1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 / TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU30%#) amended at Geneva, 1980, and at Melbourne, 1988)The requirements for the characteristics of a simple interruption counter equipment capable of detecting shortinterruptions in transmission on audio chann
2、els are described 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
3、in thelevel of a 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 GeneralAll interruptions ab
4、ove 3.5 ms shall be detected. Interruptions of less than 2 ms shall not be recognized norrestoration of the signal for less than 2 ms. Interruptions separated by more than 4 ms shall be detected separately.2.2 Interruption detection thresholdThe instrument shall be capable of adjustment to threshold
5、 levels of 6 and 10 dB. The accuracy of theinstrument at these threshold levels shall be 1 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.2.4 Input
6、 impedance (frequency range 300 Hz to 4 kHz) balanced, earth free. Input longitudinal interference loss 46 dB2.4.1 Terminating impedance (other impedances optional) 600 ohms Return loss 30 dB2.4.2 High impedance approx. 20 kohms Bridging loss across 300 ohms . 0.15 dB.2.5 Dead time2.5.1 The dead tim
7、e of an electronic instrument shall be 3 ms 1 ms.2.5.2 The dead time of an instrument with mechanical counters shall be 125 ms 25 ms.2.5.3 A switch shall be provided on the electronic instrument giving an optional 125 ms 25 ms dead time to enablecomparable tests to be made with instruments using mec
8、hanical counters.2 Fascicle IV.4 - Rec. O.612.6 Auxiliary logic outputAn auxiliary output from the detector shall be provided wired to a suitable socket giving a logic output forcomputer access or auxiliary equipment. The output from this socket shall be a two-state digital signal:logic “0”: signal
9、level above the threshold;logic “1”: interruption, signal level below the threshold.The output levels shall be as supplied by TTL (Transistor-Transistor Logic) integrated circuits. The outputimpedance shall be less than 2000 ohms, the precise value depending on the requirements of individual Adminis
10、trations.2.7 Timing clock (optional)A timing clock shall be provided which shall limit the test duration to any period up to one hour. A manualposition shall be provided on the clock for special testing purposes when test periods of greater than one hour arerequired.3 The counter3.1 GeneralAll inter
11、ruptions of greater than 3 ms shall be recorded. The interruptions shall be recorded on a single counterwhich shall have at least a three digit display. At the end of the testing period the counter display shall hold itsaccumulated total.3.2 Power failureIn the event of a power failure the counter s
12、hall hold its accumulated total and resume the count when thepower supply is restored. Should it prove impossible to meet this requirement a visual indication shall be provided toshow that a power failure has taken place.4 Simultaneous measurementsThe measurement of interruptions may be provided in
13、an instrument which also makes measurements of othertransient impairments, e.g., amplitude and phase hits. A test signal frequency of 1020 Hz 10 Hz may be used tofacilitate the integration of several measurements of transient phenomena in such a combined instrument. In all otherrespects, the measurement of interruptions shall be in accordance with the principles of this Recommendation.5 Operating environmentThe electrical performance requirements shall be met when operating at the climatic conditions as specified inRecommendation O.3, 2.1.
