1、CENELFC EN+b0244-8 94 = 3404583 OL582L 485 BRITISH STANDARD Methods of BS EN measurement for radio transmitters Part 8. Performance characteristics of vestigial-sideband demodulators used for testing television transmitters and transposers The European Standard EN 60244-8 : 1994 has the status of a
2、British Standard 60244-8 : 1995 IEC 244-8 : 1993 CENELEC EN*b244-8 94 3404.583 0358272 333 BS EN 60244-8 : 1995 Amd. No. Date O BSI 1995 Committees responsible for this British Standard Text affected The preparation of this British Standard was entrusted to Technical Committee EPL/lZ, Radiocommunica
3、tion, upon which the following bodies were represented : British Broadcasting Corporation British Radio and Electronic Equipment Manufacturers Association British Telecommunications plc Institution of Electrical Engineers Radio, Electrical and Television Retailers Association Radiocommunications Age
4、ncy The following aSI references relate to the work on this standard: Committee reference EPL/lZ Special announcement in BSI News March 1995 ISBN O 580 24869 8 CENELEC EN*b0244-8 94 m 3404583 0358273 258 m BS EN 60244-8 : 1995 Contents Committees responsible National foreword page Inside front cover
5、 11 Fore word Text of EN 60244-8 2 3 i CENELEC EN*b0244-8 94 m 3404583 0358274 194 m BS EN 60244-8 : 1995 National foreword This British Standard has been prepared by %chnical Committee EPL/12 and is the English language version of EN 60244-8 : 1994 Methods of measurement for radio transmitters Rtrt
6、 8: Per$ormance characteristics of vestigial-sideband demodulators used for testing television transmitters and tramposers, published by the European Committee for Electrotechnical Standardization (CENELEC). It is identical with IEC 244-8 : 1993, published by the International Electrotechnical Commi
7、ssion (IEC) and is part of a series describing recommended methods of measurement for assessing the performance of radio transmitters. This Part is intended to be used for type tests and acceptance or factory tests and can be used to check the performance characteristics of a VSB demodulator used fo
8、r measuring television transmitters and transposem. The measuring arrangement and method of measurement is, in most cases, identical with that described in BS EN 60244-5 Methods of measur- for radio transmitters Part 5 : 1995 Ry$mnce churacterzstics of television transmitters, provided that the tele
9、vision transmitter is replaced by a high-quality, double-sideband (DSB) modulator capable of delivering test signals suitable for measuring an instrument which is significantly better in performance than a television transmitter. Some other measurements, using RF generators to simulate vision and so
10、und carriers and sideband signais, are fully described. This Part is intended to be used in conjunction with BS EN 60244-5 : 1995. TO facilitate reproduction, some of the figures retain the French text. Other Farts of BS EN 60244 published to date are: Part 5 : 1995 Part 10 : 1993 Part 11 : 1993 Par
11、t 12 : Ry$rmunce characteristics of television transmitters Methods of meclsurement for television transmitters and transposers employing insertion test signals Transposers for FM sound broadcasting Guideline for drawing up descriptive lea - true synchronous and envelope detection, switchable; - in
12、the case of synchronous detection, a quadrature video output; - a switchable “sound trap“ and associated group delay correction filter (with the sound trap switched out, the phaselfrequency characteristic shall be linear); - independent (direct) sound demodulation, and intercarrier sound demodulatio
13、n may be used; - in the case of multiple sound channels, a suitable demodulator and decoder, and analogue or digital sound outputs depending on the system concerned. 3.2 See annex A of IEC 244-5. Description of the television systems and other relevant information 3.3 3.3.1 Output voltage The peak-t
14、o-peak voltage of the video output signal. Definitions relating to the demodulator output and input signals CENELEC EN*b0244-8 94 = 3404583 0358282 260 Page 7 EN 60244-8 : 1994 3.3.2 Reference output level An output voltage of 1 V between sync pulse level and white level. 3.3.3 Input voltage The vol
15、tage of the vision signal at the input of a demodulator for negative (or positive) modulation of the vision carrier is the r.m.s. voltage, expressed in mV or dB(mV), of a sinusoidal signal with an amplitude corresponding to the synchronizing pulse level (or white reference level) of that signal. 3.3
16、.4 Input voltage range The input voltage range of a demodulator is the range of input voltages within which the demodulator can deliver the reference output level within its performance specifications by adjusting the input aitenuator of the demodulator. 4 General conditions of operation and measure
17、ment The vestigial-sideband demodulator shall be tested under normal operating conditions. A sufficient warm-up time, in accordance with the demodulator specification, shall be allowed before commencing measurements. The power supply and environmental conditions shall be stated with the measurement
18、resu Its. If the sources of the demodulators input test signal have significant interaction between their generator outputs, it is recommended that circulators be inserted between the gener- ators and the combining network. If circulators are not available, attenuators of at least 10 dB shall be ins
19、erted at the output of each generator. The instruments used at the input of the demodulator, are connected to the input through a calibrated attenuator or directional coupler inserted in the connection between the input signal source and the demodulator. The impedance presented by the test equipment
20、 connected to the video and audio outputs of the demodulator shall have the nominal value as specified. Any video and audio output not used for the measurement shall be appropriately term i nated. In both cases the return loss of the termination shall be within the tolerances specified. If the sound
21、 trap of the demodulator is in circuit, the associated group delay precorrector in the modulator shall also be in circuit. CENELEC ENxb0244-8 74 3404583 0358283 IT7 Page 8 EN 60244-8 : 1994 All measurements, except those specifically related to one mode of demodulation only, shall be made in both mo
22、des, synchronous and envelope detection. .If the demodulator is fitted with both radio-frequency (RF) and intermediate frequency (IF) inputs, the demodulator specification may require that certain tests be repeated at the intermediate frequency input(s). 5 Measuring arrangements and standard video t
23、est signais Figure 1 gives the measuring arrangements built up from three radio-frequency gener- ators, simulating vision carrier, sideband signals and/or sound carrier(s). This arrangement is used for a limited number of measurements. Most of the measure- ments can be carried out using the arrangem
24、ents described in IEC 244-5. In such cases, the television transmitter should be replaced by the DSB test modulator. Some measurements need modulated sound signals. In these cases, a TV test transmitter should be used. Alternatively, one or two RF generators in combination with the DSB test modulato
25、r may be used, with sufficient decoupling to avoid intermodulation products, along with a switchable group delay precorrector. The precorrection should be in accordance with the standards concerned: see clause A.3 (extract from CCIR Report 624-3) Of IEC 244-5. In ali cases, the performance of the in
26、put test signal arrangements shall be known and allowed for. Standard video test signals are identified by a letter symbol and described in annex 6 of IEC 244-5. 6 Demodulator input and output characteristics 6.1 Input voltage range 6.1 .l Introduction Two different measurements are described. The f
27、irst measurement using an unmodulated RF signal at the input of the demodulator (see 6.1.5) is not applicable to a demodulator operating in synchronous detection mode. 6.1.2 Definition See 3.3. 6.1.3 Measuring arrangement The measuring arrangement according to 6.1.5, is shown in figure 1 of this sta
28、ndard. CENELEC EN*b0244-8 94 = 3404583 0358284 033 Page 9 EN 60244-8 : 1994 The measuring arrangement according to 6.1.6, is given in figure 2a of IEC 244-5, but with the television transmitter replaced by the DSB test modulator. 6.1.4 Test signal For the measurement according to 6.1.5, one unmodula
29、ted RF signal adjusted to the vision carrier frequency of the channel concerned is used. For the measurement according to 6.1.6. the DSB test transmitter shall be modulated with the saw tooth B1 (see annex B of IEC 244-5). 6.1.5 Measuring procedure using an unmodulated RF signal at the input a) Swit
30、ch the demodulator to the envelope mode. b) Switch the input signal alternately on and off. c) Set the demodulators input attenuator to the position corresponding to the lowest sensitivity. d) Adjust the output level of the signal generator to produce at the demodulator output a d.c. voltage of 1,11
31、 V (1.25 V for system I) between zero carrier and peak d.c. voltage on the oscilloscope. This is equivalent to the reference output level defined in 3.3 for a modulated input signal. e) Measure with an RF voltmeter the peak value of the input signal to the demodulator and determine the r.m.s. f) Rep
32、eat the above with the demodulators input attenuator set to the position corres- ponding to the highest sensitivity. g) Repeat the measurements for other television channels within the specified frequency range of the demodulator. 6.1.6 Measuring procedure using a vision signal at the input a) Switc
33、h the demodulator to the envelope detection mode. b) Switch the zero-carrier reference pulse on. c) Set the demodulators input attenuator to the position corresponding to the lowest sensitivity. d) Adjust the output level of the DSB modulator to produce at the demodulator output the reference output
34、 level defined in 3.3 and which corresponds to a level of 1,11 V (1,25 V for system i) between zero-carrier level and peak sync level. e) Measure with an RF voltmeter the peak value of the input signal to the demodulator and determine the r.m.s. f) Repeat the above with the demodulators input attenu
35、ator set to the position corres- ponding to the highest sensitivity. g) Repeat the measurement for other television channels within the specified frequency fange of the demodulator. h) Repeat the measurement in synchronous-detection mode. CENELEC EN*b0244-8 94 m 3404583 0158285 TT m Page 10 EN 60244
36、-8 : 1994 6.1.7 Presentation of the results The results shall be stated in mV or dB(mV) for each frequency depending.on the specifi- cations. 6.2 Input impedance For the purpose of this standard, the input impedance of the demodulator is expressed in terms of return loss relative to its nominal valu
37、e. The input impedance shall be measured within the specified input channels and the range of input levels, using any suitable measuring techniques such as those described in annex A. 6.3 Video output source impedance The methods for measuring the input impedance given in items a) and b) of clause A
38、2 of annex A may also be used for measuring the return loss at video frequencies at the demodulator output, but with no signal applied to the input. 6.4 Zero-carrier reference 6.4.1 Definition The zero-carrier reference is used to determine the relative positions of the characteristic levels of the
39、demodulated video signal. It is in the form of an internally generated pulse of a few microseconds duration, at a repetition frequency equivalent to the line or frame frequency of the television standard concerned. For the duration of this pulse, the radio- frequency section of the demodulator is sw
40、itched off and the vision signal of the demodu- lator is suppressed. 6.4.2 Measuring arrangement The measuring arrangement is given in figure 2a of IEC 244-5, but with the television transmitter replaced by the DSB test modulator. 6.4.3 Test signal For items a) and b) of 6.4.4, a radio-frequency sig
41、nal at the vision carrier frequency of the channel concerned, modulated with an all-black signal AI is used. See figure lb of IEC 244-5. In the case of positive demodulation, the signal of figure IC of IEC 244-5 shall be used. For item c) of 6.4.4, a variable luminance input signal is used. 6.4.4 Me
42、asuring procedure a) Compare the zero-carrier level indicated by the zero-carrier reference pulse with the zero level obtained when the signal generator is switched on and off alternately. CENELEC EN*b0244-8 94 m 3404583 OL582b 906 Page 11 EN 60244-8 : 1994 b) If required, check the timing of the sw
43、itching pulse during the line and field intervals to ensure stability. c) If required, check the pulse width and synchronization with the test signal and vary if necessary. 6.4.5 Presentation of the results The results may be presented in the form of photographs or hard copy of the oscilloscope disp
44、lay together with any explanatory notes. 6.5 Isolation between video outputs 6.5.1 Introduction When the demodulator has two or more video outputs which may be used at the same time, it is necessary to measure the change in video output level at one output with variations in the impedance of the ter
45、mination at any other output, and vice versa. The change in the terminated video output voltage at one of the output connectors, when any other output connector is open- and then short-circuited, is a measure of the isolation between those two outputs. 6.5.2 Measuring arrangement The measuring arran
46、gement is given in figure 5a of IEC 244-5. but with the television transmitter replaced by the DSB test modulation. 6.5.3 Test signal The video test signal A3s of IEC 244-5 is used. 6.5.4 Measuring procedure a) Adjust the luminance level x of the test signal to correspond to a mid-grey picture. b) S
47、et the sideband frequency f, to 1 MHz and adjust the peak-to-peak amplitude of the signal to extend from blanking level to white reference level. c) Suppress the sound carrier and adjust the output level of the test modulator (or the test transmitter) to reference input level. d) Determine the peak-
48、to-peak voltage of the video signal on the oscilloscope when the other outputs are open-circuited. e) Repeat the measurement with the other outputs short-circuited. 1) Calculate the difference between the two measurements. g) Repeat the measurements for different values of the frequency fs within th
49、e video- frequency range concerned. h) Repeat the measurement for all the other video outputs. CENELEC EN*b0244-8 94 W 3404583 0358287 842 Page 12 EN 60244-8 : 1994 6.5.5 Presentation of the results State the maximum difference obtained in decibels or as a percentage relative to 1 V peak- to-peak. 7 Linear distortion 7.1 Introduction This clause deals with the measurement of amplitude/f requency and group-delay (envelope-delay)/frequency characteristics, the main principles of which are given in clause 8 of IEC 244-5. 7.2 Amplitude/frequency characteristics 7.2.1 Int
