Introduction

There has often been confusion as to which channels are available for CBS assignments. This is in part due to the downgrading exercise carried out in the late 1980’s.

Due to the pressure applied by the rapid growth in standard PMR assignments, the decision was taken at that time to make individual private assignments on CBS channels. Whilst this no longer happens we are left with an historical problem.

The process of making other assignments looks at where there are current CBS services and avoids them. It follows that a move of a CBS Base Station on one of these channels is likely to be difficult without moving into the interference area of a standard service. We will still allow the takeover of a service providing it meets all of our rules for a takeover. It is our belief that using one of these channels as part of a trunked radio system is liable to result in interference problems. For this reason we will not allow trunking in any form on one of these channels.

Some of the channels available to CBS are exclusive to CBS operators only, whereas some have other types of service on. It is felt that we must offer a level of protection to these other services where we are unable to make a general statement as to the type of operation.

For those channels where it is likely that we will be able to approve the use of additional facilities (eg. data transmission) the channel has been marked in this plan with an asterisk and we will, in future, term them as “data compatible”. On these channels we will accept applications for both data and the use of CTCSS Group C, on a case by case basis.

Any data system may be used providing it is based upon Carrier Sense Multiple Access. We will not consider the data traffic when looking at channel loading. The parameters published elsewhere for either retention of an existing channel or for an application for an additional channel must be for voice traffic. This is to prevent a fundamental change in CBS services which could lead to the loss of the types of service in existence now and an evolution into primary data services. For those systems which use CTCSS, please notify us of the particular tone to be used for control of data messages as this will enable us to distinguish form voice when monitoring for channel occupancy. For those channels which are not considered to be data compatible, we will still allow the use of data providing message length does not exceed 650 ms and must be manually initiated by an operator. The protocol must conform to MPT 1379.

The use of Group C tones should prove no problem on the data compatible channels but you must obtain prior approval. Tones must be used in the sub-groups as published in the CBS Information Sheet (RA307).

Further Information

If you would like any further information please contact either your local RA office or:

Dave Howell on 020 7211 0238
E-mail - dave.howell@ra.gsi.gov.uk or
Girish Patel on 020 7211 0237
E-mail - girish.patel@ra.gsi.gov.uk

Fax 020 7211 0117

RA2/Public Telecommunication Networks Unit
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London E14 9SX