1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#) amended at Melbourne, 1988)The requirements for the characteristics of a sophisticated interruption counter equipment capable of detectingshort interruptions in transmission on audio channels are descri
2、bed below and must be adhered to in order to ensurecompatibility between equipments standardized by the CCITT and produced by different manufacturers.1 Definitions1.1 interruptionFor the purpose of this specification an interruption shall be regarded as a break in transmission or drop in thelevel of
3、 a 2 kHz test tone below a designated threshold.1.2 dead timeThe dead time is defined for the purpose of this specification as the time after which the counter is ready torecord another interruption following the end of the preceding interruption.2 The detector2.1 GeneralThe detector shall be capabl
4、e of recognizing an interruption having a nominal duration of 0.3 ms in accordancewith the probability curve given in Figure 1/O.62.This means that all interruptions exceeding 0.5 ms and 3 dB below the threshold to which the instrument is setare detected with 100% certainty whereas only 50% of these
5、 breaks occurring at 0.3 ms will be detected.2.2 Interruption detection thresholdThe threshold level selector shall be adjustable in steps to the values 3, 6, 10 and 20 dB below the normal testsignal level at the input to detector.The accuracy of the instrument at these threshold levels shall be as
6、follows:3, 6 and 10 dB: 1 dB20 dB: 2 dB.2.3 Input conditions2.3.1 The detector shall respond to a test signal of 2000 Hz 100 Hz. (See also 4.)2.3.2 The instrument shall be capable of adjustment for input levels between +10 dBm and 30 dBm.2.3.3 Input impedance (frequency range 300 Hz to 4 kHz) Balanc
7、ed, earth free. Input longitudinal interference loss . 46 dB2.3.4 Terminating impedance (other impedances optional). 600 ohms Return loss . 30 dB2.3.5 High impedance. approx. 20 kohms Bridging loss across 300 ohms . 0.15 dB2 Fascicle IV.4 - Rec. O.622.4 Auxiliary detector outputA socket shall be pro
8、vided permitting the connection of the detector logic output to an outside recordingdevice such as a tape recorder or a computer. The output from this connector shall have a two-state digital signal:logic “0”: signal level above the threshold;logic “1”: interruption, signal level below the threshold
9、The output levels shall be as supplied by TTL integrated circuits.The output impedance shall be less than 2000 ohms, the precise value depending on the requirements ofindividual Administrations.2.5 Dead timeThe instrument shall have at least two dead times:1) shortest possible, in accordance with t
10、he curve in Figure 1/O.62;2) 125 ms 25 ms for special testing purposes.d01-scFIGURE 1/O.62.D012.6 Visual indicationA visual indication shall be provided showing the condition of interruption.3 Display of measurement results3.1 Interruption countersThe detected interruptions shall be divided into the
11、 following time categories for recording purposes:a) 0.3 ms (0.6) ms-3 ms (optional, see Note),b) 3 ms-30 ms,c) 30 ms-300 ms,d) 300 ms-1 min,e) 1 min and over (optional).Facility for adjusting to other time groupings may be provided at the option of the Administrations. The countshall be presented o
12、n a visual display.Note The value of 0.6 ms applies to the 1020 Hz test tone.Fascicle IV.4 - Rec. O.62 33.2 Relative duration of interruption events (optional)To allow an easier estimation of data transmission errors which may result from interruptions, the instrumentshall provide means to calculate
13、 and indicate the relative duration of interruption events. This quantity is the ratio of thetime where the test tone is below a designated threshold to the total measurement time. Interruptions between 3 ms and1 minute shall be taken into account. Results shall be indicated in a range 1 101to 1 108
14、3.3 Seconds containing an interruption (optional)As a further option, the instrument shall provide means to calculate and indicate the percentage of secondscontaining one or more interruptions of a duration 3 ms. Results shall be indicated in a range 0 to 100% with one digitafter the decimal point.
15、3.4 Power failureIn the event of a power failure any loss of measurement results should be clearly indicated on a display forlater observation.4 Simultaneous measurementsThe measurement of interruptions may be provided in an instrument which also makes measurements of othertransient impairments, e.g
16、 amplitude and phase hits. A test signal frequency of 1020 kHz + 2 7 Hz (seeRecommendation O.6), may be used to facilitate the integration of several measurements of transient phenomena in sucha combined instrument. In all other respects, the measurement of interruptions shall be in accordance with the principlesof this Recommendation.5 Operating environmentThe electrical performance requirements shall be met when operating at the climatic conditions as specified inRecommendation O.3, 2.1.
