roskos@csed-47.UUCP (Eric Roskos) (05/09/88)
Recently, in a futile attempt to receive WEFAX satellite transmissions, I bought a VHF converter for one of my shortwave radios. Since the satellite broadcasts turned out to be discontinued, I started looking for other things of interest nearby, and found something unusual. On 152.780 MHz, there is what sounds like a telephone ringing, all the time. I have been listening to it for about 3 hours now (while doing other things) to see if anyone ever answers, but all that happens is that the amplitude of the ringing changes from time to time. It is a very normal sounding ring signal, like you hear when you place a phone call. I am wondering what this is? According to my frequency allocation tables, it says this frequency is allocated to "Mobile Telephone, Landline Companies," and that it is channel "JK". It is sent in FM mode, and is a very strong signal. 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.
jshelton@ADS.COM (John L. Shelton) (05/11/88)
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=
prindle@NADC.ARPA (Frank Prindle) (05/11/88)
Ten or eleven channels on VHF would appear to be the old (pre-cellular days) mobile phone system. I ran into this many years ago with a home-brew VHF set (vacuum tubes no less!). If you would call a mobile number (they all had the same exchange), the call would be signalled out through the lowest unused channel (presumably the remote was scanning or listening on the lowest unoccupied channel too). Because so few channels were available, and had to cover a very large area (i.e. all of Philadelphia and it's suburbs), subscribers had to be severely limited and prices per unit of time were very high. The land-line signal was very strong because of the wide area coverage required. I've wondered what became of this service now that cellular is the standard. The constant ringing sounds like a remote tried to place a call to a land-line and it never answered; perhaps this is just a test signal generated by the mobile-phone company so the FCC won't take away their license or reassign those channels; perhaps they still have some customers? Frank Prindle Prindle@NADC.arpa
tedk%ihuxv%ihnp4%cbosgd@mtune.att.COM (05/13/88)
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, |I bought a VHF converter for one of my shortwave radios. Since the |satellite broadcasts turned out to be discontinued, I started looking for |other things of interest nearby, and found something unusual. | |On 152.780 MHz, there is what sounds like a telephone ringing, all the time. |I have been listening to it for about 3 hours now (while doing other |things) to see if anyone ever answers, but all that happens is that the |amplitude of the ringing changes from time to time. It is a very normal |sounding ring signal, like you hear when you place a phone call. | |I am wondering what this is? According to my frequency allocation tables, |it says this frequency is allocated to "Mobile Telephone, Landline Companies," |and that it is channel "JK". It is sent in FM mode, and is a very |strong signal. | |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. I am sure that if you repost your question to the HAM RADIO newsgroup, that the folks over there would know. Ted G. Kekatos
dave@westmark.UUCP (Dave Levenson) (05/19/88)
In article <8805111234.AA29347@NADC.ARPA>, prindle@NADC.ARPA (Frank Prindle) writes: ... > I've wondered what became of this service now that cellular is the standard. The IMTS (Improved Mobile Telephone Service) is still offered, and is finally useable. It used to be terribly over-crowded (in major cities) because of the limited number of channels and large demand for service. Now that most users have gone to Cellular, the IMTS channels are generally available. The transmission quality is poor, compared with the UHF Cellular service. Why would anybody want it today? Cellular serves most of the 300 largest cities. It is now being deployed along the major corridors between. But for a lot of rural areas, small towns, and back roads, Cellular is not available yet. IMTS, for all of its technical shortcomings, is mature, and serves a far larger area. My partner in Sussex County, NJ, still uses IMTS, because the local phone company there (not NJ Bell) offers it. Cellular hasn't arrived yet in that corner of the state. -- Dave Levenson Westmark, Inc. The Man in the Mooney Warren, NJ USA {rutgers | clyde | mtune | ihnp4}!westmark!dave