1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#) amended at Malaga-Torremolinos, 1984, and at Melbourne, 1988)IntroductionThe most commonly found single-frequency components of phase jitter on transmitted data signals are those ofringing current, comm
2、ercial a.c. power and the second to fifth harmonics of these. Since the peak phase deviation causedby such components rarely exceeds 25 peak-to-peak (i.e. low index phase modulation) only one pair of significantsidebands is produced for each sinusoidal component. Hence the main phase jitter modulati
3、on usually exists within 300 Hz of a voice-frequency tone acting as a carrier.Since random noise can cause what would appear to be a significant amount of phase jitter, a messageweighted noise measurement should always be made in conjunction with phase jitter measurements. Also, becausequantizing no
4、ise can cause a significant phase jitter reading, care must be exercised in the choice of the carrier frequencyand in the filtering to suppress the effect of noise on the measurement.Whilst this Recommendation is concerned with measurements in the frequency bands 4-300 Hz, 4-20 Hz and20-300 Hz, it i
5、s also applicable for measuring in the frequency band 3-300 Hz and 3-20 Hz.The following specifications for phase jitter measuring equipment are proposed.1 Measuring principleA sinusoidal tone, free of phase jitter, is applied to the circuit under test at normal data transmission level. Thephase jit
6、ter measuring receiver processes the received tone as follows:1) band limit around carrier frequency;2) amplify and amplitude-limit carrier to remove amplitude modulation;3) detect the phase modulation (jitter);4) display filtered jitter (up to about 300 Hz) on a peak-to-peak indicating meter or dig
7、ital display.2 Proposed specifications2.1 Measurement accuracyObjective is better than 5 per cent of the measured value plus 0.2 degrees.2.2 Transmitter2.2.1 Test signal frequency.1020 10 Hz2.2.2 Send level . 30 dBm to 0 dBm2.2.3 Output impedance (frequency range 300 Hz to 4 kHz) Balanced, earth fre
8、e (other impedances optional) 600 ohms Return loss 30 dB Output signal balance 40 dB2.2.4 Phase jitter at source 0.1 degree peak-to-peak2.3 Receiver2.3.1 Measurement rangeAt least as great as 0.2 to 30 degrees peak-to-peak2 Fascicle IV.4 - Rec. O.912.3.2 Sensitivity and frequency rangeThe receiver s
9、hould be capable of measuring the phase jitter of signals at input levels between 40 and+10 dBm and frequencies between 990 and 1030 Hz.2.3.2 Input selectivityPower line hum protection: highpass filter with a nominal cut-off frequency of 400 Hz with at least 12 dB peroctave slope.Protection for limi
10、ter against channel noise: lowpass filter with a nominal cut-off frequency of 1800 Hz with atleast 24 dB per octave slope.2.3.4 Input impedance (frequency range 300 Hz to 4 kHz) Balanced, earth free Input longitudinal interference loss 46 dB2.3.5 Terminating impedance (other impedances optional) 600
11、 ohms Return loss 30 dB2.3.6 High impedance approx. 20 kohms Bridging loss across 300 ohms 0.15 dBNote Definitions and measurement to be in accordance with Recommendation O.9.2.4 Modulation measurement weighting characteristicsThe phase jitter modulation is measured on a weighted basis defined as fo
12、llows:Three weighting characteristics are specified to measure phase jitter in the frequency bands 4 Hz to 20 Hz,4 Hz to 300 Hz and 20 Hz to 300 Hz. Jitter components in these frequency bands are measured with full sensitivity andattenuated beyond the frequency bands.The weighting characteristics ma
13、y be measured by a 2-tone test as follows: if a pure1)1000 Hz, +10 dBm toneis applied to the input and a second pure tone 20 dB lower in level is added to this tone, values of phase jitter shall beobserved according to the frequency of this added tone as shown in Table 1/O.91. Other weighting select
14、ions may beprovided on a switchable basis.2.5 Amplitude-to-phase conversionWith the second tone at 1100 Hz, an external attenuator is used to insert flat loss in 10 dB steps up to 50 dBbetween the sources of the tones and the receiver. The spread of the readings should not exceed 0.7 degrees. All of
15、 therequirements in Table 1/O.91 should also be met at any of the flat loss settings up to 50 dB. Also, a 10 per centmodulated (20 Hz-300 Hz) AM signal in the operating level range of the set applied in place of the above tones shouldcause less than 0.2 degrees jitter indication._1)A single frequenc
16、y signal with a total nonlinear distortion at least 40 dB below the level of the fundamental signal.Fascicle IV.4 - Rec. O.91 3TABLE 1/O.912.6 Noise rejectionA 3.5-kHz band-limited white-noise signal 30 dB below 1000 Hz sine-wave carrier should indicate lessthan 4 degrees peak-to-peak jitter.2.7 Tes
17、t for peak detectionThe peak detector should measure white noise at the 2.58 (99%) point. This may be tested as follows:a) Apply the two tones as described in 2.4 above. For measurements in the frequency bands of 4 to 300 Hzand 20 to 300 Hz, the second tone should be approximately 1240 Hz. For measu
18、rements in the frequencyband of 4 to 20 Hz the second tone should be at approximately 1010 Hz. Measure and record the r.m.s.value of the demodulated signal being fed to the peak detector. The signal from this point is normallyprovided as an output for spectrum analysis.b) Remove only the second tone
19、 and apply a band limited (to at least 2 kHz) Gaussian noise signal alongwith the 1000-Hz carrier. Adjust the level of the Gaussian noise for the same 11.5-degree reading on themeter as in a). Measure the r.m.s. value of the demodulated signal being fed to the peak detector. Thisvalue shall lie betw
20、een 52 and 58 per cent of the value recorded in a).2.8 Time to display correct readingIt is desirable that the display be within 5% 0.2 degrees of its final value within 4 seconds of application ofthe test signal for the frequency band 20-300 Hz and within 30 seconds for the frequency band 4-20 Hz a
21、nd 4-300 Hz.2.9 Operating environmentThe electrical performance requirements shall be met when operating at the climatic conditions as specified inRecommendation O.3, 2.1.Phase jitter(degrees)Frequency of the second tone(Hz)Frequency band (Hz)4 to 300 4 to 20 20 to 300999.7 and 1000.3 1 1 xxx999.25
22、and 1000.75 3 3 xxx998.5 and 1001.5 8 8 xxx998.0 and 1002.0 xxx xxx 3996.0 and 1004.0 10.7 1.5 10.7 1.5 xxx994.0 and 1006.0 11.2 1.0 11.2 1.0 xxx992.0 and 1008.0 11.5 0.7 11.5 0.7 xxx988.0 and 1012.0 10984.0 and 1016.0 11.5 0.7 xxx980.0 and 1020.0 11.1 1.1 11.5 0.7967.0 and 1033.0 3953.0 and 1047.0 1760.0 and 1240.0 11.5 0.7 xxx 11.5 0.7700.0 and 1300.0 11.1 1.1 xxx 11.1 1.1500.0 and 1500.0 3 xxx 3300.0 and 1700.0 1 xxx 1xxx = Does not apply.
