1.3 The tests described in item 3 of Table 3 26 1 Shape of the spectrum envelope for class B8E and class R7J emissions modulated with white noise This section deals with the results of measurements made by several administrations on transmitters of different design for classes of emission B8E and R7J. The major characteristics of the transmitters and the test condition relating to the measurements are summarized in Table 3. TABLE 3 Transmitter characteristics and measurement test conditions for B8E and R7J emissions Item No. 1 2 3 of emission B8E B8E B8E; R7J Transmitter characteristics: Various transmitters Various transmitters – peak envelope power Pp (two tones)(1) (kW) 20 Several kW up to some tens of kW Different values – order intermodulation distortion 3(1) (dB) –35 – number of channels active during the measurement 2, in lower sideband 2 and 4 – bandwidth of speech channel (Hz) 3 000 – carrier suppression (dB) relative to peak envelope power –50 Type of modulating signal: White noise White noise White noise – bandwidth 30 Hz-20 kHz 1 dB 100 Hz-6 kHz per sideband Class of emission B8E B8E B8E; R7J signal level(1) adjusted to a value such that: – at the output, Pm  0.25 Pp (two 0.25 Pp (two Type of measuring device: True r.m.s. selective measurement device Spectrum analyser Spectrum analyser – passband (Hz) Curves C: 3 800 D: 100 0.05 F(2) Shape of spectrum See Fig. 10 See § 1.1
1.1 Necessary bandwidth If the frequency shift, or the difference between mark and space frequencies is 2 D and if m is the modulation index, 2 D/B, the necessary bandwidth is given by one of the following formulae, the choice depending on the value of m: 2.6 D  0.55 B within 10% for 1.5  m  5.5 2.1 D  1.9 B within 2% for 5.5  m 20 1.2 Shape of the spectrum envelope The of the RF spectrum for class of emission F1B is described in § 1.2.1 to 1.2.3 below for various shapes of the telegraph signal. 1.2.1 Telegraph signal consisting of reversals with zero build-up time The amplitude of the spectrum envelope relative to the amplitude of the continuous emission, A(n), is shown in Fig. 12 (solid lines) as a function of the order of the sideband component for a telegraph signal consisting of reversals with zero buildup time and equal mark and space durations. The linear or asymptotic parts of the solid curves shown in Fig. 12 may be approximated with the aid of the formula: (8) where: n : of the sideband component n = 2 f /B f : frequency separation from the centre of the spectrum (Hz) B : modulation rate (Bd) m : modulation m  2 D/B D : peak frequency deviation or half the frequency shift (Hz). 1.2.2 Periodic telegraph signals with finite build-up time The amplitude, A(x) of the envelope of the spectrum produced by a telegraph signal consisting of reversals with a finite build-up time and equal mark and space durations is given by the following empirical formula: (9) where: x  f /D E : amplitude of the continuous emission u 
The occupied bandwidth L (Hz) for  0.01 may also be calculated from the empirical equation: (11) is the relative build-up time of the shortest pulse of the telegraph signal, as defined in recommends 1.10. The occupied bandwidth so calculated is hardly affected by the of the telegraph signal, whereas the outof-band spectrum depends largely on this shape. The maximum divergence between the results obtained by equation (11) and those obtained by exact calculations, is as follows: 3% for  0; 2 m  20 9% for  m  20 10% for  m 20. The list above shows the limits within which equation (11) can be used with reasonable accuracy. The percentages indicated apply to the lower limit of m. They are less for the higher limit. Finally, Fig. 16 the results of calculations and measurements of occupied bandwidth employing different methods. 1.4 Shaping of the telegraph signal by means of filters See Annex 1, § 3. However, the use of minimum overshoot filters is not essential, when the transmitter is required to operate at more than two frequencies, for example in the case of diplex. 1.5 Adjacent-channel interference See 1, § 1.6. 1.6 Build-up time of the signal An out-of-band spectrum close to the limiting curve described in § 1.8 corresponds to a build-up time equal to about 8% of the initial duration of the telegraph dot, i.e. about 1/12 B, provided that an adequate filter is used for signal shaping. 1.7 Bandwidth occupied, for unshaped signals For the purpose of comparison with the formulae in § 1.1, it may be mentioned that, for a sequence of equal and rectangular (zero build-up time) mark and space signals, the occupied bandwidth is given by the following formulae: 2.6 D  1.4 B within 2% for 2  m  8 2.2 D  3.1 B within 2% for 8 m 20
1.8 Out-of-band spectrum If frequency is plotted as the abscissa in logarithmic units and if the power densities are plotted as ordinates (dB), the curve representing the out-of-band spectrum should lie below two straight lines of constant slope in decibels per octave, starting from the two points situated at the frequencies limiting the necessary bandwidth, and finishing at the level – 60 dB. Thereafter, the same curve should lie below the level – 60 dB. The starting ordinates of the two straight lines and their slopes are given in Table 4, as a function of the modulation index, m. TABLE 4 Modulation index Starting ordinates (dB) Slope (dB/octave) 1.5 m  6 –15 13  1.8 m 6 m  8 –18 19  0.8 m 8 m  20 –20 19  0.8 m The reference 0 dB, corresponds to the mean power of the emission. The permissible amounts of out-of-band power, above and below the frequency limits of the necessary bandwidth, are each approximately 0.5% of the total mean power radiated. The curve representing the out-of-band spectrum for modulation indexes 0.5 m 1.5 should lie below the points with the coordinates given in Table 5. 5 Formula for calculating Bx at levels X (dB) –20 –30 –40 –50 –60 3 4.1 5.8 8.1 11 m : modulation index B : modulation rate. For each of the limiting spectrum curve, the abscissa is the relative bandwidth Bx /2 B, and the ordinate is the relative level X. The reference level 0 dB is the level of the unmodulated carrier. 2 Frequency-modulated emissions for sound broadcasting and radiocommunications 2.1 Class of emission F3E, monophonic sound broadcasting 2.1.1 Necessary bandwidth The necessary bandwidth can be calculated by the formula, provided in Recommendation ITUR SM.1138: Bn 2 M 2 D K (12) where: Bn : necessary bandwidth M : highest modulation frequency D : maximum deviation of the RF carrier K : factor, equals 1 if the condition D  is met.