Two-way Radio: Analog Technologies

15 Aug. 2016   Information

APCO-16 (Association of Public Safety Communications Officials – Project 16) was an effort to establish basic requirements for a typical public safety communications system. The result was an operational/functional (non-technical) standard to which many manufacturers have responded.  The recommendation was established in 1979. It was the foundation for the further efforts of Project 25, which continued beyond Project 16 to define technical standards.

APCO-16 addressed specific characteristics and functional capabilities of trunked radio systems. The intention was to create a system concept that would satisfy the minimum needs of all potential users and permit the inclusion of more complex requirements needed by some communities then or in the future. APCO-16 published documents define the mandatory and desirable functional capabilities for a public safety analog trunked radio system.

The specifications include recommendations for analog voice modulations and trunking functions for use of the RF spectrum. As APCO-16 recommendations focus more on trunking functional specification, it does not specify how manufacturer should design the system. Manufacturers are not restricted to develop their own design to meet the required functionalities in APCO-16 recommendation. Many APCO-16 compliant products uses 3600 baud control channel for its signaling protocol.

Spectrum Utilization
As this is an analog technology, typically, APCO-16 products follow 25 or 30 KHz radio channel utilization. Thus, one 25 KHz radio channel supports one voice conversation.
Frequency Band
Following are the APCO-16 frequency bands that are typically found in the market today:
Features and Capabilities
Project 16 addressed such characteristics and capabilities as:
These capabilities bring improved features compared to previously available analog trunked system.

LTR (Logic Trunked Radio) is a signaling protocol for analog trunked radio system developed by the E. F. Johnson Company in the late 1970s. It was primarily used by private companies such as taxicabs, utilities, delivery trucks, and repair services and it is not very popular with public safety agencies.

LTR is distinguished from some other common Trunked Radio Systems in that it does not have a dedicated control channel. It uses distributed control concept. Each repeater has its own controller and all of these controllers are coordinated together. Even though each controller monitors its own channel, one of the channel controllers is assigned to be a master and all the other controllers report to it. The signaling protocol for LTR uses 300 baud control channel.

Typically on LTR systems, each of these controllers periodically sends out a data burst (approximately every 10 seconds on LTR Standard systems) so that the subscriber units know that the system is there. The idle data burst can be turned off if desired by the system operator. Some systems will broadcast idle data bursts only on channels used as home channels and not on those used for "overflow" conversations. To a listener, the idle data burst will sound like a short blip of static like someone keyed up and unkeyed a radio within about 1/2 second. This data burst is not sent at the same time by all the channels but happen randomly throughout all the system channels.

Spectrum Utilization
LTR utilizes Frequency Division Multiple Access (FDMA) technique to utilize spectrum. LTR utilizes 25 KHz bandwidths. Thus, one 25 KHz radio channel supports one voice conversation.
Frequency Band
The current available product in the market today offers the following frequency bands:
Features and Capabilities
From end user point of view, LTR provides:

MPT 1327
MPT 1327 (Ministry of Posts and Telegraph 1327) is a signaling protocol standard for analog trunked radio. It was developed in 1988 by the British Department of Trade and Industry (DTI).

The standard defines the protocol rules for communication between a trunking system controller (TSC) and users' radio units and it defines only the over-air signaling and imposes only minimum constraints on system design. The signaling protocol for MPT1327 uses 1200 baud control channel.

Systems based on MPT 1327 generally consist of several radio channels. At least one of these channels is defined as the control channel (CC) and all other channels are traffic channels (TCs). Data messages between mobiles and the network are exchanged on the control channel at 1200 bits per second. Each subscriber in an MPT-1327 trunked radio network has a unique call number. It consists of a prefix (3 digits), the fleet number (4 digits) and the subscriber’s call number within the fleet (2 or 3 digits). After it has been entered the call number will be converted in the mobile to a 20-bit address. For the duration of the call a subscriber is exclusively allocated a traffic channel from the available trunk.

Spectrum Utilization
MPT1327 utilizes Frequency Division Multiple Access (FDMA) technique to utilize spectrum. MPT1327 utilizes 25, 20, 12.5, 10 KHz bandwidths. Thus, MPT1327 has flexibility in utilizing available spectrum. Systems using 10kHz, 12.5kHz and 25kHz channel spacing have been deployed in North America.

Frequency Band
The current available product in the market today offers the following frequency bands:
Features and Capabilities
The different types of communications on an MPT-1327 network and their definitions:
        Mobile-mobile in a cell
        Mobile-mobile in different cells
        Mobile-line access unit via landline or radio
        Mobile-dispatcher station via landline or radio
        Mobile-PABX, Mobile-PSTN
        Status messages on the CC (5-bit data length)
        Short data messages on the CC (186-bit data length)
        Transparent data transmission on the TC (data communication).
        Point to point connections
        Group calls

The comparison among these analog technologies

Learn more about Digital Technologies of Two-way Radios.
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