaytee.East.Sun.COM> <4838@smithd>
Reply-To: wb8foz@mthvax.cs.miami.edu (David Lesher)
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Organization: NRK Clinic for habitual NetNews Abusers
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In <4838@smithd> grayt@spock (Tom Gray) writes:


>In this discussion, one must remeber that the object of the ringing signal
>is to alert the user. When he is alerted he will take the telephone off hook
>and the telephone system (in this case the KSU) must detect this transition.

>The 20Hz ringing signal must be a very clean sine wave for this to happen 
>releiably. Any imperfections in the sine wave will make the task more
>difficult. 

I'm getting a little confused here.
I can think of NO way a 1A2 KTU could be bothered by crummy 20 hz.
(We were talking old WECO key systems, weren't we?)

	1) The local {2,3}0 hz goes out on the CA (Common Audible) line,
	   switched by the 400 {B,D,G,H} card and the
	   motor-driven interupter. At no point is it across T&R 
	   as the CO ringing is.
	2) The card trips (stops ringing) on the basis of A_control 
	   current, run by a mechanical hookswitch contact in
	   each set.
	3) The 400 card on each line also looks at loop current
	   (mostly for the HOLD function) but that too is
	   switched by a mechanical hookswitch.

I've rung phones with really crappy stuff. I've also overloaded
small Sub-Cycle type supplies with too many ringers so they
would 'dink' one each cycle, before stalling. One advantage of
the 1A2 is it is too dumb to be confused by anything short of
lightning.

For more details, see 325-010: Bell System "Key Systems Service
Manual, vol 1 and 2."
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