What is PBR?

Professional Business Radio, also known as Private Mobile Radio (PMR) are radio communications systems which use portables, mobiles, base stations, and are sometimes based on such standards as MPT-1327. Key features of professional mobile radio systems can include:

> push-to-talk, release to listen - a single button press opens communication on a radio frequency channel
> large coverage areas
> closed user groups
> use of VHF or UHF frequency bands

Large sites with teams working in different areas means that communication cannot only be difficult but costly. Communicate around town, between sites, or with a team working throughout a region with a great range or enhanced security and safety features.

Licenses are required to operate this equipment. After the licence has been paid for there is no cost for the transmissions that are made, individual calls are not charged for.

Selective calling
Many systems operate with the remote or mobile stations being able to hear all the calls being made. This may not always be satisfactory and a system of selective calling may be required. There are two ways of achieving this. One is to use a system known as Dual Tone Multiple Frequency (DTMF) signalling whereas the other uses Continuous Tone Coded Squelch System (CTCSS).

CTCSS
The other widely used system is CTCSS. The system may also be referred to as sub audible tones or PL tones (a Motorola trademark). As the name suggests it uses sub audible tones (below about 250 Hz) to carry the selection information. These are transmitted in addition to the normal voice channel, but as they appear below the audio range passed by most mobile radios (roughly 300-3000Hz), they are filtered out not heard.

Only when the correct tone for the required station is transmitted will the squelch for that receiver be opened and the transmitted audio will be heard. The advantage of this system is that the subaudible tones are transmitted for the whole period of the transmission so if the signal fades at the beginning of the transmission is lost but later then increases in strength, the continuously transmitted tones will enable the squelch to open and the audio to be heard. Systems typically are able to provide up to 37 different tones, the lowest frequency of which is 67 Hz and the highest 250.3 Hz. This enables a variety of different mobiles to be called selectively.

PMR Trunking using MPT1327
Is the mutual sharing of a small number of communication channels among a large number of users it brings together groups of users to communicate, schedule, organise and plan the workflow of operatives in a defined area using an automatic trunked system.

Simply put, trunking permits a large number of users to share a relatively small number of communication paths - or trunks. Channel selections and other decisions normally made by the radio user are made by the central controller, a computerised switch. Channel assignment is automatic and completely transparent to the individual users.