Criteria for 400 KHz Channelling

New Zealand Ministry of Economic Development - Radio Spectrum Management

400 kHz Channelling Plan for FM Radio Final Report Criteria for 400 kHz Channelling

61844

REVISION NUMBER: 1, September 2007

Gibson Quai AAS Pty Ltd ABN 91 009 323 620

Level 2, 30 Richardson St, West Perth, WA 6005, Australia

Tel: (08) 9321 3166 Fax: (08) 9321 3226

Email: [email protected] www.gqaas.com.au

Telecommunications and IT Consultants

Gibson Quai AAS a UXC Company

New Zealand Ministry of Economic Development - Radio Spectrum Management 400 kHz Channelling Plan for FM Radio

Final Report - 400 kHz FMBC spacing_Rev1.doc i Rev 1

ABOUT THIS DOCUMENT

TITLE: Final Report Criteria for 400 kHz Channelling

PROJECT NAME: 400 kHz Channelling Plan for FM Radio

PROJECT NO: 61844

AUTHORISED: Tony Bower

ABSTRACT: The final report on the proposed criteria for the application of planning FM radio broadcast services with 400 kHz spaced stations servicing the same area.

Document History

Rev Date Description Author Reviewed

Rev A 20 July 07 Draft for Internal Review ASC AKB

Rev B 22 July 07 Draft for Client Review ASC AKB

Rev 0 13 Aug 2007 Final to Client AKB ASC

Rev 1 12 Sep 07 Revised Final to Client AKB ASC


Final Report - 400 kHz FMBC spacing_Rev1.doc ii Rev 1

TABLE OF CONTENTS 1 Introduction................................................................................................................. 1

2 Background................................................................................................................. 1 2.1 New Zealand FMBC Planning Parameters ............................................................... 1 2.2 Analogue FM Radio Signals...................................................................................... 1 2.3 Supplementary Information Systems ........................................................................ 2

3 Protection Ratios for FMBC services ....................................................................... 3 3.1 General Values for Protection Ratios........................................................................ 3 3.2 Protection Ratios in Specific Circumstances............................................................. 4 3.2.1 For Carrier Differences Greater than 400 kHz.................................................... 4 3.2.2 For Varying Wanted Signal Levels ..................................................................... 5 3.2.3 For Interference Caused by Intermodulation of Strong RF Signals.................... 5 3.3 FCC 400 kHz Protection Ratio and Receiver Performance ...................................... 6 3.4 Conclusion................................................................................................................. 7

4 New Zealand 400 kHz Spaced Trials......................................................................... 8 4.1 Background ............................................................................................................... 8 4.2 Skytower Trial............................................................................................................ 8 4.2.1 Service details..................................................................................................... 8 4.2.2 Measured field strengths and received audio quality ......................................... 9 4.2.3 Comments on the results.................................................................................. 10 4.2.4 Receiver tuning................................................................................................. 10 4.2.5 Listener survey.................................................................................................. 10 4.3 Issues Raised in Response to the Ministrys Discussion Paper ............................. 11 4.3.1 400 kHz spaced services are used in adjacent market areas .......................... 11 4.3.2 Intermodulation ................................................................................................. 12 4.3.3 Receiver tuning................................................................................................. 12 4.3.4 Future flexibility ................................................................................................. 13

5 International Research............................................................................................. 13 5.1 400 kHz Spaced Services ....................................................................................... 13 5.1.1 United States Federal Communications Commission ................................... 13 5.1.2 United Kingdom - Ofcom .................................................................................. 13 5.1.3 India .................................................................................................................. 14 5.1.4 Summary........................................................................................................... 14 5.2 In-Band On-Channel Digital Radio.......................................................................... 14 5.2.1 HD Radio .......................................................................................................... 14 5.2.2 NRSC tests for HD Radio ................................................................................. 16 5.2.3 Results of other tests for HD Radio .................................................................. 18 5.2.4 FMeXtra ............................................................................................................ 18 5.2.5 DRM+................................................................................................................ 19 5.2.6 Conclusion ........................................................................................................ 19

6 Criteria ....................................................................................................................... 20 6.1 General.................................................................................................................... 20 6.2 Co-sited Services Using a Shared Antenna............................................................ 20 6.2.1 General ............................................................................................................. 20 6.2.2 Practicality of Combining Equipment................................................................ 21 6.2.3 Basis of Criterion............................................................................................... 21 6.3 Co-sited Services using Different Antennas............................................................ 21 6.3.1 General ............................................................................................................. 21 6.3.2 Basis of Criterion............................................................................................... 21


Final Report - 400 kHz FMBC spacing_Rev1.doc iii Rev 1

6.3.3 Methodology ..................................................................................................... 22 6.3.4 Effective Radiated Power ................................................................................. 22 6.4 Non Co-sited Services (Near-sited) ........................................................................ 23 6.4.1 General ............................................................................................................. 23 6.4.2 Basis of Criterion............................................................................................... 23 6.4.3 Methodology ..................................................................................................... 24 6.4.4 Maximum Separation Distance (Identical Services) ......................................... 24 6.4.5 Maximum Separation Distance (Different Services)......................................... 25 6.4.6 Conclusion ........................................................................................................ 25 6.5 Horizontal Radiation Patterns ................................................................................. 25 6.6 Polarisation of the Services..................................................................................... 25 6.7 Modulation............................................................................................................... 25 6.8 Intermodulation........................................................................................................ 26 6.8.1 General ............................................................................................................. 26 6.8.2 Basis of Criterion............................................................................................... 26 6.9 Effects of Terrain on the Variability of the Received Signal Levels ........................ 26 6.10 Interference Contributions from Multiple Stations ................................................... 26

7 Planning New Services ............................................................................................ 27

8 Summary ................................................................................................................... 27 8.1 Findings and Conclusions ....................................................................................... 27 8.1.1 Protection Ratios............................................................................................... 27 8.1.2 The Skytower 400 kHz spaced trials and report............................................... 27 8.1.3 The listener survey (from the Skytower trials) .................................................. 27 8.1.4 Issues raised by RBA ....................................................................................... 27 8.1.5 International Research...................................................................................... 28 8.1.6 Digital Radio...................................................................................................... 28 8.1.7 Practicality of 400 kHz Spaced Combining Equipment .................................... 29 8.2 Criteria ..................................................................................................................... 29 8.2.1 Co-sited Services Using a Shared Antenna ..................................................... 29 8.2.2 Co-sited Services Using Different Antennas .................................................... 29 8.2.3 Non Co-sited Services Using Different Antennas............................................. 29 8.2.4 Intermodulation ................................................................................................. 30 8.2.5 Other Criteria .................................................................................................... 30 8.3 Planning New Services ........................................................................................... 30


Final Report - 400 kHz FMBC spacing_Rev1.doc 1 Rev 1

1 INTRODUCTION The New Zealand Ministry of Economic Development, hereon referred to as the Ministry, is currently considering the feasibility of increasing the FM broadcast band spectral efficiency and therefore increasing capacity, by using 400 kHz channel spacing for stations serving the same area . The usual spacing for stations serving the same area is 800 kHz.

Gibson Quai AAS was engaged by the Ministry to investigate and develop criteria for the use of 400 kHz channel spacing for FM broadcasting (FMBC) services.

This document is the final report incorporating comments from the Ministry and the Radio Broadcasters Association (RBA). The report addresses the technical planning issues associated with 400 kHz spaced services and details the proposed criteria for the planning of 400 kHz spaced FMBC services that are serving the same area.

2 BACKGROUND

2.1 New Zealand FMBC Planning Parameters The FMBC services in New Zealand are planned to standards set by the Ministry and these follow ITU-R Recommendations (principally BS.450-3 [Ref 1], BS.412-9 [Ref 2] and BS.704). The key planning parameters are as follows.

1. FMBC services are licensed within the range of 88 MHz 108 MHz.

2. Mode: Stereophonic with the Pilot-tone system with provision for supplementary services (see Section 2.2 for details).

3. Maximum frequency deviation: +75 kHz.

4. Emission bandwidth: 256 kHz.

5. Emission designation: 256KF8EHF.

6. Channel increment: 50 kHz, though 100 kHz in practice.

7. Pre-emphasis/de-emphasis: 50 us.

8. Polarisation: Mixed and linear.

9. For the purpose of planning FMBC services, the Ministry specifies the minimum usable field strength (MUFS) to be 66 dBuV/m.

10. Planning is for steady interference (rather than tropospheric interference).

11. Field strength measurements are made at 10 metres above ground level.

12. Protection ratios are in accordance with ITU-R Recommendation BS.412-9 (further discussed in Section 3).

2.2 Analogue FM Radio Signals The baseband analogue FMBC signal has a spectral form as shown in Figure 1 below. It contains a mono signal (left plus right audio channel), a stereo signal (left minus right audio channel) and sub-carriers for supplementary information systems 57 kHz and 67 kHz (discussed further in Section 2.3).



Figure 1: Analogue FMBC baseband signal

2.3 Supplementary Information Systems Supplementary information systems as defined in the ITU-R recommendation BS.450-3 are permitted subject to the requirements that under no circumstances may the maximum deviation of the main carrier by the total baseband signal (including supplementary signals) exceed 75 kHz. These systems are not specifically protected from interference in the planning models.

The Radio Data System (RDS) is such a system and occupies a bandwidth of 4.75 kHz, centred on 57 kHz. Although the protection ratios defined by the ITU-R do not take into account protection for RDS, this service can potentially operate within the parameters defined in BS.412-9, and therefore the potential for 400 kHz adjacent channel interference to appropriately designed RDS receivers is considered unlikely.

Though used widely in Europe, there has been limited demand for such supplementary services in New Zealand.



3 PROTECTION RATIOS FOR FMBC SERVICES The ITU-R Recommendation BS.412-9 details the planning standards including protection ratios for terrestrial FM sound broadcasting in the VHF-FM band.

The Protection Ratio is defined as the minimum value of wanted-to-unwanted signal ratio, usually expressed in dB at the receiver input, such that a specific reception quality of the wanted signal is received. The protection ratios given in ITU-R BS.412-9 provide an audio signal-to-noise ratio of approximately 50 dB for steady interference.

3.1 General Values for Protection Ratios ITU-R BS.412-9 provides curves and tables of the protection ratios (dB) for VHF FM sound broadcasting services such as Figure 2 and Table 1 below. These curves are derived from many measurements made over a number of years by different Administrations and as such represent general values for the protection ratios.

20

10

0

10

20

30

40

50

60

4003002001000

S1

S2

M1

M2

Rad

io-f

requ

ency

pro

tect

ion

ratio

s (dB

)

Difference between the carrier frequencies (kHz) of the unwanted and wanted signals

Curves M1: monophonic broadcasting; steady interference M2: monophonic broadcasting; tropospheric interference S1: stereophonic broadcasting; steady interference S2: stereophonic broadcasting; tropospheric interference

Figure 2: Protection ratios (dB) for varying carrier differences for services with a maximum frequency deviation of 75 kHz (Figure 1 in BS.412-9)



Carrier Frequency Spacing (kHz)

Stereophonic Audio (Steady Interference)

0 45.0

100 33.0

200 7.0

300 -7.0

400 -20.0

Table 1: Relevant values of protection ratios (dB) for varying carrier differences for services with a maximum frequency deviation of 75 kHz (from Table 3 in BS.412-9)

The notes associated with the general protection ratios are:

1. The values shown are based on the assumption that the maximum peak deviation of 75 kHz is not exceeded.

2. The values of protection ratio quoted apply to interference produced by a single source and represent a wanted signal to noise (S/N) ratio of 50 dB (weighted quasi-peak measurement).

3. The values are for moderate signal levels of the wanted service. Significantly stronger wanted signal levels can require higher protection ratio values than those given in Figure 2 and Table 1, because of non-linear effects in the receiver.

4. The ability to receive a wanted FMBC signal at a specific quality with minimal 400 kHz adjacent channel interference is largely dependent on the ability of the receiver to filter adjacent channel signals. The protection ratios specified in BS.412-9 assume the use of a low pass filter following the FM demodulator in the receiver that attenuates the spectral power of frequencies greater than 53 kHz for the pilot-tone system.

3.2 Protection Ratios in Specific Circumstances Annex 2 of BS.412-9 provides further information relating to protection ratios for particular interference cases. GQ-AAS has extracted the values of protection ratios relevant for the 400 kHz spaced services.

3.2.1 For Carrier Differences Greater than 400 kHz

BS.412-9, Annex 2, Section 2 states that the protection ratios are almost constant for carriers spaced at 400 kHz and onwards. FMBC services operating with the specifications as defined by the ITU-R recommendations are therefore likely to experience similar adjacent channel interference effects for services with carrier frequencies spaced at 400 kHz and at the Ministrys current planned spacing of 800 kHz.

A special case is that of frequency difference of 10.7 MHz, the FM receiver Intermediate Frequency. BS.412-9 recommends a protection ratio of less than -20 dB for this frequency separation.

The Australian Broadcasting Planning Handbook published by the Australian Communications and Media Authority (ACMA) [Ref 3], refers to a laboratory report from 1991 in which a number of receiver parameters including IF beat interference was measured for 48 receivers of varying quality.

The outcome of the tests was that the protection ratio required to ensure an audio S/N of 50 dB in 75% of the tested receivers in the presence of IF beat interference is dependent on the wanted signal level and the frequency difference.

The protection ratio required ranged from +34 dB for a wanted signal level of 106 dBuV/m with a frequency difference of 10.7 MHz to -47 dB for a wanted signal



level of 66 dBuV/m and a frequency difference of 10.3 MHz. The protection ratio for 66 dBuV/m and 10.6 or 10.8 MHz frequency difference was -14 dB.

The ACMA has recently undertaken a further study of IF beat interference, but the results have not been made public.

3.2.2 For Varying Wanted Signal Levels

Subsequent studies made and presented in recommendation BS.412-9 support potentially more relaxed protection ratios for 400 kHz adjacent channel interference, depending on the receiver input power. From one of the studies that tested 31 receivers, the average protection ratios for 400 kHz adjacent channel interference for domestic and car receivers are shown in Table 2.

Wanted Received Signal

(dBuV/m)

Protection Ratio (dB) Domestic Receivers

Protection Ratio (dB) Car Receivers

75 -32 -32

65 -34 -38

55 -34 -42

Table 2: Protection ratios (dB) based on wanted received signal levels and the use of domestic and car receivers, provided in BS.412-9 Annex 2.

Car receivers typically have lower (better) protection ratios for adjacent channel interference due to the higher selectivity of their generally better IF filters.

3.2.3 For Interference Caused by Intermodulation of Strong RF Signals

Where three equally spaced strong signals (one wanted, wf and two interfering signals 1if and 2if ) are supplied to the input of a receiver, there is the possibility of the two interfering signals producing an intermodulation product that will interfere with the wanted signal. The frequency relationship between the signals in the tests was:

or

212

122

iiwi

iiiw

fffff

fffff

====

The average protection ratios determined from the tests on 31 receivers for a f of 400 kHz for domestic and car receivers are shown in Table 3. The protection ratios for f = 800 kHz are provided for comparison.

Wanted Received Signal (dBuV/m)

Protection Ratio (dB) Domestic Receivers

Protection Ratio (dB) Car Receivers

f = 400 kHz f = 800 kHz f = 400 kHz f = 800 kHz 95 7 3 9 7

85 1 -1 4 0

75 -3 -7 -2 -5

65 -8 -14 -8 -11

55 -13 -19 -13 -16

Table 3: Protection ratios (dB) for intermodulation of strong RF signals based on wanted received signal levels and the use of domestic and car receivers, provided in BS.412-9 Annex 2.



Testing of receivers for the Swiss Federal Office of Communications [Ref 4] on a small sample of four receivers for intermodulation interference supported the findings shown in Table 3 for both 400 kHz and 800 kHz spaced services.

The report quoted experience in Rotterdam (in the Netherlands) where third order intermodulation interference had been noted around a high powered FM transmission site where many frequencies are used. The quoted case was for reception within 6.5 km of the Rotterdam transmitter site of services transmitted from 45 km away. Clearly the wanted signal levels would have been significantly less than the interfering signal levels.

From Table 3, the required protection ratio for intermodulation is positive for wanted field strengths >= 85 dBuV/m. In practice, very few receivers have the ITU reference receiving installation with an external antenna mounted at 10 m, so there is some latitude (15 to 20 dB) in the figure for the maximum field strength at which intermodulation interference becomes a significant problem.

The areas that are subjected to field strengths greater than 100 dBuV/m represent a small area, even for high powered services, and if the horizontal and vertical radiation patterns of the transmitting antenna can be arranged to minimise the populated areas with such high field strengths, intermodulation interference can largely be ignored.

For those situations where a transmitter site with high powered services is located within populated areas, there is potential for intermodulation interference for both 800 kHz and 400 kHz spaced services. For high field strengths the intermodulation protection ratio for 400 kHz spaced services is approximately 4 dB higher than for 800 kHz spaced services.

The most effective way to minimise the potential for intermodulation in high field strength areas where they fall on populated areas is to ensure that the wanted and unwanted field strengths are of similar or equal level. Preferably the wanted level would be higher, but because the wanted frequency may also be an unwanted frequency for another service, equal levels is generally the best compromise.

3.3 FCC 400 kHz Protection Ratio and Receiver Performance The FCC has adopted a 400 kHz protection ratio of -40 dB for signal levels corresponding to the edge of coverage (60 dBuV/m for most classes of service) and providing a S/N ratio of 50 dB.

In 1999 the US National Association of Broadcasters (NAB) tested 28 receivers of varying types against this performance standard [Ref 5] and found that 22 of the 28 receivers did not achieve the -40 dB protection ratio at the required S/N ratio. Of the six receivers that did achieve -40 dB protection ratio, five were car radios and one was a component receiver.

Additionally 12 of the 28 radios did not achieve the -20 dB protection ratio. These were mostly the clock, walkman and portable radios but the 12 included one component and two aftermarket car radios.

The median values of protection ratio achieved for each type of receiver are shown in Table 4.

The relevance to the New Zealand environment of these tests is high, as the tests were made in accordance with ITU R Recommendation BS.641 [Ref 6] and though the receivers are not necessarily the same types as are available in New Zealand, they represent a cross section of the receiver market.



Receiver Type No. of Receivers

Median Measured 400 kHz Protection Ratio (dB)

Wanted signal level = -55 dBm

Clock 5 -17

Walkman 5 -26

Portable 5 -16

Component 5 -31

Auto after market 5 -28

Auto OEM 3 -45

Table 4: Median value 400 kHz protection ratios (dB) from NAB tests.

3.4 Conclusion From the study of protection ratios for FMBCs, GQ-AAS concludes that 400 kHz spaced services can be used to serve the same area, with some constraints.

ITU-R BS.412-9 has some evidence for relaxation of the general protection ratios, though the NAB study indicated that the FCCs -40 dB protection ratio is not achievable by most radios and nearly half of the tested radios (mostly portable and clock radios) didnt achieve the -20 dB protection ratio.

Overall GQ-AAS considers that a prudent approach is not to relax the protection ratios provided in BS.412-9 (and used by the Ministry) and to adopt the general protection ratios given in Figure 2 and Table 1 in considering the criteria for the use of 400 kHz services providing coverage to the same area.

There is also evidence of the potential for interference due to intermodulation products in high field strength areas for both 800 kHz and 400 kHz spaced services (though in practice existing services with 800 kHz spacing do not appear to cause or suffer the noticeable intermodulation interference that is suggested by the protection ratios in Table 3). This may be due to the small areas in which the signal levels are high enough for the interference to be noticeable and that a large amount of radio listening is in a mobile environment, where the interference is often temporary.

On balance GQ-AAS considers that the intermodulation interference issues identified in Section 3.2.3 for 400 kHz spaced services, can be addressed by keeping the populated areas experiencing very high field strength to small areas and ensuring that in these areas, the wanted and unwanted signal field strengths are of similar or equal levels.



4 NEW ZEALAND 400 kHz SPACED TRIALS

4.1 Background Two trials were undertaken in New Zealand using 400 kHz channel spaced stations serving the same area. One trial commencing in 2003 was conducted at Skytower in Auckland, co-sited with two other services nominally spaced 400 kHz either side of the new service.

The second trial was conducted at Kaukau near Wellington which operates 400 kHz from an existing service at Towai 12 km away. There do not appear to be any reports from the Wellington trial.

4.2 Skytower Trial

4.2.1 Service details

The details of the services at Skytower taken from the RSM web site are as follows. Equivalent Isotropically Radiated Power (EIRP), which is the radiated power relative to an isotropic radiator.

Frequency (MHz)

EIRP (dBW)

TX Antenna Height (m)

93.4 47 263

93.8 40 253

94.2 47 263

The transmitting antenna horizontal radiation pattern (HRP) as listed in the RSM web site for the existing 93.4 and 94.2 MHz services is shown in Table 5 below.

From Bearing (Degrees)

To Bearing (Degrees)

EIRP (dBW)

0 35 47

35. 100. 44

100 130 45

130 190 47

190 230 45

230 280 44

280 295 45

295 360 47

Table 5: HRP for existing Skytower services on 93.4 and 94.2 MHz



Similarly, the HRP for the trial 93.8 MHz services is shown in Table 6 below.

From Bearing (Degrees)

To Bearing (Degrees)

EIRP (dBW)

EIRP Relative to 93.4

and 94.2 MHz (dB)

0 20 35 -12

20 35 30 -17

35 45 25 -19

45 60 20 -24

60 70 15 -29

70 80 10 -34

80 90 15 -29

90 105 20 -24

105 115 25 -20

115 130 30 -15

130. 150 35 -12

150 360 40 -7

Table 6: HRP for Skytower trial service on 93.8 MHz

The (HRPs) for the services are quite different. While the HRP for the existing services is nearly omnidirectional, the HRP for the trial service is very directional, resulting in significant differences in EIRP between the services in most directions. The fourth column in Table 6 shows the differential.

4.2.2 Measured field strengths and received audio quality

The services field strengths were measured at 20 locations with receiver heights of 1.5 m and 10 m and another Skytower service on 96.1 MHz was measured as a control [Ref 7].

The audio quality of the received signals (with an antenna height of 1.5 m) was assessed using a range of portable receivers and clock radios at each of the sites.

The summary of the results of the tests showing the average received signal levels and the average received signal quality is provided in Table 7.

Tx Frequency (MHz) 93.4 93.8 94.2 96.1

Tx EIRP (dBW) (quoted in tests) 45 37 42 27

Rx Signal Average Level 1.5 m agl (dBuV/m)

64 54.4 59.3 50.7

Rx Signal Average Level 10 m agl (dBuV/m)

83.6 75.7 80.4 68.4

Rx Signal Average Audio Quality 1.5 m agl

4.3 3.1 4.3 3.7

Rx Signal Quality Standard Deviation

0.61 0.99 0.6 1.01

Table 7: Summary of Skytower trial test results



4.2.3 Comments on the results

The TX EIRPs for the services listed in the report are slightly different from those on the RSM web site (see Section 4.2.1). Irrespective of that, given the differences in the HRPs for the existing and trial services, it is surprising that the difference in the average RX signal levels is not greater. GQ-AAS expects that there is significant interference in the east and north east of the coverage area due to 400 kHz adjacent channel interference, though none was reported in the tests.

The results for each site do show larger differences at two sites - Stevenson Reserve, Minerva Terrace (25 dB) and Bastion Point (20 dB) and the audio quality for the 93.8 MHz service is noticeably inferior at these locations. It is likely that the receivers in these locations are experiencing 400 kHz adjacent channel interference (on 93.8 MHz).

The tests were inconclusive on the potential for intermodulation interference with the 400 kHz spaced services. The potential intermodulation victims were the existing services (2 x 93.8 94.2 = 93.4) and (2 x 93.8 93.4 = 94.2), both of which are received at higher field strengths than one of the interfering services (93.8 MHz).

Also, the signal levels at the 1.5 m antenna height used for the audio quality tests were significantly lower than at 10 m, so the required protection ratio for intermodulation interference was lower than the measured difference between the wanted and unwanted services.

The audio quality of the 93.8 MHz service was consistently lower than the 400 kHz adjacent services, though no explanation was given. This is reflected in the Table 7 summary results where the average audio quality was 3.1 for 93.8 MHz compared with 4.3 for both 93.4 and 94.2 MHz services.

An additional factor was the audio quality tests were subjective and the report noted the difficulties of conducting the tests with continuous background noise and the receiver generated distortion.

4.2.4 Receiver tuning

The seven portable and clock radio receivers used in the trial were of varying ages from 30 years old to reasonably current models. All had analogue tuning, though digital tuned car radios were used in the tests for programme identification to assist with tuning the analogue receivers.

The two engineers reported on the tuning of the analogue tuned receivers and generally found that careful tuning was required to tune to the 93.8 MHz service. One of the receivers (the TEAC Multijog clock radio), which was the most recently released radio) was so difficult to tune that it was dropped from the tests toward the end of the tests.

The engineers also found that for the very low cost radios, it was not possible to tune to the 93.8 MHz frequency in high field strength areas. They presumed this was due to the inferior selectivity of these receivers.

GQ-AAS notes that the engineers are educated users and that if they found it difficult to tune the analogue radios to 93.8 MHz, it is almost certain that the general public would find it more difficult.

4.2.5 Listener survey

Research International conducted a telephone survey to investigate the effect of the trial service on the existing 400 kHz adjacent services [Ref 8]. A third service 91.8 MHz was used as a control for the survey.

The results of the survey were:

1. 86% of respondents noticed no change to the reception of the three stations.

2. Of the 14% who noticed a change:



40% noticed an improvement in sound quality and 12% noticed the change as stronger signal.

16% noticed worse sound quality and 23% noticed the change as weaker signal.

26% reported interference, drop outs or couldnt find the station. 3. Of the listeners to the listeners to the 93.4 MHz service who noticed changes,

none noticed any crossover, ghosting or interference from another station.

4. Of the listeners to the 94.2 MHz service who noticed changes, 14% noticed crossover, ghosting or interference from another station.

5. Of the listeners to the 91.8 MHz control service who noticed changes, 10% noticed crossover, ghosting or interference from another station.

Overall, Research International concluded that from the survey results,

there is no significant interference with the 93.4FM and 94.2FM frequencies with the introduction of a higher powered 93.8 FM signal

4.3 Issues Raised in Response to the Ministrys Discussion Paper In September 2005, the Ministry issued a discussion paper [Ref 9] for comment and one of the issues was:

Proposal A - The Ministry seeks comments on adopting a policy of permitting co-sited transmitters with a frequency separation of 0.4 MHz, providing that the licensed eirp of such transmitters are within 10 dB of each other. Existing planning standards for determining compatibility with licences in adjacent areas would also apply.

The Ministry received a number of submissions in response to Proposal A and the important technical issues raised are discussed in the following sections. GQ-AAS has not considered issues associated with licence values, revenues, etc.

4.3.1 400 kHz spaced services are used in adjacent market areas

The Radio Broadcasters Association (RBA) [Ref 10] raised concerns that where the 400 kHz frequency is already in use in an adjacent area to the site for which 400 kHz spacing is being considered, if the frequency is used, the relationship between stations in the adjacent areas will go from 400 kHz difference to a co-channel relationship.

RBA noted that to achieve this co-channel operation, EIRP reductions of the new service in the direction of the existing service may be required to ensure the 66 dBuV/m contour of each service is protected. This would have the effect of increasing the possibility of interference to the new service from the 400 kHz spaced services.

RBA also noted that the change to a co-channel relationship would reduce the effective coverage area of the existing service. In the extreme case the existing services interference free coverage could cease near the 66 dBuV/m contour, where previously it may have been able to be received at much lower field strengths.

GQ-AAS generally agrees with this assessment, but points out that by the Ministrys planning rules, a service could be established on a frequency co-channel with the existing service at a site different from the one being considered for 400 kHz spaced services, and have the same effect on the existing service.

Additionally, the aim of this report is to develop criteria that will ensure that the potential for interference to the new service (and other services) is minimised and GQ-AAS anticipates that if these criteria are accepted by the Ministry, the planning for new 400 kHz services would be carried so that the new services meet the criteria.



On this basis, 400 kHz services serving the same area would not automatically be introduced, but would only be introduced if they could meet all the necessary planning criteria. GQ-AAS concludes that If 400 kHz spaced services are considered for an area that has an adjacent area with services operating on these frequencies, it is very unlikely that proposed 400 kHz spaced services will be able to meet the planning criteria to operate co-channel with the existing services

4.3.2 Intermodulation

RBA commented that introducing 400 kHz spacing could double the number of spectrum licences at a site, causing far more intermodulation products, increasing the likelihood of interference to aeronautical and mobile radio services.

GQ-AAS considers that due to other interference issues, it is extremely unlikely that the number of licences at any site will be doubled by introducing 400 kHz spaced services. A further check on the potential of a proposed FMBC service to cause interference to aeronautical and land mobile services is part of the coordination required in the Ministrys Certification Requirements for new FMBC services.

If there are intermodulation products that land on the aeronautical and mobile radio services, these would either be generated at the FMBC transmitter site (which would be the responsibility of the broadcasters to resolve by further filtering) or in the aeronautical or land mobile receiver. The receivers for these services are typically well protected from interfering signals by filtering.

GQ-AAS considers that the introduction of 400 kHz spaced services is unlikely to increase the likelihood of intermodulation interference to aeronautical and mobile radio services if the usual Ministry planning procedures are followed.

4.3.3 Receiver tuning

RBA made the point that on some analogue radios, it can be difficult to tune to 800 kHz spaced stations and that tuning to 400 kHz spaced stations would be more difficult. Tuning to 400 kHz stations with digital tuners as found in all modern car radios and some portable and fixed radios is straight forward.

Research International carried out a market survey [Ref 11] to determine the number and types of radio in homes and the penetration of digital tuners. The results were:

1. On average each home has 3.4 radios.

2. 67% of the radios have analogue tuners and 33% have digital tuners.

3. 33% of homes have only analogue tuned radios, 13% of homes have only digital tuners and 54% of homes have both analogue and digital tuned radios.

GQ-AAS carried a detailed search for data on the tunability of analogue tuned radios with 400 kHz spaced services, but was unable to locate any definitive information.

GQ-AAS considers that the point made by RBA is valid, but is unable to quantify the impact on the introduction of 400 kHz spaced services. However, GQ-AAS makes the following observations on the prevalence of analogue and digital tuning.

Digital tuned radios are more expensive than an equivalent analogue tuned radio.

Analogue tuned radios vary in their ability to be tuned to the 400 kHz spaced services.

It is likely that digital tuned radios will become more common place in time, but it is likely that low cost analogue tuned radios will continue to be sold.

Stations on the 400 kHz spaced channels will not be as readily available to all listeners as those on the 800 kHz spaced channels.

Listeners wanting to tune to the 400 kHz spaced channels are likely to purchase radios (analogue or digital tuned) that will allow them to tune to the channel.



4.3.4 Future flexibility

RBA raised concerns that the introduction of 400 kHz spaced services may preclude the adoption of some digital radio formats. Digital radio is addressed in detail in Section 5.2.

5 INTERNATIONAL RESEARCH

5.1 400 kHz Spaced Services GQ-AAS researched international sources for examples and experience with 400 kHz spaced stations serving the same area. The following is a summary of the results of the search.

5.1.1 United States Federal Communications Commission

Currently the FCC does not generally permit co-sited assignments or assignments with significantly common coverage areas with 400 kHz carrier spacing. The FCC specifies the minimum distance allowed between transmission sites based on carrier frequency difference and the class1 of the FMBC radio licence [Ref 12].

However, for LP100 and LP10 FMBC services (100 W and 10 W ERP services respectively) there is no minimum distance specified between the LP100 and LP10 services for 400 kHz spacing. The potential for interference between these classes of service appears to be overcome by the FCCs protection ratio for 400 kHz spaced services of -40 dB and the restriction of antenna height to 30 m. This limits the approximate service range to 5.6 km.

5.1.2 United Kingdom - Ofcom

The Ofcom generally permits co-sited assignments or assignments with significantly common coverage areas with 400 kHz carrier spacing under the condition that the Ofcom technical criteria requirements are met for protection ratios. The protection ratio as defined by the Ofcom for 400 kHz carrier spacing is -20 dB. In planning the services, Ofcom may or may not take into account the extra protection margins achieved by other factors such as antenna directivity and polarisation discrimination, and these are dealt on a case by case basis.

In response to requests for information on the 400 kHz spaced services, Ofcom reported that 400 kHz spaced services are primarily in London. The services operating with this separation are 96.9 and 97.3 MHz and 105.4, 105.8 and 106.2 MHz. The 96.9 and 105.8 MHz services are radiated from a mast approximately 1 km from the mast that radiates the other services.

All but the 96.9 MHz service are used for London-wide services using a mixed polarised, omni-directional antenna and a total ERP of 4 kW. 96.9 MHz is used for a local service for the Brixton area of the city with a vertically polarised, directional antenna with an ERP of 36 Watts.

Ofcom has not received any reports of interference between the services mentioned above even though the 96.9 / 97.3 MHz relationship has existed since 1990. Given the 17 dB power difference, slightly different site locations and antenna patterns, the ITU protection ratio is almost certainly exceeded in some locations.

One issue that Ofcom has been unable to resolve is the combining of 400 kHz spaced services into the same antenna system; which is partly the reason for the services being radiated from different sites.

1 Classes of FM radio licences are based on the ERP of the service and height above average terrain (HAAT) of the transmitting antenna.



5.1.3 India

India is currently undergoing Phase II of their programme to release new assignments for private (commercial) FMBC services. In Phase I of the project, 400 kHz spacing was used in the four largest cities, with mandatory co-location of the transmitting equipment in each city [Ref 13].

Despite issues associated with co-locating private broadcasters at shared facilities, the Telecom Regulatory Authority of India (part of the Ministry of Information and Broadcasting) has ruled it mandatory that all 338 Phase II services shall use co-sited transmission facilities at 91 predetermined sites. This decision was taken for a number of reasons, including reduced costs from sharing infrastructure and reduced complexity in frequency analysis so that interference analysis for each service is kept to a minimum [Ref 14].

The co-sited services with channel spacing of 400 kHz are segmented into two separate combining and antenna systems. This allows a minimum channel spacing of 800 kHz per combiner system, reducing the complexity and cost of the system.

5.1.4 Summary

GQ-AASs search found that there is very little literature publicly available concerning the outcomes of introducing 400 kHz spaced services other than the reports of the New Zealand trials (see Section 4).

5.2 In-Band On-Channel Digital Radio The use of In-Band On-Channel (IBOC2) digital radio for simultaneous broadcast of analogue and digital FMBC services requires the transmission of additional radio frequency (RF) spectral energy in sub-carriers or sidebands surrounding the primary or host FM analogue signal.

There are a number of IBOC methods in use or in development such as HD Radio, FMeXtra, and DRM+. Each method potentially has different bandwidth requirements, and at present HD Radio is designed to transmit digital information within 200 kHz of the main analogue carrier (see Figure 3), while FMeXtra is designed to transmit digital information within 100 kHz of the main analogue carrier (see Figure 5).

5.2.1 HD Radio

The power spectral density (PSD) for the HD Radio hybrid (analogue plus digital) signal is shown in Figure 3 below with the current New Zealand Unwanted Emission Limits (UELs) for analogue FMBC services overlaid [Ref 15].

2 In-band/On-channel is a digital radio system that places digital signals within the current FM (or AM) bands and simultaneously transmits the digital and analogue signal within the bandwidth of the analogue channel.



Frequency offsetfrom carrier (kHz)

Power (dB)

-198 kHz -129 kHz +129 kHz +198 kHz

Analogue FM Signal

Digital IBOC Signal (LSB) Digital IBOC Signal (USB)

0 kHz

Audio (Stereo) Components

-13 dBc (typical)

-41 dBc

0 dBc

+240 kHz-240 kHz

-35 dBc

-25 dBc

NZ Unwanted Emission Limits (UELs)

Figure 3: Representation of HD Radio spectral power density with NZ UELs.

Though the hybrid signal PSD falls within the UELs for analogue FMBC services, any significant spectral components transmitted at frequencies greater than 200 kHz from the main analogue carrier have the potential to interfere with digital and/or analogue signals of other 400 kHz spaced services (see Figure 4).

Frequency (kHz)

Power (dB)

Analogue FM Signal 2

Digital Signal2 (LSB)

Digital Signal 2 (USB)

Power (dB)

Analogue FM Signal 1

Digital Signal 1 (LSB)

Digital Signal 1 (USB)

400 kHz

~4 kHz Guard Band

Figure 4: Representation of 400 kHz adjacent HD Radio FM broadcasts

The HD Radio Transmission System Specifications published by Ubiquity Digital Corporation in February 2005 [Ref 16] significantly tighten the spectral emission limits for the hybrid signal PSD compared with the analogue UELs (see Table 8 below). The aim of this is to reduce the likelihood of interference due to spectral regrowth3, which has the potential to increase the noise within the emission mask of a 400 kHz spaced service.

3 Spectral regrowth refers to energy emissions in harmonically related sidebands of the main digital signal, and are caused by intermodulation products from densely modulated digital signals due to non-linearities in transmission systems.



Frequency Offset Relative to Carrier

(kHz)

HD Radio Emission Limit

(dBc)

Frequency Offset Relative to Carrier

(kHz)

Existing NZ FMBC UELs (dBc)

100 to 200 -40 128 to 240 -25

215 -61.4 240 to 600 -35

215 to 540 -74.4

>= 600 -80 >= 600 -43 dBW EIRP, or -35 dBc if >-43 dBW

Table 8: HD Radio FM Waveform Noise and Emission Limits and the existing NZ UELs

The specification notes that in certain circumstances, additional filtering, etc may be required to reduce spectral emissions below the limits in the table to reduce mutual interference between services (co-channel, 100 kHz, 200 kHz, 300 kHz and 400 kHz spaced services).

5.2.2 NRSC tests for HD Radio

The U.S. based National Radio Systems Committee (NRSC) undertook an evaluation of the HD Radio IBOC system in November 2001. This evaluation included tests to determine the impact of an FM HD Radio signal on reception of a 400 kHz adjacent channel analogue FM signal.

The tests were carried out using four analogue receivers carefully chosen to be representative of the selectivity characteristics of the type of receiver - aftermarket car radio, OEM car radio (both very selective) portable radio (moderately selective) and home stereo hi-fi (selective). The digital receiver was an iBiquity FM IBOC prototype receiver.

The tests did not use the noise and emission limits from Table 8, as these values had not been developed at that time. The noise and emission limits used in the tests had a minimum defined value of -60 dBc at >= 270 kHz offset from the carrier.

Interference to analogue receivers

For the analogue receivers, the tests were performed to measure the audio S/N ratio of the wanted signal in the presence of a 400 kHz spaced analogue FMBC signal, compared with the effect of a 400 kHz spaced hybrid HD Radio signal. The tests were carried out for a range of wanted to unwanted signal levels (-20 dB to -40 dB).

The report from the tests - Evaluation of the Ibiquity Digital Corporation IBOC System Part 1 FM IBOC dated November 2001 [Ref 17] found that for 400 kHz adjacent channel interference to analogue receivers, with a wanted to unwanted signal level ratio in the range of -20 dB to -40 dB, automotive receivers receiving conventional FM analogue signals were not affected by the presence of IBOC digital sidebands.

Wanted to unwanted signal level ratios of about -30 dB and -40 dB affected some home hi-fi receivers to a significant extent and wanted to unwanted signal level ratios as low as -20 dB presented noticeable interference to portable receivers. The difference in performance between the devices was attributed to the selectiveness of the front-end IF filters for the receivers.

Table 9 has the data for the impact of HD Radio on the audio noise S/N ratio (that is the reduction in S/N in the presence of the HD Radio digital sidebands) for a wanted to unwanted signal level ratio of -20 dB compared with the S/N in the presence of an analogue FMBC signal for the same ratio of wanted to unwanted signals.



Receiver Type Impact on Audio S/N Ratio at a

nominal Wanted to Unwanted Field Strength Ratio of -20 dB

(dB)

Car Radio 0

Home hi-fi 0

Portable Radio -6

Table 9: Impact of HD Radio on Audio S/N Ratio at a Wanted -to- Unwanted Field Strength Ratio of -20dB

The actual audio S/N ratio for the car radio and home hi-fi was approximately 42 dB Weighted Quasi-Peak and for the portable radio 24 dB for the analogue interfering signal and 18 dB for the HD Radio interfering signal.

The relevance to the New Zealand environment is moderate, based on the methodology of the tests being different from the usual ITU-R methodologies and the small number of receivers tested. Further testing is required for a definitive answer on the impact of HD Radio on FMBC services.

Interference to Sub-carrier Systems (SCA)

The HD Radio tests included interference tests on two receivers for 67 kHz and 92 kHz sub-carrier (SCA) systems (also known as Supplementary Information Services) associated with the main analogue signal. The results from the tests were inconclusive though the report concluded that:

careful evaluation of test data shows that the digital SCA services tested (RDS and DARC) should not be adversely impacted by IBOC.

NRSC recommended further tests on SCA systems, especially for analogue SCA systems. Further tests were carried out in March 2002 at the request of the SCA industry representatives and the results were published [Ref 18].

Tests were performed on eight SCA receivers and the wanted to unwanted signal level ratio was determined that would provide a weighted quasi-peak audio signal-to-noise ratio of 25 dB for the SCA service. The tests were repeated for the interfering signal being a standard analogue FMBC signal and a hybrid HD Radio signal.

From the test results it was found that:

1. For 400 kHz spaced services, the mean wanted to unwanted ratio changed from -27.5 dB for the standard analogue FMBC signal to -17.9 dB for the hybrid HD Radio signal.

2. For 200 kHz spaced services, the mean wanted to unwanted ratio changed from +16.2 dB for the standard analogue FMBC signal to +17.4 dB for the hybrid HD Radio signal.

3. There was little difference in the susceptibility to interference of 92 kHz SCA receivers compared with 67 kHz receivers.

The tests were not made at a range of wanted signal levels, so there was no data relating to variation of the changes to the required protection ratios with wanted signal level.

These tests are relevant to the New Zealand environment in a general sense in that they show a significant degradation in the available 400 kHz protection ratios for SCA services with the introduction of hybrid HD Radio. This would apply to any 400 kHz adjacent channel services, where one service had an SCA service and the other had a hybrid HD Radio signal.



Further data on the variation of the changes to the required protection ratios with wanted signal level is required to determine whether there is a particular issue for 400 kHz service providing coverage to the same area.

Interference between HD Radio services

For the case of 400 kHz spaced HD Radio services, in Section 4.5.4 of the report, the authors found that:

Laboratory tests of digital performance in the presence of single and dual 2nd-adjacent IBOC interferers established that the iBiquity FM IBOC system is extremely robust with respect to this type of interference, and confirms that the 4 kHz guard band between 2nd-adjacent IBOC digital sidebands is adequate.

The field tests of 400 kHz spaced services were also positive for the digital performance of the HD Radio system and the performance exceeded that of the FCCs -40 dB required protection ratio for 400 kHz spaced services.

5.2.3 Results of other tests for HD Radio

GQ-AAS searched extensively for other testing of HD Radio IBOC systems, but was unable to locate any reports of other tests. All the information on HD Radio from the FCC and ITU referred back to the NRSC tests.

Brazil and France are currently undertaking trials of the HD Radio system. Both countries report that the tests have demonstrated reliable coverage for VHF operations with no reports of interference. The ITU-R is waiting for more comprehensive results from these on-going trials [Ref 19].

5.2.4 FMeXtra

The FMeXtra standard transmits digital information between 53 kHz and 99 kHz from the main FM carrier for simultaneous broadcast with the analogue stereo FM radio signal (shown in Figure 5), and between 20 kHz and 99 kHz with analogue mono FM radio signal.

GQ-AAS is not aware of any documented testing of the FMeXtra system and its potential interference to analogue FMBC services. However, the risk of adjacent channel interference appears to be inherently less than that of HD Radio due to a smaller emission mask and because the emissions are within the typical maximum bandwidth of emissions as defined by the Ministry4.

4 Typically the New Zealand FMBC services have a maximum bandwidth of emissions limited to not more than 120 kHz above and below the carrier frequency.



Figure 5: Representation of digital FMeXtra and analogue stereo FM radio spectral power

density

5.2.5 DRM+

DRM+ is still in development for VHF FM radio broadcasting. DRM+ is a further development of the original DRM standard which is based on digital radio for AM radio broadcasting. At present the power spectral density of the DRM+ system has not been finalised.

5.2.6 Conclusion

From the study of the research on digital radio in the FM band (primarily the IBOC HD Radio system), GQ-AAS concludes that the use of 400 kHz spaced services in the same coverage area will not restrict the introduction of HD Radio in the New Zealand as any effects related to 400 kHz spaced HD Radio services in the same coverage area would also apply to 400 kHz HD Radio services that are not serving the same area.

All the factors affecting the decision on whether or not to introduce HD Radio in New Zealand are beyond the scope of this study, but GQ-AAS has concerns that the testing to date of the impact of the introduction of HD Radio appears to have been extremely limited.

IBOC services have the potential to cause spectral regrowth, which may increase noise within the emission mask of a service spaced 400 kHz from the IBOC service. To overcome this, tighter spectral emissions have been adopted for the HD Radio specifications and GQ-AAS concludes that these UELs should be adopted with any introduction of HD Radio in New Zealand.

Generally, HD Radio IBOC transmission requirements exceed the parameters defined in ITU-R BS.450-3, thus potentially increasing the protection ratio requirements for 400 kHz adjacent channel interference. However in laboratory and field testing for the HD Radio system in the USA, at a wanted to unwanted ratio of -20 dB, a reduction in the audio S/N quality was only observed on the performance of a portable receiver. Car radios and a domestic hi-fi receiver were not affected by the 400 kHz adjacent channel HD Radio service.

Though the initial results are positive, further studies are required to confirm that HD Radio can be introduced without causing a change to the required protection ratio for 400 kHz spaced services.



US tests indicate that hybrid HD Radio signals have the potential to cause a significant reduction in the available protection ratio for SCA services associated with a 400 kHz spaced analogue FMBC service, whether or not the services are sharing the same coverage area.

GQ-AAS notes that the specifications and methods of measurement of other IBOC digital radio systems such as FMeXtra and DRM+ have not yet been finalised into standards and therefore the effects of these services can not be quantified at this time.

6 CRITERIA

6.1 General One of the fundamentals of the New Zealand FMBC planning model is that within the service area of an existing service, its signals shall be protected from significant interference from other services where they are greater then the MUFS. The MUFS for planning purposes as defined by the Ministry is 66 dBuV/m, unless otherwise stated in special circumstances [Ref 15].

There are multiple factors and scenarios that affect the potential operation of 400 kHz spaced services and these include:

1. The Equivalent Isotropically Radiated Power (EIRP) or the Effective Radiated Power (ERP) of the services

GQ-AAS has used ERPs in this section as the calculations are generally based on ITU curves, which use ERP, rather than EIRP.

2. Co-sited services using the same antenna

3. Co-sited services using different antennas

4. Non co-sited services (near sited)

5. The Horizontal Radiation Pattern (HRP) of the services

6. The transmitting antenna heights of the services

7. The polarisation of the services

8. The modulation of the services

9. Intermodulation

10. The terrain in the coverage area of the services

11. The number of potentially interfering services

To some extent these factors are treated separately in this document to determine the criteria associated with each factor. In practice multiple factors will come into play and the possibility of using 400 kHz spaced services will have to be assessed as individual cases, taking into account all the relevant criteria as well as the other factors required as part of the Ministrys PIB 39 for Spectrum Licence Engineering Rules for Crown Management Rights.

6.2 Co-sited Services Using a Shared Antenna

6.2.1 General

Co-sited services using the same antenna are services that are combined onto a common feeder arrangement and physically transmitted from the same radiating element(s) of an antenna or an antenna array.



Given that the bandwidth of FMBC transmitting antennas is generally greater than 5 MHz and often 10 to 15 MHz5, services separated by 400 kHz and sharing the antenna can be assumed to have the same antenna radiation patterns.

6.2.2 Practicality of Combining Equipment

GQ-AAS contacted RFS and Polar Electronic Industries (Australian manufacturers of FMBC combiners) to determine the practicality of combiners for services with a 400 kHz channel spacing.

Polar Electronic Industries advised that they do not manufacture a combiner that is capable of combining such services.

RFS advised that though at present they do not manufacture such a combiner, they have investigated the possibility of designing and producing a combiner for that purpose and determined that a four-pole cross coupled balanced combiner could be used to combine 400 kHz spaced services. One of the limitations associated with such a design is the pass bandwidth, which is likely to be restricted to approximately +/-140 kHz. This would be a limitation for upgrading to an HD Radio signal.

The power differential between the services to be combined and the maximum power capacity are also factors that would influence the design of a 400 kHz combiner.

6.2.3 Basis of Criterion

On the assumption that the combiner is not a limitation, the basis for the criterion for two co-sited 400 kHz spaced services sharing the same antenna is that the basic protection ratio between the services of -20 dB shall be achieved. That is, the difference in the ERPs of the services shall be less than 20 dB.

In practice, GQ-AAS expects that the limitations of the combiners will restrict the difference between the services transmitter powers to approximately 10 dB.

6.3 Co-sited Services using Different Antennas

6.3.1 General

Services that are considered to be co-sited using different antennas are those services transmitted from the same antenna mounting structure (ie. mast, tower or building) and transmitting from separate antennas at different antenna heights. This could be the approach used in India, with the co-sited services segmented into two separate combining and antenna systems with a minimum channel spacing of 800 kHz for each combiner/antenna system.


The basis for the criterion for adding a new service to be co-sited with an existing or planned service using different antennas is that the protection ratio between the services of -20 dB shall be achieved. The complicating factor is the different radiation patterns of the transmitting antennas, even for those nominally having the same pattern, such as folded dipoles. In practice there can be a variation in the pattern of +3 dB from the nominal gain at any angle.

Therefore to account for the potential variations in the antenna radiation patterns, the maximum difference in the ERPs of the services is reduced by 6 dB to 14 dB) and this applies in all directions. That is, the 14 dB difference between the ERPs is the maximum difference in ERPs on any bearing in the antenna radiation pattern.

5 RFS and Polar Electronic Industries catalogues



6.3.3 Methodology

The methodology GQ-AAS used for calculating the maximum ERP of the proposed service relative to the existing or planned service was based on the ITU-R propagation curves provided in ITU-R Recommendation P.1546-2 [Ref 20].

1. GQ-AAS chose representative maximum ERPs and antenna heights above average terrain.

The antenna height above average terrain (HAAT) is taken to be the height in metres of the centre of the transmitting antenna above the terrain height averaged between distances of 3 to 15 km from the transmitter in the direction of the coverage. Refer to Recommendation P.1546-2 for methods of determining antenna HAAT.

2. GQ-AAS determined the estimated distance to the Minimum Usable Field Strength (MUFS)

The estimated distances were determined from P.1546-2, Figure 1 (propagation curve for 100 MHz, land path, 50% time).

The estimated distance to the MUFS (66 dBuV/m) for a range of ERP services and antenna HAAT is shown in Table 10. Note that in practice the distances from the transmitting service to the MUFS in any direction will vary depending on the effects of terrain and clutter in that direction.

Estimated Distance to MUFS (66 dBuV/m) (km)

Antenna HAAT ERP

100 W 1 kW 10 kW 100 kW

10 m 2.5 5 9 14

20 m 3.2 6.5 11 18

37.5 m 4.1 9 15 24

75 m 5.6 12 21 32

150 m 8.1 16 28 44

300 m 13 24 40 59

600 m 19 36 55 78

1200 m 27 54 80 110

Table 10: Estimated distance to estimated MUFS (66 dBuV/m)

3. For an existing antenna HAAT of x, GQ-AAS determined the effect on the predicted signal level at the MUFS for an antenna HAAT of 0.5x, 2x and 4x.

Doubling the antenna HAAT can cause up to +8 dB increase in field strength at distances 50 km from the transmitting site. However a more typical increase is 5 to 6 dB at the MUFS.

4. This change (in dB) in field strength due to changes in the antenna HAAT represents the inverse change in the maximum ERP of the proposed service, as tabled in the next Section.

6.3.4 Effective Radiated Power

The ERP6 of the proposed service shall not exceed the values shown in Table 11 in any direction relative to existing or planned 400 kHz adjacent services. These values incorporate the base maximum difference of 14 dB from Section 5.3.2.

6 As per ITU-R recommendation P.1546-2, Figure 1.



Maximum ERP of Proposed Service Relative to Existing or Planned Services (dB)

ERP HAAT

Transmitting Antenna HAAT of Proposed Service Relative to Existing or Planned Services.

0.5x 2x 4x

100 W 37.5 m +16 dB +9 dB +4 dB

1 kW 75 m +16 dB +9 dB +3 dB

10 kW 150 m +16 dB +8 dB +2 dB

100 kW 300 m +16 dB +7 dB +1 dB

Table 11: Maximum ERP of the proposed service relative to the existing service for co-sited services using different antennas.

The actual difference between the ERPs of the existing and proposed service shall be such that the unwanted signal level (dBuV/m) compared to the wanted signal level (dBuV/m) is no greater than 20 dB higher than the wanted signal level at any point within the coverage area of the wanted signal (defined by the MUFS contour).

6.4 Non Co-sited Services (Near-sited)

6.4.1 General

Non co-sited services transmit are considered to be services transmitted from separate antennas at locations in the order of 50 metres to several kilometres from each other (depending on the maximum ERPs of the services), where there is not a significant portion7 of the population to be served within the high field strength areas8 of each service.

Generally, it is expected the proposed service is intending to achieve the same, similar, or highly-overlapping coverage area as the existing services that are operating on carrier frequencies 400 kHz spaced from the proposed service.


The basis for the criterion for non co-sited services is that the protection ratio between the services of -20 dB shall be achieved. As with the co-sited services using different antennas, the complicating factor is the different radiation patterns of the transmitting antennas. In practice there can be a variation in the pattern of +3 dB from the nominal gain at any angle.

A further complicating factor is the different propagation paths and possibly conditions from the different sites, including different antenna HAATs and terrain profiles to the coverage areas.

Therefore, to account for the potential variations in the antenna radiation patterns, the maximum difference in the ERPs of the services is reduced by 6 dB to 14 dB) and to account for differences in propagation conditions the maximum difference in the ERPs of the services is further reduced by 4 dB to 10 dB. In practice, the variation due to propagation differences may be much higher; the 4 dB is taken as an average figure for reasonably close sites.

7 A significant proportion constitutes 0.1% of the population or 50 persons, whichever is less. 8 High field strength areas constitute the areas within the proximity of closely sited services where a wanted signal is likely to be interfered with by a 400 kHz adjacent signal, due to very high field strengths around the unwanted signal transmitter.



6.4.3 Methodology

The methodology GQ-AAS used for calculating the maximum distance between the proposed service and the existing or planned services was based on coverage and interference predictions using the Planet EV radio prediction software and the digital terrain model for Melbourne, Victoria, representing largely flat terrain. GQ-AAS:

1. Chose representative combinations of ERP and antenna HAAT (see Table 7 below).

2. Determined the estimated distance9 to the MUFS (66 dBuV/m) for the chosen combinations (see Section 6.3.3).

3. Assuming an omnidirectional radiation pattern, flat terrain and a circular coverage area, calculated the estimated coverage area in km2.

4. Calculated 0.1% of the coverage area (representing the maximum permissible area of interference) and determined the equivalent radius of the interference area.

5. Conducted coverage predictions for the existing and proposed services at varying distances apart, based on the services having the same:

4. Maximum ERP

5. Omnidirectional radiation pattern

6. Antenna height.

6. Calculated the area of interference for each service based on a required protection ratio of -10 dB, using the Planet EV software. The interference tends to be located close to the transmitter sites of the services (where the unwanted field strength is highest).

7. Determined the maximum separation that meets the requirement for the area of interference to be at most 0.1% of the coverage area.

6.4.4 Maximum Separation Distance (Identical Services)

The maximum distance separation for same power services with the same antenna HAAT, operating at 400 kHz spacing is shown in Table 12.

ERP of both

services

Antenna HAAT

(m)

Estimated Distance to

MUFS (km)

Estimated Coverage

Area (km2)

Radius of Interference Area (based on 0.1% of

Estimated Coverage Area)

Maximum Distance

Separation(m)

100 W 20 3.2 32 100 m 250 m

1 kW 37.5 8.5 230 270 m 500 m

10 kW 75 21 1,400 700 m 1.5 km

10 kW 150 28 2,500 900 m 2.2 km

100 kW 150 44 6,100 1.4 km 2.8 km

100 kW 300 59 11,000 1.9 km 5 km

Table 12: Maximum distance separation for same power, same antenna height near-sited services

9 As per ITU-R recommendation P.1546-2, Figure 1.



6.4.5 Maximum Separation Distance (Different Services)

A similar process was carried out for same power services with different antenna HAATs.

The maximum distance separation for these services operating at 400 kHz adjacent channels is shown in Table 13.

Service 1 Service 2

Power Antenna

HAAT (m)

Power Antenna

HAAT (m)

Maximum Distance

Separation

100 W 20 100 W 10 0

1 kW 75 1 kW 37.5 400 m

10 kW 150 10 kW 75 1.5 km

100 kW 300 100 kW 150 2.8 km

Table 13 Maximum distance separation for same power, different antenna height near-sited services

The maximum distance separation is dictated by the service with the lower antenna HAAT.

6.4.6 Conclusion

This criterion generally excludes the situations where there are high powered non co-sited services with transmitter sites located within the population centres being served by the service. Non co-sited high powered services are possible where the transmitters are located in relatively remote locations providing wide coverage.

6.5 Horizontal Radiation Patterns The differences in the horizontal radiation patterns (HRPs) of the proposed and existing services must be taken into account when calculating the maximum ERP of the proposed service relative to the existing service (Table 11) in any direction of the HRP of the co-sited 400 kHz adjacent service.

The HRPs must also be taken into account in calculating the maximum separation distance for non co-sited services (Tables 12 and 13).

6.6 Polarisation of the Services Orthogonally polarised services may provide additional protection margin between services of up to 10 dB due to orthogonal discrimination of the receiving antenna. This figure was provided for Band II FM broadcasting services in the now superseded CCIR Report 122-3 [Ref 21] and is included in the Australian Broadcasting Planning Handbook.

The current ITU-R recommendation covering the discrimination of orthogonally polarised antennas is for television antennas only and does not include Band II antennas. Further consideration is required.

There may be minimal advantage in this criterion as the majority of services are listed as mixed or linear polarisation in the Ministrys radio database.

6.7 Modulation As detailed in Section 5.2.2, in laboratory and field testing for the HD Radio system in the USA, at a wanted to unwanted ratio of -20 dB, a reduction in the audio S/N quality was only observed on the performance of a portable receiver. Car radios and a



domestic hi-fi receiver were not affected by the 400 kHz adjacent channel HD Radio service.

GQ-AAS considers that further research and additional results for the current tests in France and Brazil are required before this criterion can be finalised.

6.8 Intermodulation

6.8.1 General

Intermodulation was investigated in Section 3.2.3 and it was found to be a potential problem where there are three (or more) 400 kHz spaced channels serving the same area and there are populated areas with high unwanted field strengths (>100 dBuV/m). This occurs when a high powered transmission site is located within an urban area, such as the Skytower site in Auckland.


The potential intermodulation victim services in populated high field strength areas are the two services 800 kHz apart (see Sections 3.2.3 and 4.2.3). The basis for the criterion for three 400 kHz spaced services is that the required protection ratio for the potential victim services is approximately 1 dB at the 100 dBuV/m contour. This is based on the values in Table 3 for a wanted field strength of 85 dBuVm and a factor of 15 dB to take account of the likely receiver antenna height being 1.5 m rather than 10 m.

To limit the potential for interference, it may be preferable that the middle frequency service (presumably the new service) has a lower field strength in the interference areas than the 800 kHz spaced services. However, if there is another 400 kHz spaced service (existing or in the future), that is four (or more) 400 kHz spaced services in a row, the original victim services will become potential interferers and the new services the victims. If the new services have lower field strengths than the existing services, they would be more susceptible to intermodulation interference.

Therefore the most effective way to minimise the potential for intermodulation interference in high field strength areas where they fall on populated areas is to ensure that the wanted and unwanted field strengths are of similar or equal level.

This is best achieved by having the services co-sited or very closely sited with similar or the same ERPs and antenna radiation patterns.

6.9 Effects of Terrain on the Variability of the Received Signal Levels The maximum distance between transmitting sites for services spaced at 400 kHz for common coverage areas should apply in areas only where the effects of terrain are similar for both services. In cases where terrain unfavourably causes significantly greater signal attenuation of one service than the other, the effects of terrain should be considered in more detail.

Exceptions to the minimum distance between transmitting sites spaced at 400 kHz for separate coverage areas (Section 6.4.4,) may be granted for situations in which the terrain favourably attenuates signals between the two coverage areas.

6.10 Interference Contributions from Multiple Stations For multiple interfering stations the total interference contribution would be determined using the Root Sum Square method (with a 6 dB exclusion principle). The process is to calculate the individual values of usable field strength (Eu) for the service considering each individual source of interference acting alone.

The individual values of Eu are then summed arithmetically (ie not in dB) excluding any individual Eus that are -6 dB or more relative to the highest value of Eu.

The resultant overall Eu is the required level of usable field strength.



7 PLANNING NEW SERVICES The planning of a new 400 kHz spaced service can use these criteria and in simple cases (co-sited using the same antenna) they may be sufficient to meet the Ministrys planning requirements.

However, the likelihood is that the planning of the services will require a more complex treatment. In these cases the criteria provide the basis of the planning in the specific area of the 400 kHz considerations, though the services will need to be planned taking into account all the relevant criteria as well as the other factors required as part of the Ministrys PIB 39 for Spectrum Licence Engineering Rules for Crown Management Rights.

8 SUMMARY

8.1 Findings and Conclusions As a result of the study, Gibson Quai-AAS determined the following findings and conclusions.

8.1.1 Protection Ratios

1. GQ-AAS considers that the existing co-channel and adjacent channel protection ratios used in the planning of FMBCs should remain unchanged for the use of 400 kHz services providing coverage to the same area.

2. GQ-AAS considers that the intermodulation interference issues for 400 kHz spaced services, can be addressed by keeping the populated areas experiencing very high field strength to small areas and ensuring that in these areas, the wanted and unwanted signal field strengths are of similar or equal levels.

8.1.2 The Skytower 400 kHz spaced trials and report

3. GQ-AAS is surprised that no 400 kHz adjacent channel interference reported, though the differences in HRP in some directions (> 20 dB) would indicate that it was likely.

4. GQ-AAS notes that the audio quality of the 93.8 MHz service was consistently lower than the 400 kHz adjacent services, though no explanation was given in the report.

5. GQ-AAS notes that the two engineers generally found that careful tuning was required to tune to the 93.8 MHz service and that for the very low cost radios, it was not possible to tune to the 93.8 MHz frequency in high field strength areas

6. GQ-AAS finds that the tests were inconclusive on intermodulation interference.

8.1.3 The listener survey (from the Skytower trials)

7. GQ-AAS notes that Research International who conducted the survey concluded that from the survey results,

there is no significant interference with the 93.4FM and 94.2FM frequencies with the introduction of a higher powered 93.8 FM signal

8.1.4 Issues raised by RBA

8. GQ-AAS concludes that If 400 kHz spaced services are considered for an area that has an adjacent area with services operating on these frequencies, it is very unlikely that proposed 400 kHz spaced services will



be able to meet the planning criteria to operate co-channel with the existing services.

9. GQ-AAS considers that the introduction of 400 kHz spaced services is unlikely to increase the likelihood of intermodulation interference to aeronautical and mobile radio services if the usual Ministry planning procedures are followed.

10. Receiver Tuning. GQ-AAS makes the following observations on the prevalence of analogue and digital tuning.

Digital tuned radios are more expensive than an equivalent analogue tuned radio.

Analogue tuned radios vary in their ability to be tuned to the 400 kHz spaced services.

It is likely that digital tuned radios will become more common place in time, but it is likely that low cost analogue tuned radios will continue to be sold.

Stations on the 400 kHz spaced channels will not be as readily available to all listeners as those on the 800 kHz spaced channels.

Listeners wanting to tune to the 400 kHz spaced channels are likely to purchase radios (analogue or digital tuned) that will allow them to tune to the channel.

8.1.5 International Research

11. GQ-AAS notes that 400 kHz spaced services have been introduced successfully in India, on a smaller scale in the UK (primarily London) and for low power services in the US. The Indian services are mandated to be co-sited with antenna sharing by 800 kHz services.

12. GQ-AAS finds that there is very little literature publicly available concerning the outcomes of introducing 400 kHz spaced services.

8.1.6 Digital Radio

13. From the study of the research on digital radio in the FM band (primarily the IBOC HD Radio system), GQ-AAS concludes that the use of 400 kHz spaced services in the same coverage area will not restrict the introduction of HD Radio in the New Zealand, as any effects related to 400 kHz spaced HD Radio services in the same coverage area would also apply to 400 kHz HD Radio services that are not serving the same area.

14. GQ-AAS has concer

Criteria for 400 KHz Channelling

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