Motorola MOTRAC, MOTRAN and MOCOM

Motorola MOTRAC, MOTRAN and MOCOM: The Radios Behind the Dash

If you’ve ever looked inside a police car from the 1960s-1970s, then you’ve probably seen one of the iconic Motorola radio control heads mounted to the dash. What you’re looking at, however, isn’t the entire radio. It’s the control head for a much larger radio system, with the main radio chassis typically mounted elsewhere in the vehicle.

One of the most recognizable names associated with these radios is MOTRAC, which stands for MOtorola TRansistorized Automobile Communications. The name reflected one of the radio’s most important advances: the introduction of transistorized circuitry into a professional mobile two-way radio.

Motorola’s MOTRAC was introduced in 1958, at a time when mobile two-way radios were still heavily dependent on vacuum tubes. Tubes required considerable electrical power and generated substantial heat, creating significant challenges when the radio was installed in an automobile. A police radio also had to remain available for dispatch traffic even when the patrol car was parked with its engine turned off.

The MOTRAC addressed this problem by incorporating transistorized circuitry into the receiver and power supply, dramatically reducing the power required while the radio was receiving. Motorola’s advertising made this one of the radio’s major selling points, promoting the ability to leave the receiver operating without having to leave the vehicle’s engine running.

The MOTRAC was only the beginning of Motorola’s development of this type of mobile radio. As the technology continued to advance, Motorola produced later versions and related models carrying the MOTRAC, MOTRAN and MOCOM names.

Although these radios were not identical, they shared enough of the same philosophy, equipment and control-head design that they are often encountered together when looking at vintage police cars.

Before the Motorola MOTRAC

By the 1950s, two-way radio had become an essential tool for police departments. Patrol cars could remain in contact with dispatch while officers were away from the station, allowing calls and information to be sent directly to officers in the field.

The equipment that made this possible, however, was considerably different from the compact communications equipment we are familiar with today.

Earlier mobile radios relied heavily on vacuum tubes. Tubes were large, consumed substantial amounts of electrical power and produced considerable heat. In a patrol car, the radio was competing for electrical power with everything else the vehicle needed to operate.

This created a particular problem when a patrol car was parked with the engine off. An officer could be investigating a call, writing a report or otherwise away from the vehicle while the radio still needed to monitor the dispatch channel. A high-current vacuum-tube radio could eventually drain the vehicle’s battery.

Leaving the engine running solved the problem but meant unnecessary fuel consumption and engine idling.

The development of the transistor offered a way to dramatically reduce the power required by electronic equipment. Motorola was among the companies working to bring this technology into practical mobile communications.

The Motorola MOTRAC Arrives

Motorola introduced the MOTRAC in 1958. Its name—MOtorola TRansistorized Automobile Communications—identified the technology that distinguished it from many earlier mobile radios.

The MOTRAC did not simply replace every vacuum tube with a transistor. Instead, Motorola used solid-state circuitry where it provided the greatest practical advantages.

The receiver, power supply and exciter were solid-state, while the transmitter’s driver and final amplifier continued to use vacuum tubes. This combination allowed Motorola to take advantage of transistor technology while still producing the relatively high RF power required of a mobile police radio.

Motorola offered MOTRAC radios in different power levels and configurations, including models capable of 40, 60 and 100 watts of RF output. Depending on the model, radios could also be configured for multiple operating frequencies.

The result was a radio that combined considerably lower standby power consumption with the high transmit power and ruggedness expected of a professional mobile communications system.

Motorola’s contemporary literature emphasized several other improvements as well. The company promoted the radio’s rugged construction, reduced battery drain, high-power audio, frequency stability and reliability.

The MOTRAC was therefore not simply a transistorized radio. It was a purpose-built mobile communications system designed around the demands of vehicles that were expected to remain in service all day, every day.

The Motorola MOTRAC Family Evolves

The MOTRAC did not remain unchanged throughout its production life. Motorola continued developing its mobile-radio technology as transistor technology improved. The MOTRAN represented a later generation of Motorola mobile equipment that eliminated the remaining vacuum tubes and moved the radio to an all-solid-state design.

This evolution is one reason vintage Motorola mobile radios can sometimes be confusing to identify. Similar-looking equipment may carry the names MOTRAC, MOTRAN or MOCOM, even though the radios themselves represent different stages or branches of Motorola’s mobile-radio development.

MOTRAC

The MOTRAC was the starting point for this family of radios. Early MOTRAC designs used a combination of transistorized receiver and power-supply circuitry with vacuum tubes in the transmitter’s higher-power stages.

That hybrid approach provided an important advantage. The receiver could remain operating continuously while the patrol car monitored dispatch without requiring the power consumption of an entirely tube-based radio.

MOTRAN

As transistor technology improved, Motorola continued moving toward an entirely solid-state mobile radio.

The MOTRAN (MO: Motorola TRAN: Transistorized) represented this later development, eliminating the remaining vacuum tubes and using transistorized circuitry throughout the radio. It retained the professional, high-power mobile-radio characteristics associated with the earlier equipment while taking advantage of the improvements in solid-state technology.

MOTRAN equipment can therefore look surprisingly familiar to someone who has seen a MOTRAC installation. The control head may look like a development of the same basic system even though the electronics inside the radio chassis had evolved considerably.

MOCOM

The MOCOM (MO: Motorola COM: Communications) name appeared on another Motorola mobile-radio line that occupied a different position in the company’s product lineup.

Models such as the MOCOM 35 and MOCOM 70 are frequently encountered when researching vintage Motorola mobile equipment. The later MOCOM 70, in particular, incorporated all-solid-state technology while retaining characteristics and control-head arrangements associated with Motorola’s earlier mobile-radio systems.

This is why a vintage police car can sometimes have a Motorola control head that looks very much like a MOTRAC installation but carries a MOCOM designation.

The names matter when identifying the equipment, but the similarities are important too. Motorola was developing a family of mobile communications equipment during a period when the industry was making the transition from vacuum tubes to transistors.

The Radio System Nomenclature

One of the easiest things to misunderstand when looking at a restored police car is the relationship between the dashboard equipment and the actual radio.

The Motorola ‘radio’ mounted to the dashboard or console was the radio control head and microphone and usually had a separate Motorola speaker mounted close to it. This control head gave the operator access to the controls needed to operate the radio, but it did not contain the complete transmitter and receiver. The main radio chassis contained the receiver, transmitter, power supply and associated circuitry and was a separate, much larger unit typically mounted in the trunk and connected to the control head by a heavy multi-conductor cable.

A coaxial cable connects the radio chassis to an external antenna.

Understanding the Motorola Control Head

The control head was the part of the system the officer actually saw and operated from the driver’s seat. Motorola produced numerous control-head configurations depending on the radio model, number of channels and options ordered by the customer.

While the appearance varied, the basic purpose remained the same: put the functions an officer needed directly in front of the driver while keeping the larger radio equipment elsewhere in the vehicle.

On/Off and Volume Control – The arrangement of the power and volume controls varied between control-head designs. Some control heads used a combined on/off/volume control, with the radio switched on or off by turning the volume knob through its detent. Other control heads used a separate power switch and volume control. The exact arrangement depended on the particular radio, control head and options installed.

Squelch Control – The squelch control allowed the officer to adjust how the receiver responded to weak signals and background noise. Properly adjusted, the radio remained quiet when no transmission was being received but opened when a sufficiently strong signal was present.

Channel or Frequency Selector – Motorola produced radios with different numbers of operating frequencies. Depending on the particular installation, channel selection could be accomplished with a switch, selector or rotary control. A four-frequency control head, for example, could use a rotary selector with four positions. Other control heads were designed for more channels.

Green / Red Indicator Lights – The green indicator showed that the radio was powered on. The red indicator illuminated when the transmitter was keyed, giving the officer a visual indication that the radio was transmitting.

Bottom Row of Lights – Some multi-frequency control heads may have a row of colored indicator lamps across the bottom of the face. These lights were there to help the operator quickly identify which frequency they were hearing radio traffic on.

Private-Line (PL) Switch – Control heads equipped with Motorola’s Private-Line system could include a switch to enable or disable the system. See more about Private-Line below.

Microphone – A heavy-duty Motorola microphone was connected to the radio system and included the push-to-talk (PTT) button that the operator pressed to transmit messages.

Features and Options

Motorola offered a wide range of features and options as these mobile radios evolved. Not every MOTRAC, MOTRAN or MOCOM installation had all of them.

The equipment installed in a particular police car depended on the agency’s requirements, the radio model, the number of channels and the options ordered when the system was installed.

Private Line (PL) – Because radio waves travel long distances, police or fire departments in adjacent counties often stepped on each other’s transmissions. Private-Line ensured a department only heard its own base station and mobile. While it was named “Private-Line,” it did not encrypt the transmission. Anyone with a standard scanner could still listen to the audio. It simply provided “receive privacy” so users didn’t have to hear outside interference.

Extender – Motorola’s Extender option was designed to reduce electrical interference (noise) caused by the vehicle ignition system and other electronic devices.

Time-Out Timer – Motorola offered a Time-Out Timer to prevent a transmitter from remaining keyed indefinitely. If the microphone’s push-to-talk switch was accidentally held down, the timer could shut down the transmitter after a preset period. Motorola documentation describes a 60-second time-out followed by an alert tone. This prevented an accidentally keyed transmitter from unnecessarily tying up a radio channel.

Automatic Dimmer – Some control heads could be equipped with an automatic dimmer for the indicator lamps. The circuit adjusted the lamp intensity according to the surrounding light, reducing the brightness at night while maintaining greater visibility during daylight.

Channel Scanning – Some installations were equipped with channel scanning equipment. A multi-frequency radio could have several operating channels, and scanning equipment allowed the receiver to monitor those channels automatically. The exact scanning equipment and controls varied according to the radio and installation.

Priority Channel Scan Box – A Motorola Channel Scan Control Module with Priority Rate Control is a radio accessory that enables advanced scanning behavior, allowing you to monitor multiple channels while prioritizing certain ones for faster response to critical communications. When installed, the priority channel scan box was mounted above the control head.

Quick Call Box – When installed, the Quick-Call box was mounted above the control head and includes a “Call” indicator light and a reset switch. When dispatch sent the unit’s unique Quick-Call tones, the radio would un-mute, a buzzer or light would activate in the cab to alert the officer, and the light would stay lit until the officer pressed the reset button to acknowledge the call.

5-Position Selector Box – Some installations included a separate five-position selector mounted below the control head. The additional selector provided five selectable positions in addition to the positions available on the main control head, allowing the radio system to accommodate more operating selections than the control head could provide by itself.

From Vacuum Tubes to Solid State

The significance of the MOTRAC becomes clearer when viewed as part of the larger transition from vacuum-tube electronics to solid-state technology.

Early MOTRAC radios were hybrid designs. The receiver, power supply and exciter could take advantage of transistorized circuitry while vacuum tubes remained in the transmitter’s high-power stages.

This arrangement allowed Motorola to reduce the amount of power consumed during normal receiving while retaining the high-power RF output required of a professional mobile radio.

As transistor technology improved, Motorola was able to eliminate the remaining vacuum tubes.

The MOTRAN represented this progression toward fully solid-state mobile communications. Later related equipment, including the MOCOM 70, also used all-solid-state circuitry.

The change was more than an electronics upgrade. Solid-state components were smaller, generally more resistant to vibration and required less power than vacuum tubes. They also eliminated the need for the tube warm-up associated with older transmitters.

For equipment that spent hours bouncing down roads, sitting in hot patrol-car trunks and operating throughout a shift, those advantages were significant.

MOTRAC, MOTRAN and MOCOM Specifications

Specifications varied according to the particular model, frequency range, power level and configuration. The following comparison provides representative specifications for the three Motorola radio families discussed in this article.

Technical Category	Motorola MOTRAC	Motorola MOTRAN	Motorola MOCOM (e.g., MOCOM 70)
Circuit Design Architecture	Hybrid (Transistorized Rx/PS; Vacuum tube Tx PA)	100% Solid-State (Zero tubes; all-transistor circuitry)	100% Solid-State (Low-end versions vary; MOCOM 70 is all-transistor)
Chassis Dimensions	40/60-watt: 3¼ × 11¾ × 16¼ in. 100-watt: 3¼ × 13¾ × 18¼ in.	AAR: 18 1/16 × 4 7/16 × 13½ in. Universal: 22¾ × 5 × 16 in.	30/45-watt: 4 × 10¾ × 16½ in. 60/100-watt: 4 × 10¾ × 18 in.
Chassis Weight	Approximately 25–30 lb., depending on model	Not available	Approximately 25 lb.
Frequency Bands	Low Band (25–50 MHz) High Band VHF (136–174 MHz) UHF (406–420, 450–470 MHz)	Low Band (25–50 MHz) High Band VHF (136–174 MHz) UHF (450–470 MHz)	Low Band (25–50 MHz) High Band VHF (150–174 MHz) UHF (450–470 MHz)
RF Transmit Power Output	• Low Band: Up to 100 W • High Band: 30 W, 60 W, 110 W • UHF: 15 W, 30 W, 65 W	• Low Band: Up to 100 W • High Band: 30 W to 50 W • UHF: 30 W max.	• Low Band: Up to 100 W • High Band: 30 W to 50 W • UHF: 10 W, 25 W, 45 W
Standby Current Consumption	~0.3 A to 0.5 A (Incredibly low for its era)	~0.3 A to 0.5 A	~0.2 A to 0.4 A (Highly efficient integrated circuit design)
Channel Capacity	1–4 frequency configurations	Multi-frequency configurations, including 5-channel control heads on some installations	Multi-frequency configurations, including four-channel control heads
Control Infrastructure	Remote control head with connected microphone and speaker	Remote control head with connected microphone and speaker	Self-contained front panel (local control) or backward-compatible 19-pin remote
Squelch / Signaling System	Sub-audible “Private Line” (PL) tone boards	Sub-audible “Private Line” (PL) tone boards	Sub-audible “Private Line” (PL) tone boards

 

These specifications varied considerably depending on the radio model, frequency range, power level and options. The figures in the table are therefore representative rather than universal specifications for every MOTRAC, MOTRAN or MOCOM radio.

The most significant difference between the three systems was their underlying technology. The MOTRAC used a hybrid transistor/vacuum-tube design, the MOTRAN was fully solid-state, and later MOCOM models such as the MOCOM 70 were also fully transistorized.

Three Similar Systems

The MOTRAC, MOTRAN and MOCOM systems can look remarkably similar at first glance. They share a common approach to mobile radio equipment, with a control head in the passenger compartment, a separate radio chassis elsewhere in the vehicle, a microphone and speaker for the operator, and an external antenna connected to the radio.

Despite those similarities, they were different Motorola radio systems, representing different designs and stages in the development of mobile communications. The familiar control head may look almost interchangeable from one installation to another, but the name printed on its face identifies the radio family it was designed to operate with.

Documents

Motorola MOCOM – 70 Instruction Manual

Motorola MOTRAN Instruction Manual – Railroad

Motorola MOTRAC Instruction Manual

• The MOTRAC manual is in Portuguese. Your browser should have a translator function. I haven’t been able to find it in English.

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