1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#)&)#!4)/.3G0G0&/2G0G0-%!352).G0G0%15)0-%.42/50G13$%,!9G0G0-%!352).G0G0%15)0-%.4&/2G0G04(%G0G02!.%G0G0 G0G04/G0G0 G0G0K(Z)45G134G0G0RecommendationG0G0/ (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendat
2、ion O.82 was published in Fascicle IV.4 of the Blue Book. This file is an extract from theBlue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright conditions remain un
3、changed (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in any form or by a
4、ny means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.4 - Rec. O.82 1Recommendation O.82Fascicle IV.4 - Rec. O.82GROUP-DELAY MEASURING EQUIPMENTFOR THE RANGE 5 TO 600 kHz(Geneva, 1972)The requirements for the characteristics o
5、f a group-delay measuring set for data circuits which are describedbelow must be adhered to in order to ensure compatibility between equipments standardized by the CCITT, andproduced by different manufacturers.1 Measuring principleIn the case of group-delay distortion measurements over a line (strai
6、ghtaway measurements), a signal for phasedemodulation is required on the receiving side whose frequency corresponds exactly to the modulation (split) frequencyon the transmitting side and whose phase does not change during the measurement. With the proposed measuringprinciple, this frequency is gene
7、rated in a split-frequency oscillator in the receiver whose frequency is controlled withthe aid of a reference carrier. The reference carrier is amplitude modulated with the same modulation frequency as themeasuring carrier and is transmitted over the path to be measured in periodical alternation wi
8、th the measuring carrier.During the changeover from measuring carrier to reference carrier no phase or amplitude surge must occur in thesending signal. For the sake of identification the reference carrier is furthermore amplitude modulated with anidentifying signal.If the path to be measured has dif
9、ferent group delay and/or attenuation for the measuring carrier and thereference carrier, a phase and/or amplitude surge appears at the output of the path to be measured at the carrierchangeover point within the receiver. This phase or amplitude surge is evaluated by the receiver of the measuring se
10、t.Thus, the receiver is provided with a phase measuring device for the purpose of group-delay measurements. Thismeasuring device includes the above-mentioned frequency controlled split-frequency oscillator whose phase isautomatically adjusted to the mean value derived from the phases of the split fr
11、equencies transmitted with the measuringand the reference carriers. The split-frequency voltage fed to the phase meter is taken from the output of an amplitudedemodulator which can simultaneously be used for measuring amplitude variations. In order to recognize the actualmeasuring frequency on the r
12、eceiving side particularly during sweep measurements a frequency discriminator maybe provided.If the frequency of the measuring carrier differs from the frequency of the reference carrier during themeasurement and if the path to be measured has different group-delay and attenuation values for the tw
13、o frequencies, asquare-wave signal appears at the outputs of the phase meter, the amplitude demodulator and the frequency discriminatorin the receiver, whose amplitudes are proportional to the respective measuring results referred to the frequency of thereference carrier and whose frequency correspo
14、nds to the carrier changeover frequency on the transmitting side. Thesethree square-wave signals are subsequently evaluated with the aid of controlled rectifiers and allow indications, togetherwith the correct signs, of differences in group-delay distortion, attenuation and measuring frequency betwe
15、en measuringand reference carrier frequencies.2 Technical details2.1 TransmitterThe modulation split frequency shall be 416.66 Hz (= 10 000 Hz/24). With the aid of this signal the referenceand measuring carriers are amplitude modulated to a modulation depth of 40%. Both sidebands are transmitted. Th
16、emodulation distortion factor shall be smaller than 1%. The changeover from measuring carrier to reference carrier iscarried out within a switching time of 100 microseconds. The changeover frequency is rigidly tied to the modulationfrequency by binary frequency division and is 41.66 Hz (416.6 Hz/10)
17、. The carrier changeover occurs at the minimum ofthe modulation envelope. Deviations of 20 microseconds are admissible. The carrier frequency which is nottransmitted in each case has to be suppressed by at least 60 dB referred to the sending signal.The identifying signal which is required for identi
18、fying the reference carrier is also rigidly tied to themodulation (split) frequency. The assigned frequency of 1666 Hz is derived by multiplying the modulation (split)frequency by four or by dividing 10 kHz by six. The rectangular-shaped identifying signal derived from 10 kHz throughfrequency divisi
19、on can be used for direct modulation after having passed through an RC lowpass filter with a time2 Fascicle IV.4 - Rec. O.82constant of T = 43 microseconds since a pure sinusoidal form is not required in this case. The modulation depth is 20%.The identifying signal is only transmitted during the las
20、t 2.4 milliseconds of the reference carrier sending time. Theshape of the different signals on the transmitting side shown as a function of time and their respective forms can be seenfrom Figure 1/O.82.d01-scFIGURE 1/O.82.D012.2 Receiver2.2.1 Group-delay measurements (see Figure 2/O.82)The signal co
21、ming from the path to be measured is demodulated and the modulation frequency of 416.6 Hz soobtained is filtered out by a bandpass filter. This modulation voltage is rectangularity phase modulated, the frequency ofthe phase modulation being equivalent to the changeover frequency, 41.66 Hz. The phase
22、 deviation is proportional to thegroup-delay difference between the measuring carrier and the reference carrier. The phase demodulation is carried out ina phase meter whose second input is fed, for example, by a 10 kHz oscillator via a frequency divider 24/1. This oscillatorforms a closed-phase cont
23、rol loop involving the phase meter and a lowpass filter which suppresses the changeoverfrequency. Thus, the modulation frequency generated in the receiver corresponds exactly to the modulation frequencycoming from the transmitter.At the output of the phase meter a 41.66-Hz square-wave voltage is obt
24、ained, whose amplitude is proportionalto the measuring result. In order to enable a correct evaluation of this signal, controlled rectification is required. Thecontrol voltage is derived from the modulation (split) frequency which is generated in the receiver by frequency division(10/1). The correct
25、 phase position with regard to the transmitting signal is enforced with the aid of the identifyingsignal 1666 Hz. The controlled rectifier is connected both to an indicating instrument and to the direct current output.2.2.2 Amplitude measurementsIf the amplitude measurement is to be referred also to
26、 the reference carrier, the signal at the output of theamplitude demodulator (41.66-Hz square-wave proportional to a) can be subsequently evaluated as already describedin the case of the group-delay measurements. Furthermore, it is possible to indicate the respective absolute carrieramplitude.Fascic
27、le IV.4 - Rec. O.82 32.2.3 Frequency measurementsFor sweep measurements it is necessary to generate in the receiver a voltage which is proportional to themeasuring frequency. This can be achieved with the aid of a frequency discriminator which, in turn, supplies its outputvoltage to a controlled rec
28、tifier. The indicated measuring result is the frequency difference between the measuring carrierand the reference carrier. Optionally, only the measuring carrier frequency may be indicated.d02-scFIGURE 1/O.82.D012.2.4 Blanking of transient distortionDue to the carrier changeover it may happen that t
29、ransient distortions occur in the path to be measured as wellas in the receiver. These interfering signals can effectively be blanked out by means of gate circuits. The gates willrelease the ensuing measuring devices only during those periods which are indicated in Figure 1/O.82.3 GeneralThe transmi
30、tter output and the receiver input shall provide 135 and 150 ohms conditions which must bebalanced and earth free. In addition, 75 ohms unbalanced conditions shall be provided.4 Fascicle IV.4 - Rec. O.824 Specifications for a group-delay measuring set for the range 5 to 600 Hz4.1 General4.1.1 Accura
31、cy of group-delay measurements (see also 4.2.1 below): 005 kHz to 010 kHz. 5 microseconds 010 kHz to 050 kHz. 2 microseconds 050 kHz to 300 kHz. 1 microsecond 300 kHz to 600 kHz . 0,5 microsecond 3% of measuring range(see Note 1 at the end of thisRecommendation)Outside a temperature range of + 5 C t
32、o + 40 C the stated accuracy may be affected by variations of themodulation frequency, causing a measuring error of 4% instead of 3% (see 4.1.4 below).The additional error due to amplitude variations shall not exceed: variations up to 10 dB. 0.5 microsecond variations up to 20 dB. 1.0 microsecond va
33、riations up to 30 dB. 2.0 microseconds4.1.2 Measuring frequency . 5 kHz to 600 kHz4.1.2.1 Measuring frequency accuracy: in temperature range + 5 C to + 40 C . 1% 500 Hz of actual reading in temperature range + 5 C to + 50 C . 2% 500 Hz of actual reading4.1.3 Reference frequency switchable 25 kHz(See
34、 Note 2 at the end of this Recommendation) 84 kHz432 kHz4.1.3.1 Reference frequency accuracy: in temperature range + 5 C to + 40 C . 1% in temperature range + 5 C to + 50 C . 3%4.1.4 Modulation frequency accuracy1): in temperature range + 5 C to + 40 C 416.66 Hz 0.5% in temperature range + 5 C to +
35、50 C 416.66 Hz 1%4.1.4.1 Modulation depth1). 0.4 0.054.1.4.2 Modulation distortion factor1). 1%(See Note 3 at the end of this Recommendation)4.1.5 Identifying frequency1)(derived from modulation frequency). 1.666 kHz4.1.5.1 Modulation depth1). 0.2 0.054.1.5.2 Sending time of identifying signal1)2.4
36、milliseconds terminating with the end ofthe sending time of the reference frequency4.1.5.3 The identifying signal shall commence with an increase in the amplitude of the carrier as shown inFigure 1/O.82.4.1.6 Changeover frequency2)(derived from modulation frequency) 41.66 Hz4.1.6.1 Carrier changeove
37、r time2). less than 100 microseconds4.1.6.2 Deviation between carrier changeover point and envelope minimum2) 0.02 millisecond_1)Requirements that have to be met on grounds of compatibility between equipments made by different manufacturers.2)Requirements that have to be met on grounds of compatibil
38、ity between equipments made by different manufacturers.Fascicle IV.4 - Rec. O.82 54.1.7 Range of environmental conditions3)4.1.7.1 Power supply voltage variation . 10%4.1.7.2 Temperature range + 5 C to + 40 CTemperature range for storage and transport 40 C to + 70 C4.1.7.3 Relative humidity. 45% to
39、75%4.1.8 Additional facilities4.1.8.1 Speaker facilities. Optional4.1.8.2 Internal checking circuit shall be provided to verify the proper operation of the group-delay and attenuationdistortion measurement functions using appropriate outputs from the sender.4.1.8.3 Facilities for fitting external fi
40、lters to reduce interference from adjacent trafficbands. Optional(See Note 4 at the endof this Recommendation)4.2 Sender4.2.1 Error introduced by the sender in the overall accuracy of the group-delay measurements (as indicated in 4.1.1above) shall not exceed2): 005 kHz to 010 kHz. 0.5 microsecond 01
41、0 kHz to 050 kHz. 0.2 microsecond 050 kHz to 300 kHz. 0.1 microsecond 300 kHz to 600 kHz . 0.05 microsecond4.2.2 Range of send levels (average carrier power) 40 dBm to + 10 dBm(The maximum send level may be restricted as an option.)4.2.2.1 Send level accuracy . 0.5 dBAt the reference frequency. 0.3
42、dB4.2.3 Output impedance (frequency range 5 to 600 kHz):4.2.3.1 Balanced, earth free 135,150 ohmsReturn loss 30 dBSignal balance ratio. 40 dB4.2.3.2 Unbalanced . 75 ohmsReturn loss 40 dB4.2.4 Harmonic distortion of send signal. 1% (40 dB)4.2.5 Spurious distortion of send signal. 0.1% (60 dB)4.2.6 Fr
43、equency sweep rate Adjustable from 0.2 kHz/sec to 10 Hz/sec.At least 6 sweep rates shall be provided4.2.7 A facility shall be included in the sender so that, if required, prior to measurement the test and reference carrierfrequencies can be measured to a resolution of 1 Hz. This may be achieved by p
44、roviding suitable outputs at the senderfor use with an external frequency counter.4.3 Receiver4.3.1 Input level range 40 dBm to + 10 dBm4.3.1.1 Dynamic range of receiver. 30 dB_3)These values are provisional and require further study.6 Fascicle IV.4 - Rec. O.824.3.2 Input impedance (frequency range
45、5 to 600 kHz):4.3.2.1 Balanced, earth free . 135, 150 ohmsReturn loss . 30 dBSignal balance ratio 40 dB4.3.2.2 Unbalanced 75 ohmsReturn loss . 40 dB4.3.3 Range for measuring group-delay/frequency distortion: 0 to 10, 20, 50, 100, 200, 500, 1000 microseconds.4.3.3.1 Accuracy of group-delay measuremen
46、ts in accordance with 4.1.1 and 4.2.1 above.4.3.4 Measuring ranges for attenuation/frequency distortion measurement: 0 to 2, 5, 10, 20, 50 dB4).4.3.4.1 Accuracy (+ 5 C to + 50 C) . 0.1 dB 3% of measuring range4.3.5 Measuring range for input level measurements at the reference frequency. 20 dBm to +
47、10 dBm4.3.5.1 Accuracy (+5 C to +40 C) . 0.25 dBAccuracy (+5 C to +50 C) . 1 dB4.3.6 D.c. outputs shall be provided to drive an X-Y recorder.4.3.7 Measuring range for frequency measurements 5 to 060 kHz50 to 150 kHz150 to 600 kHz4.3.7.1 Accuracy of frequency indication. 2% 500 HzNote 1 Measuring ran
48、ge indicated value at full-scale deflection on the range in use.Note 2 It was originally proposed to use a fixed reference frequency of 1800 Hz. Due to the fact that theinstrument for higher frequencies shall be applicable in three main frequency ranges (6 kHz to 54 kHz, 60 kHz to108 kHz, 312 kHz to
49、 552 kHz), three reference frequencies have to be provided which are in the middle of the respectivefrequency band.Note 3 Modulation distortion factor:r.m.s. value of unwanted sidebandsr.m.s. value of wanted sidebands 100%.Note 4 Administrations requiring to make measurements in the 60-108 kHz or 312-552 kHz ranges withoutremoving traffi
