In the July 28, 1945 Saturday Evening Post magazine, the commissioner of the F.C.C., E.K. Jett, hinted at a cellular radio scheme, without calling it by that name. (These systems would first be described as "a small zone system" and then cellular.) Jett had obviously been briefed by telephone people, possibly Bell Labs scientists, to discuss how American civilian radio might proceed after the war.

What he describes below is frequency reuse, the defining principle of cellular. In this context frequency reuse is not enabled by a well developed radio system, but simply by the high frequency band selected. Higher frequency signals travel shorter distances than lower frequencies, consequently you can use them closer together. And if you use F.M. you have even less to worry about, since F.M. has a capture effect, whereby the nearest signal blocks a weaker, more distant station. That compares to A.M. which lets undesired signals drift in and out, requiring stations be located much further apart:

"In the 460,000-kilocycle band, sky waves do not have to be taken into account, day or night. The only ones that matter are those parallel to the ground. These follow a line of sight path and their range can be measured roughly by the range of vision. The higher the antenna, the greater the distance covered. A signal from a mountain top or from an airplane might span 100 miles, by one from a walkie talkie on low ground normally would not go beyond five miles, and one from a higher powered fixed transmitter in a home would not spread more than ten to fifteen miles. There are other factors, such as high buildings and hilly terrain which serve as obstacles and reduce the range considerably."

"Thanks to this extremely limited reach, the same wave lengths may be employed simultaneously in thousands of zones in this country. Citizens in two towns only fifteen miles apart -- or even less if the terrain is especially flat -- will be able to send messages on the same lanes at the same time without getting in one another's way."

"In each zone, the Citizen' Radio frequencies will provide from 70 to 100 different channels, half of which may be used simultaneously in the same area without any overlapping. And each channel in every one of the thousands of sectors will on average assure adequate facilities for ten or twenty, or even more "subscribers," because most of these will be talking on the ether only a very small part of the time. In each locality, radiocasters will avoid interference with one another by listening, before going on the air, to find out whether the lane is free. Thus the 460,000 to 470,000 kilocycle band is expected to furnish enough room for millions of users. . . "

The article was deceptively titled "Phone Me by Air"; no radio-telephone use was envisioned, simply point to point communications in what was to become the Citizens' Radio Band, eventually put at the much lower 27Mhz. Still, the controlling idea of cellular was now being discussed, even if technology and the F.C.C. would not yet permit radio-telephones to use it.

In 1946, the very first circuit boards, a product of war technology, became commercially available. Check out the small board in the lower right hand corner. It would take many years before such boards became common. The National Museum of American History (external link) explains this photo of a 'midget radio set' like this: "Silver lines replace copper wires in the 'printed' method developed for radio circuits . . . One of the new tiny circuits utilizing midget tubes is shown beside the same circuit as produced by conventional methods." These tiny tubes were called "acorn tubes" and were generally used in lower powered equipment. Car mounted mobile telephones used much larger tubes and circuits.

 

 

The first commercial American radio-telephone service

 

On June 17, 1946 in Saint Louis, Missouri, AT&T and Southwestern Bell introduced the first American commercial mobile radio-telephone service to private customers. Mobiles used newly issued vehicle radio-telephone licenses granted to Southwestern Bell by the FCC. They operated on six channels in the 150 MHz band with a 60 kHz channel spacing. [Peterson] Bad cross channel interference, something like cross talk in a landline phone, soon forced Bell to use only three channels. In a rare exception to Bell System practice, subscribers could buy their own radio sets and not AT&T's equipment.

 

 

 

A simplified picture of Radio Telephone Service -- A Non-Zoned System

The diagram above shows a central transmitter serving mobiles over a wide area. One antenna serves a wide area, like a taxi dispatch service. While small cities used this arrangement, radio telephone service was more complicated, using more receiving antennas as depicted below. That's because car mounted transmitters weren't as powerful as the central antenna, thus their signals couldn't always get back to the originating site. That meant, in other words, you needed receiving antennas throughout a large area to funnel radio traffic back to the switch handling the call.. This process of keeping a call going from one zone to another is called a handoff.

 

 

The 1946 Bell System Mobile Telephone Service in St. Louis -- A Zoned System

M: mobile R:receiver. PSTN: Public switched telephone network.

 

As depicted above, in larger cities the Bell System Mobile Telephone Service used a central transmitter to page mobiles and deliver voice traffic on the downlink. Mobiles, based on a signal to noise ratio, selected the nearest receiver to transmit their signal to. In other words, they got messages on one frequency from the central transmitter but they sent their messages to the nearest receiver on a separate frequency.

 

Placed atop distant central offices, these receivers and antennas could also "be installed in buildings or mounted in weather proof cabinets or poles." They collected the traffic and passed it on to the largest telephone office, where the main mobile equipment and operators resided. [Peterson2]

 

Installed high above Southwestern Bell's headquarters at 1010 Pine Street, a centrally located antenna transmitting 250 watts paged mobiles and provided radio-telephone traffic on the downlink or forward path, that is, the frequency from the transmitter to the mobile. Operation was straightforward, as the following describes:

 

How Mobile Telephone Calls Are Handled

 

Telephone customer (1) dials 'Long Distance' and asks to be connected with the mobile services operator, to whom he gives the telephone number of the vehicle he wants to call. The operator sends out a signal from the radio control terminal (2) which causes a lamp to light and a bell to ring in the mobile unit (3). Occupant answers his telephone, his voice traveling by radio to the nearest receiver (4) and thence by telephone wire.

 

To place a call from a vehicle, the occupant merely lifts his telephone and presses a 'talk' button. This sends out a radio signal which is picked up by the nearest receiver and transmitted to the operator.[BLR1]

 

The above text accompanies a Bell Laboratories Record illustration (346K), from the 1946 article that first described the system. It gives you a good idea of how the system worked. Click on the link to view this big, but slow to load graphic.)

 

Simple block diagrams can be hard to follow. Click here to see another MTS illustration; it is from Bell Labs and my cellular telephone basics article.)

 

The lower powered 20 watt mobile sets did not transmit back to the central tower but to one of five receivers placed across the city.[BLR2] Once a mobile went off hook all five receivers opened. The Mobile Telephone Service or MTS system combined signals from one or more receivers into a unified signal, amplifying it and sending it on to the toll switchboard. This allowed roaming from one city neighborhood to another. Can't visualize how this worked? Imagine someone walking through a house with several telephones off hook. A party on the other end of the line would hear the person moving from one room to another, as each telephone gathered a part of the sound. This was the earliest use of handoffs, keeping a call going when a caller traveled from the zone in the city to another.

 

Next page--->

Resources

Peterson, A.C., Jr. "Vehicle Radiotelephony Becomes a Bell System Practice." Bell Laboratories Record April, 1947: 137 (back to text)

Peterson2 ibid. 140 (back to text)

BLR1"Telephone Service for St. Louis Vehicles." Bell Laboratories Record July, 1946: 267 (back to text)

BLR2 ibid.(back to text)

My comments for reading: The following three volumes chronicle American military radio development during World War II, focusing on the United States Army. They are indispensable for anyone researching radio, especially those looking at the beginning of F.M. for handheld and mobile operations. Part of a larger series, the United States' official chronicle of World War II, these should be available through any major university. Out of print, used copies exist, figure $25 to $30 a volume; I paid $80 for my set. They have been reprinted a number of times, any edition is serviceable. For used books try ABE below.

Terrett, Dulany. The Signal Corps: The Emergency (to December 1941). Washington, Office of the Chief of Military History, Dept. of the Army, 1956. xiii, 383 p. illus., ports. 26 cm. Series title: United States Army in World War II. Technical services

Thompson, George Raynor. The Signal Corps: The Test (December 1941 to July 1943), by George Raynor Thompson [and others] Washington, Office of the Chief of Military History, Dept. of the Army, 1957. xv, 621 p. illus. 26 cm. Series title: United States Army in World War II : The technical services

Thompson, George Raynor. The Signal Corps: The Outcome (mid-1943 through 1945), by George Raynor Thompson and Dixie R. Harris. Washington, Office of the Chief of Military History, U.S. Army;1966. xvi, 720 p. illus., maps, ports. 26 cm. Series title: United States Army in World War II. Technical services (back to text)