18 GHZ

CAMTECH/S/2002/18GHZ/ER-2 1

18 Ghz Communication Systemand Radio Block Interface

NOTES ON

18 GHZ COMMUNICATION SYSTEM

AND RADIO BLOCK INTERFACE.

ST-57



18 GHz COMMUNICATION SYSTEM AND RADIO BLOCK INTERFACE

:: C O N T E N T S ::

1. Basic concept of Digital Communication.2. Line of sight Microwave Communication.3. Basic equipment for Microwave Digital Communication.4. Radio Equipment.5. Mux Equipment.6. Radio Block Interface / LEEMAH.7. Emergency communication.8. Power Equipment for the system.9. Test and Measuring set up.10. Maintenance Requirements and Practices.11. Do’s and Don’ts.



COURSE DURATION

Sub:- 18 GHz Communication System and Radio Block Interface (ST- 57).

SL NAME OF THE LENGTH OF NO. OF DURATION NO. COURSE THE COURSE DAYS IN HOURS----- --------------------- -------------------- ----------- ----------------1. Equipment Course Long 6 362. Initial Course Medium 3 183. Refresher Course Short 1 6

LESSON PLAN

CHA- CONTAINTS TIME ALLOCATION IN HOURSPTER -------------------------------------------------------------------------- THEORY HOURS PRACTICAL HOURS TECHING AIDS

IN HOURSTRANSPERENCIES

---------------------- --------------------------- ---------------------Long Med- Short Long Med- Short Long Med- Sho

ium ium rt_____ ____________________ ____ ____ ____ ____ ____ _______ ____ ____ ___

01. Basic concept of Digital 3 2 ½ - - - - - - Communication.02. Line of sight MW Commn. 2 1 ½ - - - - - -03. Basic equipments for MW 1 ½ - - - - - - - Digital Communication.04. Radio Equipment. 3 1 1/8 - - - ½ ¼ -05. Multiplexing Equipment. 4 2 1/8 4 2 ½ ½ ¾ ½06. Radio Block Interface/ 3 1½ ¼ 2 1 ½ 1½ ¾ ½ LEEMAH.07. Emergency Communication. 1 ½ 1/16 1 ½ ¼ 1 ½ ½08. Power Equipment for the 1 ½ 1/16 ½ ¼ 1/8 - - - System.09. Test and Measuring Set up. 1 ½ 1/8 ½ ¼ ¼ ½ ¼ ¼

10. Maintenance Requirements ½ ¼ 1/8 1 ½ 1/8 ½ ¼ 1/8 and Practices.

11. Do’s and Don’ts. ½ ¼ 1/8 1 ½ ¼ ½ ¼ 1/8



T O T A L :- 20 10 2 10 5 2 6 3 2_______________________________________________________________________________

TRANING MODULE FOR 18 GHz COMMUNICATION SYSTEMAND RADIO BLOCK INTERFACE.

Introduction

In this era, communication system plays a vital role to build up the world as a singlefamily. The nation which can afford top most communication link up, will come forward topioneer the nations in the race of universality.

In India communication system has come up slowly but steadily from earliest O/H lines torecent fibre communication system. Very recently India is going to set up optical fibrecommunication and satellite communication system.

Following stages of communication systems gradually developed in our country:- 1. Over Head Lines. 2. Under ground cables. 3. HF, VHF and UHF communication. 4. Microwave communications. 5. Optical Fibre communication ( very recent development ). Thus same system developed and shortfalls revealed and the next system has come as aremedy to the shortfalls and extra development over the former one.

CHAPTER – 1

1. Basic concept of Digital Communication :- In case of Analogue communication we have seen that Analogue Microwave carrier ismodulated by Analogue base band inside Microwave (Analogue) transmitter. Similarly in digital communication Analogue microwave carrier is modulated by Digitalbase band inside Microwave (Digital) transmitter.

1.1 Now, coming the case of formation of digital base band. We know analogue base bandis formed by the MUX working on the principle of AM-SSB-FDM.(Amplitude Modulation– Single Side Band- Frequency Division Multiplexing). Here, type of modulation ismostly FM.(Frequency Modulation).

Similarly digital base ;band is formed by DIG MUX (Digital Multiplexing) equipmentworking on the principle of pulse code modulation PCM – TDM.(Pulse Code Modulation-Time division Multiplexing). Here, type of modulation is BPSK / FSK.(Bipolar Phase shiftkeying or frequency shift keying).



Let us now consider a suitable block diagram to describe about digital microwavecommunication in a nut shell.

Telephone DIG MUX DIG MW DIG MW DIG MUX Telephone

( PCM) RADIO RADIO ( PCM)

Let us now consider the case of time division multiplexing. Here the domain of time isdivided into a large number of time slots. Thus 1st. T.S is responsible for 1st channel, 2nd

TS is responsible for 2nd channel and so on.

Now, coming the case of digital modulation. In general the analogue MW carrier ismodulated here by a modulating digital signal with binary status. Here, as O and 1 are theonly two possible states so, shift keying technique is inevitable here. We may shiftAmplitude, frequency or phase of the carrier.

1.1.1 Let us suppose we are interested in Amplitude. Shift keying then we should changethe amplitude of the RF carrier as in the following :-

analogue carrier

modulating digital signal

digitally modulated signal

Here ON-OFF nature of binary signal produces keying effect.



1.1.2 In case of digital communication system ( 18 GHz communication )frequency shiftkeying technique is utilised.

Carrier (unmodulated)

1 0 1 0 1 0 1 Modulating binary signal

Digital Modulated - FSK.

Digital Modulated - PSK 1.1.3 N.B:- In case of digital communication analogue signals ( VF sig. ) are taken andconverted to digital form. The stages involved in this operation are :- 1) Filtering. 2) Sampling. 3) Quantisation. 4) Encoding. 5) Line coding.

Basic idea regarding the above phenomenon in nut shell :-

1) Filtering :- LPFs are provided to limit speech (VF signal) to VF band (.3 to 3.4KHz )

2) Sampling :- It is nothing but formation of samples by making and breaking someswitches. Signal appears only when switch is closed. Now, rate at which switch isclosed is known as sampling frequency.

N.B. – Here, amplitude of signal depends upon amplitude of I /P signal at the instant ofsampling. Duration of sample = Duration of closing the switch ‘S’.



3) Quantisation:- This is a process in which a continuous amplitude range is broken down toa finite number of amplitude values or steps. Here, pulse amplitude modulated signal isconverted to digital signal by the process of quantisation. 7(b) - - - - - - - - - - - - - - - - - - - - - - - - - - 5 (a) - - - - - - - - - - - - - - - - - - 4(c) - - - - - - - - - - - 3(e) - - - - - - - - - - - - - - - - 2(d) 0

Let us suppose, the signal is sampled at instants a, b, c, d & e and maximum amplitude is 8volts. In this case total amplitude may be subdivided into 8 parts.

4) Encoding process :- It is a process by which quantized analogue signals are converted tobinary signals.

5) Line coding :- Before describing line coding we should know some thing about line code.

Line code :- It is a code interfacing between the MUX and Line Terminal equipment (LTE). Line coding is the process in which line coder converts unipolar NRZ O /P of thePCM coder in to a signal suitable for transmission on line. N.B – NRZ = Non-Return to zero. +5V 1 1 1 1

0V 0 0 0 0 0 0 00

1.1.4 The digital signal given above shows that o level = o V and 1 level is +5V. Thissignal is called Non-return to zero (NRZ).

Popular Line codes are :-

AMI = (Alternate Mark Inversion ). HDB-3 = (High Density Bipolar of order-3). CMT = (Coded Mark Inversion ).

Now arising the case of formation of 2 MBIT base band. Bit rate in 30 CNL PCM system:-

Here, each time slot contains 8 bits. Now, 1 TS = 8 bits. 32 TS = 8 x 32 = 256 bits ( 32 TS = Frame ). So, 1Frame = 256 bits. Now, 16 Frame = 256 x 16 = 4096 bits ( 16Frame = 1 multi frame ). Again 500 Multi Frame =4096 x 500 = 2048000 bits = 2.048 M BIT. N.B – 500Multi Frame is transmitted in 1 second.



Thus here in digital communication 2.048 M BIT base band is sent to the line.

CHAPTER - 2 2. Line of Sight MW Communication :-

A

B B

Line of sight literally means sight in the same line. In general in microwavecommunication transmitting antenna and receiving antenna exists in the same line as if oneis sighting the other in the some straight line.

Here, in the figure A is the direct ray and B is the ground reflected ray. Thus the rays travelthrough lower atmosphere known as troposphere.

Now, the wave responsible for line of sight communication is space wave.

As there is limitations due to critical frequency (cut of frequency) in sky wave propagationand maximum absorption in ground wave propagation so only space wave mode ofpropagation holds good in case of VHF,UHF, MW etc. frequency.

Now, the space wave exists in troposphere extending up to 10 KM above the ground level. Now coming the case of problems experienced by space wave in L.O.S communication.

Those are :- (1) Optical Behaviour. (2) Atmospheric effect.

2.1 (1)Optical behaviour of space wave implies that space wave resembles light waveand possesses optical property like light i.e .[a] Refraction [b] Reflection [c] Diffraction

(2)Atmospheric effect –In this case space wave suffers



(a) Attenuation(loss) (b) Ducting (c) Fading .Now ; as L-O-S .communication takes place in troposphere and as space wave existing introposphere is directly responsible for MW communication so MW communicationsuffers the problems faced by space wave .

2.1.1 Refraction—It is known thatthe layer of atmosphere becomeslighter stage by stage. As heightincreases density of air reduces.Thus rays suffer refraction as in the following. Thus the Microwave suffers bending due to refraction.

2.1.2 Reflection—Similarly; as the Mfields river etc. those suffer reflection different phases .

Figure is shown in the above .

2.1.3 Diffraction- When MW frequenby any mountain cliff on the way thenpass on the other side and communicati

W rays passes through plane surface like paddydue to this transmitted rays reach the Rx antenna at

cy travels through troposphere and gets opposition a part of the rays gets diffracted and manages to

on is possible .



CHAPTER -3

3. Basic Equipment For Microwave Digital Communication :-

Introduction In India Digital Microwave flourished just after the flourishing of analoguemicrowave.

In case of analogue microwave, certain difficulties arose which caused problem in smoothrunning of communication. Those problems have been overcome in Digital Microwave.Thus mostly noise free communication occurred at the advent of digital communication.

In case of digital communication some basic equipments are utilised step by step in aparticular sequence to get a smooth and reliable digital communication utilisingmicrowave frequency i.e. 18 GHz MW ( analogue) frequency.

3.1 Now, to study basic equipments incorporated in digital microwave some basic ideasshould be followed. Those are :-

1. Analogue signals to be taken as inputs to some units inside which limiting, filtering,sampling etc. of the signal (analogue) would be done.

2. These processed signals should be taken to the next stage, inside which standard levelsshould be maintained by some means or so.

3. Out put of that stage should be taken into a device inside which analogue signals should bechanged into digital and should be codified in proper order.

4. In the next stage that signal (DATA) should be confirmed to send on line.

5. Out put of that device should be taken out and injected in a device in which necessarymodulation should be done then up converted to microwave frequency and ultimately MWdigital communication should be performed in trans smoothly with maximum reliabilityand stability. The opposite phenomena will be adopted in case of reception.

Basic equipments to serve the above mentioned purposes may be named as :-

(1) Filter (2) Quantizer (3) Sequentially operated gates. (4) Encoder (5) Linecoder (6) Modulator (7) Up converter etc. units in trans path and



(1) Down converter (2) Demodulator (3) Line decoder (4) Decoder etc. units in receivepath

3.1.1 Let us now proceed more precisely into the basic equipments for MW digitalcommunication. Different units may be categorised into two main parts viz. (i) Trans pathand (ii) Receive parts.

Different equipments incorporated in those two parts may be listed in the following waywith a brief note to functions of those units.

Trans part Receive part 1) Console 1) DPLS 2) PLS/DPLS card 2) PLS/ Receive card ( party line signal ) 3) TCM card (2w,4w, CONF, semi CONF) 3) TCM card (Telephony channel module) 4)a) D/I (drop/ insert) card or 4)a) D/I card or b) E1IM (European first Interface b) E1IM card or Module card) or c) LEM card ( Line Equipment. Monitor) c) LEM card. d) DRBC card (Digital Radio Base Control) d) DRBC (receive) card. (despatch) Up to this multiplexing equipment is formed inside which analogue to digital and digital toanalogue transformation takes place. This part forms digital base band which is basic bandin the way of performance of digital communication. 3.1.2 In the next coming Microwave Radio Equipment which will form MW frequencyand to be transmitted / received with digital base band impressed inside itself.

To do that the following units are utilised as basic building blocks of the equipments.

Trans Part Receive Part

1) BU converter (Bi – polar to Unipolar ) 1) Down converter 2) Trans code converter 2) Digital demodulator 3) Digital modulator 3) Receive code converter 4) UP converter 4) U-B converter 5) DSC, ASC etc(Digital and analogue service SL No. 5,6&7 are same as intrans part channels for maintenance). 6) Parity bit for detection of fault. 7) Alarm indicator.

3.1.3 After considering all these one ;by one and stage by stage we can concluded thatbasic equipments for MW Digital Communication are :-

1. Multiplexing equipment for analogue to digital conversion and modulation and digital baseband formation.



2. Radio equipment (single stage) to modulate and up convert the digital base band (2M bit). 3. Radio equipment (Double stage)

i) Inside indoor (Inside equipment room). ii) Out side indoor (At tower top).

Here, (i) in indoor equipment room indirect modulation takes place and (ii) in out sideRadio, Direct Modulation takes place with direct up conversion to MW range.

4. Last of all feeder and antenna (Shrouded parabolic antenna) may be considered as basicequipment as, if these are not provided, provision of all the equipments will be in vain asno transmission and reception is possible without feeder and antenna.



CHAPTER- 4

4. Digital MW Radio Equipment :-

It is basically divided into three sections each for Transmission and reception. Blockdiagrams of the 18 GHz MW Radio is as in the following :-

HDB3 Trans digital Digital Transmitter Signal input processor modulator

HDB3 Receiver Digital Digital Receiver Signal output Processor demodulator

4.1 Description of Radio Transmitter:-

Block diagram of trans digital processor-

HDB3 To DIG radio

modulator B-U converter Multiplexing Parity Scrambler Differential And trans code check Encoder converter



Receive digital processor:-

From radio data HDB3signal demodulator

Differential Scrambler Parity Multiplexing U-B

Decoder checker Equipment converter

4.1.1 B – U converter :-

This unit converts HDB3 coded parallel serial bipolar data stream in to 4 Unipolar paralleldata streams. Before this conversion incoming bipolar data stream is amplified and waveshaped (by equalizer). Wave shaping is required to reduce pulse spreading (Inter symbol –Inter ference). Trans Code Converter :- In this unit the following should be inserted –

i) House keeping bits. ii) Frame alignment bits. iii) Party bits. iv) Route identificationbits etc. This also contains scrambler, differential decoder, Alarm (inhibit) indication signaldetector, additional. Bits for digital service channel (DSC) way side signal (WS) andsystem control signal (SCS). Digital service channel :-

2 M bits is used for order wire maintenance purpose. It can carry a maximum of 30channels

i) For express order wire (Connected to channel dropping or modem station.)ii) For omni bus order wire (Connected to all regenerator station) iii) For remote supervision and control of repeater equipments enroute .The 2M bit stream

DSC is injected in to TCC.

Way side signal :-

The 2 M b/s stream are meant for linking the small traffic of WS with that of the mainstation in the link. Analogue service channel (ASC) :-

This is a single voice channel meant for omnibus order wire purpose. This ASC modulatesthe digital modulator directly. Hence, the Analogue service channel will help inmaintenance when DSC will fail. Supervisory or system control signal (SCS) :- This monitors all repeater stations fromHQ.



House keeping bits :-

These are the spare bits inserted for the purpose of conveying the supervision information,to cause alarm at remote stations in case of any fault.

Pulse stuffing or justification :-If different digital streams, derived from different clocksources, are to be combined then all the streams are to be synchronised to a common clocksource. This process is known as pulse stuffing or justification.

Parity Bit :-In digital transmission errors can be caused in the bits. To detect the bit errorsan extra bit called parity bit is transmitted along with a group of bits (digital word). At the receiving end, the error detection circuit, detects the errors if any with the help ofparity bit and activates the alarm circuit.

In even parity method an even no. of 1’s are transmitted (odd no. of 1’s read = error).

Scrambler :- Available in the trans terminal to ensure always a clock component whetherdata are fed or not fed at the in put of the transmitter.This is device ( shift register) used to recode long strings of 1 s or 0 s in a datacommunication system otherwise long sequence of 1s and 0s can fail to recover the clockat Rx. Scrambler is used in case of Tx and De-Scrambler is used at Rx.

Differential Encoder :- Data is differentially encoded to overcome the problem of phase –potential ambiguity in the receiver. But this can increase the error rate and grey codepenalty comes forward. Thus Differential Encoder is an interface between scrambler and digital modulator whichencodes the binary data.

AIS (Alarm inhibit indication signal ) :- This alarm signal indicates that a particular partof the local equipment has gone out of order due to a fault else where in the link not at thelocal equipment. Here, facility is that unnecessary tampering of local unit may be avoided. This circuit alsodetects HDB3 code in the I / P showing ‘All 1’ indication. Draw and label block diagram of a digital MW Trans receiver and explain the basicworkings.

4.1.2 Digital MW Radio basically performs two main functions :-

1) Digital Modulation :- Here, Modulation; may be in RF or in IF stage. Modulation in RF(Direct modulation):-Here, digital base band signal is directly impressed on the microwavecarrier. Thus; modulation is done at RF. Modulation in IF Stage (Indirect modulation):- Here, digital base band signal is firstimposed on an IF signal and then the O/P is up converted to raise the frequently to RF. Modulator is the digital part of the MW radio transmitter

2) Up conversion to RF:-This portion up converts the modulated signal to MW frequenciesby inserting the local oscillator frequency.

This part of transmitter is an analogue part. Similarly, the receiver down converts the RFsignal and produces the IF signal. The IF then demodulated by the digital demodulator.



4.2 Some Important Features of Digital MW Radio (18 GHz) :-

1) Range of microwave radio = 18.36 Hz to 19.04 GHz.2) It is a low cost, easily transportable, lighter in weight, easy to install and highly

reliable Microwave Radio.3) Range of distance (Hop distance) between two MW Stations vary from 3 KM to 17

KM. Hop distance is considered as 10 KM as a whole.4) Different options are :-a) Monitored Hot stand by protection. (b) Antenna diameters

are 0.3m, 0.6 m, 1.2 m or 1.8 m, (c) Wave guide pressurisation.5) Modulation is F S K (Frequency Shift Keying).6) IF = 66 MHz.7) Capacity 120 voice.

4.3 Other Features of 18 GHz Digital Microwave :-

1) This is a way station to way station Radio Relay System.2) Omnibus control and block circuits are operated on this system.3) This has drop insert facility for the channels in each way station by PCM MUX.4) Radio repeaters are regenerative type and so no accumulation of noise is there. It also

ensures an earror free output.5) This system utilises 100 % stand by facility.6) All the stations are channel dropping stations.7) This system provides means of emergency communication by providing with VHF

base stations. Any intelligence sent from mobile VHF sets (Walkie Talkie) arereceived by nearest VHF base station and the same is put through to PCM MUX tosend the same to the controllers (HQs) end. The controller can also call the mobile setsselectively. Mobile VHF sets are handled by Drivers/Guards of the train and VHF setsare fully duplexed to replace portable control phones.

8) Wave guide loss per metre = 1.2 metres. Hence, to minimise loss wave guide length isminimised between 1 to 2 metres between Radio Set (18 GHz) and antenna. Hence,radios are placed at tower top and other units are placed inside an equipment room.

9) Size of antenna is 1.2 m dia. Parabolic disc type antenna is utilised here and for VHF 1m long whip antenna is provided.

10) Tower height is 30-35 metres. 11) Power supply arrangement :- MW stations is provided with battery of capacity 150

AH and 48 V DC supply.12) Equipment earth resistance is 0.5 to 1.0 ohms.13) Each control telephone contains 6 wires :- (a) 1 Pair for TX, (b) 1 Pair for RX and (c)

1 Pair for Signalling (E&M).14) For Block working 11 Pairs from MW to cabin is provided with. 15) VHF Base Station :- One set is provided for every third MW station. That is spacing is

20-22 KM. It has 3 pairs of frequencies. Frequency separation is 0.1 MHz. Frequencyseparation between TX and RX. Frequency Range = 146 to 152 MHZ, VHF coveragerange = 12-13 KM.

16) Operating frequency range = 18.36 to 19.04 GHz.17) TX O/P Power = + 18 dBm (63 MW).18) Modulation :- F S K.19) Bit rate is 2.048 M Bits.



Advantages of 18 GHz Digital MW Radio :-

1. RF section is placed on tower top so power consumption is less and power gain is high.2. Due to increase of frequency antenna size and weight is reduced so, tower structure may be

simple.3. It is suitable for connecting both voice and D A T A.4. Narrow beam width requires very little path clearance. Multipath effect has also been

reduced..



CHAPTER -55. Multiplexing Equipment :-

Introduction :- In strowger exchange it has been understood that multipled wiring arethere in different gears like Uni-selector, two motion selector and the like. That multipleconnection analogy has become fruitful in Multiplexing equipment.

5.1 Description of Multiplexing Equipment :- When several channels (Carrierchannels, speech channels utilised in UHF, MW etc.) are multiplied i.e. combined to forma band (Of frequency/digits) i.e. base band then multiplexing equipment is formed.

In other words :- When an equipment combines several numbers of channels in one thenthat equipment is called multiplexing equipment.

5.1.1 Types of Multiplexing Equipment :- Multiplexing equipments are of two typesaccording to construction viz. :- (a) Frequency Division Multiplexing (FDM) and (b) TimeDivision Multiplexing (TDM).In FDM, frequency domain is sub-divided into a huge nos. of parts i.e. Frequency Bands(Each frequency band comprises a channel band). In TDM, Time domain is sub divided into a huge parts i.e. time slices (Each time slice isknown as time slots) in general.

Difference between F D M and T D M :- F D M T D M

1. FDM is frequency division multiplexing. 1. TDM is time division multiplexing.2. FDM is generally applied in ANALOG. 2. TDM is generally applied inDIGITAL case.3. Its band width is lesser so better utilisation 3. As its band width is larger so betterutilisa- of transmission medium capacity can be done. tion of transmission medium is notpractice- able here.4. Here, noise accumulates due to repeated 4. Here, noise accumulation is lesscompared amplification and length of the system. to FDM system as the signal isregenerated enroute.5. Prone to cross talk. 5. Immune to cross talk.6. Equipment is bulky one. 6. Equipment is lighter here.7. This system consumes more power. 7. This system consumes less power.

In present subject i.e. Digital Microwave communication, time division multiplexingsystem should be utilised. In other words, TDM may be called as digital multiplexing.

5.1.2 Digital Multiplexing :- This is the type of multiplexing in which VF band (o.3 to3.4 KHz band) is converted to digital form. A number of such digitised speech channelsare combined (Multiplexed) to form a single digital stream called Digital Base Band.Thus in short, Digital MUX is utilised to form Digital Base Band.Now, this digital multiplexing can be achieved by the principle of pulse code modulation.



5.1.3 Pulse Code Modulation :- Here, analogue signal (continuous electrical signal) isbroken vertically into a number of pulses known as samples (sampled pulses).Now, these samples are not sent to the line. These samples are first converted to digitalsignals (binary digits) and then sent to the line, That is, in short, sampled pulses are codedbinarily to sent on line. This process of modulation is known as pulse code modulation.

Now this type of digital transmission has some definite advantages. Those are :-1. Easy to switching (Either 0 or 1 to be selected),2. Easy to store binary information.3. Data transmission become practicable in digital transmission.4. Large scale integration (LSI) makes the system more economical and compact. 5. Digital system can work with ease in case of worst possible S/N ration also.

Now, in analogue system modulation techniques utilised are :-1. Amplitude Modulation.2. Frequency Modulation.3. Phase Modulation.

But, in digital transmission system, TDM (Time division multiplexing) technique isapplied. Thus we can conclude that PCM-TDM principle is applicable in case of digitaltransmission system.Thus we see that PCM system works on TDM techniques. We should try to establish thefact.Here, in TDM technique different subscribers share the same transmission medium fordifferent intervals of time in sequence. The same may be illustrated like this :- SENDING END RECIVING END

This system works like uniselector acting in strowger auto exchange where differentoutlets are connected to the single transmission path.In figure, output of CH1 is first connected to the common transmission medium for a fixedtime. In the next instant the CH2 is connected to the line and CH3 is also connected inanother instant sequentially.In the 2nd. Rotation again the cycles are repeated sequentially.

CH 1

CH 2

CH 3

CH 1

CH 2

CH 3



From this we can conclude that a particular time interval may be subdivided into a largenumber of mini-time intervals to transmit a large number of speech channelsindependently.Thus a trans MUX is formed by utilising different time intervals sequentially. Thisexpressed as time division multiplexing.When these speech channels are transmitted sequentially one afteranother, a system shouldbe developed so that those speech channels may be received at the other end in toto. Thatcould be done if and only if proper synchronisation between trans and receive be achieved.

Now, we should investigate the generation of P C M :-

5.1.4 Generation of P C M : -Generation of PCM is done stage by stage as described below :-1. Analogue to digital conversation both for speech and signal.2. Combining of digital outputs so formed into digital base band.3. Processing of the final digital O/P into a suitable form for transmission over a

communication medium.

Here, to convert speech into digital form we should generate the following one afteranother :

a) Generation of PAM Signals and (b) Generation of Digital Output from PAM Signals.

(a)Generation of PAM Signals :- PAM means pulse amplitude modulation. It is wellknown that span of human speech band i.e. VF band is from 0.3 KHz to 3.4 KHz. This isanalogue signal and it is sine wave in nature.

PAM streams so formed coded binarily to form digital stream which is also known asPCM digital output. Now, the above informations are explained as detailed below :-

5.1.5 (a) Generation of PAM Signal Stream :- This involves the following stages :- 1) Equalizing, (ii) Filtering and (iii) Sampling.

(i) Equalising :- It is the process of correcting the frequency response characteristics ofthe incoming signal.

(ii) Filtering :- It is meant for limiting the voice frequency band to 3.4 KHz.

(iii) Sampling :- It is the process of slicing VF analogue signal at equal intervals (125 µs)to generate the pulses required for pulse code modulation. This is done by channel gatesactuated by clock pulse (Timing pulses) at the correct instants.

These samples are amplitude modulated to get PAM signals.

Defination of PAM Signals :- PAM signal means pulse amplitude modulated signal-Sampled pulses when amplitude modulated by varying I/P speech signal amplitude at therespective instants of sampling, PAM signal is produced.



b) Generation of PCM Digital Output :- This is done in the following stages – (i)Quantising , (ii) Encoding.

(i) In this process sampled pulse amplitudes are subdivided into a finite number of stepsfor the purpose of assigning a digital status (Binary code).(ii) In this process varying amplitude samples of PAM signal are assigned a digital status. Conversion of Signalling :- Here, all the signalling parts of all the channels are processedto get a combined ( MUXED)digital out put. 5.1.6 Combiner (Digital Processor) :- This unit processes the digital O/Ps of theencoded speech and signalling parts of the VF channels into a combined digital base band.After this operation the digital base band is put through to line. Now, to put it through toline with ease, the following operations should be done prior to sending the same to theline.

BIPOLAR CONVERSION :- This process converts unipolar binary output into bipolarcode so that the same may be sent easily to the transmission line. This process is alsoknown as line coding. Stage by stage formation of PAM signals are given in the following :

2) Continuous Analogue Signal –

3) Pulse Sampled Signal –

4) Pulse amplitude modulated Signal -

A detailed study of the following operations should be completed to attain pulse codemodulated signal at the output of multiplexing equipment in digital MW Communication.1. Sampling, 2. Quantization, 3. Encoding, 4. Line coding of MUX output.

5.1.7 SAMPLING :- Sampling literally means to collect samples (in any case). In thepresent case collection of pulse samples should be done from VF signal/speech signal.Now, to collect the same we should know the sampling theorem first.

Sampling Theorem :- To state sampling theorem we should first know about samplingfrequency.Sampling frequency is the base of sampling theorem. This is actually twice of themaximum frequency of VF band.

We know, span of VF band is 0.3 to 3.4 KHz. In that case maximum frequency of VF bandshould be 3.4 x 2 = 6.8 KHz but we should consider VF band as 0-4 KHz and in that casesampling frequency should be 4x2 = 8 KHz.



Now, sampling frequency has been considered as 8 KHz to (i) Simplify filter design and(ii) To allow leakage frequency (if any) to fall outside voice channel.

STATEMENT OF SAMPLING THEOREM :- This theorem states that in case of bandlimited signal if twice or more of the highest frequency be considered as samplingfrequency then only a few number of samples (Pulse) contain the total information of thevoice frequency signal.

Sampling Operation :- Here, the VF signal is taken and sliced at regular intervals to getpulse samples at different instants.Here we see that sampling frequency is 8 KHz = 8000 Hz.i.e. 8000 Hz are transmitted in 1 sec.So, 1 Hz is transmitted in 1/8000 sec. = 125 µs.This 125 µs is the sampling time period i.e. a period between two consecutive samples(Pulses). In general clock pulses are utilised sequentially to form different channels at differentinstants of times by opening the gates sequentially.Thus a time division multiplexing results as a outcome of pulse samples and sequentiallyserved clock pulses.Like speech samples, signalling samples may also be generated by sampling operation.Sampling rate of signalling is 500 samples/seconds.

MAIN POINTS TO NOTE REGARDING SAMPLING :-

1. If it is supposed that two consecutive channels are required after a period of 125 µsthen the pulse duration will be 125 µs.

2. If 5 speech channels be required to be sampled then pulse duration for speech channelwill be 125 ÷ 5 = 25 µs as 125 µs is the sampling time period. Here, pulse duration willalso be 25 µs.

3. If 10 speech channels be required to be sampled then pulse duration for each speechchannel will be 125/10 = 12.5 µs = Pulse duration.

Figure will clear the idea of sampling different nos. of speech channels (as describedabove):-

a) Pulse duration for 1 Channel. (Duration between two consecutive pulses) 125µs

b) Pulse duration for 5 Channels. 25µsc) Pulse duration for 10 Channels. -------------- 12.5µs 10th The figures show that if it is required to sample 30 channels then the sample timeperiod must be divided by 30 i.e. 125 / 30 = 4.16 µs. But if 30 channels be considered to transmit and receive than other two separate channelsmust also be considered for :-



Signalling of all the 30 channels. Synchronisation (Tx to Rx) of all the 30 channels.

Thus 30 channel PCM will contain 32 channels. In that case pulse duration = 125/32 =3.9Us = Pulse per channels.

Figure supporting Sampling :-

Here, 15 channels have been studied and found that sampling is done sequentially byopening gates sequentially. CH1 Speech CH1 clock pulse

CH2 Speech CH2 clock pulse

CH15 Speech CH15 clock pulse

5.1.8 Quantisation:- Quantisation means to assign a quantity to the pulses. If the sampled pulses of differentheights i.e. different amplitudes be quantised than each and every samples may be assigneda discrete value to differentiate among the sampled pulses.

In this way perfect levelling of speech/signal samples should be done and the next stagemay be approached later on.

A concrete figure is drawn to show quantisation of Sampled Pulses.



The figure shows different sampled pulses of different heights i.e. amplitudes.

8 +Ve 7 6 5 quantising level 4 3 2 1 S7 S8 0 S1 S2 S3 S4 S5 S6 1 2 3 4 5 6 7 8 -Ve

Some reference levels known; as Quantising levels have been drawn towards positive andnegative side of the Axis.

Now, the samples are quantised by comparing with quantising levels as in the following :- Sample Nearest quantising levels Remarks

S1 3 Here, S3 and S4 have the S2 4 same quantising level no

S3 6 means of seperation so S4 6 error is there. It is quanti- S5 5 sing error. S6 0 S7 -5 S8 -5

Here, for S3 and S4 as quantisation level is same as quantising error results and thedistortion so formed is quantising noise. To minimise this quantising ;noise, quantising levels should be increased to an optimumvalue. Presently, 256quantising levels are considered for proper quantisation. Here, 128quantising levels are (+)ve and next 128 quantising levels are (-)ve. Here, the codebecomes Log2 256 = log2 (2)8 = 8log 2/2 = 8x1 = 8bits.



Quantisation is of two types :- 1) Linear quantisation and 2) Non-Linear quantisation.

(1) Here, quantisation is done in equal steps and as a result steps remain uniform whether thestrength of signal is high or low. Due to this differentiation of two samples in same rangebut slight unequal amplitudes become impracticable. Here, same problems of quantising noise exists. To over come this problem, Non Linearquantising process has been developed.

(2) Here, in Non-Linear quantisation more quantum steps have been provided to weaker part ofsignals and less quantum steps have been provided to stronger part of signals. Thusquantisation levels of low amplitude values have been done closed i.e. compressed.

128 Quantisation levels 112 96 80 64 48 32 segment-1 16 0 16 segment-1 32 Input signal levels 48 64 80 96 112 128

13 Segmented compressed curve ( two segments each above zero and below zeroconsidering as single segment this 16 segmented curve appears to be 13 segmentedcurved).

In the 13 segmented compressed curve two examples are given whose segment numbersand position numbers are found out from the curve.

Side of the Curve Segment No. Position No. Remarks

Positive side (Upper- 7 8 Represents amplitude of side). sample P on the curve. Negative side (Lower- 5 6 Represents amplitudes of side). sample Q on the curve.



5.1.9 Some important terms regarding Quantisation :-

1) Companding = Compressing + Expanding. For non linear quantisation the signal is compressed at transmitting end and naturally thesignal is expanded at the receiving end with a view to normalise the signal. Thus COMPANDING = COM pressing + Ex PANDING.

Prupose of Companding is to provide a uniform S/N ratio for low and high amplitude I/Psignal.

2) Band Width (BW) :-

B = f log2N N = No. of quantising level. , f = Highest signal frequency. Here, when pulse width is reduced then no.of channels will be more and so, frequency willbe more. If frequency be more. B = f log2N will be more and as a result BW will be more.

3) Encoding / Coding :-

This is a process by which quantised samples are converted to binary signals by assigninga binary code depending on its quantising level.

So, far it has been understood that if no. of quantising levels be 256 then the code will be 8bit code among which.

i) First bit will represent polarity. ii) Second, Third and Fourth bit will represent segment no. 0 to 7 and iii) Fifth, Sixth, Seventh and Eighth bits will represent segment no. ( 0- 15) on the particular

segment. Examples :-

Polarity Segment No. Step No.

1) + 7 82) - 5 6 Will be written in 8 bit code as in the following :- 1) 1 111 (2 2 2 ) = 4+2+0=7 1000 (2222)=8 2) 0 101 (2 2) = 4+1=5 0110 (2+2)=4+2=6

This 8 bit code is called WORD. (One Time slot = 8 bit word). N.B:- Practically, quantising and encoding is done by ‘Coder’.



5.1.10 LINE CODING :- Coding when done for sending a signal to line comfortablythen that type of coding is known as line coding. So far, it has been observed that in PCMsystem stage by stage processes viz. Sampling, quantisation, encoding are followed toform :

i) Pulse samples.ii) Quantising them according to quantising levels.iii) Coding the quantised samples to a unipolar form i.e. unipolar binary coding

In such a binary coded condition also it is not possible to send the so converted samples tothe lines due to the following reasons :-

i) Presence of DC component and ii) Presence of a long sequences of 1’s and o’s, clock recovery becomes difficult due to poor

content of timing information.To over come these difficulties the unipolar O/P of PCM coder is converted into a signal,suitable for transmission on line. This process is known as line coding and this is done byline coder.

Popular Line Codes are :- a) AMI (Alternate Mark Inversion). b) HDB3 (High Density Bipolar code).

c) CMI (Coded mark inversion).

5.1.11 AMI Code :- Mark – Binary ‘1’ and space = Binary ‘O’ +5V 1 1 1 1I. Unipolar Binary Code :- 0 0 0 0 0 0

+5V 1 1

II. Biplolar AMI Code :- 0 0 0 0 0 0

-5V 1 1

Process is Binary to AMI conversion:-

Here, mark is alternately inverted according to (+) ve and (-) ve voltages and as a resultaverage voltage comes near to zero and the problem of DC component is almostneutralised.



Moreover, this alternate mark inversion affords inbuilt error monitoring facility to whichany shortfall observed in time of mark inversion will be treated as error. But one problemhere is that timing is lost in case of large nos. of zero and to overcome this a scrambledwill be needed to return back the timing pulses.

5.1.12 HDB3 :- This code also follows the theory of alternate mark inversion but avoidslong series of zero’s. It allows consecutively three zeros In a series of 4 zeros 3 zeros willbe allowed consecutively and the 4th. Zero will be replaced by 1.

1 1 1 1 1 1 1 1 1 1

1 1 1 1

1 1 1

V B V

Specialities of V- Bit :- 1. In HDB3 code each 4th. Zero is replaced by 1. This 1 is V.2. It attains same polarity as the proceeding mark.3. It will attain (+) ve and (-) ve polarity alternately.4. Polarity of V bit will be same as B bit in the same block.

Specialities of B-Bit :-

1. If no. of 1’s between two consecutive Vs be even then first zero of 4 consecutive zeroswill attain 1’s. This 1 is B.

2. It attains the opposite polarity of the immediately proceeding mark.

5.1.13 Coded Mark Inversion :- Here, in coded mark inversion the following cases asgiven in the figure happens :-

1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0



1. Binary 1’s are given (+) ve and (-)ve polarities alternately.2. Binary zeros are given (-) ve and (+)ve polarities alternately for each half of zero

durations.

5.1.14 SOME SPECIALITIES OF LINE CODE :-

1. Line code AMI (Alternate Mark inversion) need scrambler to attain perfection.2. Line code HDB3 is best suited for lower bit rates.3. Line code CM1 (Coded mark inversion) is best suited for higher bit rates (140 Mb/s).4. Line code is used as interface panel in between MUX panel and LTE panel (LTE =

Line terminal equipment panel).5. Block codes are also available in Line code those are :

(i) 4B/3T and (ii) 5B/6B.

i. 4B/3T = 3 level code i.e. (+)ive level, o level and (-)ive level. ii. 5B/6B = Binary code suitable for optical communication. Light = 1 and No Light =

0.

2. Any violation of code at receiving end can be used for error monitoring.

Thus stage by stage description is given regarding sampled pulses, their quantisation andcoding of the pulses and their conversion in the interface panel between MUX and LTEi.e. line coding for sending on the line with ease.

Now, after the theoretical discussion done so far we should try to establish the fact inpractical circuitry i.e. in different components of the MUX EQUIPT.

Now, before starting modular description regarding the MUX EQUIPMENT, the followingterms to be understood, so that modular description may be practically understandableperfectly.

Those terms are :-

1) Time slot or channel slot.2) Frame.3) Multiframe. 4) Digital Base Band.

5.1.15 DESCRIPTION OF THE TERMS :-

Time slot/channel slot :- Time slot literally means the slot or span or time interval presentin time domain. It may be explained in the following way :-Pulse of each channel should be transmitted at a particular time interval. This time intervalis known as time slot (for channel) or channel slot. Nos. of this type of time slots should bekept in a frame or several frames to form a multiplexed group to transmit throughtransmission medium.Now, if we want sampling of some nos. of channels then we should sample them one byone but at the same rate as given in sampling theorem.



CHAPTER-6 6. RADIO BLOCK INTERFACE

Introduction The terms Radio Block Interface is self explanatory. This means the unitwhich interfaces between Radio and Block Instrument.So far the block working was going on through RE Communication cable. But it has beenobserved that tendency of generation of noise is taking the Block Working from bad toworse. This is as usual as any type of leakage of cable can caused power hum and the likeproblems.Now, to eliminate the complication of power hum and surge voltage Radio Block Interfacecircuit has been taken into consideration. In such a circuit digital radio is a must because digital radio is immune to any type ofnoise.

6.1 Need for Universal Radio Block Interface :- As Digital Microwave has come intopicture so the days for block working through RE cable is gone. Now, these RE cablesshould be replaced by digital microwave link as is going on in the Eastern Railway. Henceforth, the station to station block working has been established replacing RE cable (asmedium).Now, in the existing block working system through LEEMAH some deficiencies havebeen observed. Those are :-

1) Availability of DATA bits is only 14 which is insufficient to accommodate 10 digit countof axle counter together with 11 DC Signals.

2) As the system utilised only one parity bit so it is insufficient to carry on block workingthrough out the Block Sections unless different FSK frequencies for different blocksections are considered.

3) For heavier traffic when we go in for IB signalling and block working by axle counters, thechannel should be very reliable of the order of 99.5% availability. Now, to carry on point to point block working properly Leemah Equipment should also beprovided with Radio patch facility.Thus the Leemah system of block working is not suited where an omnibus type of Blockcircuit is required which can be radio patched.

4) The Leemah signals after binary coding are sent out as analogue FSK signals and require amodem at each station. Since use of modem in each station is a costly affair and as AxleCounter data and control signal data are digital so it will be economic to transmit signals asDIGITAL DATA.

Hence, it is needed to develop a radio block interface capable of working on an omnibuschannel in the VF band and it is preferred to use data transmission.

6.1.1 Method of Block Working using Radio Block Interface :- As Omnibus channelis to be used for Block working. So, RBI should be worked on a system of time sharing ofthe channel by each Block Section in a cyclic order so that Block Message of only oneblock section is operated at any given time and others are blocked out at that time.



For this purpose only when the station concerned is polled the RBI shall send out thedata even if the message is ready duly encoded earlier. The method of Block working should be devised in such a way that the system becomeconformable to continue smoothly keeping an eye on the following factors :-

a) Use of an omnibus channel in 18 GHz link for a group of stations for station to stationcommunication.

b) Use of a common UHF frequency channel communication for intermediate Block signallingwith adjacent stations.

The system should contain :- (1) Master Computer at Control (HQ) end and (2) Slave Computer at different way side

station at the block section . Master to slave connection should be done by a separate omnibus channel. The systemshould contain three (3) channels comprising of :- (1) One channel for poling and (2) Othertwo channels to share Block working of 20 channels each.

The Master Computer shall allocate time slots to each slave computer which in its turnsuitably controls the block data communication on the 18 GHz digital channel betweenblock station for normal block working and the block data communication via UHFchannels between block stations and their adjacent intermediate block signalling posts ifany.The Master system informs the slave system to take control by means of packetinformation which is safety coded. An eight to ten byte packet shall be sent three times ifrequired and retransmission shall also be catered for. Thus a total of 60 bytes should besent to each slave computer. The Master system will sequentially activate the slaves in different group in thefollowing fashion:-

1. Activate slave 1 at group 1.2. Activate slave 1 at group 2.3. Activate slave 2 at group 1 on receipt of message from slave 1, group 1.4. Activate slave 2 at group 2 on receipt acknowledgement message from slave 1, group 2.

A PC based system for both master and slave is required which will contain the followingitems :-

a) MP based system with 256 KB Memory (Microprocessor).b) Floppy drive 5-1/4” (2).c) Key Board.d) Monitor (Monochrome).e) Modem (4800 bbs). f) Inverter.g) Relay drive circuit.h) The master in addition shall have a printer.



6.1.2 RBI-18 GHz Communication :- The information about relay logic and slaveevaluator should be sent in a 20 byte packet. This packet will be sent 3 times and at thereceiving RBI the information shall be accepted only if two pockets match. It shall alsocater for one retransmission. Thus a max.of 120 bytes has to be transmitted in a given timeslot. The transmission time for different band rate are in the following :- BAND RATE TIME (ms) 4800 bps 250 9600 bps 125

There may be 3 alternatives for RBI- 18 GHz MW Link those are :-

Alternative 1 :-

As RBI output is available in digital form an interface with the omniplexer throughinterface data card taking digital input is preferred. By using this digital input interfacecard the system should eliminate use of modem at each station. Also with use of higherbaud rate the system response time can be improved.

Alternative 2 :-

In case of semi conference TCM card of the amplifier is utilised at each station a modemfor interfacing RBI with omniplexer is required. This alternative is costlier (as modem isneeded in each station) so may be avoided.

Alternative 3 :-

Here RBI requires information about channel free condition from 18 GHz MW system.This information can be suitably provided from the channel modules of the omniplexer.

After detection of channel free condition each RBI shall use this after a specified timedelay. After delay it will again search for the same (Channel free condition) and aftergetting free RBI will exchange information through channel.

Time delay for each RBI is different. Here, one thing important to note is that after eachtransmission RBI should wait for 8 seconds before retransmission.

6.1.3 Physical Configuration of RBI :-

The RBI system contains :- (1) Rack, (2) DC-DC Converter and (3) RBI Evaluator.

(1) Rack Contains (19”) – (a) DC-DC Converter.

(b) RBI Evaluator and (c) Input/Output connector interface.

(2) DC-DC Converter :- This unit supplied power to RBI evaluator for its operation. This unitgets an input of ± 24 V DC from a battery on float charge.



Outputs provided by DC-DC Converter are :-

a) + 5V (VCC-A) 7.5 Amps. d) +5V (VCC-D) 5 Amps.b) + 5V (VCC-B) 7,5 Amps. e) ± 12V 1.0 Amp. c) + 5V (VCC-C) 7.7 Amps. f) +10 V ISO 1.5 Amps. :: 28 ::

VOLTAGE DISTRIBUTION CHART FOR RBI SYSTEM :-

SL DC VOLTAGE DC VOLTAGE SUPPLIED TO THE UNITNO. SUPPLY

1. + 5V (A,B,C) Processor Cards A, B and C.2. + 5V (D) Communication Card D.3. ± 12V DATA Trans. (TTL) and DATA receive.4. + 24V Drives relays, relay input card and relay output card.

3. RBI EVALUATOR :- RBI has the following functions :-

i) Receive/Feed information from/to relay logic.ii) Receive count and status information from slave evaluator.iii) Generate 5 KHz simulated signal for axle counter.iv) Communication link for 18 GHz/UHF.

These functions are performed by the following units :-

(a) (i) Relay input interface (RBI receives information from this unit) (ii) Relay output interface (RBI sends commands to relays).

(b) Slave evaluator interface. (c) 5 KHz simulator interface. (d) Radio communication interface. (e) Microprocessor circuit. (f) Mother Board.(g) Display Circuit.

6.1.4 Short Descriptions of the Units :- RELAYS THREE PROCESSOR

DIGITAL(a)Relay input interface :- This unit

CCTS. interfaces the analogue and digital circuits through OPTO coupler device. Status of 16 pairs of optically isolated inputs are received by this unit.

RELAYINPUTINTE-RFACE



(b) Slave Evaluator Interface :- Here information is received From slave evaluator in the Form of packets in the process 2 out of 3. That is if 2 nos. of packets of information be received OK then RBI accepts the information.

:: 29 ::

(C)5 KHz simulator interface :- TELECOM CABLE Here, count and status information Send by slave evaluator of other Stns. Arises at 5 KHz simulator Interface through radio (of that Station). Then it is sent to axle Counter evaluator which accepts SLAVE RADIO 5 KHZ SIMULATOR AXLE

COUNTER Only 5 KHz AM signal (AM = EVALUATOR INTERFACE

EVALUATOR Amplitude Modulated).

d) Radio Communication Interface :- MP circuits(for reading of status)

e) Relay Output (Drive) Interface :- Relays

Here 16 optically isolated outputs are Interfaced to drive. 24 V plug in Signalling relays. Its main function is to drive.

Relay driverf) MP-Circuit (Microprocessor circuit):- interface

Here, both the processors can exchange MASTER MP Information with the communication Card through their individual buses. SLAVE MP

Functions :- (i) Controls, (ii) Supervises and (iii) Checks the function of all interfaces.

Function of Master MP :-

1. Controls communication with slave evaluator and other RBI over radio.2. Controls relay drive circuit.3. Processes information received from relay logic and slave evaluator.4. Compares the received information.

SLAVEEVALU-ATOR

SLAVEEVALU-ATORINTER-FACE

MICROPROCE-SSORCCTS.

24V plug inminiaturetype relay(sig. Relay)



Function of Slave MP :-

1. The information received/transmitted is verified by this unit.2. Controls relay drive circuit.3. Processes information received from relay logic and slave evaluator.4. Compares the received information.5. Formulates information packets.6. Transmits packet information 3 times.

Reception of Information :- At the receiving end 3 packets of information are decodedand verified and packed information is accepted if minimum two packets of informationmatches otherwise ignored.The information is feed to relay logic and axle counter through respective interfaces.

6.1.5 Equipments essential for Block Working in case of Intermediate BlockSignalling :-Equipments at I B H (Intermediate Block Hut) :-

1) Slave Evaluators - 4 Nos.2) Radio Block Interface - 1 No.3) VHF Equipment - 2 Nos.4) Relay logic system - 1 Set.5) Power supply system - 1 Set.6) Modem (2400 bps) - 1 No.7) 24V DC/230V AC 250V A Inverter for Modem - 1 No.

Equipment at Adjacent Station :- Equipment kept at adjacent stations are as in thefollowing :-

A. Equipments in Cabin :- 1. Axle Counters - 2 Nos. 2. Slave Evaluators - 1 No. 3. Relay logic system - 1 Set. 4. Power supply system - 1 Set.

B. Equipment in MW Equipment Room :- 1. RBI – 2 Nos. (1 where no IBH exists).2. VHF Equipment – 2 Nos. ( NIL where IBH does not exist).3. Power supply system – 1 set. 4. Interface relay logic system – 1 Set.5. Channel protocol system (Slave PC) – 1 No.6. Modems – 1 No. (One 2400 bps for VHF NIL where no IBH exists).7. 24 V DC/230 V AC 250 VA inverter for modem and channel protocol system.



6.1.6 BLOCK DIAGRAM OF BLOCK WORKING ON RADIO THROUGH R B I :-

Block Relay RBI Eqpt. MUX Radio Radio

Instrument Logic (18 GHz) (18 GHz)

Block Relay RBI Eqpt. MUX Instrument Logic

Block diagram of Radio Block Interface uniformly:- Power supply Monitor card

Communication Relay out put

Relay input Processor cards (3Nos) card(1No) card (1No) Card (1No) Operation 2 out of 3

The figure reveals the following particulars :-

1. CPU is composed of three processors. P1, P2 and P3.2. CPU get inputs from RI card (Relay input card).3. Processors send command to relay output cards and thus relays are driven accordingly.

6.1.7 Functions of different units incorporated in Radio Block Interface System :-

RI Card :- It performs following functions :-

a) Reads relay ground from either front or back contact of relay to decide the condition ofrelay and passes on the information to the processor card.

b) Reads 32 inputs from 16 relays to know about their status.c) A packet from other end is decoded only when the address contained in the packet

matches with ID code. Thus RI card reads ID code only when it is matched one.

PROCESSOR CARD :-a. Receives input from RI card.

P1 P2 P3


18 Ghz Communicand Radio Block In

b. Sends command to RO Card.c. Communications with communication card.d. Communications with other processor card.e. Forms packets with the obtained information.f. Decodes packets received from other end by communication card.

Here, processor card – 1 is considered as Master; processor card – 2 is considered as slavebut when PC-1 fails it becomes Master; processor card – 3 is always slave.Another thing important to note is that 2 out of 3 processor cards should work to run thesystem.

SLOT POSITIONS :-Card with A-ROM should be placed in slot -1.Card with B-ROM should be placed in slot -2.Card with C-ROM should be placed in slot -3.Communication card must always remain in slot -4.

COMMUNICATION CARD :-

a) Communicates with the three processor cards.b) Transmits information in form of packets.c) Receives information in form of packets.

RO CARD

Relay outpu ves information from processor cards and picks up a particular relayas per decis y processor card.

PSM CARD

a) Mon30V.

b) Moncard

c) Switdrainswitc

PARTICULCircuits/Co

1. Indepenprocesso

2. Inbuilt r3. Voltage 4. Safety s

FUNCTIO

1. Voltage

:-

t card receiions made b

ation Systemterface

(POWER SUPPLY MONITOR CARD) :-

itors input 24V (VR) for relays and cuts it off if it is below 22V or above

itors 5V supply to MP (Microprocessor) cards 1,2 and 3 and communicationsignals being designed as VMA, VMB, VMC and VMD.ches the regulated 24V path through switching relays so that high currentage through one path does not result in welding of the contacts of PSM supplyhing relays.

ARS OF PSM (POWER SUPPLY MONITOR) CARD :-mponents incorporated in P S M Card :-

dent voltage monitoring circuits 5V DC A, 5V DC B, 5V DC C, (for 3r cards) and one +5 V DC D (for communication card).

egulator supply for relay drive.monitor +24V DC for high and low voltage trip.hut down.

NS OF PSM CARD :-

monitoring of processor cards.



2. +24 V DC regulation and protection.3. Relay status monitoring.4. Opto isolation of relay actuation signals (for voltage below +19.5 V).

6.1.8 DESCRIPTION OF SOME ITEMS IN PARTICULAR :-

(I). VOLTAGE MONITORING CIRCUIT :- This is a stable multivibrator, initiated tooscillate by the reset signal from its processor. The output of the astable multivibrator isamplified, rectified and filtered to provide the voltage monitoring signal.

Besides, these three 8255 programmable peripheral interfaces provided to monitordifferent signals in the PSM Card.

Again, 8255 PPI also provides relay actuation signals optically isolated to actuate relays.

(II) WORKING OF RELAY LOGIC :- Let us consider a concrete example to knowabout working of relay logic :-

When station A wants to send a train to station B then the sequences of operations are as inthe following :-

1. Station A exchanges private No. with stati2. Station Master of Station B moves the ha f the block instrument from line closed to

line clear position.3. With the former operation, LCR Relay pic

relay picks up at microwave equipment ro4. M1 picked up state is read by RBI at Stati

LS DCM for which M5 relay picks up at MW o

5. With this, Top Needle of Block Instrumenup M7 relay in series. Here, needle voltagfrom DC-DC converter.

6. With acknowledgement of M5 & M7 pickethe bottom needle of station B to line clea

7. After this operation the last stop signal can8. In the next the train starts and hits the adv

SR relay drops at the cabin and SBPR rela9. In the next M4 relay of the station B i.e. r

cabin of station B and confirms entry of th10 After this SM at station B turns the han

TOLR Relay pick up & LCR RelayTOL .

11 Due to picking up of TOLR Relay, M2 pMW of Station B. This relay condition is read at stn B and co

13 At station A M5 drops and M7 picks up instation A goes to TOL (Train on Line).

on B.ndle o

k up at Relay room (at Station B), as a result M1om. on B and sent to the RBI at station A through

f station A.

t of Station A move to line clear position pickinge is 72 V DC (48-72 converter) supplied by MW

d up at station A M3 picks up at station B takingr position. be lowered at station A for starting the train.ance starter track circuit at Station A. As a resulty at microwave picks up at station A.eceiving station picks up and buzzer operates ate train in the section.dle of the Block Instrument to TOL, resulting drops at Relay Room and Bottom NDL goes to

icks up and dropping of LCR Relay drops M1 at

mmunicated to station A through microwave. series with M6 due to this the Top Needle of the



14 In the next M3 drops & M4 picks up at station B due to M5 drop & M6 pick up at stationA. Resulting bottom needle of station B goes to TOL position .Then SR Relay picks up atRelay Room and SBPR Relay drops at MW of Station A.

15 After complete arrival of train at Station B, Commutator of Block Instrument turn to LineClose position. As a result TOLR Relay and M2 Relay drops at Station B.

16 Finally, M4 at station B & M6 Relay at Station A drop and Bottom Needle of Station B &Top NDL of Station A come to line closed position.

Operation of different units right from RBI to cabin is as in the following BlockDiagram :-

RBI unit LSDCM E1IM 2W/4W TCM PLS TAG block

CABIN CT Box Surge arrestor

TOL & LC code TX A OW E cabin TX relays TX B OW E TN TN feed TX A OW W BN feed TX B OW W BN RX A OW W COM to RX B OW W CO LC RX A OW E block to TOL RX B OW E instrument Branching andTN- top needle combining net work.BN- bottom needle Equipment as COM- commutator above for east side.

CHAPTER –7

7. EMERGENCY COMMUNICATION

Introduction :- This is the communication which is taken into consideration during anytype of calamites like flood, Accident, Landslide and the like. In brief, this may be takenup during emergency when immediate remedy is a striking requirement. This is acommunication between site (affected area) and Headquarters during emergency. Now adays this communication is set up through a particular type of equipment in which bothportable and stable (Base) equipments are utilised.

CODEGenera--tionandRecept-ion unit

(relayrackW)

PADSerial conv-erter andFSK modul-Ator (Leem-Ah TX)FSK demodAnd parallelConverter(LeemahRX west)

0



7.1 SET UP OF COMMUNICATION LINE (DURING EMERGENCY) :-

Here, portable VHF sets (Mobile sets) are used from accident site to VHF base stationsnear by and that base station is then connected with existing microwave links to put thecommunication through to the head quarters stations.In Headquarters station control exchange is existing. When site is connected with controlexchange, the control exchange operates a push button to make the transmission of theaccident site MW station “ON” remotely and thus duplex working is established betweenthe accident site and control exchange.

7.1.1 BLOCK DIAGRAM OF EMERGENCY COMMUNICATION :-

MOBILE VHF BASE DIGITAL SEMI CONFE- DROP/INSERT RADIO RADIO D/I CARDSEMI CONFVHF SET STATION RADIO BASE RANCE CARD CARD (18GHZ)CARD (PATCH- RECEIVE CONTROLCOM / MODE MELTRON) RADIO BASE DRBC

ANTENNA Diagram of portable VHF sets with PTT switc

TX/RX PAIRS

Diagram of portable VHF set in stage by stageANTENNA +12 v

MIC

VOICEOPERATEDSWITCH

FMMODU-LATOR

FMMOD

VOICE OPERA-TED SWITCH

BUF-FERAMPLIFIER

OSC

AFAMP

CNLTROL CONTROL

CONSOLD EXCHANGE

h in brief:-

: -

dc

RF POWERAMPLIFIER

R E L A Y

RFPREAMP

RFPWRAMP



7.1.2 SOME SPECIAL POINTS TO NOTE REGARDING PORTABLE VHF SET

1. Mobile VHF is a duplex type set.2. PTT is pressed only for talking and not to be pressed during listening. Otherwise power

drainage will be maximum due to presence of RF power AMP stage.3. To solve the problem, voice operated switching arrangement may be attached so that

the switching will be done only when speech will be made on microphone. At that timeonly supply will be applied on RF power amplifier stage via operated contact of a relay.

ONE TO ONE CORRESPONDANCE IN DIFFERENT CHANNELS :-

SL MELTRON PATHCOM RADIO BASENO.

1. CH1 = CH1 = CH12. CH2 = CH3 = CH23. CH3 = CH5 = CH3

7.1.3 BLOCK DIAGRAM OF MOBILE VHF SET (DUPLEXER) :- VHF ANTENNA

MIC

LOUD AF AMP DISCRI- LIMITER 2nd IF AMP 2nd MIXER 1st IF AMP 1st MIXERRFA SPEAKER MINATOR

Characteristic Features of VHF set :- Mobile V H F :-a) Trans power – 10 Watts ±1 Watt.b) Frequency – 41.1 to 146 MHz, (c) Working Mode = Duplex.d) Antenna Used = Whip Antenna (e) Receiver Threshold= 110 db without squelch.f) Power supply = 12V/10A NICAD battery.g) Current = 1.5 Amp.

INTERMEDIATEP0WERAMP.

2nd

MULT-

PLIER

1st

MULT-IPLIER

OSCMOD

AMPL-IFIRETRANS

DUPL-EXER

POWERAMP.

1s t LOCAL OSC 2nd LOCAL OSC SQUELCH AMPLIFIER



CHAPTER –8 8. POWER SUPPLY ARRANGEMENTS IN MW/DIGITAL COMMUNICATION :

In each Microwave station power supply arrangements is a must for running of differentpower equipments like light, fan, exhaust fan, air cooler, battery charger, voltage stabilizerand the like.

Provision of diesel generator is also a must mainly for the microwave stations whereemergency power supply is not available (either from traction or from centralised dieselgenerator of the place).Moreover, for running of different units/equipments concerning communication a foolproof and systematic distribution of power is also most essential.Thus a systematic distribution of power supply for both AC and DC supply is required ineach and every microwave station.A pictorial description of power supply arrangements in a microwave station is given stageby stage in the following :-

8.1 1st Stages :- Distribution of AC supply at Microwave premises

TO LIGHTS,FANS,EXHAUST FANS,AC MACHINES Etc.

PREMISES DIESEL SET

LOCALPOWERSUPPLY ( 220V,50 HZ )

TRACTIONPOWER SUPPLY( 220V, 50 HZ )

1st CHANGE OVER PANEL

2nd CHANGE OVER PANEL

FUSE BOX

SURGEPROTECTOR

VOLTAGESTABILIZER

SURGEPROTECTOR

AVIATIONLAMPS

Extra provisionFor AC machine

Float cum BoostCHARGER



8.2 2nd Stage :- Distribution of DC Supply at Micro Wave premises ( in block )

8.3 3rd Stage :- ( I.) Power Supply arrangement for Microwave Equipment ( DM 18): --Ve 48V +7.5V

0-21V+7.5V

+Ve 48V -21V

SUPPLY FROM BATTERY

BATTERY ( 48V DC ) SET-1

CONTROL PANEL

BATTERY ( 48V DC ) SET- 2

FCBC

FUSE BOX ( BASE WITH GRIP )

POWER SUPPLY UNIT ( PSU )FOR MULTIPLEXING EQUPT.

MICROWAVE RADIOPOWER SUPPLY UNIT ( PSU )

O

O

O

PSU A

PSU B

RADIO TRANS-RECEIVER A

RADIO TRANS-RECEIVER B



SPECIAL NOTE

Three core power cable 1) +7.5V is MOD and other digital right from equipment circuits. room to tower top. 2) –21V is m

3) +Ve is G 4) PSU Pow DC.-DC.

( II ) Power Supply arrangement for D

- Ve 48 v

+ Ve 48 v

DC Supply from Battery.

( III ) Stage :- Power Supply arrang (At Radio (Microwave R

- Ve 48 v

+ Ve 48v

DC Supply from Battery

MODEM A

MODEM B

meant for OSC-

eant for Analogue circuit. rounded here .er Supply Unit which is nothing but

Converter.

C-DC. Converter (At Equipment room) :-

Special notes Modem Unit Contains :- In built DC-DC. Converter. Out put of DC –DC. Converter are, i) + 5 Volts for digital circuits

ii) + 18 Volts for Analogue circuit.

ement for DMC Radio ( continued ) :-adio Equipment ) Placed at Tower Top.

A TX/RX A
PS
PS B TX/RX B



SPECIAL NOTE

1) Three core cable from Equipment Room to Tower Top.

2) PSU -A and PSU –B are DC-DC. Converters in built .

3) Voltages are, (a) + 5v DC supplied for OSC- MOD and digital circuit.

(b) + 18 v DC supplied for Analogue circuit.

CHAPTER- 9

9. Test and Measuring Set Up

In case of measurement of digital MW signals the following measuring instruments arerequired:-1. DTA - Digital Transmission Analyser.2. DMSA - Digital MW System Analyser.3. DMPM - Digital MW Power Meter.

9.1 Brief Description of Measuring Instruments :- 1. D T A – This instrument has the following functions :-a) Error detection function.b) Measurement function.c) Filter modulation and measurement function.d) Multiplexer test function.

Description of Functions :-

a) Bit error, Parity error, Frame error, Polar violation error.b) Measurement functions are :-

(i) Error Rate, (ii) Error Count, (iii) Error Seconds, (iv) % of error free seconds, (v) Threshold error seconds, (vi) Alarm seconds, (vii) Filter measurement.

Besides these, the DTA can conduct the following functions :-a) Commissioning Test, (b) Production Test and (iii) Maintenance and trouble shooting indigital radios and MUXs.Contents of D T A :-1. A transmitter part.2. A RX Part.3. A built in printer and recording arrangement.

N.B:- During occurrence of error/alarm the printer gives print out and records themeasured Values automatically.



9.2. DIG/MW SYSTEM ANALYSER ;- This instrument measures the following :-

a. Delay/amplitude characteristics.b. Two route propagation delay time differences.c. Harmonic distortion.d. Third inter modulation distortion.e. Spectrum analysis.f. Return loss.g. S.D propagation delay time difference.h. IF transmission band characteristics.i. Amplitude linearity of R/Equipment.

9.3 DMSA is applicable only over IF range but not over RF ranges measurement done byDMSA are :1. Power 2. Frequency IF Range.3. AGC and squelch characteristics.4. Return loss.5. Amplitude frequency response.6. Delay characteristics.7. Frequency deviation (Analogue service channel)8. Inter modulation distortion.9. Transmission delay difference.

9.4 DIG/MW POWER METER :-

For MW PWR meter a thermistor mount is necessary to show change of resistance due totemperature rise. But as thermistor itself is also affected by temperature. So thermocouplesassociated power meters are utilised now a days. This is done as temperature rise isdetected electrically in thermo couple.Different sensors are utilised here to sense different frequency and level ranges. The rangesare 100 KHz to 32 GHz and –30 dBm to +20 dBm respectively.Hybrid ICs are used for stable readings. Built in MP provides compensation for the nonlinearity of the sensors at high power.Now coming the case of measurements. How we should know how measurements aredone.



9.5 Different Test Set ups for Different Measurements :-

1. RF Power Measurement :- 1.RF OUT

(of Transmitter )

2. TX Frequency Measurement :- 2. RF OUT ( of Transmitter )

3. RLO Frequency Measurement :- 3. RF IN

FREQUENCY

MONITOR

4. RX IF O/P Level Measurement :-

RF IN

IF RX

5. BIT ERROR RATE MEASUREMENT :-

RF OUT

RF & N

AGC-V

DATA IN

DATA OUT

RF ATTENU-ATOR (in DB)

MW POWERMETER (in DBM)

RF ATTENU-ATOR(in DB)

FREQUENCYCOUNTER

TX RX

FREQU-ENCYCOU-NTER

TX RXRF ATTE-NUATOR

RF SWEEP SIGNALGENERATOR

RF. LEVEL METER SET RX FREQUENCY

RF ATTE-NUATOR

FREQUENCY SHIFTER

CHECKMETER

BIT ERROR RA-TE TEST SET(SENDING UNIT)

BER TEST SET(RECEIVINGUNIT )

RX TX



Let us now consider the cases of Bit error and BE rate. :-

BIT ERROR :- It is bit inversion in the binary sequence.BIT ERROR :- It is the ratio between No. of errors and total no. of bits received.

No. of errors.So, BER = ----------------- Total no. of bits received. N.B :- One error in 1000 bits is denoted as 1/1000 or 1 x 10 -3 or 10 -3 or IE 3.

9.6 Error performance of Digital TX System:-

1. Unavailable seconds (UAS) :- No. of seconds during which the error rate is above 10 for10 consecutive seconds.

2. Error seconds (ES) :- No. of seconds affected by a minimum of one error during gate time.3. Severely error seconds (SES) :- No. of seconds for which the error performance is IE 3.4. Degraded Minutes (DM) :- No. of minutes which have error performance of IE 6.5. Error free seconds (EFS) :- No. of seconds that are free from error.

Thus :- Total time = Available time + Unavailable time.i) Acceptable, (ii) Degraded, (iii) Unacceptable quantity.



CHAPTER –10

10. MAINTENANCE REQUIREMENT AND PRACTICES

Necessary particulars regarding control communication :-Regarding Block Phone :- Block instrument sends signal in M lead which appears at the Elead of the next station and that RX signal operate Block Bell Relay.

Problems Arising are Remedy 1. GND in E- lead Card should be changed.2. No GND extn. to E lead Take out the card & reinsert3. No V in M lead of sending station. Card should be changed.

10.1 Signalling Problems :- Sounder may not operate due to absence of S/Voltagesupplied by DPLS RX Card.As per DPLS RX 4 phone lines are connected then if S/V for one line is absent then S/V ofanother one among the other 3 lines are connected and sounder is operated.

Inter connection between D/I card and different modules.

TELEPHONE

1) If OEN relay problem is there, then we should check fitting between base and contactpoints- if loose, to be fixed firmly.

What is the function of OEN relay ? Is it has another name ?

2) If switching panel (CNL Card) is creating problem then remedy is :-

AUTO If auto fails manualchange over is done by rotary mechanism.

MANUAL

D/ICARD

DATA BUSDIGITAL

DPLSMODULE

TCMMODULE

SWITCHPANNEL



10.2 SPEECH PROBLEMS :- D/I RX – DPLS RX – CNL Phone DPLSR provides –48 V DC supply to CNL Phone TX.1 DPLS RX – 4 CNL Phone i.e. 48 V DC supply is present for each of 4 CNL phones.

So, if supply of one is out to be connected to the other. Card will never be taken out untileach phone is out of –48 V DC.

Sometimes barrator lamp is disconnected.By DPLS RX – CNL RX signal code is RX.

Fault localisation in 18 GHz communication :-EAST BAS

WEST BAS

No indication is there in the faulty station. But the following cases will happen to wardsthe next station forward and back.

1) In EAST CARD – All ALM indication and (2) Other east ward stations up to nearestbreak site will get remote ALM (Yellow).

In such a case the following remedial measures should be taken :-1) At first testing should be done between the suspected station and next east ward station to

detect the faulty station i.e. A&B in the figure.

A will change its TX and effect on B’s RX will be observed.B will change its RX (Set) and effect on the suspected (RX itself) station will be observed.

In the next case D/I east card of the faulty station will be taken out and reinserted.If fault is existing, D/I EAST card should be changed.

4) In the mean time (before replacement of the card) by passing of D/I E card of the faultystation will be done manually.

Same will be the case with WEST BUS.Now, how BY PASS IS DONE? -BY PASS _______________________________ Manual SWC (Switch) Digital SWC (Switch-------------------------------------------------------------------------------------------------------------DATA from nearest E bass will come Here, case is same as in Manual case.up to D/I card then looped back to Radio The only speciality is DATA will be shaped

by Manual switching. and looped back.-------------------------------------------------------------------------------------------------------------

STN. A STN.B STN.C STN.D



10.3 Kinds of Failure in 18 GHz (CC) :-

1. Link failure due to Radio :- (a) E-Bus, (b) W-Bus, (c) Both E&W Bus (Due to Rain).2. Dislocation / Rotation of ANT.3. Water infiltration into W/G.4. Link failure (Due to MUX) (a) E-B, (b) W-B, (c) E&W-B, (d) Switching panel

problem.5. Speech problem in CHL MODEM (TCM) card.6. Signalling problem in CHL MODEM card.7. Speech and ring problem in Block Working.8. Lima problem affecting Block working :- (a) TX, (b) RX, (c) Common Unit, (d) CNL

CARD, (e) Y PAD, (f) IP 150 Relay, (g) DC-DC Converter (for 48 V DC- 72 V DC).

1. When this happens automatic change over of set takes places in radio.2. This should be seen and rectified.3. W/G pressure should be kept 2-5 PSI.4. When E-BUS fails, D/I E card is responsible, remote ALM will come in the E direction

up to break site.

10.4 DESCRIPTION OF SOME UNITS IN M U X :-

TCM (Telephony CHL Module) – 2W, 4W, CONF (Omnibus), Semi CONF, CNL Card.

Specialities :- CONF CARD – D/A CONVERTER

MULTIPLEXER – A/D CONVERTER.

I/P Analogue signal O/P digital signal 2 MBIT.

Speech is via- TCM card (2W, 4W, CONF, Semi CONF, etc.)

DPLS DIS PATCH – In CNLR Station.

DPLS RX – In intermediate station.

DTC (Data transfer card) at break site.

D/I card contain :- E&M Card and END TERM CARD.

CONFERAN-CE CARD DPLS D/I

DROP INSERT RADIO



10.5 PROBLEMS AND REMEDY IN 18 GHz MAINTENANCE :-

PROBLEMS REMEDY

1. Telco connectors and kulka blocks loosen 1. Tightened by clamps, screws periodically due to passage of train (vibration).And types of connectors to be changed.

2. Power cable to the radio may be damaged. 2. Strongly insulated power cable should be installed.

3. Malfunctioning of protection switch 3. Manually this should be operated to I/C & O/G data passes through protection select proper TX/RX signal. Switch and selects wrong signals.4. TX ALM 4. TX to be changed and faulty set to

be sent to Lab a) Shifting of trans. Freq.. b) AFC unlocking. c) Dropping of O/P power. RX ALM a) Detuning of O/P freq. Do on RX.

5. Malfunctioning of D/I card 5. We should observe alms and will detect Function :- Data flowing through a particular the faulty stn. And replacement of D/I bus drops down at intermediate Station and card should be done. mixes up with local data and retransmitted . If this malfunctions then remedy will be:

6. Break of data flow in a jack field :- 6. Routine maintenance is required. I/C and O/G data passes through jack field to radio. Now for free setting some contacts are kept in open air and so dust accumulate and DATA interrupts.

7. Mother board female connectors getting 7. Should be clamped tightly and routine loose due to vibration caused by passage maintenance is required. of train.8. Malfunctioning of CHL modem cards 8. Thorough study of ALM in D/I card in (introduces wrong data in wrong timeslot forward & back stn. should be done and causes interruption of whole link). and faulty stn. to be located and card replaced.

9. Intermittent noise in all CHLs.:- As it is a 9. In such a case ET/BS to be localised. digital system so over all CNL of circuit Then end cards should be checked up is done from a particular point i,e. ET-End and replaced. Terminals BS/Break site.

10. Interruption in communication for a particular 10. Fault localisation and replacement is

control. required.



Problems Remedy

a) From CNL stn. To onwards culprits are :-1) CNLR’s console.

2) DPLS despatch card. 3) TCM.Card.

b) From a break site onwards problems are in :- Fault localisation and re- 1) 2 CHL MODEM cards for either directions. Placement is required. 2) DPLS RX interfacing two directions.

c) From a particular site problems are in :- Fault localisation and

1) CHL MODEM CARD. replacement is required.2) DPL-SRX cards. 3) Telephones connected. 11. Problems in controller’s console.

a) Dialler trouble. Replacement of controller’sb) Trouble in conversation unit. Console is required.

(due to wrong handling by controller).



CHAPER-11

11. DO’S AND DON’Ts IN MW WORKING :- Digital Microwave Communication is the latest development in Microwave workingin which noise less communication has become practicable for speech, signal and DATA.

For smooth running of Microwave Digital Communication each and every units andcomponents inside MW equipment room should be kept fool proof. For such anarrangement proper maintenance of different components along with the atmosphere insideequipment room is a must.

Now, for proper maintenance of MW communication what should be done and whatshould not be done to be considered; stage wise Do’s and Don’t’ are as listed below :-

11.1 Dos’ :-

1. Terminals of battery should be cleaned regularly to avoid sulphation at battery terminals.2. In case of float mode battery both the battery sets and equipment load draws current

simultaneously. In such a position a close look should be maintained on ampearage of thecharger. More clearly current should be adjusted in such a way so that it becomes sufficient torun the equipment as well as charges the battery with optimum ampearage.

3. Measurement of specific gravity, per cell voltage and terminal voltage should be done at leastonce in each shift.

4. Working of DG set should be observed on load for at least 10 minutes per day to keep the DGset in readiness so that the DG set can work on emergency immediately.

5. Each and every electrical equipments/units, their connections should be cleaned properly withbrush, vacuum cleaner and the like ailments.

6. Earthing of tower, cable/coaxial cable, antenna, radio equipment, Modem and MUXequipment etc. should be done properly.

7. Radio patch circuit (if provided) should be checked periodically.8. Dehydrator pressure should be checked properly. Aviation lamps should be made on during

evening and extinguishing at dawn.9. Performance of radio patch circuits should be periodically checked so that they can work

smoothly during link failure at different Microwave Stations.10. 10.Circuits concerning emergency communication should be checked properly and routine

tests should be done in each shift so that in case of emergency the circuit can work properlyand smoothly.

11. 11.In way side stations each and every plugging in type units should be checked periodicallyand tightened if required as jerks may keep those units loosely fitted.

12. 12.AC machines should be maintained properly and in case of failure of AC Machinesimmediate rectification should be done and in the mean time emergency fans should be madeon to keep the equipments cool.



11.2 DON’Ts :-

1. Entry with shoes is strictly prohibited inside equipment room to avoid entry of dust inequipment room. The dust may cause harm to electronic components and AC Machines.

2. Smoking should be strictly avoided inside the equipment room as smoke can do harm tosophisticated electronic units and components remaining inside the equipment room.Moreover, fire may result inside equipment room due to smoking.

3. Doors and Windows of equipment room should not be kept open other wise it can do harmto AC Machines.

4. Temperature of equipment room should not be increased above optimum temperature(Temperature should be kept well below the normal temperature outside in the room).

5. Electronic units and other detachable parts should not be tampered (Opening andreinserting unnecessarily) other wise frequency of failure will be increase abruptly.

6. As MW equipments rooms in way side stations are located beside the running lines so jerksmay cause different cards, fuses, GD tubes etc. components loose. So, checking oftightness of components should not be avoided for long time other wise communicationmay hamper every now and then.

7. Periodical check up of different attachments (Like coaxial cable, flexible wave guide,antenna etc.) should not be delayed for long time. Other wise in time of failure prolongedsearch of each and every component may cause long duration of RM thus efficiency willbe less.

8. Battery terminals should not be kept un maintained for long time other wise sulphasionmay damaged the individual cells and reliability of the system may be hampered.

9. Battery should not be maintained carelessly other wise in one fine morning a havoc failuremay occur due to loose connection of different components of battery.

10. As one set of charger is there in 18 GHz MW (Control Communication) system and as thischarger works on float mode in general so current adjustment should not be maintainedcarelessly other wise in one fine morning communication may be stopped due to reachingof battery set below standard capacity.

11.Irregularity in changing over the battery sets should be avoided. Otherwise efficiency ofbattery sets will be go down.

18 GHZ

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