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Foreword

It is required by the Wireless Telegraphy Acts, 1949 that no radio apparatus shall be installed or used in the United Kingdom, except under the authority of a licence granted by the Secretary of State. It is a condition of such a licence that the performance of the radio equipment meets certain minimum standards laid down in the appropriate Technical Regulation or Voluntary National Specification.

This document details the frequency assignment criteria and principles that will be employed by RA in the selection of frequencies for use by scanning telemetry radio equipment operating in the band or frequency ranges specified.

These assignment criteria are subject to updating and amendment, and intending operators / manufacturers should consult the latest version of this document complete with any amendments. Single copies of this document are available free from the RA library at the address below:

ADDRESS:

Radiocommunications Agency
Information and Library Services
Wyndham House
189 Marsh Wall
London E14 9SX.
Switchboard and 24 hour enquiry service (for either address):
Telephone: +44 (0)20 7211 0211
Library:
Telephone: +44 (0)20 7211 0502 / 0505
Fax: +44 (0)20 7211 0507
E-mail: library@ra.gsi.gov.uk
Website: www.radio.gov.uk

1 Introduction

1.1 Foreword

This Frequency Assignment Criteria details the principles used to co-ordinate scanning telemetry systems in the band 457·5 to 458·5 MHz and 463·0 to 464·0 MHz. These systems may be used for the transmission of telecontrol or telemetry signals, as well as data distribution and gathering systems. Worked examples are included to show the practical application of the planning assumptions.

A discussion of the issues relating to the continental interference affecting UK scanning telemetry schemes and what measures may be undertaken to ameliorate the problem by making affected systems more resilient to the interference in the short term is also included. Long term solutions to this problem have yet to be finalised and form no part of this publication.

Further information on this Frequency Assignment Criteria can be obtained from the following technical enquiry contact:

Fixed Terrestrial and Satellite Links Unit (FTSLU)
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London, E14 9SX.
Tel: +44 (0)20 7211 0300
Fax: +44 (0)20 7211 0113

1.2 R&TTED Directive

The Radio Equipment and Telecommunications Terminal Equipment Directive (R&TTED), sometimes referred to as Directive 99/5/EC, was implemented in the United Kingdom (UK) on the 8th April 2000 by the Radio and Telecommunications Terminal Equipment Regulations 2000, Statutory Instrument (SI) 730. Nothing in this publication shall preclude the need for equipment or antennas to comply with the requirements of Directive 99/5/EC.

RA has publicly consulted with manufacturers and operators on all aspects of this publication and the assumptions within made for the frequency assignment (based on the planning and propagation aspects required) to assign scanning telemetry systems in geographical areas administered by the RA.

All radio systems (equipment and antennas) must comply with the "essential requirements " detailed in Article 3.2 of Directive 99/5/EC and will be licensed and co-ordinated on the basis stated within this Frequency Assignment Criteria. It is also an expectation of Directive 99/5/EC, and the purpose of this document, that the quantitative and qualitative planning procedures be published in the public domain.

A Candidate Harmonised Standard is intended as the generic standard which implements the "essential requirements " of Directive 99/5/EC. Usually ETSI have the responsibility for drafting these standards. However, in the absence of any recognised Candidate Harmonised Standard for scanning telemetry RA has prepared the Voluntary National Specification (VNS) 2111 [1]. This document was notified under Directive 98/34/EC so as to avoid any trade barriers within the European Union. There is no longer any national type approval regime under Directive 1999/5/EC. This VNS does not provide any presumption of conformity under Directive 1999/5/EC. In all situations, the submission of the appropriate technical documentation will be required to obtain the opinion of a notified body on equipment conformity to Directive 1999/5/EC. It is then the responsibility of manufacturers to proceed with self declaration under Directive 1999/5/EC as they see fit.

1.3 System protected status

Any parameters which are "non-essential requirements" under Article 3.2 of Directive 1999/5/EC are described as "non-essential parameters" within this document. Usually all "essential requirements" are specified within the generic Harmonised Standard which implements these requirements. Meeting both "essential requirements" and the "non-essential parameters" entitles the system to be licensed with "Licensed Protected Service" status, while meeting just the mandatory "essential requirements" under Article 3.2 entitles the system to be licensed with "Licensed Unprotected" status. Please refer to the UK Radio Interface Requirement 2037 [2] for further details of the protected/unprotected status.

1.4 Licencee’s responsibility

The establishment, use or installation of the systems is subject to the issue of a licence by the Secretary of State for Trade and Industry. Under the conditions of the licence it will be the responsibility of the licensee to ensure that equipment meets the minimum licence requirements stated in the UK Radio Interface Requirement 2037 [2]. Licences to authorise the use of scanning telemetry radio systems will only be granted to those identified by this reference.

1.5 References

2 Channel information

2.1 Adaptable Cellular Plan

The Adaptable Cellular Plan (Adaptable Channel Plan) was devised as a means of maximising the use of the scanning telemetry band and providing a defined planning and frequency co-ordinating environment for the major utilities of scanning telemetry; namely the Gas, Electricity and Water industries. A full description and discussion of the Adaptable Cellular Plan is given in the reference [3].

The UHF scanning telemetry band comprises of 80 channels, 72 of which are reserved for use with the Adaptable Cellular Plan. The 72 channels are arranged on a twelve cell, six channels per cell, regular frequency re-use plan. Each of the three utilities has access to two exclusive channels per cell. Eight channels (T73 to T80) are reserved for other users of scanning telemetry services and these are not subject to the Adaptable Cellular Plan.

The use of alternative planning and frequency co-ordination strategies by one or more of the aforementioned utilities within their own allotted channels is permitted by RA, providing that prior agreement is achieved and its efficacy over the present arrangement can be adequately demonstrated.

The basic parameters of the plan, as conceived in 1989, are:

• system availability approaching 99·9%;
• co-channel carrier to interference ratio of 26 dB;
• data transmission speeds of 1200 to 2400 bits/second nominal;
• cells with 25 km radii;
• six channels per cell, giving two channels per utility;
• 12 cells per cluster, giving a co-channel re-use distance of 150 km; and
• potential channel re-uses of 23 times across the UK.

This Frequency Assignment Criteria varies some of the above parameters, as well as some other aspects of the baseline standards/specifications identified in reference [1]. In light of current practice and the need to provide well-defined methods of ameliorating continental interference to UK scanning telemetry systems, these variations are:

• carrier to interference ratio has been reduced from 26 dB to 22 dB.
• data transmission speeds in excess of 2400 bits/second are permitted where this can be accommodated within the limits of IR2037, VNS2111 and RA375.
• cell radii remain at 25 km, but outstations with path lengths of up to 30 km are allowed in the first instance, with longer paths permitted on a case-by-case basis.
• the 90% rule has been replaced by a statistically based method for determining the assigning path. This makes use of the end-to-end circuit loss (EECL) rather than just the path loss.
• major user groups, such as the Joint Radio Committee1 (through JRC) and the Technical Advisory Committee2 (through CSS-SMS) may be permitted, subject to prior agreement with the Radiocommunications Agency, to use alternative planning, assignment and frequency co-ordination criteria so as to achieve improved frequency management and re-use across the UK.

The distribution of channels between the three major utility operators of scanning telemetry systems on a per cell basis is shown in table 1 below:

1 JRC - The user consultative group organised by The Joint Radio Company Ltd for the gas and electricity industries.

2 TAC - The user consultative group organised by CSS Spectrum Management Services Ltd for the water industry.

Table 1: Distribution of channels between the three major utility operators

Table 2: The preferred optimum use of the interleave channels within the Adaptable Channel Plan on a per cell and per industry basis

The cellular re-use strategy is illustrated in figure 1 and the cell centres are listed in Annex I.

Figure 1: UK cellular plan for scanning telemetry services for the utilities.

2.2 Maritime use of the scanning telemetry band

The use of on-ship communications is permitted in coastal waters, estuaries and tidal rivers for maritime safety purposes. Three 25 kHz channels are available for this service and these encompass the following channels inclusively; Group A, T2 to T7 and Group B, T1b to T7b. Consequently these channels may not be assigned in areas subject to maritime traffic. Table 3 below shows the maritime channels in relation to the interleave channel plan, which provides 79 additional 12.5 kHz channels. These interleave channels will be defined as group B; the existing channels will be defined as group A. See clause 4.2 for further details.

Table 3: 25KHz Maritime channels in relation to the interleave channel plan

Notes: * New maritime channels (UK, as defined by the RA)

# New maritime channels (International, as defined by the ITU-R)

3 Transmitting and receiving installations

3.1 General

The installations shall be in accordance with good engineering practice and conform to the advice within this document.

3.2 Antennas

The primary concern is for the transmitting antenna of a station, since radio emissions have the greatest potential to affect other users. In principle, it will be possible to use any antenna, or configuration of antennas for receive purposes without needing type approval, providing it can be co-ordinated with both co-channel and adjacent channel users, and meets the cross-polar rejection requirement. This should also extend to the use of more complex arrangements, such as passive or active cancellation techniques for the rejection of unwanted co-channel signals. The receive antenna configuration and its radiation pattern will, however, need to be registered with RA, and acceptance for registration will still depend on successful frequency co-ordination with other co-channel systems. Note that frequency assignments will be made on the assumption that all antennas comply with the "essential requirements" under Article 3.2 of Directive 99/5/EC and the "non-essential parameters", respectively described in clauses 1.2 and 1.3.

3.2.1 Antenna directivity

The co-polarised and cross-polarised directivity of an individual antenna installed at the licensed premises shall be such that the effective isotropic gain in the horizontal plane (0° elevation) at any azimuth does not exceed the value specified in references [1] and [2].

3.2.2 Directional antenna arrays

Complex directional arrays of type approved antennas will be considered on a case-by-case basis.

3.2.3 Antenna nulling techniques

Active and passive antenna nulling techniques and their arrays will be considered on a case-by-case basis.

3.2.4 Antenna discrimination

When assigning frequencies which are in use in the same geographical area, due consideration shall be taken of the antenna discrimination available where this is deemed possible.

3.2.5 Antenna polarisation

RA will specify the plane of polarisation of emissions for a particular system when frequencies for the system are assigned and in general will either be horizontal or vertical linear polarisation.

The antenna alignment for both vertically and horizontally polarised systems shall be within ±1.5° of the true vertical or horizontal plane respectively.

3.2.6 Mixed polarisation systems

The use of vertical transmit and horizontal receive polarisation at the scanner for the purpose of improving system resilience is permitted. The use of mixed polarisation receive antenna systems at the scanner for unusual circumstances, e.g. due to re-direction of outstations, is permitted. A typical example would be the normal system being vertically polarised with perhaps a more distant, possibly re-directed, outstation being "pulled-in" by means of a horizontally polarised, say 12-element, yagi antenna. Such scenarios will be considered on a case-by-case basis.

3.2.6.1 Horizontal polarisation

The use of horizontal polarisation can be of benefit in a number of circumstances; whether this is for receive purposes only, where separate transmit and receive antennas are used at all sites in the system, or for combined transmit and receive where shared antennas are used. The former would result in a mixed polarisation scheme.

The use of horizontal polarisation can give between 6 dB and 15 dB polar discrimination protection against the interfering signal. Operators in the south east of England have found this to be particularly beneficial. However, the longer the path length of the interfering signal, the more likely it is to suffer greater depolarisation and hence the lower protection figure may apply. However, care needs to be exercised in areas of flat terrain as excessive ground reflections may occur. Such scenarios will be considered on a case-by-case basis.

3.2.7 Choice of outstation antenna

A 12-element yagi is the minimum specification outstation antenna from the viewpoint of frequency management, spectrum conservation and good engineering.

Other antennas may be considered where appropriate and their possible use is discussed in section 6.0.

RA will encourage any operator to use the higher performance antennas such as an 18-element yagi antenna with a forward gain of 16·7 dBi. These antennas will be particularly useful for re-directed outstations.

3 Transmitting and receiving installations

3.1 General

The installations shall be in accordance with good engineering practice and conform to the advice within this document.

3.2 Antennas

The primary concern is for the transmitting antenna of a station, since radio emissions have the greatest potential to affect other users. In principle, it will be possible to use any antenna, or configuration of antennas for receive purposes without needing type approval, providing it can be co-ordinated with both co-channel and adjacent channel users, and meets the cross-polar rejection requirement. This should also extend to the use of more complex arrangements, such as passive or active cancellation techniques for the rejection of unwanted co-channel signals. The receive antenna configuration and its radiation pattern will, however, need to be registered with RA, and acceptance for registration will still depend on successful frequency co-ordination with other co-channel systems. Note that frequency assignments will be made on the assumption that all antennas comply with the "essential requirements" under Article 3.2 of Directive 99/5/EC and the "non-essential parameters", respectively described in clauses 1.2 and 1.3.

3.2.1 Antenna directivity

The co-polarised and cross-polarised directivity of an individual antenna installed at the licensed premises shall be such that the effective isotropic gain in the horizontal plane (0° elevation) at any azimuth does not exceed the value specified in references [1] and [2].

3.2.2 Directional antenna arrays

Complex directional arrays of type approved antennas will be considered on a case-by-case basis.

3.2.3 Antenna nulling techniques

Active and passive antenna nulling techniques and their arrays will be considered on a case-by-case basis.

3.2.4 Antenna discrimination

When assigning frequencies which are in use in the same geographical area, due consideration shall be taken of the antenna discrimination available where this is deemed possible.

3.2.5 Antenna polarisation

RA will specify the plane of polarisation of emissions for a particular system when frequencies for the system are assigned and in general will either be horizontal or vertical linear polarisation.

The antenna alignment for both vertically and horizontally polarised systems shall be within ±1.5° of the true vertical or horizontal plane respectively.

3.2.6 Mixed polarisation systems

The use of vertical transmit and horizontal receive polarisation at the scanner for the purpose of improving system resilience is permitted. The use of mixed polarisation receive antenna systems at the scanner for unusual circumstances, e.g. due to re-direction of outstations, is permitted. A typical example would be the normal system being vertically polarised with perhaps a more distant, possibly re-directed, outstation being "pulled-in" by means of a horizontally polarised, say 12-element, yagi antenna. Such scenarios will be considered on a case-by-case basis.

3.2.6.1 Horizontal polarisation

The use of horizontal polarisation can be of benefit in a number of circumstances; whether this is for receive purposes only, where separate transmit and receive antennas are used at all sites in the system, or for combined transmit and receive where shared antennas are used. The former would result in a mixed polarisation scheme.

The use of horizontal polarisation can give between 6 dB and 15 dB polar discrimination protection against the interfering signal. Operators in the south east of England have found this to be particularly beneficial. However, the longer the path length of the interfering signal, the more likely it is to suffer greater depolarisation and hence the lower protection figure may apply. However, care needs to be exercised in areas of flat terrain as excessive ground reflections may occur. Such scenarios will be considered on a case-by-case basis.

3.2.7 Choice of outstation antenna

A 12-element yagi is the minimum specification outstation antenna from the viewpoint of frequency management, spectrum conservation and good engineering.

Other antennas may be considered where appropriate and their possible use is discussed in section 6.0.

RA will encourage any operator to use the higher performance antennas such as an 18-element yagi antenna with a forward gain of 16·7 dBi. These antennas will be particularly useful for re-directed outstations.

4 Principles of assignment and EIRP derivation

4.1 Background

In the interest of economy of use of the radio frequency spectrum and of limiting interference between different radio transmissions, it is the responsibility of the Secretary of State for Trade and Industry to decide the frequency assignment, the limits of EIRP and other engineering characteristics to be permitted under the licence for each separate or group of radio installations.

Factors, which may affect the most suitable frequency, include the antenna polarisation, antenna heights, and the end-to-end circuit loss of potential interference paths, together with the Adaptable Channel Plan. An assessment may also include site intermodulation products etc, before the final frequency assignment is decided. Furthermore, when assigning frequencies in the same geographical area, due consideration is given to available antenna discrimination when this is deemed possible.

4.2 Frequency channelling

The bands 457·5 to 458·5 MHz and 463·0 to 464·0 MHz may be considered as a lower half band "L" and an upper half band "H" respectively.

A frequency assignment will generally comprise of a channel comprising a pair of transmit frequencies. One frequency chosen from the "L" half band will be assigned to the base station (scanner) and the corresponding frequency from the "H" half band to the outstation. There are both group A and interleaved group B channels within the band. The interleaved group B channels are offset from the group A channels by 6·25 kHz. The use of interleaved group B channels shall be considered on a case-by-case basis.

The frequency difference between two adjacent group A or group B channels in both the "L" and "H" half bands will be 12·5 kHz and the difference between a pair of corresponding "L" and "H" channels will be 5·5 MHz (see Annex A).

Wherever possible frequency re-use will be employed. In the case of channels T1 to T72, together with their interleave channels, this will be in accordance with the Adaptable Cellular Plan where possible. See tables 1 and 2.

The interleaved channels have been allocated to cells so as to give a two cell radii separation between the cell centres of the adjacent channels both above and below the interleaved channel, whilst retaining the industry grouping of channels. The interleave channels shown in italics in table 2 belong to another industry’s group of channels, thus they can only be used providing they have been successfully negotiated with the donor industry.

A total of 15 group A and 20 group B channels have been identified as nominally interference free on account of their offset from adjacent continental cellular radio channels. Where feasible, the scanners in interference prone areas will be assigned on these channels. Scanners assigned group B channels will generally be polarised orthogonally to adjacent group A systems. However, there can be no guarantee that any channel will remain free from continental interference in the future. The combination of the 6.25 kHz frequency offset and the use of cross-polar discrimination may provide 12 dB, or more, of isolation between adjacent group A and group B channels. These channels are;

Group A: 2, 7, 10, 15, 18, 23, 26, 31, 34, 39, 42, 47, 58, 63 and 74.

Group B: 3, 5, 11, 13, 19, 21, 27, 29, 35, 37, 43, 45, 51, 53, 59, 61, 67, 69, 75 and 77.

Channels shared with the Maritime Service will not be assigned in coastal areas and estuaries. These channels are shown in table 3.

4.3 Co-channel interference limits

RA will, as far as possible, assign frequencies on the basis that a wanted Carrier to Co-Channel Interference ratio (C/I) of 22 dB will be protected. Which in normal circumstances, for a single unwanted source at the receiver input, should not exceed -144 dBW for 99·9% of the time.

For co-ordination purposes, the EIRP is that radiated in the horizontal plane (0° elevation).

It is important that the wanted Carrier to Co-Channel Interference (C/I) ratio between the existing co-channel operators and the applicant’s systems should be maintained. The applicant’s EIRP’s should not degrade the co-channel operators’ C/I ratios, however it may be that an acceptable degradation could be negotiated with the co-channel operator(s) which will permit increased EIRP’s for the applicant. It will be the applicant’s responsibility to demonstrate that a satisfactory agreement has been reached with the co-channel operator(s).

4.4 Channel selection and assignment

For applicants other than the gas, electricity and water industries, the choice of frequency to be assigned to the system(s) will depend on the ability of RA to co-ordinate a channel, selected from within channels T73 to T80, with existing co-channel operators. In the case of a multi-site scheme, the re-use of a chosen frequency within the scheme may be necessary.

In the case of the gas, electricity and water industries, the assignment will generally be in accordance with the Adaptable Cellular Plan. These channel allocations are shown in table 1. Where it is not possible to select a channel from table 1 which is appropriate to both the cell and the applicant’s industry (which may be due either to existing assignments or maritime operations, or where it is required to import channels to satisfy increased demand for services) a channel will need to be selected by one of the following criteria:

• Where there is a high density of scanning stations and it is either inappropriate, or not possible, to use an adjacent cell channel, then a channel can be selected from either the first or second tier non-adjacent cells. The selection criteria are shown in Annexes A, B, and C for the Gas, Electricity and Water Industries respectively. For instance, if the home cell is "A", the first tier channels for the gas industry will be T48, T50, T65 and T69, the second tier channels will be T53, T55, T61, T63, T64 and T66.
• Where the density of existing scanning stations is low, or where the proposed site is on, or adjacent to, a coastal area, then it may very well be possible to import a channel from an adjacent sea-bound cell. However, the importing may result in the sterilisation of the adjacent donor cell, thus preventing the full capability of the Adaptable Channel Plan being realised in that area.
• Home cell group B channels are usually reserved for normal two frequency telemetry schemes; whereas non-adjacent cell group B channels are generally assigned to other telemetry systems, such as rural automation and single frequency schemes. An interleave channel can only be assigned provided that it is both viable to the applicant and it can be successfully frequency co-ordinated with other co-channel and adjacent channel systems. The applicant will be responsible for seeking the agreement and co-operation of all affected co-channel users. With respect to table 2, the interleaved channels have been allocated to cells so as to give a two cell radii separation between the cell centres of the adjacent channels both above and below the interleaved channel, whilst retaining the industry group of channels. The interleave channels shown in italics belong to another industry’s group of channels, and can therefore only be used provided that they have been negotiated with the donor industry.

With the above selection processes, the use of a channel will generally be at a lower EIRP than usual because of the reduced co-channel frequency re-use distance. The use of imported channels may require both the adoption of a polarisation orthogonal to that used in the channel’s home cell and directional scanner antennas. If either channel selection process fails to identify a suitable channel, then it may be possible to assign one from another industry’s group of channels, providing this can be successfully negotiated with the donor industry. In all cases, the choice of channel must be co-ordinated with existing co-channel systems.

4.5 Link Length Policy

In the interests of spectrum efficiency, RA will generally consider only those outstations, whether standard, non-standard or relay, which are grouped within a 30 km radius of the associated base station. Outstations greater than 30 km from the base station will only be considered on a case-by-case basis. This provision is to enable those outstations whose path lengths cannot readily be kept below 30 km, due to either practical or external constraints, or any procedure that has been adopted in order to ameliorate the effects of continental interference. Such outstations will need to be successfully frequency co-ordinated with other users and must comply with the planning assumptions stated within this Frequency Assignment Document.

4.6 Equivalent Isotropically Radiated Power (EIRP)

The maximum value of EIRP will be a condition of the licence. In no circumstance will RA issue a licence for any system which requires an EIRP in excess of 250 W (24 dBW).

4.7 Total path loss

The total path loss is the sum of the free space propagation, ground terrain obstruction and building and vegetation clutter losses. In general, computer based prediction methods use the first two, however some models also predict clutter losses as well. The terrain obstruction loss may be zero for some paths. This may also be the case for clutter loss. The losses may alternatively be manually calculated. The various elements of the path loss are shown in figure 2.

Total path loss = free space path loss + terrain obstruction loss +

building and vegetation clutter loss

(The free space loss is that which corresponds to a first fresnel zone clearance of 0·6, using an earth curvature factor of K=4/3).

The total path loss for assignment purposes may not exceed 143 dB under any circumstances. If it does so, the value used for assignment purposes will be restricted to 143 dB.

Figure 2: Losses along a path

4.7.1 Clutter loss

Clutter losses comprise of the following components:

• The loss due to the effects of buildings and vegetation on top of a terrain obstruction along the path.
• The loss due to buildings and vegetation in the immediate locality of the outstation. The clutter loss near an outstation may comprise of one or both of the above two components as illustrated in Figure 2.

In order to encourage operators to minimise excessive local clutter, the specification limit for clutter loss shall be 20 dB, although losses up to, but not exceeding, 30 dB will be considered on a case-by-case basis.

Where clutter losses exceed 20 dB, supporting documentation will be required which shall indicate the cause of the excess clutter and confirm that all reasonable attempts have been made to minimise local clutter effects.

For existing systems this limitation will only apply when the inclusion of additional outstations require an increase in the scanner EIRP. This limitation will apply to all new systems.

The clutter loss may be estimated by a database, calculated by a computer prediction model in conjunction with a terrain height database. It may also be determined by the actual measurement of the end-to-end circuit loss. This measured value will include further losses which will be comprised of the difference between the computer generated path profile and the actual path profile together with antenna radiation pattern anomalies created by its support structure. JRC and TAC experience indicates that clutter losses of up to 20 dB are relatively common, and up to 30 dB is sometimes unavoidable.

Any outstation whose measured path loss includes more than 20 dB of clutter ought to be re-engineered, where practicable, so as to reduce the clutter loss. This could be achieved by increasing antenna height and / or changing its spatial location on the site. There may be occasions when this is not possible, in which case the outstation may suffer poorer performance if the EIRP necessary to overcome the clutter loss cannot be successfully co-ordinated with existing co-channel systems. It will be the clutter losses in the locality of the outstation which are most likely to be reduced by the re-engineering of the outstation. For practical assigning purposes, clutter loss is defined as the difference between the RA predicted and operator measured path losses (the path loss being extracted from the measured end-to-end circuit loss).

4.8 End-to-end circuit loss

In order to optimise frequency re-use it is necessary to keep scanner and outstation EIRP’s to the minimum compatible with achieving the system performance objective. This has in the past been achieved by limiting the total path loss. However, this does not take into account other factors such as the antenna characteristics, or feeder loss, which could lead to significant increases in EIRP levels.

With reference to figure A1, the system block diagram shown in Voluntary National Specification 2111 [1], the end-to-end circuit loss comprises of the sum of all losses and gains between the transmitting station transmitter output port (C’) and the receiving station receiver input port3 (C), inclusive of both stations’ antenna radiation pattern in the direction under consideration.

Where:

The antenna gain is that gain along the direction of the path, as defined by the radiation patterns.

3 The receiver input port shall include any antenna combination or branching elements which may be used between the antenna feeder connections and the receiver unit input connection.

4 Other losses are namely, connector and feeder tail losses etc.

Table 4: A worked example for determining the assignment path

Table 5: Typical values of components

The reference values chosen are from typical systems and are based on those used in reference [3].

The values are not limiting values, except that the total end-to-end circuit loss shall not exceed 134 dB and the total path loss shall not exceed 143 dB.

4.9 Assigning Path

The method for determining the assigning path and hence the maximum outstation EIRP is described below. This replaces the former 90% rule for all new systems. In the new method the Standard Deviation of the scanner’s own family of outstation end-to-end circuit losses, multiplied by 1·6, will be used to provide an offset value. This offset value is then added to the mean end-to-end circuit loss to enable the maximum assignable end-to-end circuit loss (EECLmax ) for the group of outstations to be determined. The assigning path defines the EECLmax which will be allowed for that particular system.

The assigning path is that path whose end-to-end circuit loss (EECL) does not exceed the calculated maximum outstation permissible value EECLmax for that system. Those paths whose actual EECL exceeds EECLmax will be assigned EIRPs corresponding to EECLmax. The EECLmax is defined thus:

The above criteria will apply to existing schemes when an alteration to the system results in an increase of scanner EIRP.

In the worked example, shown in table 6, two outstations are excluded from having their desired EIRP. However, if the OS14 outstation end-to-end circuit loss, by means of a better feeder, can be reduced by 2 dB to 113·9 dB, only one outstation will be excluded. If the OS14 outstation end-to-end circuit loss is reduced by 5 dB to 110·9 dB (3 dB total path loss and 2 dB feeder loss) and the OS12 outstation end-to-end circuit loss is reduced by 6 dB to 111·9 dB (5 dB total path loss and 1 dB feeder loss), then no outstations are denied their desired EIRP. Reduction of the end-to-end circuit loss by means of an appropriately engineered system is the key to maximising the number of outstations which can be assigned their required EIRP. In a well-engineered system this usually includes all the outstations.

4.10 Path profile

To determine the maximum radiated power for both base station and associated outstations, RA will require a suitably scaled path profile corresponding to an effective earth radius to real earth radius of K = 4/3. The profile shall show the path having the assigning end-to-end circuit loss as defined in clause 4.8. Details of terrain features such as vegetation, buildings, etc, must be clearly identified along with their relative positions and heights.

4.10.1 Receiver input port signal level

Scanning telemetry systems shall be so designed that the receiver input port level will be -122 dBW for both unprotected equipment and duplicated stations utilising individual receive antennas, and -117 dBW for those operators who wish to use duplicated receivers with a common antenna. Outstations with end-to-end circuit losses that are less than the calculated maximum end-to-end circuit loss will benefit from a higher received signal at the receiver input port. A scanner receiver input port level of up to, but not exceeding, -103 dBW may be permitted in special circumstances. These will be considered on a case-by-case basis, the actual value being determined by the received level of continental interference and by what other ameliorating measures have been adopted by the operator.

New schemes to be installed in parts of the UK that are susceptible to interference, for example, south east of England, may be assigned levels greater than -122 / -117 dBW in the first instance.

In general, operators will be dissuaded from simply seeking EIRP increases and encouraged to implement more appropriate methods of engineering their system. Increased receiver input port levels will only be assigned upon the operator providing adequate evidence of the duration and magnitude of the received continental interfering signal levels, together with a statement of what other ameliorating measures the user intends to adopt to assist in combating this interference. The new levels assigned will be chosen so as to overcome the continental interference in conjunction with other practicable changes that will make the system more resilient. It may be that they will be allowed greater increases of scanner receiver input port level, and hence EIRP, for a short period of time during periods of severe interference or while other improvements are being implemented. It is accepted that there may be occasions when increased scanner receiver input port levels, and hence EIRP’s, may be the only practicable solution.

The use of these higher EIRP’s will be subject to satisfactory co-channel frequency coordination. This may require the operator, requesting these increased levels, to negotiate with the co-channel users; possibly paying for the modification of the other user’s system so as to prevent it from suffering interference as a consequence of the operator’s increased EIRPs.

The application of the receiver input port levels within a system is shown in Figure 3. These are examples of the configurations most commonly employed.

Figure 3

4.11 Calculation of Equivalent Isotropically Radiated Power (EIRP)

The maximum system EIRP will be calculated using the greatest total path loss permitted by the limiting end-to-end circuit loss determined by the method described below. The end-to-end circuit loss (EECL) comprises the total path loss + feeder losses + other losses - antenna gains in the direction under consideration. The free space and terrain obstruction loss value may be obtained by computer prediction, which may include a generalised figure for building / vegetation clutter loss.

Alternatively, the EECL may be directly measured. This measured value will include a further additional loss which will be composed of the difference between the computer generated path profile and the actual path profile together with antenna radiation pattern anomalies created by its support structure, as well as all those parameters previously defined for the EECL. It is assumed that the operator has already satisfied himself that the installations are fault free and that the measurements are taken in a prescribed manner.

When measurements are taken, it is usually the EECL that is measured and hence these values may be used directly. However, they will be compared with the predicted EECLs so as to examine the extent of the clutter loss. In the event that this exceeds 20 dB, RA will investigate the application more closely; this may involve a site visit. The assigning process can then continue when the above investigation has taken place, as is current practice for the path loss.

The method for determining the maximum system EIRPs now fully characterises a scanning telemetry system and thus ensures that no parameter need be excluded when applying the limiting rule. It is slightly more complicated than the former 90% rule, but gives the operator a greater degree of flexibility in "fine-tuning" their system so as to bring all, or most, of the outstations within the assigning rule.

Calculation of the permitted maximum EIRP will be based on the appropriate receiver input port level, as defined in clause 4.10.1, and the EECL, as defined in clause 4.8, for both the base station and outstations and the appropriate loss-to-scanner or loss-to-outstation as shown below:

Where:

EECLwc = Worst case outstation EECL (dB)

LTO = Loss-to-outstation (dB).

LTS = Loss-to-scanner (dB).

RIL = Receiver input port level (dBW).

The maximum assignable EIRP for a given scanner and its family of outstation(s) is that EIRP determined by clause 4.6.

The minimum assignable EIRP will normally not be less than -20 dBW, although lower EIRPs can be assigned.

Table 6: The application of EIRP to the example shown in table 5.

In the event that no measured end-to-end circuit or path losses are provided, then the clutter losses will not be known and the assignment will be based on computer predicted end-to-end circuit losses only. Some computer models may estimate the prospective clutter losses, in which case an improved assignment will follow. This does not preclude a user from applying for a re-assignment using measured values at a later date once his system has been commissioned; or from seeking a temporary channel to permit a survey of preferred receive signal levels for a new scanner in advance of the full application

Under normal circumstances, the EIRP that a scanner or outstation will be assigned will be limited to a minimum of -20 dBW, even though the calculated EIRP may be lower. There may be occasions where the assigned EIRP will be less than -20 dBW.

The EIRP of the system will be calculated for each outstation and the scanner in the normal manner; in that the outstation EIRP is set so as to give the correct receiver input port level at the scanner, except that the maximum assignable EIRP is set by the method described below.

• The scanner EIRP is determined from the loss-to-outstation value (LTO) and the outstation receiver input port level, as defined above.
• The outstation EIRP is determined from the loss-to-scanner value (LTS) and the scanner receiver input port level (RIL), as defined above.
• It must be noted that when the end-to-end circuit loss (EECL) for a scanner-outstation pair exceeds the calculated maximum end-to-end circuit loss (EECLmax) value, then this value is substituted for the measured, or predicted, EECL in the modified loss-to-scanner and loss-to-outstation formulae. It is this substitution which limits the EIRP which may be assigned to outstations with large EECLs, relative to the remainder of the outstations.

In the example in table 4, this results in outstations OS12 and OS14 being restricted to EECL of 114·9 dB for assignment purposes, rather than their actual end-to-end circuit loss of 117·9 and 115·9 dB. This EECLmax for the family of outstations results in loss-to-scanner values of 127 and 126 dB for OS12 and OS14 respectively and a loss-to-outstation value of 120 dB.

5 Other telemetry services

It is considered that there are six basic classes of scanning telemetry system. These are:

• Systems with standard outstations only.
• Systems with both standard and non-standard outstations.
• Systems with only non-standard outstations.
• Single hop relay systems for circumnavigating severe obstructions.
• Single standard outstation scanning telemetry systems for obstructed paths.
• Multi-hop single frequency relay systems.

The following special systems fall within one of the above categories and consequently this governs their method of assignment.

5.1 Relay outstations

RA will permit the use of relay outstations as a means of communicating with other outstations that are difficult to reach. This technique is already used by some non-utility operators. In effect, a relay outstation becomes a secondary scanner to communicate with one or more other outstations, which cannot be reached from the main scanner. The relay outstation will onward route the transmission using either the parent scanner’s transmit frequency or an alternative channel. Such relay outstations may only be used where they form an extension to a main telemetry scheme. The relay outstation will utilise antennas designated for outstation or scanner sector use and the antenna height above ground may not exceed 15 metres. The calculated EIRP will in many cases be below -20 dBW, but, where possible, a minimum EIRP of -20 dBW may be assigned. The relay outstation shall not be more than 30 km from the parent scanner.

The assigning path is determined in accordance with clauses 4.9. Non-standard outstations, as described in clause 5.4, are included in the calculations used to determine the assigning path. The calculation of the permitted maximum EIRP for the system shall be in accordance with clauses 4.6 and 4.11, except that the maximum assignable EIRP of the relay outstation and its corresponding target outstations, regardless of whether the target outstations are standard or non-standard, shall not exceed 0 dBW.

Relay outstations are not intended as an alternative to the establishment of a main scanning site, but to give access to isolated outstations where the establishment of a new main scanner site is not practicable.

Such relay outstations, together, with their target outstations, would have to be successfully frequency co-ordinated with all co-channel systems before an assignment could be made.

5.2 Regulated on-site and local area telemetry services

RA will permit the use of regulated scanning telemetry services for on-site and local area schemes. Major user groups may reserve one or more of their allocated channels for such a service if considered appropriate. Service areas of up to 1 km are envisaged. The antenna height above ground shall normally not exceed 15 metres; however, a height greater than 15 metres will be considered on a case-by-case basis. Where non-standard outstations are employed, they will be assigned according to clause 5.4. Such systems shall utilise suitable antenna systems and EIRP so as to confine their service area to the boundary of the site