Path: utzoo!attcan!uunet!zephyr.ens.tek.com!tekfdi!videovax!bill
From: bill@videovax.tv.tek.com (William K. McFadden)
Newsgroups: sci.electronics
Subject: Re: "Caller ID" signal detection.
Message-ID: <5844@videovax.tv.tek.com>
Date: 7 Jun 90 16:32:22 GMT
References: <235@ulticorp.UUCP> <2387@rsiatl.UUCP> <1990May22.151642.18729@utzoo.uucp> <1417@oucsace.cs.OHIOU.EDU>
Reply-To: bill@videovax.tv.tek.com (William K. McFadden)
Organization: Tektronix TV Measurement Systems, Beaverton OR
Lines: 26

In article <1417@oucsace.cs.OHIOU.EDU> bwhite@oucsace.cs.OHIOU.EDU (Bill White) writes:
>	I've heard (from several people) of "homebrew" caller-ID boxes that
>worked entirely by themselves, ie no phone company modifications were
>needed.  I seem to recall that they had something to do with sending
>certain frequencies.  Or is this a myth?  If so, it's a very persistent one.

I believe modem-like tones are sent between the first and second ring to
identify the caller.  Several third parties offer decoder boxes.  For more
information, subscribe to comp.dcom.telecom.

>	Also, does anyone know what the fourth wire in standard telephone
>hookups is for?

Tip & ring are the red & green wires (I keep forgetting which is which).  These
carry the loop to the phone company.  Yellow is ground, and is connected to a
safety ground on the premises (primarily for lightning protection).  The black
wire, I've been told, is used to supply power to dial lights in phones that
have them.  The power comes from a small doorbell-like transformer the phone
company installs in your house.

If any of this is wrong, I'm sure I'll be corrected.
-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077
bill@videovax.tv.tek.com,     {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
Phone: (503) 627-6920       "The biggest difference between developing a missle
component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI