PULSE CODE MOULATION (PCM)

PAGE

PULSE CODE MOULATION (PCM)

For

ENGINEERING SUPERVISORS

UNDER KIND SUPERVISION OF

WALAYAT ALI KHAN LASHARI

DIRECTOR TELECOM TRAINING, LAHORE CANTT

REGIONAL TELECOM TRAINING SCHOOL Lahore-Cantt

COURSE TITLE

Maintenance & operation

Of

PCM 30/32

Channel Equipment (CTI)

COURSE CONTENTS

S/No. Topics

Page No.

1. Introduction of TDM

4

2. Mentis of TDM

7

3. Working principle of P.C.M system

8

3.1. Sampling

8

3.2. Quantization

9

3.3. Types of Quantization

10

3.4. Encoding/Decoding

11

3.5. Construction of 2 M bit/s pulse frame & Multi-frame

13

3.6. AMI and HDB3 Line Codes

15

3.7. A and ( Laws

17

3.8. PCM transmission systems and corresponding

Characteristics

17

4.Function and description of regenerative repeater

18

5.Functional diagram of PCM 30G System

19

6.Interfaces and connecting options of PCM 30G system

20

7.Technical data of PCM 30G system

21

8.Functional Diagram and Description of PCM 30G system

23

9.Function and operation of various Alarms

28

10.Alarm indication in SDA/SAD

29

Practical.

1. Measurement of gain level dependent

30

2. Measurement of gain freq. dependent

31

3. Measurement of quantization distortion

32

4. Measurement of cross talk coupling

33

5. Measurement of idle channel. noise

34

6. Measurement of different working voltages of PCM system

35

1. INTRODUCTION OF TDM

When telephone communication began individual connecting paths were used i.e. separate pair of wires was used for every telephone connection. This was known as space-division multiplex (SDM) on account of the fact that multitude of lines were arranged physically next to each other. Since a particularly large proportion of capital is invested in the line plant, efforts were made at an early stage to make multiple use of atleast those lines used for long-range communications. This led to the introduction of frequency-division multiplex (FDM). This involves subdividing a wide frequency band into narrower sub-bands. Fig. 1 shows a 48 KHz band subdivided in to 12 sub bands. The sinusoidal signal of a sub-band (carrier) is modulated by a telephone signal. Since a sinusoidal signal acts as the carrier for a telephone signal. This process is known as carrier transmission. Following demodulation on the receive side the telephone signals are again available at their original frequencies.

It is not the only way of making multiple uses of lines however. Another possibility is offered by time-division multiplex (TDM). Here the transmitted telephone signals are separated in time. Fig. 2 shows a period containing 32 time slots each time slot is approximately of 3.9 (s time. This sub-division is repeated every 125 (s in consecutive periods. One time slot in each of the consecutive periods is allocated to each telephone signal. In TDM, the analog or Digital samples of a number of telephone channels are transmitted over the same line.

Fig.1 Frequency Division Multiplex

subdivided into 32 time slot, each approx. 3.9 (s

Fig.2 Time Division Multiplex

The principle of time-division multiplex is based on the theory that a complete waveform is not required in order to transmit signals such as those encountered in telephony. It is sufficient to sample the waveform at regular intervals and to only transmit these samples (see Fig. 3). When a waveform is sampled, a train of short pulses is produced. The amplitude of each pulse represents the amplitude of the waveform at the specific sampling instants. This conversion is known as pulse amplitude modulation (PAM). The envelope to the PAM signal reflects the original form of the curve (see Fig. 4).

Relatively large intervals occur between each sample. These intervals can be used for transmitting other PAM signals, i.e. the samples of several different telephones signals can be transmitted one after the other in repeated cycles. When the pulses of several PAM signals are combined they form a PAM time-division multiplex signal (see Fig. 5)

Fig. 3 Periodic sampling of the analog telephone signal a

Fig.4. PAM signal consisting of the samples of analog telephone a

Fig.5. PAM time-division multiplex signal consisting of samples taken from the three

analog telephone signals, a, b and c in repeated cycles.

Fig.7. PCM time division multiplex signal consisting of the coded samples of analog

Telephone signals a, b.

If the waveform samples, i.e. the pulses with differing amplitudes, are converted to binary character signals, the term pulse code modulation (PCM) is used. During this process the pulse-like samples are quantized and coded 8 bits are normally used here. The digital signal in Fig.6 is shown in simplified form with 4-bit character signals (PCM-words) instead of 8-bit PCM words.

When the PCM signals of several telephone signals are interleaved they produce a PCM time-division multiplex signal (see Fig.7).

2. MERITS OF TDM.

Digital transmission has number of merits over analog. Some of these advantages are:

1. Transmission quality is very largely unaffected by distance and environmental change.

2. Process of regeneration at suitable intervals largely minimizes these accumulations.

3. Expensive filters are not required in the multiplexing equipment.

4. Testing procedures are simplified.

5. High noise immunity

6. PCM time-division multiplex signals permit the multiple use of lines and electronic circuits.

7. PCM signals are much less sensitive to interference than are analog signals (e.g. PAM signals).

8. Low space requirements.

3.Working principle of PCM.

3.1Sampling.

Sampling theorem.

The sampling theorem is used to determine the minimum rate at which an analog signal can be sampled without information being lost when the original signal is recovered.

The sampling frequency (fA) must be more than twice the highest frequency contained in the analog Signal (fA):

fA>2fs

A sampling freq (fA) of 8000 HZ has been specified internationally for the freq band (300 HZ-3400 HZ) used in telephone system i.e. the telephone signal is sampled 8000 times per second. The interval between two consecutive samples from the same telephone signal (sampling interval = TA) is calculated as follows.

TA=1/fA= 1

=125us

8000 HZ

Fig. 8 Generation of a PAM Signal

Fig shows telephone signal is fed via L.P.F. to an electronic switch the L.P.F. limits the freq band to be transmitted. It suppresses frequencies higher than half the sampling freq. The electronic switch driven at the sampling freq of 8000 HZ takes samples from the telephone signal once every 125 us. A pulse amplitude modulated signal is thus obtained at the output of the electronic switch a P.A.M signals

Fig. 9. The Sampling Process

Fig. 10 Representation of Sampling and Encoding

Fig. 11 Representation of Time Division Multiplexing

3.2QUANTIZATION.

The first stage in the conversion to a digital signal in pulse code modulation is Quantization. The whole range of possible amplitudes values is divided in to quantizing intervals.

Uniform Quantizing

Non Uniform Quantizing

Fig. 12 Quantization

In this Fig, 16 equal quartizing intervals are indicated, the quartizing intervals are numbered +1 to +8 in the +ve range of the telephone signal and 1 to 8 in the ve range. The quartizing interval is determined for each sample. Decision values form the boundaries between adjacent quatizing intervals. On the transmit side, therefore several different analog values fall within the same quantizing interval. On the receive side one signal value corresponding to the mid point of the quantizing interval is recovered for each quantizing interval.

Fig. 13 The quantizing process

3.3Types of Quantization.

There are two types of Quantization.

1. Uniform Quantization.

2. Non-Uniform Quantization.

Quantization distortion decreases as the number of quantizing intervals are increased. If the quantizing intervals are made sufficiently small the distortion will be minimum and the noise imperceptible.

Uniform Quantization.

Quantization in which all the quantizing intervals are of equal size. In this type equal and large quantizing intervals are used over the whole amplitude range, relatively large discrepancies will occur in case of small signal amplitudes.

Non-Uniform Quantization.

Quantization in which the quantizing intervals are not all of equal size, small quantizing intervals are usually allocated to small signal values (Samples) and large quantizing intervals to large signal values to make the quantizing distortion ratio nearly independent of the signal level.

Fig 14. Uniform Quantization

Fig.15. Non-Uniform Quantization

3.4Encoding/Decoding

Encoding

The PCM signal to be transmitted is obtained by encoding the quantized intervals.

The encoder allocates an 8-bit PCM word to each individual sample. In PCM transmission systems an 8-digit binary code is used for the 128 +ve and 128 ve quantizing intervals (128+128=256= 28 ). The PCM words therefore have 8 bits.

Fig.16. Encoding of quantized samples with 8 quantizing levels (3 binary

digits/code word where the most significant bit is used to devote the sign).

Decoding.

On the receive side a signal amplitude V out is allocated to every 8 bit PCM word, it corresponds to the mid point of the particular quantizing interval. The characteristic for decoding is the same as that for non-uniform encoding on the transmit side.

The PCM words are decoded in the order in which they are received and converted to a PCM signal, finally the PAM signal is fed to a low pass filter, which reproduces the original analog telephone signal.

3.5Construction of 2 M bit/s pulse frame

Pulse frame

8000 samples per second are transmitted as 8 bit PCM words in both directions for each of the 30 speech circuits. This means that, within a period of 125 (s (reciprocal of 8 KHZ) 30 PCM words each with 8 bits, are transmitted consecutively in each direction. In addition to these 30 PCM words a further 2(8 bits are also transmitted, 8 bits for signaling and 8 bits which contain alternately a bunched frame alignment signal and a signal word. The 30 PCM words together with the other 2(8 bits form a pulse frame. Pulse frames are transmitted directly one after the other.

Fig-17 Frame structure of the 30 channels PCM system

Multi frame.

In the 30 channel PCM system a multiframe is made up of 16 frames within a multiframe the signal time slot contains four bits each for signaling information of the 30 telephone channels. It is a set of consecutive frames in which the position of each frame can be identified by reference to a multiframe alignment signal.

Fig.18 Frame and Multiframe structure for CCITT30 channels PCM system

AMI and HDB3 Line codes

AMI code

A code derived from a binary by inverting the polarity of the alternate pulses representing binary 1 and by representing binary 0 with a zero voltage. The AM1 code is therefore a pseudo ternary code.

Pseudoternary signals are better suited for line transmission than are binary signals. The alternation between +ve and ve allows the regenerative repeaters to recover the timing signal required for their own synchronization.

Fig. 19. Conversion of AMI to HDB3 CodeHDB3 Code

Long sequences of zeros which would occur when a channel is idle must be avoided since the lack of transitions may allow timing recovery circuit to malfunction.

A popular code family which over comes the timing recovery problems is known as high density bipolar (HDB3)

In HDB3 code, the maximum number of zero is three. Conversion from AMI to HDB3 involves the following rules.

When four consecutive zeros occur, the code is changed to 000 V. Note that is V a violation pulse having the same polarity as the preceding pulse of the AMI sequence.

An odd number of pulses occur between successive V-pulses to ensure the successive V pulses are of opposite polarity.

An additional pulse is added so that the preceding rule is achieved. This ensures that the mean value of the signal is zero.

Fig. 20 Code forms of AMI and HDB3

3.7A and ( Laws

3.7.1A Law

Law for specifying the 13-segment characteristic for non- uniform quantizing in PCM codecs. Recommended by the CCITT for PCM30 transmission systems.

3.7.2 ( Law

Law for specifying the 15-segment characteristic for non-uniform quantizing in PCM codes. Recommended by the CCITT for PCM 24 transmission systems.

3.7.3A/( Law Conversion

Used on international connections when a conversion has to be made from a PCM30 transmission system to a PCM24 transmission system and vice versa. The A/( law conversion is carried out in that country employing the (-law.

3.8PCM Transmission systems and Corresponding characteristics

The transmission systems recommended by the CCITT are the PCM30 system, with 2048 kbit/s (CCITT Recommendation G.732), and the PCM 24 system, with 1544 kbit/s (CCITT recommendation G. 733); these combine 30 and 24 telephone channels per transmission direction respectively to form a time-division multiplex signal. PCM30 transmission systems are used through out Europe and in many non-European countries. PCM 24-transmission systems have been installed mainly in the USA, Canada and Japan. PCM30 and PCM 24 are also known as primary transmission systems or basic systems. Their most important features are given in Table1.

Common characteristics PCM30 and PCM24

a.Sampling frequency 8 kHz

b.No. of samples per telephone signal8000/s

c.Pulse frame period1/b =1/8000/s = 125 (s

d.No. of bit in PCM word8 bit

e.Bit rate of telephone channelb . d =8000/s . 8bit =64 kbit/s

System-specific characteristicsPCM 30PCM 24

f.Encoding/decoding

No. of segments in characteristicA-Law

13( - law

15

g.No. of channel time slots per pulse frame3224

h.No. of bits per pulse frame

( = additional bit) d. g = 8 bit. 32

= 256 bitd. g + 1 =

8 bit. 24+ 1

= 193 bits

i.Period of an 8-bit channel time slotc.d/h=125(s . 8/193

= ca 3.9 (sc.d/h = 125 (s. 8/193 = ca 5.2 (s

j.Bit rate of time-division multiplex signal b. h = 8000/s. 256 bit = 2048 kbit/sb. h = 8000/s 193 bit =1544 kbit/s

Table 1. Characteristics of the PCM 30 and PCM 24 transmission systems

4.Function and description of a regenerative repeater.

4.1Function of Regenerator:

The function of a regenerator is to discriminate between the presence and absence of pulses in the received signal and to transmit a replica of the digital signal transmitted from the terminal or proceeding regenerator.

A typical regenerator contains circuits to regenerate the line signal in both directions of transmission, the regenerator circuits for each direction of transmission being separate and independent of each other.

4.2 Description of Block diagram:

It contains an equalizer with amplifier, a timing recovery circuit and a regenerating circuit. The incoming and attenuated, distorted signal is fed to a preamplifier with a fixed equalizer, the amplifier is a two stage differential amplifier (wide band type) with a gain of 52 db. A detector detects a signal amplitude regulated circuit makes the amplitude of the digital signal independent of the line loss at equalizer out put by compensating attenuation of 40 db. Now this signal is fed to a timing recovery circuit via full wave rectifier which produces the retiming signal with the help of pulse synchronized OSC which is locked in phase The delay element use a capacitor to determine sampling instants in the time decision circuit. The +ve and ve pulses amplitude of 2 M bit/s signal are processed separately. It is sampled in time decision circuit with the help of recovered timing. During sampling if a binary digit 1 is detected a time decision circuit produces a new pulse and if a binary 0 is detected no pulse is produced. At the out put stage signal is again amplified up to 3 V P-0 and is transmitted to the next direction.

5.FUNCTIONAL UNITS OF PCM-30 G SYSTEM

The functional units are divided into central section, peripheral section and line terminating unit(if required).

Central section arranged into central multiplexer, supervision unit , central signaling section (divided into signaling multiplexer and signaling processor) and power supply.

The peripheral sections are the channel units which in each case have three functionally identical channel circuits. A maximum of 10 channel units can be used.

If required , the line terminating unit consisting of a slide in line terminating unit and a slide- in unit power feeding unit can be used.

Fig.22 Primary Multiplexer PCM 30 G with

Line Terminating Equipment Functional Units.

6. INTERFACES AND CONNECTING OPTIONS OF PCM 30 G SYSTEM.

To meet the different requirements of the telecommunications networks, the PCM 30 G primary multiplexer offers a number of interfaces and interconnection options.

2-Mbit/s device interface according to G.703 with F1 connections(75

floating or 120 balance ) for the outgoing and incoming 2Mbit/s signal in HDB3 code.

2Mbit/s line interface with the F1 connections for the transmission line (operation with integrated line terminating equipment)

Exchange Interface for connection to analog switching systems. 30 signaling converters maximum, optionally for loop or F signaling.

64-Kbit/s, interface for a maximum of 30 incoming and outgoing 64-Kbit/s signals with co-directional clock assignment.

Clock interfaces, these interfaces exist for operating the primary multiplexer in a synchronous data network, with clock input T3 in for synchronizing the internal oscillator and clock output T3 out for synchronizing external devices.

7. TECHNICAL DATA OF PCM 30G PCM SYSTEM

References G.7..relate to the appropriate CCITT Recommendations in

Red book III.3.

7.1 System parameter.

7.1.1 General Information on Telephone Transmission

Number of telephone circuits ..30

Voice frequency band 300 Hz to 3400 Hz

7.1.2 Pulse Code Modulation

Sample rate (G.711/2)..8000 Hz + 50x 10-6Encoding law (G.711/3).A law

Load capacity (G.711/4).+ 3.14 dBmo

7.1.32 Mbit/s Pulse Frame (G.704, 3.3)

Interval between two samples of a telephone signal

(=pulse frame period) 125s

No. of time slots per pulse frame..32 (0 to 31)

Duration of one time slot .3.906s

Number of bits per pulse frame 256

Number of bits per time slot 8

Duration of one bit ..488 ns

Transmission of telephone signals ..in time slots 1 to 15 and 17 to 31

Transmission of signaling information ..in time slot 16

Transmission of frame alignment signal

and Service word ...alternately in time slot 0

Transmission of the remote loop command.by bits of the service word

7.1.4

Signaling Pulse Frame (G.704, Table 7)

Duration of one signaling pulse frame2 ms

Number of signaling time slots per signaling pulse frame 16 ( 0 to 15)

Number of bits per signaling time slot ..8

Number of signaling bits

assigned to a telephone signal ...4 (a, b, c, d)

Transmission of signaling

bits for telephone signals 1/16 to 15/30 in signaling time slots 1 to 15

Multi frame alignment signal and

signaling service word

Number of bits ...4 each

Transmission jointly in signaling time slot 0

7.1.5 Bit Rates

Bit rate

of PCM multiplex signal 2048kbit/s + 50 x 10-6Bit rates

of the coded telephone signals .. 64 kbit/s + 50 x 10-6Bit rate of the signal carrying

the signaling information 64 kbit/s + 50 x 10-68. FUCTIONAL BLOCK DIAGRAM & DESCRIPTION OF PCM 30G SYSTEM (CTI)

8.1 Facial View of PCM 30G System

Fig. 24 (a ) Primary Multiplexer PCM30 G

Fig.24 (b) Functional Block Diagram of PCM 30 G

8.2 Primary Multiplexer PCM 30 G SYSTEM.

The Primary Multiplexer PCM 30 G forms the first level within the hierarchical

structure of the digital signal transmission systems. In addition to multiplexing 30 telephone channels signals for 64 kbit/s data signals, the PCM 30 G primary Multiplexer handles talks of matching the existing analog network to digital network.

The equipment contains the PCM multiplexing unit and the signaling converter for 30 analog telephone signals. Instead of the VF channel units, 30 digital channel units with co directional 64 kbit/s interface can be used.

The primary multiplexer can be equipped with a line-terminating unit for transmitting the 2 M bits/s signals.

8.3Voltage Converter.

The voltage converter supplies the direct voltages required for units of PCM transmission system. It is designed for an input voltage of 36 V to 75 V DC and is therefore suitable for connection to 48 V and 60 V station batteries. The voltage converter supplies four operating voltages. +5V, -5V, -12V and 11.5V.All outputs are isolated from the input and are provided with no-load, over load and short circuit protection. Outputs are monitored for over voltage and under voltages in the 5V circuit.

Fig.25 Voltage Converter

8.4Central Multiplexer.

The Central Multiplexer acts as a central clock supply for transmit and receive direction with voltage controlled crystal oscillator. The slide-in-unit also carries out framing and receiving alignment for the 2 M bit/s signal. The digital signal is produced in the transmit direction from the tributary information streams. These are derived from the slide-in-unit channel units, supervision unit and signaling multipexer.

8.5Supervision slide-in-unit

The supervision slide-in-unit is used in PCM 30 G Primary multipexer, it monitors proper operation, indicates fault and initiate fault alarms.

8.6Signaling Multiplexer

The signaling multipexer slide-in unit, is a part of the central signaling section of primary multipexer PCM 30 G. The signaling Multiplexer (S Mux) is directly connected to the central multipexer, the supervision unit, the signaling processor and the signaling converters.

8.7 Signaling Processor,

The signaling Processor (SPROZ), expands the function of the signaling Multiplexer. The slide-in-unit processes the signaling for the signaling converter. It is omitted if the PCM 30 G is equipped only with signaling converters that require no special signaling procession (e.g. with E & M)

8.8 Telephone channel unit (SEM 38 GOU)

The telephone channel slide-in-unit SEM 38 GOU is installed for interoperation with switching equipment with E&M signaling. The SEM 38 GOU processes with three telephone channels, each of these channels units contain a transmission oriented section with CODEC/ filter device and exchange oriented section

SEM stands for signaling converter E & M 38 for 3 channels, 8 wires, GOU for ground or open un symmetrical signaling.

The primary multipexer PCM 30 G can be equipped with up to ten telephone channel units SEM 38 GOU, these are linked via bus circuits to the central multipelxer.

8.9SDA 32 LDL signaling converter.SDA 32 LDL slide in signaling converter unit is used in the PCM 30 G primary multipelxer. In PCM 30 links and when used in EWSD systems. It is connected to call processing equipment using loop signaling. One slide-in unit accommodate three telephone channels. Each channels is made up of a transmitter part with a hybrid circuit and a CODEC filter circuit plus a call processing part.

SDA stands for signaling converter digital to analog, 32 indicates 3 channels 2 wires and LDL for long distance loop.

The PCM 30 G system can be equipped with a maximum of ten SDA 32 LDL slide in-units. By means of buses, they are connected to a common signaling processing equipment or the central multiplexer.

8.10SAD 32 BEL signaling converter.

The signaling converter SAD 32 BEL is used on PCM 30 G transmission routes, and interoperates with EWSD systems in switching equipment with loop signaling

The PCM 30G can be equipped with upto ten slide in units. These are linked via buses to the central multiplexer. One slide in-unit SAD 32 BEL processes the three telephone channels. Each of these channel circuit contain a transmission oriented section with hybrid and Codec /Filter device and an exchange oriented section.

8.11SAD 33 FXU Signaling Converter

The SAD 33 FXU slide in signaling converter unit is used in PCM 30G primary multiplexer. In PCM 30 links and when used in EWSD systems, it is connected to call processing equipment using F-signaling. One slide in-unit accommodates three VF channel units. Each channel unit is made up of a transmitter part with a hybrid circuit and a codec filter circuit. The units are interconnected with the central signaling processing facilities or the multiplexer centre.

The PCM 30 G primary multiplexer can be equipped with a maximum of ten signaling conversion units, representing the equivalent of 30 transmission channels.

8.12Signaling converter SDA 33 FXU

The signaling converter slide-in-unit SDA 33 FXU is installed in the primary multiplexer PCM 30 G, on PCM 30 transmission routes and in interoperation with EWSD system. It is connected to switching equipment with F-signaling. One slide-in-unit accommodates three channel circuits. Each of these channel circuits contain a transmission-oriented section with hybrid and CODEC filter device and an exchange oriented section.

The slide in units are connected via bus lines to the central signaling processor and central multiplexer.

The PCM 30 G units are connected via bus lines to the central signaling processor and central multiplexer.

The PCM 30 G inset is equipped with upto ten signaling converter slide-in-units this corresponds to 30 transmission channels.

9. Function and operation of various Alarm.

Indications in system unit A.

LED displays (central Mux section)

INT

SYN (AIS, FH)

DEXT

INTIt glows in case of failure of any central unit or central function of clock unit.

SYNIt glows in case of incorrect bit rate or loss of frame alignment or feeding current disconnection.

D EXT: Urgent alarm of distant end in the same section, it is associated in D-bit in service word of pulse frame.

LED displays (central signaling section)

INT

SYN (AIS 16)

DEXT

BQ EXT

INTIt glows in case of clock supply failure and disturbance on signaling bus.

SYNLoss of multiframe alignment in K-bit of M.F.A.S

D-EXT Distant and urgent alarm in D-K bit in service word of multiframe

BQ-EXT:.Distant end urgent alarm in NK bit in service word of multiframe.

10. Alarm indication in SDA/SAD

1. Normally off (chl in good working condition or chl in idle)

2. Flashes 5 times/sec during dialing, it glows permanently on seizure of chl.

Alarm indication

A) Mux central unitLine on Loop DisconnectionINTSYND.EXT

SYS 1SYS 2SYS 1SYS 2SYS 1SYS 2

XX

Failure by pulling central unitXXXX

From far end terminal Sys-AlarmXX

(B) Signaling Central Unit

INTSYND.EXTBQ EXT

SYS 1SYS 2SYS 1SYS 2SYS 1SYS 2SYS 1SYS 2

By pulling processor unitXX

By pulling central memory unitXX

By pulling logic adapter

--------/ /---------XXXX

By pulling central unit at other stationXX

Faulty chl unit at other stationXX

PRACTICALS

1. Measurement of Gain level dependent

Test instrument:-

PCM Terminal test set P2012 A702

Procedure:-

(i) Loop two PCM systems under test at 2M-bit DDF stage at far end.

(ii) Connect transmit BU2 of PCM terminal test set to respective chl of one system and connect receive BU3 of PCM terminal test set to same chls of second system.

(iii) Basic Setting:

VF impedance trans

900Ohms

Rel. Level trans

0.0 dBr

VF impedance receive

900 Ohms

Rel. Level receive

-7.0 dBr

Trans Signal:

Freq

1016Hz

Level range

-60.5 dBmO

Step width

1dB

(IV) Evaluation:

Tolerance Mark

CCITT

Measuring range

-/+ 2.5 dB

Mode

Auto.

V)Press function start/stop and wait for graphics result.

Observation:

(1) The graphic result should be within mark giving variation and various levels.

(2) Using cursor observe and record gain variation at various freqs. for any two chls. in both directions.

Systems A:

Chl.No./Trans Level

Limit0.5db1.d.b

Systems B:

Chl.No./Trans Level +3.00-10-20-30-40-45

Limit0.5db1.d.b

2. To Check Gain freq. Dependent:

Test instrument: PCM terminal test set P2012-A702

Procedure:

(i) Loop two PCM systems under test at 2Mbit DDF stage at far end.

(ii) Connect transmit BU2 of PCM terminal test set to respective channel of one system and connect receive BU3 of PCM terminal test set to same channel of second system.

(iii) Select measuring configuration as Analog, Manual Adjustment as 11 and select parameter as below.

(iv) Basic Setting:

VF-impedance Trans

900Ohms

Rel. Level

Trans

0.0 dBr

VF impedance Receive900 Ohms

Rel-Level

Receive-7.0 dBr

Trans Signal:

Freq. 3003400 Hz level 0.0 dBmO

Reference freq. 1016 Hz

Evaluation:

Tolerance

Mark

CCITT

Measuring

Range

- / + 2.5 dB

Mode

Auto

Press function start / strop and wait for graphic result.

Observations:

(i) The graphic result should give variations on various levels.

(ii) Using cursor, observe and record gain variations at various freqs. for two chls in both directions.

Systems A:

Transmit Level = 0 dBm

Receive Level = -7 dBm

Chl.No./Trans Level 300Hz400Hz1000Hz2000Hz2400Hz3000Hz3400Hz

Limit0.5db1.d.b

Systems B:

Transmit Level = 0 dBm

Receive Level = -7 dBmChl.No./Trans Level 300Hz400Hz1000Hz2000Hz2400Hz3000Hz3400Hz

Limit-2.0

+0.6-1.5

+0.60.7

+0.6-1.1

+0.6-7.0

+0.6

3. Measurement of Quantization Distortion:Test instrument: PCM Terminal test set P2012-A702.

Procedure:

(i). Loop two PCM systems under test at 2M- bit DDF stage at far end.

(ii.) Connect transmit BU2 of PCM terminal test set to respective channel of one system and connect receive BU3 of PCM terminal test set to same channel of second system.

(iii). Select measuring configuration as analog, manual adjustment as 12 and select parameters as below:

(iv). Basic Setting :

VF-impedance

Trans

900 Ohms

Rel-Level

0.0 dBr

VF- impedanceReceive900 Ohms

Rel- Level

-7.0 dBr

Trans Signal:

Frequency

1016 Hz

Level

-605dBmO

Step width

1dB

Evaluation:

Tolerance

Mark CCITT

Measuring

Range0 15 dB

Mode

Auto.

v. Press function start/stop and wait for graphic result.

i. The graphic result should give variation on various levels.

ii. By using cursor observe and record quantizing distortion at various levels on two channels in both directions.

QUANTIZING DISTORTION

Sys A and B

Trans level

Chal No.0 dBmO-10 dBmO-20 dBmO-30 dBmO-40 dBmO-45 dBmO

1

30

Limits >33 dB27dB22dB

4. Measurement of cross talk coupling

Test instrument: PCM Terminal test set P2012.

Procedure:

i. Loop two PCM systems under test at 2M- bit DDF stage at far end.

ii. Connect transmit BU2 of PCM terminal test set to respective channel of one system and connect receive BU3 PCM terminal test set chl (n + 1) chl of same system.

iii. Select measuring configuration as analog manual adjustment as 13 and select parameters as below.

iv. Basic Setting:

VF- impedance Trans

900 Ohms

Rel-Level

0.0dBr

VF-impedance Receive900Ohms

Rel-Level

-7.0dBr

Evaluation:

Measuring range

-90.50

Measuring frequency

1016 Hz

v. Press function start/stop and wait for graphic result.

Observations:

The graphic result should give various readings on various levels.

Chl (n)n+1n-1Chl (n)n+1n-1

1-8516-86

15-8330-84

Limit 65 dB

5. Measurement of idle chl noise:

Test instrument:

PCM Terminal set P2012-A702

Procedure:

i. loop two PCM systems under test at 2M-bit DDF stage at far end.

ii. Connect receive BU3 of PCM terminal test on chl of testing system.

iii. Select measuring configuration as analog manual adjustment as 14 and select parameters as below.

iv. Basic Setting:

VF-impedance

Receive900 Ohms

Rel-Level

-7.0 dBr

Evaluation:

Recording time 3.5 minutes

Measuring range-90..50 dB

v. press function start/stop and wait for graphic result and record reading.

Basic Noise

Chl No.

Sys No.123456789101112131415

Sys 1

Sys 2

Limit: -65 dBmO P

6. Measurement of different working voltages of PCM system.

Test instruments:

Multimeter, connecting cords.

Procedure:

1. Following different voltages are available at the output of main supply unit.

2. Measuring socket is provided at test panel for the measurement of above voltages with the help of multimeter.

VoltageMeasured Valuelimit

-12 VDCSystem 1System 212 5%

-5 VDC5 5%

+5VDC55%