ITU-T N 73-1988 MAINTENANCE OF PERMANENT INTERNATIONAL TELEVISION CIRCUITS LINKS AND CONNECTIONS《维护长期性国际电视线路 联系和连接-维护国际声音节目和电视传输电路的第4研究组 13页》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 . TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0G0/ the titles of those test-signal elements with the reference designations are given below:Field bar Signal A Figures A-1/N.73 and A-2/N.73Sine-squared pulse Signal B1 Figures A-3/N.73 and A-4/

2、N.73Luminance bar Signal B2 or, B3 Figures A-3/N.73 and A-4/N.73Multiburst Signal C Figures A-5/N.73 and A-6/N.73Staircase Signal D1 and D2 Figures A-7/N.73 and A-8/N.73Composite pulse Signal F Figures A-9/N.73 and A-10/N.73Chrominance bar Signal G1 (625-lines only) Figure A-11/N.73Three level chrom

3、inance bar Signal G2 (625-lines only) Figure A-11/N.73Three level chrominance bar Signal G (525-lines only) Figure A-12/N.733 Test equipment3.1 GeneratorsCCIR Recommendation 473 2 defines the insertion test signals required for measurement purposes. Theassembly of test signal elements in test lines

4、is also referred to in Recommendation N.67 and most modern test signalgenerators can originate the test signals, either as insertion test signals or as full-field test signals. In the latter modemeasurements can be carried out at standard values of average picture level (APL).The assembly of test si

5、gnal elements in the test lines is sufficient for the measurement of the large majority oftelevision circuit parameters, that is, distortions occurring at line frequency and above. However, additional test signalsare needed for low and very low-frequency measurements. A field bar is required for the

6、 measurement of field timedistortions and, for the measurement of long-time waveform distortion, a signal is required which is switched at intervalsof a few seconds between low and high APLs. (For further details see CCIR Report 636 3.)3.2 Measurement equipmentThe measurement equipment may consist o

7、f: an oscilloscope or television waveform monitor with additional equipment for making nonlinearitymeasurements1);_1)A line selector for selecting insertion test lines for display with older type waveform monitors or oscilloscipes is commerciallyavailable.2 Fascicle IV.3 - Rec. N.73 modern televisio

8、n waveform monitors equipped with line-selection and means for measuring nonlinearitydistortion; automatic measurement equipment.4 Measurement definitionsCCIR Recommendations 567 1 and 569 4 define the measurements that may be made on television circuits.There are slight differences in the way certa

9、in similar parameters are defined, for example, insertion gain and luminancebar amplitude, and differences in the way the results are expressed, for example, luminance bar amplitude and luminancebar amplitude error. To standardize routine maintenance measurements, it is recommended that the definiti

10、ons given inRecommendation 569 4 be used for maintenance purposes whenever possible. The results are then easier to analyzebecause the result of a measurement is zero for an undistorted parameter.5 Access pointsMeasurements are taken at television signal access points which are well-defined points a

11、ssociated with theinput and output of a television circuit. To suit the characteristics of the measurement equipment, the standardlevel/impedance at the access point should be 1 volt peak-to-peak into 75 ohms. The return loss at the access point shallbe better than 30 dB.The access point may be the

12、point of interconnection or may be connected to it by a distortion-free circuithaving zero loss or gain.For flexibility, and to ensure that measured parameters are comparable to transmission parameters, it isnecessary that the interconnection system in the ITC should handle programme and test signal

13、s in the same way.Figure 1/N.73 shows one method of realizing that objective.d01-scFIGURE 1/N.73.D016 Routine verification of test equipmentTo ensure that test equipment errors will not lead to incorrect adjustment of a television circuit, the testequipment should be verified regularly.The connectio

14、n between the test signal generator and the measurement equipment, via the interconnectionsystem, should be verified at intervals of, say, three months and the results should be within the limits given inTable 1/N.73.Fascicle IV.3 - Rec. N.73 3TABLE 1/N.73Limits for measurement chains7 Maintenance l

15、imitsThe figures given in Table 2/N.73 showing the maintenance limits are based on the design objectives forhypothetical reference circuits given in CCIR Recommendation 567 1 but refer to international television circuits,nominally one-third of the length of the hypothetical reference circuit, betwe

16、en terminal ITCs which are normally inadjacent countries. These limits are expected to apply for most of the time but may be exceeded for part of the time.Hence, maintenance staff must exercise judgement on the action to be taken when a circuit is outside the maintenancelimits for any parameter. If

17、the results are well outside the limits, for example, if the error is greater than twice the limitvalue or the signal-to-noise ratio is 3 dB worse than the limit value, the fault should be located and corrected. On theother hand, if the limits are only exceeded by a relatively small amount, correcti

18、ve action should not be carried outunless a given parameter exceeds the maintenance limits in two successive months.Maintenance limits for circuit sections which are different in length and construction from the circuit sectionequal to one third of the hypothetical reference circuit may be derived b

19、y the application of the Laws of Additionspecified in CCIR Recommendation 567 1 to the limits quoted in Table 2/N.73, but the precautions in 10 should benoted.Parameter LimitsLuminance bar amplitude error 1%Bar tilt/Base line distortion 1%2T pulse/bar ratio error 2%Peak differential gain 1%Peak diff

20、erential phase 1Chrominance/luminance gain inequality 2%Chrominance/luminance delay inequality 5 nsSignal-to-continuous-noise ratio (unified weighted) 65 dB4 Fascicle IV.3 - Rec. N.73TABLE 2/N.73Maintenance limits for permanent international television circuitsItem(Note 12)Parameter Test waveforms(s

21、) Maintenance limits525 6251 Luminance bar-error(Note 1)B2 or B3 11IRE units 11%( 1 dB)2 Variation of luminance bar-error(e.g. 1 s)B2 or B3 3IRE units 2%( 0,2 dB)3 Variation of luminance bar-error(e.g. 1 hour)B2 or B3 8IRE units 11%( 1 dB)4 Signal-to-continuous-weighted-noise ratio No input signal(N

22、otes 1, 3)or“quiet” line(Notes 2, 4) 56 dB 52 dB(Note 10)5 Signal-to-periodic-noise ratio (power supplyfrequency 0,1 kHz)(Note 2)No input signal 35 dB(Note 5)6 Signal-to-periodic-noise ratio (1 kHz fc)(Note 2)No input signal 55 dB7 Signal to impulsive noise ratio (Note 2) No input signal 25 dB8 Lumi

23、nance-non-linearity (Note 1) D1 3% 10%(Note 6)9 Chrominance gain non-linearity (Note 2) G or G2 4% 7%(Note 6)10 Chrominance phase non-linearity (Note 2) G or G2 4 5 (Note 6)11 Peak differential gain (Note 1) D2 10% 8%(Note 6)12 Peak differential phase (Note 1) D2 3 5 (Note 6)13 Chrominance-luminance

24、 intermodulation (Notes 1, 2) G or G2 3%(Note 6)14 Sync. amplitude error (Note 1) (Note 7) 10%(Note 6)15 Long-time waveform distortion(Note 2)“Bump” signal 40%(Notes 13, 14)Fascicle IV.3 - Rec. N.73 5TABLE 2/N.73 (cont.)Note 1 As defined in CCIR Recommendation 569 4.Note 2 As defined in CCIR Recomme

25、ndation 567 1.Note 3 Noise measured via unified weighting filter and low and high pass filters specified in Annex II to Part C of CCIRRecommendation 567 1.Note 4 Noise measured on line(s) allocated for noise measurement with weighting network and filters as given in Note 3 plus achrominance frequenc

26、y notch filter as specified in CCIR Recommendation 569 4.Note 5 The maintenance limits refer to circuits without clamps. When clamps are used the maintenance limits are 50 dB.Note 6 Measured at APLs of 10% and 90%.Note 7 Video signal containing synchronizing signals with normal amplitude.Note 8 Meas

27、urements on C2 may be referred to C1 taking account of any difference in the amplitude of the two elements. Theresults of this test may conflict with those obtained with test waveforms. If this occurs the waveform results should be considered tobe definitive.Note 9 The value is positive if the lumin

28、ance component leads the chrominance component.Note 10 Further data is required to consider amendment to this figure.Note 11 A window signal is specified in CCIR Recommendation 567 1 for use on 525-line systems. Test results are requiredbefore limits for this signal can be included. Use of this sign

29、al should be noted in the measurement results.Note 12 Routine measurements made at regular intervals may be limited to less than the complete list of items given inTable 2/N.73 by agreement between the Administrations concerned.Note 13 The value is provisional and for further study.Note 14 The maint

30、enance limit applies to testing a circuit without clamping. This is the preferred method of measurement. Whenclamps are used, the maintenance limit is 6%.Item(Note 12)Parameter Test waveform(s) Maintenance limits16 Field-time waveform distortion(Note 2)A(Note 11) 2% 6%17 Line-time waveform distortio

31、n (Note 2)Bar tilt (Note 1)B2 or B3 1% 3%18 Base line distortion (Note 1) B2 or B3 1% 3%19 2T pulse/bar ratio error (Note 1) B1 and B2 or B3 6% 8%20 Short-time waveform distortion(Note 2)B1 1stadjacent lobe6%2ndadjacent lobe3%21 Gain/frequency characteristic(Note 2)C(Note 8) 1 dB + 1,5 dBto 1 dB22 C

32、hrominance-luminance gain inequality(Note 1)B2 or B3and G, G2 or F 10% 10%23 Chrominance-luminance delay inequality(Note 1)F 80 ns(Note 9)6 Fascicle IV.3 - Rec. N.738 Schedule for routine maintenance measurementsThe performance of routine maintenance measurements between two ITCs requires adherence

33、to routineprocedures and a due regard to the allocated time. Tests (Table 3/N.73) should start at a scheduled time (Z) which hasbeen agreed between the Administrations/broadcasting organizations concerned and should progress in accordance withthe fixed timetable. This will give adequate time for mea

34、surements to be repeated if there is a possibility that one or morecircuit parameters are outside tolerance limits.It is necessary for the maintenance staff to book the routine maintenance period with the programme bookingcentre (PBC) on a regular basis so that the PBC can intervene when bookings ar

35、e made for programme transmissions atthe same time, and propose a different period for the routine maintenance measurements.The test schedule shown in Table 3/N.73 should be used by the sub-control station at the sending end of thecircuit unless there is a specific agreement between the Administrati

36、ons/broadcasting organizations concerned to use adifferent test schedule.TABLE 3/N.73Schedule for routine maintenance measurements9 Maintenance of international television circuitsIn general the programme booking centre (PBC) will not know when permanent connections are in use forprogramme transmiss

37、ions and the agreement of the customer must be obtained before such connections are interrupted inITCs to carry out maintenance on a circuit.10 Maintenance of international television circuits, links and connectionsInternational television circuits, links and connections will comprise chains of circ

38、uit sections, both nationaland international, connected in tandem, which are maintained and may be leased as separate entities. Each of thesecircuit sections may have suitable maintenance limits derived as quoted in 7.Duration Operation SignalZ to Z + 5 min Check level B2 or B3Z + 5 to Z + 10 min Me

39、asurement of linear distortions (APL low) Test linesZ + 10 to Z + 15 min Measurement of nonlinear distortions(APL low)Test linesZ + 15 to Z + 20 min Measurement of nonlinear distortions(APL high)Test linesZ + 20 to Z + 25 min Measurement of noise NoneZ + 25 to Z + 30 min Measurement of field-time wa

40、veformdistortionAZ + 30 to Z + 35 min Measurement of long-time waveformdistortion“Bump”Z + 35 to Z + 95 min Variation of luminance bar amplitude B2 or B3Note Z is the agreed time to commence the tests.Fascicle IV.3 - Rec. N.73 7The Laws of Addition may also be used to derive expected performance lim

41、its for such chains but precautionsare necessary in the use of such limits for maintenance purposes. It is possible that the overall response of the circuit,link or connection may fail to meet the calculated performance expected, even though the response of each circuitsection comprising the chain m

42、eets the individual maintenance limits used for the calculation of the overall response. Insuch cases the calculated response of the chain can only be used as a guide to the expected overall response on the initiallining up, unless additional overall equalizers are employed.There is also the possibi

43、lity that the difference between the actual and the calculated overall response of thechain can vary with time, even though the responses of the individual circuit sections remain within their respectivemaintenance limits.ANNEX A(to Recommendation N.73)Test signal elementsAn indication of the signal

44、 elements required to carry out the tests mentioned in this Recommendation is givenbelow in the form of figures. Preferred assemblies for insertion test signals are given in Recommendation N.67.d02-scFIGURE A-1/N.73.D02d03-scFIGURE A-2/N.73.D038 Fascicle IV.3 - Rec. N.73d04-scFIGURE A-3/N.73.D04d05-

45、scFIGURE A-4/N.73.D05Fascicle IV.3 - Rec. N.73 9d06-scFIGURE A-5/N.73.D06d07-scFIGURE A-6/N.73.D0710 Fascicle IV.3 - Rec. N.73d08-scFIGURE A-7/N.73.D08Fascicle IV.3 - Rec. N.73 11d09-scFIGURE A-8/N.73.D0912 Fascicle IV.3 - Rec. N.73d10-scFIGURE A-9/N.73.D10Fascicle IV.3 - Rec. N.73 13d11-scReference

46、s1 CCIR Recommendation Television performance of television circuits designed for use in internationalconnections, Vol. XII, Rec. 567, ITU, Geneva, 1986.2 CCIR Recommendation Insertion of test signals in the field blanking interval of monochrome and colourtelevision signals, Vol. XII, Rec. 473, ITU, Geneva, 1986.3 CCIR Report Long-time waveform distortion in long distance television circuits, Vol. XII, Rec. 636, ITU,Geneva, 1986.4 CCIR Recommendation Definitions of parameters simplified for automatic measurement of television insertiontest signals, Vol. XII, Rec. 569, ITU, Geneva, 1986.