GE "DIAL" RADIO TELEPHONE SYSTEM
Explanation of operation
When the mobile subscriber takes the handset off its hanger the unit is prepared for the initialization of a call. If the channel is not busy the subscriber pushes the Initiate button in the center of the channel selector knob and the mobile transmits a one-second burst of 1700 Hz and 1100 Hz tones. This combination of tones constitutes the Connect signal which is accepted by the terminal equipment. The terminal equipment connects to a free telephone trunk line and returns a dial tone to the mobile unit on the land side transmit frequency. The subscriber, once he hears the dial tone, then dials the desired number. When this is done, the dial is pulled off rest, keying the mobile's transmitter, and the mobile transmits 1700 and 1100 Hz tones. When the dial is released, as it returns to the rest position it pulses 1100 and 1500 Hz alternating tones corresponding to the digit dialed. Once the digit has been outpulsed and the dial returns to rest, the mobile transmitter un-keys and its carrier drops. Successive digits dialed repeat the process. Once the number has been dialed, the terminal connects to the land party's number being dialed and completes the circuit path if the party answers. In the Dial system, the conversation is normally carried on in the Push-to-Talk mode of operation. The mobile transmitter is nonetheless operating in the full duplex mode and for all practical purposes the Push-to-Talk operation is constructive in only preserving current drain on the battery and minimizing mobile signal flutter heard by the called party.
At the conclusion of the call, the mobile subscriber ends the call by hanging up the handset. This triggers the transmitter to send 1700 and 1300 Hz tones for one second. This tone transmission constitutes the Disconnect signal from the mobile. The land terminal then closes down and returns to the standby mode.
In Dial operation, the mobile subscriber has to pick the channel to use, although the typical control head has a "Revert" switch which returns the control head to the Home channel if the handset is hung up after completing a call on a channel other than Home. Dial operation does not transmit the mobile's ID number for billing purposes. Therefore some systems would not return a dial tone to the mobile subscriber, but would instead bring the mobile operator on line, who would ask for the ID of the mobile unit. Upon being given the ID, the operator would then leave the circuit and connect dial tone to the mobile. Other systems provided a flat rate billing to local numbers so that it was not necessary to identify the mobile user for billing purposes, but calls were limited by a timer at the land terminal to a maximum of some time period such as 5 or 10 minutes. Long distance calls then required dialing "O" for operator. Thus, the principal problem with the Dial system was that at least local service either had to be charged as a flat rate to all customers or an operator had to intervene to obtain the mobile's ID number, which defeated the purpose of having an automatic dial system.
GE "IDENTIFIED DIAL" RADIO TELEPHIONE SYSTEM
The Identified Dial system is almost the same as Dial, except that the connect and disconnect sequences differ slightly. In Identified Dial, the Initiate sequence (see above) begins with the mobile transmitting a 1700 Hz tone for one second followed by a series of 1100 Hz pulses representing the number of the mobile subscriber unit, along with the 1700 Hz tone. After the mobile's number is recognized by the terminal, dial tone is sent by the land terminal and the mobile dials the call as described above in the "Dial" arrangement. The disconnect sequence is similar. When the handset is returned to the cradle, a 1700 Hz tone is transmitted for one second, followed by remaining on while a string of 1300 Hz pulses are sent representing the number of the mobile subscriber unit.
Identified Dial in the MASTR Professional series is done using solid state logic on the supervisory chassis. First used in the vacuum tube Progress Line DTD Series mobiles, Identified Dial on those units was done by a special solenoid arrangement which ran the stepper wheel in the mechanical decoder assembly by itself so that the triggering pins on the correct digits could be used to stop the ID pulses at the right number for that digit and then go on to the next. In the later solid state CC56 GE MASTR radiotelephones, jumpers could be selected to make the unit either Dial or Identified Dial. In the older Progress Line equipment, it was one or the other at the time of manufacture.
Both Dial and Identified Dial operate exactly the same as conventional MTS systems for the land to mobile signaling. A string of alternating 600 and 1500 Hz tones corresponding to the digits of the mobile's number following a "clearing pulse" of 1500 Hz are sent and at the end of the last digit the signal tone rings from the mobile control head. All GE control heads ring by use of an electronic ringing signal and small speaker.
In most or all cases where Dial and Identified Dial schemes were used by a Bell System affiliate, the terminal equipment was also set up to operate with "foreign" MTS mobiles. In other words, a mobile simply placing a carrier on the channel by holding down the Push-to-Talk bar on the handset, as would be done in MTS operation, would trigger the terminal to summon the operator, who would appear on the channel and request billing and dialing information from the roaming mobile subscriber. When the foreign MTS mobile hung up, a "dead air" timer at the land terminal would terminate the call, if the terminal did not detect a disconnect from the called party earlier. Some systems using Dial or Identified dial simply did not allow "roamers" at all, and there would be a notation in the channel guide stating "no roamers."
Dial and IMTS seem to have been regularly confused in the mobile telephone roaming directories published by AT&T, and later, Communications Publishing. Since Dial and Identified Dial signaling does not require duplex operation as IMTS does, it appears that some low band "Z" channel systems were fitted with Dial or Identified Dial equipment at the exchange. At least some of the low band entries say "Dial." The odd thing is that so far I have not been able to determine that GE ever offered any low band equipment with Dial or Identified Dial signaling capability.
GE seems to have been the only manufacturer to sell Dial format equipment, although it appears that years later, the Xilex mobile phones could be configured to emulate it. Also, it is possible that the Lenkurt "Mobiltel" equipment (Chapter 4) may have been configured to signal in the same format.
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