NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/sci/skeptic/19881

Internet Message Format | 1992-11-19 | 3.0 KB

Path: sparky!uunet!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!nntp-server.caltech.edu!SOL1.GPS.CALTECH.EDU!CARL
From: [e-mail] (Carl J Lydick)
Newsgroups: sci.skeptic
Subject: Re: Making Your Telephone a Feephone
Date: 19 Nov 1992 15:34:23 GMT
Organization: HST Wide Field/Planetary Camera
Lines: 43
Distribution: world
Message-ID: <[e-mail]>
References: <[e-mail]>
Reply-To: [e-mail]
NNTP-Posting-Host: sol1.gps.caltech.edu

In article <[e-mail]>, <[e-mail]> writes:
>'Everyone' in England a few years ago knew of someone who had converted
>his telephone so that no charge pulses were passed back to the person
>who originated the call.....supposedly, the conversion consisted of
>wiring a capacitor & resistor in the phone line, so that the incoming
>charge pulses were blocked, and the exchange electronics 'saw' a phone
>where the handset had been replaced, whereas sufficient dc still flowed
>thru the phone to keep the circuit open. Was there any truth in these
>rumours ? I never met anyone who had actually done it, but there was
>always some guy three or four acquaintances across reputed to use it !

Seems unlikely on the face of it, though given my experiences with British
electronic equipment, I suppose they could've managed to put together a
telephone network so screwed up that something like that would work :-).

I *CAN* tell you how it works in the U.S.  British systems probably work
similarly.  When someone phones you, the CO starts sending a ring signal to
your phone.  That signal continues as long as there is a DC open circuit at
your phone (i.e., the handset is in the cradle).  When the DC circuit is
closed, the CO senses this and:
    1)  Discontinues the ring signal;
    2)  Connects the call;
    3)  Registers the fact that the call has been put through.
Things remain in this state until the DC circuit opens again.  At this point,
the CO:
    1)  Disconnects the call;
    2)  Registers the fact that the call has ended.
Now, if the CO is actually transmitting voice signals down the line, it
believes there is a call in progress.  Period.  No combination of capacitors
and resistors is going to have it sending voice signals and not realizing it's
sending voice signals.

As I said, though, my experience with British electronic equipment leads me to
allow for the possibility that the Brits managed to create a system that was 10
times more complicated and 1/10 as reliable as the obvious way to do things.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: [e-mail] | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.