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=