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About WestCom – terms and expressions

Some terms and expressions

Closed network

A closed network is one where only radios programmed to the frequency (channel) on which it operates can use the system. Such networks are licensed by the government, which also allocates frequencies to new systems. The advantage of a closed network is that a user can reach several people immediately with a single button press, without delay. This is the great strength of two-way communication, while no talk charges are incurred.

Licence

A licence from the Norwegian Post and Telecommunications Authority (NPT) is required to operate a private closed network in Norway. Buying radio equipment before a licence has been granted is pointless. Go here for general information about private mobile radio (PMR) networks in Norway and the rules governing them.

VHF/UHF

The VHF (very high frequency) band for commercial radio starts at about 136 megahertz (MHz) and goes up to 174 MHz. VHF radios have the advantage of longer range in the open. On the other hand, they are more easily blocked by constructions such as buildings, oil installations and so forth. UHF (ultra high frequency) is divided into the SHF (super high frequency) and EHF (extremely high frequency) bands, running from 403-430 MHz and 440-470 MHz respectively. The advantage of UHF radios is that they have higher penetration and are therefore better for such enclosed locations as hotels, industrial buildings and oil installations. Radios in the UHF band are often divided into SHF and EHF models, but an increasing number of types cover the whole frequency range.

PL tone

Short for private line, this is a low-frequency tone in the 67-250 hertz (Hz) range which is superimposed on the carrier wave and remains constant as long as the radio transmits. Programming all the radios in a system to keep the receiver closed until the right PL tone is received makes it possible to reduce distracting signals from other systems. However, that does not prevent radios in other systems from listening to conversations in a PL-enabled system. This kind of signalling is also called a continuous tone coded squelch system (CTCSS).

Five-tone signalling

Five-tone signalling can have several functions. It often works almost like a phone number in order to call up a specific radio, but can equally well be used to start up repeaters or for remote operation of other functions. Such signalling is also used as caller identification, so that the person called can see who is calling. In fact, imagination is the only limiting factor for the uses of 5-tone. The most widely used version today is known as CCIR, but other systems such as ZVEI can also be found.

Ex radio

An Ex-approved radio must be used in explosive atmospheres, such as areas where hydrocarbons could occur. This means that the product is tested or modified to ensure that none of its surfaces exceed specified temperatures. That also applies to internal components.
Ex batteries are also protected against excessive use of current, in order to prevent heating and sparking.

Repeater

As its name suggests, a repeater is a repeating device – usually a free-standing radio receiver/transmitter. The receiver component accepts signals transmitted from the radio units in a system, which are then converted to another frequency, boosted, and re-transmitted via the repeater’s antenna to the system. A repeater is usually positioned in a high and unobstructed location, thereby dramatically improving the radio system’s coverage. Since radio units in such a system transmit and receive on different frequencies, they cannot be used to communicate with each other outside the range of the repeater.

Digital radio

MotoTRBO and Tetra are examples of digital radios. The first is intended for small systems with up to 30-100 terminals and the second for larger installations – at an oil terminal, for instance, or as a nationwide emergency network. Common features of both are that available frequencies are used in a more efficient way, voice quality is better and opportunities are provided for data traffic (GPS or SDS/SMS, for example). Digital radios operate with call groups rather than the radio channels normal in analogue networks. Call-group and one-to-one conversations cannot be overheard by others. Encryption can also be adopted. MotoTRBO is a free-standing system corresponding to analogue radio. Using a repeater provides two slots/channels for the price of one. Radios are supplied both with and without built-in GPS for fleet management. Tetra is a centrally-controlled system, with permissions defined from the management console. The system corresponds to the GMS network found in mobile telephony, in that radios connect to the nearest base. Among its many functions, this system can handle SDS/SMS internally (replacing alarms and pagers), act as a phone in relation to switchboards or external lines, provide fleet management, carry data traffic, allow database searches and transfer images. Atex terminals are also available for use in the offshore industry.