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Sharing of Private Mobile Radio Channels |
This fact sheet explains why it is necessary for most users to share their PMR radio channel with other users, and what can be done to make sure that users can operate satisfactorily.
At the end of 1998 there were some 3 million mobile and hand-portable radios, and over 80,000 base stations licensed. In the UK less than 1,000 channels are available for private mobile radio (not including those allocated to the new services in Band III or those used by the cellular radio operators). It is clear from those figures that each channel has to support many base stations and many mobiles. Demand for radio tends to be concentrated in the urban areas and the countryside within easy reach of cities. This means that the coverage areas of many users overlap, so many users must share radio channels by taking turns to have access to a channel.
An "exclusive" channel is one on which a user has sole use of the channel within their coverage area whether national or local. The Agency does not have any power under Section 1 of the Wireless Telegraphy Acts 1949 and 1998 to make it a licence term that the licensee shall have exclusive use of a frequency. A PMR licence which is a permission to use wireless telegraphy apparatus on the frequency specified in it, does not confer any right on the licensee to use a frequency exclusively. There are many more applicants for PMR licences than the radio spectrum can accommodate and in order to fit in as many of these applicants as possible the Agency normally authorises the use of frequencies on a shared basis by exercising its power to grant licences for a particular frequency to as many users as it considers appropriate. For very limited categories of licensee, such as the emergency services involving safety of life, the Agency accepts that there are strong grounds for an exclusive channel and if possible confers sole use of a frequency by exercising its discretion not to issue more than one licence for the channel.
If a user is operating in an area where there is very little radio use, there may be no need to resort to channel sharing in order to accommodate all those who wish to use PMR.
Such areas are fewer than many imagine, and tend to be in North West Scotland and parts of Wales. Since mobile radio use is continuing to increase, the fact that users have in the past had channels to themselves is no guarantee that they will continue to do so. A new user may be allocated the same channel in the same area at any time. It is then essential that all sharers observe proper radio practice to avoid creating a nuisance to other users. Failure to do this may break the licence conditions.
When a user is of sufficient size (in terms of the number of mobiles used) that even if proper radio practice is observed and messages are kept short, the traffic is heavy enough to fully load a radio channel.
Shared use is then impractical and Radiocommunications Agency (The Agency) avoids allocating the same channel to others within range. But loadings well above 100 mobiles are normally necessary before sharing is genuinely impractical. However, there is no rule on this point: the volume of traffic is the deciding factor. The Agency regularly monitor channels to establish traffic volumes and check that efficient radio techniques are being used. Demand for PMR channels is such that the Agency has to periodically review the criteria for exclusive frequencies making them even tighter. The Agency can therefore give no undertaking that a frequency will remain exclusive and licensees that have had exclusive frequencies in the past may find that they have to start sharing in the future.
For commercial operators of radio services for third parties. Operators of common base stations (community repeaters) and message handling services come into this group but this depends on the operators reaching an acceptable channel loading within a predetermined time. Apart from these limited types of user, pressure of demand dictates that most users must share channels.
First, every user should be aware that the primary purpose of PMR is to pass messages connected with business. PMR is a relatively low cost service (compared, say, with cellular radio) and the available radio channels cannot support long conversations. Messages should be kept short. When passing messages over 20-30 seconds, pause occasionally to allow other stations to give urgent messages.
When beginning a transmission always use your authorised call sign. This enables sharers to readily identify messages intended for them. It also enables the Agency, when monitoring channels, to get a better idea of the true level of occupancy, and to identify unauthorised users who may be causing a nuisance to those who have paid for licences. (Failure to use call signs is in fact a breach of licence conditions.)
You should not persistently call to unmanned vehicles or base stations. In poor reception areas, a mobile should move rather than clog the channel with broken transmissions. If a vehicle remains unmanned for long periods of time, for example those used by service engineers, it is better to use either selective signalling with automatic status acknowledgement or a paging system.
Transmission of music or radio programmes is not permitted. Obscene or offensive language must not be used on the air.
Before attempting to transmit, always check that the channel is not already being used. Much of today's equipment has a "busy" light to indicate if the channel is occupied. Never interrupt a user already on a channel; even if your message is an emergency it will be quicker to let them finish their transmission. If you try to transmit over the top, both messages will be lost. The use of continuous tone controlled signalling system, or selective call, will reduce the annoyance from other users sharing your channel. However, because the sharers cannot be heard it is necessary to open the receiver and listen out before transmission.
The sheet attached to this fact sheet sets out this advice simply and may be given to staff using radio. It also has a list of common abbreviations and the phonetic alphabet.
Try to persuade the other user that it is in everyone's best interests to observe proper radio procedure and to behave considerately. If this fails, report the matter to your local RA office which is responsible for ensuring that the radio is used only in accordance with the licence granted. We can prosecute for breaches of licence conditions or unlicensed use. In addition, an offender's licence can be revoked for persistent failure to observe good radio practice or matters such as the use of obscene language on the air.
However, any complaint must be well-founded. The fact that a user may not have instant access to a channel because of another's operations does not generally mean there is a problem that needs investigation. We charge a fee to visit a user's site to investigate a case and, if the problem stems from the user's own equipment, the full cost of the investigation will be payable.
Please make any further enquiries to:
RA2/Private Business Systems Section
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London
E14 9SX
The addresses of the Agency's Local Offices are listed in RA 206 which is available from the RA Library 020 7211 0502 or 0505.
For advice on other radio matters contact the Agency General Enquiry Point on 020 7211 0211.
Suitable radio frequencies for mobile communications are in very short supply. It is, therefore, of the utmost importance that all radio systems are operated to make the maximum use of the available frequencies.
Private Mobile Radio (PMR) systems are licensed for BUSINESS USE ONLY and this Agency expects all users to comply with the Licence Conditions.
Using a radiotelephone is extremely simple. This guide illustrates how, by following a few simple rules, you will help yourself and other radio users to obtain the most efficient use of the frequencies available.
Please remember that all radio systems are shared. Use your radio as you would expect other users to do. The Agency regularly monitors radio use and may withdraw a licence if there is persistent abuse of the licence conditions.
ETA - Estimated time of arrival
ETD - Estimated time of departure
Wait or Standby - Indicates that you are unable to reply immediately and is normally followed by an indication of time, for example Wait/Standby One = wait one minute.
Say again - Repeat your last transmission
Roger - Your message has been received and understood
Over - I have finished my transmission and I await your reply. (This word is not used at the end of a final transmission).
| A = | ALPHA | N = | NOVEMBER |
| B = | BRAVO | O = | OSCAR |
| C = | CHARLIE | P = | PAPA |
| D = | DELTA | Q = | QUEBEC |
| E = | ECHO | R = | ROMEO |
| F = | FOXTROT | S = | SIERRA |
| G = | GOLF | T = | TANGO |
| H = | HOTEL | U = | UNIFORM |
| I = | INDIA | V = | VICTOR |
| J = | JULIET | W = | WHISKY |
| K = | KILO | X = | X-RAY |
| L = | LIMA | Y = | YANKEE |
| M = | MIKE | Z = | ZULU |
| RA53(Rev7) May 1999 |
