MTS (1946 to 1984)
Mobile Telephone Service. This system was introduced in 6-17-1946. Also known as Mobile Radio-Telephone Service. This was the founding father of the mobile phone. This system required operator assistance in order to complete a call. These units do not have direct dial capabilities.
Mobile Telephone Service (MTS) was one of the earliest standards for mobile communication. By utilizing operators and VHF radio equipment, MTS tied users into the Public Switched Telephone Network (PSTN) of the time. MTS was operator assisted in both directions. If you called an MTS phone from a landline, the call would be routed to a mobile operator who would then route it to your mobile phone. To call from your MTS mobile phone, you also needed to go through an operator who would ask for both your mobile number and the number you were calling to connect the call. Before the advent of MTS, mobile radio telephones could only connect to other nearby radios and not to the PSTN.
MTS was developed by AT&T using Motorola equipment. On June 17th, 1946, Bell Systems, a part of AT&T at the time, began offering MTS to private customers. Although originally implemented with six channels in the 150 MHz band, bad cross channel interference caused Bell to drop the system down to only 3 channels. No more than 25 people could use the system at one time. Three minutes on the MTS network cost thirty-five cents in the late 1940’s, the equivalent of roughly $5.00 today. Despite frequent busy signals and expensive service, waiting lists developed in every city that MTS was offered. The main problem with the service was that the FCC would not delegate enough channels for a high capacity system. Later, the FCC finally allowed more frequencies to be used up the total to 25 channels across 3 bands (see illustration). As of 2008, only rural and wilderness locations such as the forest service continue to use the MTS standard.
How did it work?
In smaller cities and more contained areas, all MTS calls were controlled by a central headquarters or operator. Because of the limited area covered, the mobile phones could reach the HQ under it’s own power (see diagram).
In larger areas, the mobile phones simply did not have enough power to reach the central headquarters from all locations. To solve this problem, auxiliary stations were also set up to receive voice transmissions from MTS phones. The central HQ would send out the voice signal to the mobile phone but the returning voice traffic would be routed through the closest station and then through to the land based telephone network (see diagram).
The MTS system works on a half-duplex system, meaning they also used the push-to-talk system and the callers cannot talk simultaneously. The MTS system was primarily used in the 1940’s and 1950’s until the development the Improved Mobile Telephone Service (IMTS). This system was the state-of-the-art in mobile phone system during that time. IMTS was the second generation of mobile telephony next to the MTS.
MTS uses 25 VHF radio channels in the United States and Canada.
|12-ChannelMobile||Ident||24-ChannelMobile||Base Station MHz|
Why was MTS discontinued?
MTS, still being prone to long periods of busy signals and interference due to stronger radio equipment nearby, required a more stable and reliable overhaul. A major factor in the replacement of MTS for most of the United states was the fact that due to the limited VHF frequencies available, only 25 people could use the system at a time. Improved Mobile Telephone Service (IMTS) solved this problem by utilizing cellular (UHF) frequencies that typically would not reach as far as the previously used VHF frequencies, therefore allowing channels to be reused within a small area. IMTS was able to use signal strength to choose a channel and split cells into smaller units to increase the channel capacity.
In remote areas, MTS was replaced not out of necessity for more channels as it was rare for more than 24 calls to be placed at one time, but because the equipment became obsolete. As technology improved and manufacturers moved on to IMTS and eventually AMPS devices, even remote locations would struggle to keep their service operating and equipment in repair.
Is MTS Still Used Today?
Many MTS frequencies are used for local paging services in some of the most rural parts of north America. The great majority of areas have replaced MTS with cellular technology over 25 years ago
One exception is Northwestel, which still caters to a number of locations in the Yukon, British Columbia, and the Great Slave Lake region. Their MTS service currently operates at a deficit, but cellular telephone service has been ruled too expensive to install instead as limited reach would require more cellular sites, costly equipment and continuing to use a good deal of the same resources (electric power supplied by diesel generators).