1、 Recommendation ITU-R SM.1268-4 (11/2017) Method of measuring the maximum frequency deviation of FM broadcast emissions at monitoring stations SM Series Spectrum management ii Rec. ITU-R SM.1268-4 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and
2、economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performe
3、d by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to b
4、e used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found
5、. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radio
6、determination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SN
7、G Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2017 ITU 2017 All rights reserved. No part of this
8、 publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R SM.1268-4 1 RECOMMENDATION ITU-R SM.1268-4 Method of measuring the maximum frequency deviation of FM broadcast emissions at monitoring stations (1997-1999-2011-2014-2017) Scope This Recommendation
9、describes methods to measure deviation and multiplex power of FM broadcasting stations during normal programme operation and verify compliance with the conditions assumed by broadcast network planning procedures. Keywords FM broadcasting, frequency deviation, measurement, modulation power, monitorin
10、g. Related ITU Recommendations, Reports Recommendation ITU-R BS.412. NOTE In every case the latest edition of the Recommendation/Report in force should be used. The ITU Radiocommunication Assembly, considering a) that planning parameters of FM broadcasting networks are provided in Recommendation ITU
11、-R BS.412; b) that protection ratios for the planning of broadcasting transmitter frequencies are based on a maximum frequency deviation of 75 kHz (or 50 kHz) and a maximum power of the modulation signal which does not exceed the power of a sinusoidal tone which causes a 19 kHz frequency deviation;
12、c) that various broadcast transmissions exceed the maximum frequency deviation and/or modulation power owing to different types of programmes, additional components of the composite signal (e.g. radio data system (RDS) and audio compression; d) that limitation of peak frequency deviation and modulat
13、ion power is required owing to mutual protection of broadcast planning and the aeronautical radionavigation service in the frequency band above 108 MHz; e) that monitoring of broadcast emissions is necessary to prevent transmissions from exceeding a maximum frequency deviation and a maximum modulati
14、on power; f) that common measurement procedures are necessary in order to achieve mutual acceptance of measurement results by the parties concerned, e.g. frequency managers, monitoring services and broadcasters; g) that the number of broadcasting stations using additional signals as RDS and high spe
15、ed data signals is increasing and these systems are highly sensitive to interference from adjacent channels, 2 Rec. ITU-R SM.1268-4 recognizing a) that the method described in Annex 1 is a simple “go-no go” test based on a spectrum mask which cannot replace precise measurements of the frequency devi
16、ation; b) that the method described in Annex 1 cannot be applied on transmissions with 50 kHz peak deviation due to the fact that no appropriate spectrum mask is available; c) that the method described in Annex 2 is also applicable on transmissions with 50 kHz peak deviation, recommends 1 that the m
17、ethod described in Annex 1 may be used as a verification to indicate whether the frequency deviation of an FM broadcasting station exceeds the limits; 2 that the method described in Annex 2 should be used when the values of the deviation and modulation power are required. Annex 1 Simple spectrum mas
18、k based method to indicate the exceeding of frequency deviation limits 1 Requirements For this measurement any spectrum analyser and test receiver with analyser capabilities can be used. 2 Connection transmitter and spectrum analyser With the aid of a measurement antenna. 3 Measurement conditions du
19、ring three measurements of 5 min each, the transmitter to be judged should be modulated with a representative programme material for that particular transmitter. Additional measurements may be carried out to ensure that the programme material is truly representative; impulse interferences should not
20、 occur (for example interference from an ignition source); signal/interference noise should be 50 dB. 4 Adjustments of the spectrum analyser The spectrum analyser should be adjusted as follows: centre frequency (CF) f0 (carrier frequency of the transmitter); RBW 10 kHz (IF filter); VBW 10 kHz (video
21、 filter); Rec. ITU-R SM.1268-4 3 span: 340 kHz; sweeptime: 340 ms (1 ms/kHz); max hold mode; input attenuation is dependent on input level. Settings for digital signal processor (DSP) analysers will be different but should provide equivalent results. 5 Measurement instruction a) Record the transmitt
22、er signal over a 5 min period. b) Observation of the analyser and acoustic controls at the receiver should be used as a means to ensure that no measurement results are evaluated which have been distorted by impulse interference. For the same reason the measurement is repeated twice. c) Overlay the g
23、raphical measurement with the mask as described in 7. d) The centre of the x-axis of the mask shall correspond with the centre frequency (f0). e) Adjust the reference level so that the maximum amplitude of the measurement corresponds to 0 dB. f) Determine whether the measurement is within the limits
24、 of the mask. 6 Limits If any of the measured spectra exceeds the mask, the transmitter deviation is assumed not to meet the requirements. 7 Mask construction a) The calibration of the mask should be consistent with the analyser settings. b) The centre of the x-axis is aligned to f0. c) The top of t
25、he y-axis corresponds with the 0 dB reference level. d) Straight lines connect the coordinates: x-axis (kHz) y-axis (dB) x-axis (kHz) y-axis (dB) f0 74 0 f0 74 0 f0 107.5 15 f0 107.5 15 f0 124 30 f0 124 30 f0 152.5 40 f0 152.5 40 The graphic display of the table is shown in Fig. 1. 4 Rec. ITU-R SM.1
26、268-4 FIGURE 1 Shape of the mask S M . 1 2 6 8 - 0 1 1 5 2 .5 1 2 4 1 0 7 .5 7 4 741 0 7 . 51241 5 2 . 5dB(relativetopeak)Fre q u en cy s ep arat i o n fro m carri er (k H z)0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 1 7 0 1 3 6 1 0 2 6 8 3 4 0 34 68 102 136 170f0Annex 2 Method of measuring the maximum
27、 frequency deviation of FM broadcast emissions at monitoring stations 1 General 1.1 Definitions Frequency deviation: In the case of frequency modulation, the deviation of the frequency from the frequency of the unmodulated carrier f0. Instantaneous deviation: In the case of frequency modulation, the
28、 instantaneous deviation f(t) is the difference between the instantaneous frequency at any given time (t) and the unmodulated carrier frequency (f0). The instantaneous frequency is: f(t) f0 f(t) Peak deviation: In the case of frequency modulation, the peak deviation f is the absolute maximum of the
29、difference between the unmodulated carrier frequency (f0) and the instantaneous frequency f(t). Composite signal: This signal includes all stereo information (including the pilot tone) and may also include the traffic radio signal, the RDS signal and other additional signals. Rec. ITU-R SM.1268-4 5
30、Modulation power (also called multiplex power): The relative power averaged over 60 s of the modulation signal according to the formula: modulation power = 10 log (2/60 s) (f(t)/19 kHz)2 dt dBr 0 dBr: Is the average power of a signal equivalent to the power of a sinusoidal tone which causes a peak d
31、eviation of 19 kHz. 1.2 Introduction There are various reasons, such as a reduction in the time required for the measurements, which make it seem sensible to carry out frequency deviation measurements in the field and not directly at the transmitter output. Compliance by the signal to be measured wi
32、th the characteristics listed below is required in addition to compliance by the measuring equipment with the requirements described in 3 in order to avoid measurement uncertainties. 1.3 Limits The protection ratios specified in Recommendation ITU-R BS.412 for the planning of FM sound broadcasting t
33、ransmitters apply on the condition that a peak deviation of 75 kHz is not exceeded and that the average modulation power over any interval of 60 s does not exceed that of a single sinusoidal tone which causes a peak deviation of 19 kHz. 1.4 Observation time The observation time should be at least 15
34、 min. In some cases, one hour or even longer may be required to be sure to measure programme material that leads to maximum values for frequency deviation and modulation power. 2 Required conditions for measurements 2.1 Required wanted-to-unwanted RF signal level ratio En/Es at the measurement equip
35、ment This ratio depends on the characteristics of the equipment used for the measurements. For the required accuracy defined in 3.1 and 3.2, the level of unwanted emissions has to be below the values given in Tables 1 and 2. Measurement receivers usually have either Gaussian or channel filters. In p
36、ractical environments, Gaussian filters may be less suitable for peak deviation measurements than channel filters. a) Measurement receivers with Gaussian IF filters TABLE 1 Frequency difference f (kHz) Required protection ratio (dB) 0 40 X 2)2(*2lnlo g*2040 BXe6 Rec. ITU-R SM.1268-4 In Table 1, “B”
37、is the nominal 3 dB bandwidth of the measurement filter in kHz. The following diagram illustrates the required protection ratios with three example measurement bandwidths. FIGURE 2 Required protection ratios for receivers with Gaussian filters S M . 21 2 6 8 - 0500 400 300 200 100Freq u en cy o ffs
38、et (k H z)100 200 300 400 500010010Attenuationrelativetowantedsignal(dB)304020IF-BW = 1 5 0 k H zIF-BW = 2 0 0 k H zIF-BW = 2 5 0 k H zb) Measurement receivers with channel filters TABLE 2 Frequency difference f (kHz) Required protection ratio (dB) 0 40 B/2 35 X (for X B/2) 35 0.2*(X B/2) In Table 2
39、, “B” is the nominal 3 dB bandwidth of the measurement filter in kHz. A linear interpolation is used between discrete values. The following diagram illustrates the required protection ratios with three example measurement bandwidths. Rec. ITU-R SM.1268-4 7 FIGURE 3 Required protection ratios for rec
40、eivers with channel filters S M . 31 2 6 8 - 0500 400 300 200 100Fre q u en cy o ffs et (k H z)100 200 300 400 5000200Attenuationrelativetowantedsignal (dB)304020IF- BW = 2 0 0 k H zIF- BW = 2 5 0 k H zIF- BW = 3 0 0 k H z1010It is essential that the applicable protection ratios given above are obse
41、rved because even a minor increase in unwanted signal levels will result in considerable measurement errors. 2.2 Multipath propagation and distortion Delayed signals from the wanted transmitter as well as signals from other co-channel or adjacent channel transmitters shall be small enough to ensure
42、that measurement results are not influenced by the effects of multipath propagation. In case of multipath reception only, it is considered to be sufficient if the product of delay time and amplitude ratio in percent is: (Ur/Ud) 80 kHz 5% 3.3 Modulation power measurements The modulation power (dBr) i
43、s specified in dBr according to 1.1. The measuring equipment shall be able to measure modulation power in the range from 6 dBr to +6 dBr. The instrument accuracy shall at least meet the values specified in Table 4. TABLE 4 Instrument accuracy for modulation power measurements Modulation power (dBr)
44、Required accuracy (dB) 2 0.4 4 Result evaluation It is considered inappropriate to regard the occurrence of single samples of the instantaneous frequency deviation above 75 kHz as a violation of the deviation limit, because: a) the dynamic modulation of an FM broadcast transmitter by normal programm
45、e content may include modulation peaks that occur extremely seldom, and may not be reproducible in a second measurement; b) even when the measurement conditions stated in 2 are met, external interference cannot completely be avoided at all times. For these reasons, and considering the measurement un
46、certainty with an aimed confidence level of 95%, an FM broadcast transmitter can be regarded as violating the deviation limit if a certain number of measurement samples exceed (75 kHz plus measurement uncertainty). 104% (equal to 106) of the measurement samples exceeding 77 kHz deviation (see Table
47、3) may be considered as a practical value. Since the modulation power is averaged over a period of 60 s, short peaks included in the programme content or caused by external interference are already cancelled out to a great extent. Therefore, an FM broadcast transmitter can be regarded as violating t
48、he modulation power limit if the highest measured multiplex power value exceeds 0 dBr + measurement uncertainty. 0.2 dBr may be considered as a practical value, see Table 4. 10 Rec. ITU-R SM.1268-4 NOTE In the case that the network operator himself monitors the limits, it is recommended that the act
49、ual measurement uncertainty of the test receiver is subtracted from the limit values (75 kHz for deviation and 0.0 dBr for multiplex power). This ensures that these limit values are not violated when independently supervised by authorities according to the result evaluation above. 5 Presentation of measurement results 5.1 Modulation power The modulation power shall be presented as a function of time during the measurement interval. The ma
