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Reverse Frequency Working for Private Mobile Radio |
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What is Reverse Frequency Working or as it is more commonly called RFW?
RFW is a method of controlling a Private Mobile Radio (PMR) base station transmitter utilising the radio frequency used by the licensee as opposed to a landline. Control is achieved by the use of a fixed control point, normally a permanently located mobile transmitter, which is located within the normal service area of the base station. All radios used as control points must meet a current base station specification at the time of installation.
The control point is normally found within the licensee's premises or at a location from which control is required, e.g. an office or transport depot. The remote base station re-transmits messages received from the control point.
Most Private Mobile Radio (PMR) licensees operate in dual frequency mode. The term Reverse Frequency Working is used to reflect the control point acting as a main base station whilst using the frequencies normally assigned to a mobile i.e. the control point transmits on the normal base station receive frequency and receives on the normal base station transmit frequency.
RFW is one of several possible methods used to connect a remote base station transmitter to a licensee's business location. Other methods include connection by landline, dial up landline, microwave link or by low power device. Details of these alternative methods can be found in the following RA information sheets:-
RA327 Remote Control of Base Stations by Landline control
RA334 Remote Control of Private Business Systems Using
Licence Exempt Low Power Devices Type Approved To and Compliant With ETS 300
328.
The main advantage of RFW is its ease and speed of installation.
A potential licensee planning to install a new PMR system can apply for RFW at the same time as applying for a licence. Applications should be made using form RA1.
RFW may be added to an existing PMR system by using form RA1a or by letter. Details must be given of the RFW fixed mobile address and national grid reference, the height of the top of the fixed mobile antenna above ground level and its direction of maximum radiation in degrees east of north. All applications should be sent to the Agency's Local Office responsible for the area, unless the licensee normally deals with Central Licensing Unit at the Agency's HQ in which case it should be sent there.
The application will be evaluated according to the type of channel used. There are four main kinds of channel: shared wide area, regionally exclusive, On-Site and nationally exclusive.
Shared wide area and regionally exclusive channels
RFW will generally be allowed. The exceptions to this are in circumstances where it is judged that use of RFW would adversely affect existing or future planned use of the spectrum.
Where RFW is used antenna height and power will normally be limited to 10 metres and 5 Watts respectively. The maximum operational range will typically be up to 30km. These limits are flexible provided acceptable reasons can be justified by the applicant and the impact on the spectrum of such flexibility can be accommodated.
Restrictions on the use of RFW mean that, while most rural area applications will be allowed, it is likely that applications may be refused in major urban areas. Where an application is refused it may be because the proposed RFW installation could adversely affect the quality of service received by other licensees or constrain the Agency's ability to make new assignments to future licensees.
RFW will normally be allowed. As on-site channels use low powers and antenna heights most applications will be allowed except where there is exceptional channel congestion or where special restrictions apply. Typically the maximum on-site operational coverage area is up to a radius of 3 km.
RFW will normally be allowed. Again the typical operational coverage area is up to a radius of 30km. It should be noted that any channel congestion caused by the system operator's own RFW will not be accepted by the Agency as a valid reason for requesting additional channels.
If the RFW application is successful, a licence schedule will be issued showing the details of the RFW control point. On shared wide area channels only one RFW fixed mobile is normally allowed per base station, however in certain cases, where the necessity of more than one control point can be justified on operational grounds, additional RFW control points may be allowed.
In all such cases it should be noted that the control point may only be used as a method of connecting the remote main base station transmitter to the licensee's business location. Extra control points will be allowed solely for the purpose of facilitating use of the mobile units. Communication between control points is not permitted except for system control signalling. Control tones must be used to prevent the control points from communicating with each other.
Use of more than one control point will not be permitted in cases where it may cause interference to other users or where it would adversely affect existing or future planned use of the spectrum.
RFW equipment should not be purchased or installed before receipt of a schedule authorising RFW as a method of control. The schedule will state the location and national grid reference for the control point, antenna characteristics, antenna height, direction of maximum radiation and power.
RFW is available on a non-interference basis. If the RFW equipment causes interference to other radio users the Agency may require technical modifications to be made to the RFW control point or require operations to cease.
All applications will be given full and careful consideration. However the Agency may not be able to meet all requests for RFW particularly in areas of dense radio use. Where spectrum is scarce, priority has to be given to making channels available for communication to and from mobiles for which there is no non-radio alternative.
Should an application be refused the Agency's Local Office may be able to suggest changes to the request to facilitate its acceptance on re-application.
The equipment that will be used to comprise the control point of a RFW system must meet the following standards:
Any questions you may have on RFW should be directed to your radio supplier or to your normal point of contact within the Agency, either your Local Office or Headquarters as appropriate. Local Office addresses are available on our information sheet RA 206 or from our Enquiry Point on 020 7211 0211.
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London
E14 9SX
Website: www.radio.gov.uk
RA 360
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