ted one bit sequence in a random data stream. The measured 2. Voltage and impedance. signal should be terminated in a well matched resistive load. The 3. Coding (HDB3, CMI, B3ZS, B6ZS, B8ZS). 4. Clock frequency. Table 61.2 PCM measurements in a typical test set 5. Framing (G.704, G.706). 6. Timing jitter and wander (G.823, G.824). Standard measurements 61.2.2.1 Pulse shape Digital mW gain The pulse shape of the equipment transmit output is normalised and compared to the mask specified in the standard. This is usually an Level (including harmonic distortion) Gain vs level (using tone) Gain vs level (using noise) Gain vs level (using synch CCITT G 714 HALF CHANNEL LIMITS 2kHz) Gain vs frequency Idle state (choice of filters) Coder offset and peak codes Noise with tone Quantising distortion (using tone) Quantising distortion S(dBm0) (using noise) Intermodulation (two tone) Figure 61.3 S/N characteristic of the A-law for tones Intermodulation (four tone) Interface measurements 61/5 pulse is also sometimes specified at a crossconnect point after Table 61.3 Clock tolerance at hierarchical interfaces traversing a standard length of coaxial cable. Clock rate Tolerance 61.2.2.2 Voltage and impedance Signal voltage is usually measured as part of the pulse shape test, 64kbit/s 100ppm though some specifications quote the average signal power for a particular pattern density. 1.544Mbit/s (DS-1) +50ppm Impedance is normally 75 ohm unbalanced coaxial, except at the 2.048Mbit/s (E1) +50ppm primary rates of 1.544Mbit/s and 2.048Mbit/s where balanced 110 8.448Mbit/s +30ppm ohm and 120 ohm connections may be used. The return loss should be typically 15 to 20dB and ideally be maintained at 6 to 10dB up 34.368Mbit/s 20ppm to 2 to 3 times the clock frequency, otherwise undesirable overshoot 44.736Mbit/s (DS-3) 20ppm will appear on the pulse transitions. 139.264Mbit/s 15ppm SONET/SDH, 61.2.2.3 Coding 51.84Mbit/s (STS-1) 4.6ppm Interface codes are intended to ensure satisfactory clock recovery 155.52Mbit/s (STS-3, STM-1) < 4.6ppm under 