1、 ES1 BS*EN*b05LO- 2-5 9b m Lb24bb9 0544232 LTT BRITISH STANDARD Methods of Measurement for radio equipment used in satellite earth stations Part 2. Measurements for sub-systems Section 2.5 Frequency modulators The European Standard EN 60510-2-5 : 1994 has the status of a British Standard ICs 33.060.
2、30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAU BS EN 1996 1992 50510-2-5 : EC 510-2-5 : BS EN 60610-2-6 : 19% Amd. No. Date The following BSI references relate to the work on this standard: committee reference EPU12/5 I)I-aR announced in BSZ Naus, Update September 1995 ISB
3、N O 680 26113 1 Committees responsible for this Text affected British Standard The preparation of this British Standard was entrusted by Technical Committee EPU12, Radio communication, to Subcommittee EPY12/5, Radio communication systems, upon which the following bodies were represented British Broa
4、dcasting Corporation British Radio and Electronic Equipment Manufacturers Association British Telecommunications plc ERA Technology Ltd. institution of Electrical Engineers Radio, Electrical and Television Retailen Association Radiocommunications Agency This British Standard, having been prepared un
5、der the direction of the Electrotechnica Sector Board, was published under the authority of the Standards Board and comes into effect on 15 July 1996 o BSI 1996 BSI BS*EN*b0510- 2-5 96 Lb24bb9 0544234 T72 BS EN 60510-2-5 : 1996 Contents Committees responsible National foreword Page inside front cove
6、r ii Foreword Text of EN 60512-5 2 3 O BSI 1996 i ES1 BS*EN*b05LO- 2-5 9b lb24bb9 0544235 909 = BS EN 60610-2-6 : 1996 National foreword This Section of BS EN 60510 has been prepared by Subcommittee EPU126 and is the English language version of EN 60510-2-5 : 1994 Methods of masurnt for radio equipm
7、ent used in sateUite earth stations Part 2: Measurements for sub-systems Section five: I“requency modulators, published by the European Committee for Electrotechnical Standardization (CENELEC). It is identical with IEC 510-2-5 : 1992, published by the international Electrotechnical Commission (IEC).
8、 This standard is published in three Parts. The other Parts are: Part I Meuzods common to sub-systems and combinations of sub-systems Part 3 Methods of rneasurernent for combinations of sub-systems References in the text to IEC page numbers should be ignored. For ease of reproduction, some of the fi
9、gures also include the French text. Cross-references Publication referred to Corresponding British Standard BS EN 60510 Mewds of measurement for radio equipment used in satellite earth stations Part 2 Measurements for subsystems Section 2.6 : 1996 Frequency demodulators Part 3 MeuLods of measurernen
10、t on combinations of Section 4 : 1996 Measurements fwj?vquency division multiph gd.m.1 hnsmission EN 60510-2-6 : 1994 (IEC 510-2-6 : 1992) EN 6051W : 1994 (IEC 51W : 1992) sub-systems Compliance with a British Standard does not of itself confer immunity from legal obligations. ii O BSI 1996 EUROPEAN
11、 STANDARD NORME EUROPENNE EuROPttive are part of the body of the standard. in this standard, annex ZA is normative. Contents 6 7 8 9 10 11 Scope Defintion General LE output characteristics Baseband input impedence and return loss Deviation sensitivity Sense of modulation Differential gainhion-linear
12、ity and differential phase/group delay Unwanted amplitude modulation Baseband amplituddfrequency characteristic Frequency division multiplex (f.d.m.) telephony measurements 12 Television measurements 13 Carrierenergy dispersal subsystem 14 References Annex ZA (normative) Other international publicat
13、ions quoted in this standard with the references of the relevant European publications Figures Page 3 3 3 4 5 5 7 7 9 10 11 12 12 13 16 14 O BSI 1996 BSI BS*EN*bOSLO- 2-5 96 W 3624669 0544238 bL8 = Page 3 EN 60510-2-5 : 1994 METHODS OF MEASUREMENT FOR RADIO EQUIPMENT USED IN SATELLITE EARTH STATIONS
14、 Part 2: Measurements for sub-systems Section five: Frequency modulators 1 Scope Methods are given in this section for the measurement of the electrical characteristics of frequency modulators. Furthermore, where possible, only measurements involving the basic modulator are considered, that is exclu
15、ding the baseband section comprising the pre-emphasis network and the networks associated with sound sub-carrier signals, pilot signals and auxiliary signals. Methods of measurement for frequency demodulators are given in section six of part 2 of this publication. Measurements between baseband termi
16、nals of modulator/demodulator assemblies are covered by various sections of pari 3 of this publication. 2 Definition For the purpose of this standard, a frequency modulator is a sub-system which, by analogue means, modulates an intermediate frequency (i.f .) carrier by a baseband signal: this may be
17、 a multi-channel f.d.m. telephony signal or television signal with associated sound sub-carrier signals, pilot signals and auxiliary signals. Such baseband signals are normally analogue but digital signals are not excluded. How- ever the methods of measurement described in this section are intended
18、for assessing the performance of the modulator when analogue signals are transmitted. A modulator sub-system usually comprises the following three main sections: - a baseband section; - - an i.f. section. a baseband to i.f. section (modulator); 3 General A block diagram for a typical modulator sub-s
19、ystem is shown in figure 1. The characteris- tics to be measured can be divided into three principal categories: - non-transfer characteristics; - baseband to i.f. characteristics; - certain baseband-to-baseband transmission characteristics in conjunction with a measurement demodulator. The first ca
20、tegory concerns measurements at the baseband port only or at the i.f. port only including frequency and spurious/harmonic signal measurements at the i.f. output. These measurements are described elsewhere in this publication. The second category of measurements forms an essential part of this sectio
21、n because of the nature of the device under test - transfer from baseband to i.f. The third category of measurements includes those to be carried out on a complete modulator/demodulator (modem) assembly except that the actual or system demodulator is replaced by a measurement demodulator. It is very
22、 important to know the separate contribution of a modulator to the total permitted tolerances of performance characteristics because in an operational situation, modulators of one design or manufacturer may have to work with demodulators of another design or manufacturer. Compensation effects betwee
23、n modulator and demodulator are therefore undesirable and each modulator should fulfill the prescribed specification in association with a measurement demodulator. This procedure requires the measurement demodulator to have a better performance than that specified for the modulator under test. 4 I.F
24、. output characteristics 4.1 Return loss See part 1, section three of this publication: Measurements in the i.f. range. The measurement shall be made without the modulator output signal being present. This can be achieved, for example, by disabling the oscillator within the modulator. 4.2 Level See
25、part 1, section three of this publication: Measurements in the i.f. range. 4.3 Carrier frequency See part 1, section three of this publication: Measurements in the i.f. range (Amendment 1). 4.4 I. F. spurious and/or harmonic signals 4.4.1 Method of measurement The i.f. output of the modulator shall
26、be checked by means of a suitable spectrum analyzer or selective level-meter to verify that the level of any i.f. spurious and/or harmo- nic signals is within specified limits. It shall be noted that the measurement of i.f. spurious and harmonic signals shall be made without modulation and with the
27、energy-dispersal generator disabled. BSI BS*EN*b0510- 2-5 96 1624667 0544240 276 W Page 5 EN 60510-2-5 : 1994 4.4.2 Presentation of results The results should be presented preferably as a photograph, plot or X-Y record of the calibrated spectrum analyzer display. Alternatively, the more significant
28、spurious and/or harmonic levels may be expressed in decibels relative to the level of the wanted signal. 4.4.3 Details to be specified The following items should be included as required in the detailed equipment specification: a) permitted maximum level of spurious signals in decibels relative to th
29、e wanted signal: b) permitted maximum level of harmonics in decibels relative to the wanted signal; c) the frequency range over which measurements are required; d) the level of the wanted signals. 5 Baseband input impedance and return loss See part 1, section four of this publication: Measurements i
30、n the baseband. 6 Deviation sensitivity 6.1 Definition and general considerations The deviation sensitivity (S,) of a modulator for a sinusoidal signal of a given frequency is expressed as the ratio of the frequency deviation (AT) to the value of the baseband input voltage (vb): Af “b s =- (MHz/V) r
31、n Vb and Af are both expressed either in peak values or in r.m.s. values. The deviation sensitivity is usually a function of the baseband frequency due to the effect of the pre-emphasis network I 2. When it is possible to gain access to the baseband input point (see figure 1) after the pre-emphasis
32、network, the measured deviation sensi- tivity of the modulator is independent of the baseband frequency used. 6.2 Method of measurement The method of measurement is known as the “Bessel zero“ method which is based on the fact that, in the case of sinusoidal modulation, the carrier frequency spectral
33、 line first dis- appears at a modulation index (mf ) as follows: Af f mr = - = 2,404 83 where At is the peak frequency deviation and fis the modulating frequency. The figures in square brackets indicate the references given in clause 14. BSI BS*EN*b0510- 2-5 9b m 3b24bb9 0544243 302 m Page 6 EN 6061
34、0-2-6 : 1994 The “zero“. .e. the point where the i.f. carrier first disappears, is observed on the spec- trum analyzer, but a perfect zero may not be obtained due to residual harmonic distortion of the baseband signal generator. However, a decrease in carrier level of 30 dB or more is regarded as ad
35、equate. Since there are many values of the modulation index at which a carrier-zero may be ob- tained, the best way of ensuring that the first zero is used is by increasing the modulating voltage smoothly from zero to the point where the carrier disappears for the first time. The measurement procedu
36、re is as follows: a) the baseband generator is set to the required frequency at which the deviation sen- sitivity is to be measured: b) the output level of.the generator is set to zero and then smoothly increased until the i.f. carrier on the spectrum analyzer first disappears; c) the r.m.s. voltage
37、 (Vb) at the baseband input of the modulator is measured; d) the modulator deviation sensitivity (S,) at modulation frequency fis then calculated from equation 6-3: 2,404 83 f MHzN Sm fi vb (6-3) NOTE - As a modulation index of 2.404 83 corresponds to an occupied i.f. bandwidth which increases line-
38、 arly with modulation frequency, the use of this method is restricted to modulation frequencies which do not cause the modulated signal spectrum to exceed the system bandwidth. An alternative method is to employ a calibrated measurement demodulator. 6.3 Presentation of results The results should be
39、presented as in the following examples: “The deviation sensitivity (S,) was (MHzN)“ or “At a baseband input level of dBm, the r.m.s. frequency deviation was kHz“. 6.4 Details to be specified The following items should be included as required in the detailed equipment specification: a) the method of
40、measurement (see 6.2 or note); b) the frequency of the baseband input signal; c) the frequency deviation of the i.f. output signal; d) the required deviation sensitivity or output deviation at the specified input level; e) the baseband connection point (.e. before or after pre-emphasis - see figure
41、1); f) the pre-emphasis characteristic employed (if appropriate). - BSI BS*EN*b05LO- 2-5 9b 3624bh9 0544242 O49 Page 7 EN 60510-2-5 1994 7 Sense of modulation 7.1 Definition and general considerations The sense of modulation of a frequency modulator is positive if a positive-going change of the inpu
42、t voltage results in an increase in intermediate frequency. The sense of modula- tion is important in television transmission. 7.2 Method of measurement A simple method of checking the sense of modulation is to apply to the modulator under test an assymetrical waveform and to apply the i.f. signal t
43、o a measurement demodulator having a known sense of demodulation. If the demodulator output signal polarity and the modulator input signal polarity are the same then the sense of modulation is the same as the known sense of demodulation. Another method is to observe the modulator i.f. spectrum as sh
44、own on a spectrum analyzer with a signal comprising line synchronization pulse and a positive-going peak luminance signal applied to the baseband input. The frequency of the highest level spectral line will be higher than the carrier frequency for a positive sense of modulation. 8 Different ia1 g ai
45、n/non- linear it y and different ia1 phase b) permitted DG distortion in the above range (e.g. 3 %); c) permitted DP distortion in the above range (e.g. 0,8“); d) test frequency used; e) the baseband connection point (.e. before or after the baseband amplifier). 9 Unwanted amplitude modulation 9.1 G
46、eneral considerations Frequency modulators normally exhibit a small degree of amplitude modulation which may originate either in the modulator itself or be due to the amplitude/frequency response of the i.f. circuits following the modulator. This amplitude modulation is unwanted because, as a conseq
47、uence of subsequent a.m. to p.m. conversion or of a.m. sensitivity of the demodulator, it may result in additional baseband distortion. 9.2 Method of measurement A simplified arrangement for the measurement of unwanted amplitude modulation is shown in figure 2. This is the same arrangement as used f
48、or the measurement of differ- ential gain and phase, but in the receiver part, instead of the measurement demodulator and following circuits, an i.f. envelope detector is used. The modulator under test is driven by the sweep-signal source (the test-signal of the trans- mitter part is not used), the
49、i.f. output level is sensed by the i.f. envelope detector, and the output of this detector is used for the vertical deflection of the display. The shape of this characteristic in a specified frequency range is a measure of the amplitude modulation. ES1 BS*ENtbOSLO- 2-5 96 Lb24bb9 0544245 858 Page 10 EN 60610-2-6 : 1994 For this measurement, a sweep width corresponding to the highest frequency deviation under operational conditions is chosen. Commercial link analyzers have a mode switch in the receiver pari allowing the choice between DG or DP me
