Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!nrl-cmf!mailrus!tut.cis.ohio-state.edu!bloom-beacon!ADS.COM!jshelton
From: jshelton@ADS.COM (John L. Shelton)
Newsgroups: comp.dcom.telecom
Subject: Re: Continuously Ringing Telephone (on VHF)
Message-ID: <3833@zodiac.UUCP>
Date: 11 May 88 01:27:58 GMT
References: <8805090023.AA00938@csed-47.csed.com>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: jshelton@ads.com (John L. Shelton)
Organization: Advanced Decision Systems, Mt. View, CA (415) 960-7300
Lines: 48
Approved: telecom@xx.lcs.mit.edu


In article <8805090023.AA00938@csed-47.csed.com> roskos@csed-47.UUCP (Eric Roskos) writes:
>Recently, in a futile attempt to receive WEFAX satellite transmissions,
...
>
>On 152.780 MHz, there is what sounds like a telephone ringing, all the time.
...
>
>I am wondering what this is?  According to my frequency allocation tables,
>it says this frequency is allocated to "Mobile Telephone, Landline Companies,"
...
>
>The channel names listed in this table also do not seem to make much
>sense mnemonically, does anyone know what they mean?  The channels listed,
>in order, are JL, YL, JP, YP, YJ, YK, JS, YS, YR, JK, and JR.

The channels you mention are 11 of the 12 "IMTS" (Improved Mobile
Telephone Service) channels put into operation in the early sixties.
The original mobile telephone service was entirely manual.  IMTS
improved on this by making the mobile phone call almost entirely
automatic.  It worked as follows:

1.  An idle telephone in a car hunts until it finds the "next"
channel.  All idle phones are listening to this channel, and a special
tone or signal is broadcast on this channel to help the phones find
it.  (Perhaps your ringing sound *is* that signal.)

2.  If a landline customer rings a mobile phone, the landline customer
is connected to the idle channel; the mobile unit's id is broadcast on
that channel, and the correct mobile phone recognizes and starts
ringing.  All other idle phones move to the next channel.

3.  If a mobile user wishes to place a call, he/she picks up the
phone.  The mobile unit siezes the line (by transmitting a special id
tone) and once again all other phones hunt to the next line.

It is interesting to note that originally 12 frequencies were all that
were available.  Most cities had fewer than that because of
interference with adjacent towns.  (For much the same reason that no
city has all 12 VHF channels.)  Eventually another batch of 10 or 12
channels were allocated.  Now, with Cellular Mobile Telephony, 666
channels have been  allocated by the FCC, with 333 more in reserve.
Since these channels can be reused within a city, the potential is
there for many more customers.  

I recall inquiring once (in 1973) about the wait for IMTS service in
Dallas, Texas, and being told the wait was 7 *years*.

=John Shelton=