1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#) amended at Melbourne, 1988)1 GeneralThe equipment described below is compatible with the measuring method described in Annex A to thisRecommendation.2 Principle of operationThe instrument shall be capab
2、le of measuring the error in the reconstituted frequency of a carrier channel in thefollowing modes:Test 1: Measurement of frequency shift A B ( Hz): transmitting from A and measuring at B (seeFigure 1/O.111)The sinusoidal test frequencies having a 2 : 1 harmonic relationship are transmitted simulta
3、neously from A. AtB these two test signals, each shifted in frequency by an amount Hz, are modulated together in such a way asto detect , the frequency shift in the AB direction.Test 2: Measurement of loop frequency shift ( + Hz) transmitting and measuring at A with the channelslooped at B (see Figu
4、re 2/O.111)This test is carried out in a similar manner to Test 1 and the loop frequency shift ( + Hz) is detected.d01-scFIGURE 1/O.111.D01 =2 Fascicle IV.4 - Rec. O.111d02-scFIGURE 2/O.111.D02 =There may be a need to measure the frequency shift from B to A while the operator is still located at poi
5、nt A.This measurement can be accomplished in two ways:Test 3a: Measurement of frequency shift B A ( Hz) transmitting and measuring at A with B looped via aharmonic producing unit see Part a) of Figure 3/O.111A sinusoidal test frequency is transmitted from A and received at B where it passes through
6、a harmonicproducing unit. This received signal and its second harmonic are then returned to A, both undergoing afrequency shift of Hz where they are modulated together in such a way as to detect , the frequency shift inthe B A direction.Test 3b: Measurement of frequency shift B A, transmitting and m
7、easuring at A with an instrument at B,which sends out two test tones having harmonic relationship as in Test 1, initiated by receiving a single1020-Hz tone from A see Part b) of Figure 3/O.111.A sinusoidal test signal having a frequency of 1020 Hz is transmitted from A and received at B. If the rece
8、iverdetects only a single tone at B, a generator producing 1020 Hz and 2040 Hz (harmonic relationship) isconnected to line B A, enabling the frequency shift measurement to be made in that direction.If the receiver at B detects a measuring signal consisting of the two test tones 1020 Hz and 2040 Hz (
9、leveldifference 6 dB), the line is looped back at B automatically allowing the measurement described as Test 2see Part c) of Figure 3/O.111.The use of the frequency shift measuring equipment for Tests 3a and 3b requires the transmission of a single1020-Hz tone from A B. Therefore this facility could
10、 be provided as an option for the instrument for this type ofmeasurement. The specification of the equipment at B (harmonic producer or switched generator) should be left open forbilateral agreement between Administrations.Fascicle IV.4 - Rec. O.111 33 Transmitting equipmentThe equipment shall trans
11、mit sinusoidal test signals as follows:3.1 Frequenciesa) 1020 and 2040 Hz 2%. These two frequencies shall be in exact harmonic relationshipNote If this transmitting equipment is intended to be used in phase jitter measurements, an accuracy of 1%will be required.b) optional additional output for Admi
12、nistrations wishing to cooperate Figure 3/O.111 typemeasurements. 1020 Hz 2%.3.2 LevelThe r.m.s. total output power of the transmitted signal shall be adjustable in the range 0 dBm to 30 dBm.Where two frequencies are transmitted the difference between the two levels shall be less than 0.5 dB.3.3 Out
13、put impedance (frequency range 300 Hz to 4 kHz) Balanced, earth free (other impedances optional). 600 ohms Return loss . 30 dB Output signal balance. 40 dB4 Receiving equipmentThe receiving equipment shall accept the two test tones and shall indicate the frequency shift on a meter orother suitable i
14、ndicator.4.1 Measuring rangesFull-scale measuring ranges of 0-1 Hz and 0-10 Hz shall be provided. The algebraic sign of the shift shall alsobe indicated.4 Fascicle IV.4 - Rec. O.111d03-scFascicle IV.4 - Rec. O.111 5FIGURE 3/O.111.D03 =4.2 Measuring accuracy 0.05 Hz on 0-1 Hz range, 0.5 Hz on 0-10 Hz
15、 range.4.3 The meter or indicator shall be such that frequency shifts down to 0.1 Hz shall be readable.4.4 It shall be possible to determine frequency shifts of less than 0.1 Hz by a suitable additional visual facility.4.5 Input levelThe receiving equipment shall give the specified accuracy with tes
16、t signals having levels in the range +10 dBmto 30 dBm (see, however, 4.8 below). A device shall be provided to confirm that test signals are being received.4.6 Input impedance (frequency range 300 Hz to 4 kHz) Balanced, earth free (other impedances optional). 600 ohms Return loss . 30 dB Input longi
17、tudinal interference loss . 46 dB4.7 Input frequencyThe receiving equipment shall operate correctly with test signals up to 2% from nominal frequency asapplied at the transmitting end and having experienced a frequency shift of up to 10 Hz in the transmission circuitconcerned.4.8 Level differenceWhe
18、n the two-frequency test signal is transmitted the receiving equipment shall operate correctly when, due tothe insertion loss/frequency characteristic of the circuit, the two frequencies arrive at the input to the receivingequipment with a level difference of up to 6 dB.4.9 Recorder outputA d.c. out
19、put for operating a recorder shall be provided.4.10 Noise immunityThe r.m.s. value of the error in the indication due to a 300-3400 Hz band of white noise 26 dB below the levelof the received test signal shall not exceed 0.05 Hz.5 Operating environmentThe electrical performance requirements shall be
20、 met when operating at the climatic conditions as specified inRecommendation O.3, 2.1.6 Fascicle IV.4 - Rec. O.111ANNEX A(to Recommendation O.111)Method for measuring the frequency shift introduced bya carrier channelThe principle of the method is that the harmonic relationship between two sinusoids
21、 is destroyed if to both isadded the same frequency shift. Figure A-1/O.111 is a block schematic of the arrangement and is largely self-explanatory. From one 1000-Hz oscillator are derived two signals, one at 1000 Hz and the other at 2000 Hz, which areboth transmitted. At the receiving end of a chan
22、nel introducing Hz shift they are no longer harmonically related andthe frequency shift can be extracted and counted while at the same time a cathode-ray oscilloscope can be arranged toindicate the sense of the frequency shift. This method is used by the United Kingdom Administration and others.d04-scFIGURE A-1/O.111.D04 =
