1、 BSI BS*EN*bQ5LO- 2-b 9b Lb24bb9 0553382 T70 D BRITISH STANDARD Methods of Measurement for radio equipment used in satellite earth stations Part 2. Measurements for sub-systems Section 2.6 Frequency demodulators The European Standard EN 60510-2-6 : 1994 has the status of a British Standard ICs 33.06
2、0.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 1996 1992 60510-2-6 : fEC 510-2-6 : BS EN 60510-2-6 : 1996 Amd. No. The following BSI references reiate to the work on this standard: Committee reference EPU135 Draft announced in BsZNeWs, Update September 1995 ISBN O
3、580 28114 X Committees responsible for this British Standard Date Terrtaffm The prepamtion of this British Standard was entrusted by Technical CommiUee EPU12, Radio communication, to Subcommittee EPU126, Radio communication systems, upon which the following bodies were represent 1996 A-equenq modula
4、tors part 3 Meulods of ?neusurement cm mbinut.ions of SUbsySW EN 60510-25 : 1994 EN 60510-3 Compliance with a British Standard does not of itself confer immunity from legal obligations. ii O BSI 1996 BSI BS*EN*b0510- 2-6 9b 1624669 0551LBb 616 EUROPEAN mARD NORME EUR0PEE”E EuROPmHE NORM EN 60510-2-6
5、 June 1994 UDC 621.396.6: 629.783: 621.317.08 Descriptors: Radiocommunications, telecommunications, satellite broadcasting, radio equipment, earth stations, charackiistics, measurements, frequency modulation, demodulators English version Methods of measurement for radio equipment used in satellite e
6、arth stations Part 2: Measurements for subsystems Section six: Frequency demodulators (IEC 510-2-6 : 1992) Mthodes de mesure pour les quipements radiolctriques utiliss dans les stations terriennes de tlcommunidon par satellites Partie 2: Mesures sur les sousensembles Section six: Dmodulateurs de frq
7、uence (CE1 510-2-6 : 1992) MeBverfahren fur Funkgert in Satelliten-Erdfunkstellen Teil 2: Messungen an Untersystemen Hauptabschnitt Sechs: Frequenzdemodulatoren (IEX 510-2-6 : 1992) This European Standard was approved by CENELEC on 1994-03-08. CENELEC members are bound to comply with the CENKENELEC
8、Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENEL
9、EC member. This European Standard exists in three official versions (English, French, Gem). A version in any other language made by tramlation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions. CENE
10、LEC members are the national electrotechnical committees of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CENELEC European Committee for Electrotechnical Standardization
11、Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B-1050 Brussels O 1994 Copyright reserved to CENELEC members Ref. No. EN 60510-2-6: 1994 E BSI BS*EN*605LO- 2-6 96 I1624669 0553387 552 D Page 2 EN 60610-2-6 : 19
12、94 Foreword The CENELEC questionnaire procedure, performed for finding out whether or not the Intemational standard IEC 51M-6 : 1992 could be accepted without textual changes, has shown that no common modifications were necessary for the acceptance as European standard. The reference document was su
13、bmitted to the CENELEC membeis for formal vote and was approved by CENELEC as EN 60510-2-6 on 8 March 1994. The following dates were fixed: - latest date of publication of an identical national standard (dop) 199503-15 latest date of withdrawal of conflicting national standards (dow) 199503-15 - Ann
14、exes designated nonnative are part of the body of the standard. in this standard, annex ZA is nomiative. Contents 1 Scope 2 Definition 3 General 4 IF. input return loss 5 6 7 8 9 10 11 12 13 Baseband output impedance and rem loss Deviation sensitivity Sense of demodulation Differential gain/non-line
15、ar and differential phasdgroup delay Baseband ampituddfrequency CharaCteristC Frequency division multiplex (f-dm.) telephony measurements Television measurements Threshold performance Measurement of impulsive noise in telephone channels near the threshold Annex ZA (normative) Other hternationai publ
16、ications quoted in this standard with the references of the relevant European publications Figures we 3 3 3 4 4 5 7 8 10 12 12 12 15 26 18 O BSI 19% BSI BS*EN*h05LO- 2-b 76 Lb24bb7 055LLB 479 Page 3 EN 60510-2-6: 1994 METHODS OF MEASUREMENT FOR RADIO EQUIPMENT USED IN SATELLITE EARTH STATIONS Part 2
17、: Measurements for sub-systems Section six: Frequency demodulators 1 Scope Methods are given in this section for the measurement of the electrical characteristics of frequency demodulators. Threshold and carrier-to-noise ratio measurements are included because these are essential for satellite syste
18、ms. Where possible, only measurements involving the basic demodulator are considered, excluding the equipment comprising the de-emphasis network and the networks associated with sound sub-carrier signals, pilot signals and auxiliary signals. Methods of measurement for frequency modulators are given
19、in section five. Measure- ments between the baseband terminals of modulator/demodulator assemblies are covered by the various sections of part 3 of this publication. 2 Definition For the purpose of this standard a frequency demodulator is a sub-system which, by analogue means, demodulates an interme
20、diate frequency (i.f .) carrier which has been frequency modulated by a baseband signal. This may be a multi-channel telephony 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
21、excluded. However, the methods or measurement described in this section are intended for assessing the performance of the demodulator when analogue signals are transmitted. A demodulator sub-system usually comprises the following three main sections: - an intermediate frequency (i.f,) section; - an
22、i.f. to baseband section (e.g. discriminator); - a baseband section. 3 General A block diagram for a typical demodulator as used in satellite earth stations is shown in figure 1. Currently, two different types of demodulator are used, namely conventional demodulators and threshold-extension demodula
23、tors. BSI BS*EN*b05LO- 2-6 96 1624669 0551189 325 W Page 4 EN 60510-2-6 : 1994 The characteristics to be measured can be divided into three principal categories: - non-transfer characteristics; - i.f. to baseband characteristics; - certain baseband-to-baseband transmission characteristics in conjunc
24、tion with a measurement modulator. The first category of measurements applies to i.f. input measurements (see 4) and baseband output measurements (see 5). The second category of measurements forms the essential part of this section because of the nature of the device under test - transfer from i.f.
25、to baseband. In order to assess the influence of the i.f. input level, some specified tests shall be made at nominal, minimum and maximum specified i.f. input levels. NOTE - Measurement of the influence of spurious amplitude modulation is not included in this Standard since the input level is assume
26、d to be entirely within the operating range of the limiter, the arnplitudeiphase conversion of the latter being assumed to be negligible. The third category of measurements includes those to be carried out on the complete modulator/demodulator (modem) assembly except that the actual or system modula
27、tor is replaced by a measurement modulator. It is very important to know the separate contribution of a demodulator to the total permitted tolerance of performance characteristics because, in an operational situation, demodulators of one design or manufacturer may have to work with modulators of ano
28、ther design or manufacturer. Compensation effects between modulator and demodulator are therefore undesirable and each demodulator should fulfil the prescribed specification in association with a measurement modulator. This procedure requires that the measurement modulator has a better performance t
29、han that specified for the demodulator under test. 4 I.F. Input return loss See part 1. section three of this publication: Measurements in the i.f. range. Measurements at harmonics of the intermediate frequency may also be required. 5 See part 1, section four of this publication: Measurements in the
30、 baseband. Baseband output impedance and return loss - BSI BS*EN*b05LO- 2-b 9b m Lb24669 055LL90 OY7 m Page 5 EN 60510-2-6 : 1994 6 Deviation Sensitivity 6.1 Definition and general considerations The deviation sensitivity (sd) of a demodulator for a sinusoidal signal of a given frequency is expresse
31、d as the ratio of the peak value of the baseband output voltage (vb) to the frequency deviation (Ar): b Af Sd = - (V/MHz) Vb and Af are both expressed in peak or r.m.s. values. The deviation sensitivity of the demodulator is usually a function of the baseband frequency because of the effect of the d
32、e-emphasis network. In some cases, however, it is possible to gain access to the baseband output point (figure 1) before the de-emphasis network: in such cases, the measured deviation sensitivity of the discriminator is inde- pendent of the baseband frequency used. 6.2 Methods of measurement Two met
33、hods for obtaining the deviation sensitivity by means of a test signal of accurately known deviation may be used, namely, the Bessel zero and the two-signal methods as discussed be low. In the first method, the measurement is made with a well-defined modulation index of 2,404 83 at relatively low mo
34、dulation frequencies, e.g. less than about 2 MHz, whilst in the second method a low modulation index (e.g. not exceeding about 0,2) at relatively high modulation frequencies (e.9. above 2 MHz) is used. This latter method is therefore especially applicable to measurements at the pilot and sound sub-c
35、arrier frequencies. 6.2.1 The Bessel zero method A suitable arrangement for measuring the deviation sensitivity of the demodulator and for calibrating the deviation of the measurement modulator is shown in figure 2. The method of measurement is known as the Bessel zero. method and calibration of the
36、 deviation sensitivity of the measurement modulator is based upon the fact that, in the case of sinusoidal modulation, the carrier frequency spectral line first disappears for a modu- lation index (m,) given by: ml= - = 2,404 83 (6-2) f where Af is the peak frequency deviation and f is the modulatin
37、g frequency. The “zero“ or point of first disappearance of the i.f. carrier is observed on the spectrum 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 d6 or more is regarded as adequate
38、. BSI BS*EN*b0520- 2-6 96 1624669 055L19L T83 W Page 6 EN 60510-2-6 : 1994 Since there are many values of the modulation index at which a carrier-zero may be obtained, the best way of ensuring that the first zero is used is by increasing the modu- lating voltage smoothly from zero to the point where
39、 the carrier disappears for the first time. The measurement procedure is as follows a) the baseband generator is set to the required frequency at which the deviation sensitivity is to be measured; b) the output level of the generator is set to zero and then smoothly increased until the i .f. carrier
40、 on the spectrum analyzer first disappears; c) the r.m.s. voltage ( Vb) at the baseband output of the demodulator is measured: d) The demodulator deviation sensitivity (S,) at modulation frequency f is then calculated from equation 6-3: fi Vb s- VIM Hz - 2,404 83 f (6-3) NOTE - As a modulation index
41、 of 2,404 83 corresponds to an occupied i.f. bandwidth which increases linearly 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 m
42、easurement demodulator in place of the spectrum analyzer. 6.2.2 The two-signal method A suitable arrangement for measuring demodulator deviation sensitivity by the two-signal method is shown in figure 3. The method is used to calibrate the demodulator deviation sensitivity at low modulation indices,
43、 up to about 0,2 and uses high modulating frequencies between 2 MHz and 10 MHz; it is therefore especially applicable at the pilot and sound sub-carrier frequencies. An accurate frequency deviation at a specified frequency is generated by means of two i-f. crystal oscillators having equal output lev
44、els but different frequencies - the first at the nominal carrier frequency (e.9. 70 MHz) and the second at a frequency differing from the carrier frequency by a known value fx. As shown in figure 3, the output signal from crystal oscillator No. 2, suitably attenuated as specified below, is added to
45、the signal from crystal oscillator No. 1. The level of the composite signal is then adjusted by attenuator No. 2 to the appropriate input level of the demodulator under test. Due to the limiting action in the demodulator, a practically pure angle-modulation signal is generated. In order to reduce th
46、e unwanted amplitude modu- lation, an extra limiter has to be inserted before the demodulator under test. This limiter shall have a low a.m/p.m. conversion in order to reduce the measurement error to an acceptable level. The r.m.s. frequency deviation is given by: fx a fi Af= - (6-4) where a is the
47、voltage attenuation of attenuator No. 1 BSI BS*EN*bO510- 2-6 96 = 1624bb9 0551192 91T Page 7 EN 60510-2-6 : 1994 From this equation, the required attenuation can be calculated. For example, to produce a frequency deviation of 140 kHz r.m.s. at a frequency f, of 8 500 kHz, the required attenu- ation
48、is 20 log, a where a is given by: 8 500 I40 fi a = which corresponds to 32,7 dB. It is advisable in practice to apply a high enough modulation frequency so that f, Af (e.g. 20 log, a I4 dB). Once the known frequency deviation is produced by the method described above, the demodulator deviation sensi
49、tivity may be calculated from: 4-5- Vb Sd = - a ViMHz X where Vb is the r.m.s. voltage of frequency fx at the demodulator output. 6.3 Presentation of results The results should be given as in the following examples: “The deviation sensitivity (S,) was . V/MHz“ or “At an r.m.s. frequency deviation of . kHz the baseband output level was . dBm”. 6.4 Details to be specified The following items should be included as required in the detailed equipment specification: a) the method of measurement (see 6.2.1 or 6.2.2); b) the modulation frequency of
