configuration of narrow band radio systems

7/31/2019 Configuration of Narrow Band Radio Systems

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Note: The source of the technical material in this volume is the Professional

Engineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for Saudi

Aramco and is intended for the exclusive use of Saudi Aramcos

employees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,

or disclosed to third parties, or otherwise used in whole, or in part,

without the written permission of the Vice President, Engineering

Services, Saudi Aramco.

Chapter : Communications For additional information on this subject, contact

File Reference: CTR20101 J. S. Phillips on 873-0228

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Configuration OfSaudi Aramco Narrowband Radio Systems


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Engineering Encyclopedia

Saudi Aramco DeskTop Standards 2

CONTENTS PAGES

Saudi Aramco Narrowband Radio Systems: Infrastructure And Services........ 1

Major Saudi Aramco System Configurations .................................................. 18

Function And Characteristics Of Saudi Aramco Narrowband RadioEquipment ....................................................................................................... 70

Glossary ........................................................................................................ 116


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SAUDI ARAMCO NARROWBAND RADIO SYSTEMS: INFRASTRUCTURE AND

SERVICES

The following topics that pertain to the infrastructure and the services of Saudi Aramco

narrowband systems are covered in this section:

Infrastructure

Land/Mobile Radio

Marine Radio

Aviation Radio

INMARSAT

Infrastructure

Figure 1 shows an overview of the major communication sites within the Saudi Aramco

communications network. Basically, communications sites are located where Saudi Aramco

activities occur. The major Saudi Aramco centers (Dhahran, Abqaiq, Ras Tanura, Safaniyah,

and Udhailiyah) have the greatest concentration of communication facilities.

Base station transceivers for the various narrowband communication systems are located at

Saudi Aramco sites along the eastern coast from Safaniyah to Haradh. Further inland, base

station transceivers are located at Khurais, Abu Jihan, and Mazalij. Base station transceivers

also are located along the East-West pipeline to Yanbu.


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Saudi Aramco Communications Sites

Figure 1


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The narrowband communications systems that are used by Saudi Aramco can be categorized

as push-to-talk systems, Improved Mobile Telephone Service (IMTS) systems, paging

systems, extended subscriber systems, and the INMARSAT system.

Push-to-talk systems are the conventional two-way radio systems, that is, push-to-talk systems

are those systems that include components such as hand-held radios, vehicle-mounted radios,

and base stations. Push-to-talk systems are configured to provide simplex or half-duplex

operation.

Simplex operation uses one frequency for communications between base stations and mobile

radios, and for communications between mobile radios. When a user depresses the push-to-

talk switch, that user may transmit from his radio. All other radios that are tuned to that

frequency (and within ranges) may hear the information that is transmitted from the

transmitting radio. The radios may not transmit while another radio transmission is in

progress. Half-duplex operation uses two frequencies: one frequency for base station tomobile transmissions and one frequency for mobile to base station transmissions. With the

half-duplex arrangement, the base stations can communicate with all mobile stations;

however, the mobile stations cannot communicate directly with each other. Information to be

conveyed between mobile stations must be transmitted through a base station. As with

simplex operation, simultaneous transmissions from mobile stations and base stations do not

occur with half-duplex operation.

The IMTS and extended subscriber systems are full-duplex systems. IMTS provides mobile

telephone service to designated individuals. The extended subscriber system connects

telephones that are located at remote fixed locations into the Saudi Aramco telephone

network. Full-duplex operation allows simultaneous two-way communications between base

stations and either mobile or remote stations. Full-duplex operation also requires separate

frequencies for the base station transmit (mobile receive) and base station receive (mobile

transmit).

The paging system is a one-way communication system. Base stations transmit signals that

activate "beepers" that are carried by designated individuals. The "beepers" are small

receivers that provide some sort of tone, vibration, or message upon reception of a designated

signal. The reception of the signal informs the individual that he has a message.

The transmitters for the IMTS systems, the paging systems, and several of the push-to-talksystems are networked together to allow narrowband communication system users in one area

of the country to communicate with users in other areas of the country. These base station

transceivers are connected through use of wideband communications systems.


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Wideband communications systems include microwave systems, fiber optic systems, and

metallic cable systems. The majority of these base station transceivers are located at the

major Saudi Aramco communication centers.

Because transmissions pass through the INMARSAT satellite, the operation of the

INMARSAT system is different from the operation of conventional communications systems.

The INMARSAT system allows users, who have no other communication facilities, to

communicate from remote locations through the satellite with other stations at virtually any

other location in the world.

Land/Mobile Radio

The majority of Saudi Aramco narrowband communication systems are land/mobile radio

systems. The systems that are included in the land/mobile radio systems are the IMTS,extended subscriber, paging, and push-to-talk systems. The following topics that pertain to

land/mobile radio systems are covered in this section:

Purposes

Frequencies

Performance Characteristics

Typical Saudi Aramco Applications

Purposes

The purposes of land/mobile radio systems vary with the type of land/mobile system. The

purpose of IMTS is to provide mobile telephone service to certain designated individuals

throughout the Eastern Province. The purpose of the extended subscriber service is to provide

telephone service to fixed locations in remote areas. The purpose of the paging system is to

inform those individuals who are issued beepers that a message has been left for them. The

purpose of the push-to-talk systems varies from system to system.

Many of the push-to-talk systems are configured with stand-alone base stations. Stand-alone

base stations are base stations that are not connected to other base stations via the wideband

system. This configuration is used for organizations that require only local communication.

The systems that have stand-alone base stations may be designed for simplex or half-duplexoperation. For example, the transportation, water injection, tactical fire, and old emergency

networks are configured for one frequency: simplex operation. The gas local, emergency,

and ISD division networks are configured for half-duplex operation.


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Many of the push-to-talk systems are configured with networked base stations. These

land/mobile systems provide service over a wide area, and they allow system users in one part

of the country to communicate with system users in other parts of the country. This

configuration is used for organizations that require communication between widely separatedparties. Both half-duplex operation and simplex operation are used with networked base

stations. The following are some of the organizations that use a half-duplex networked

configuration for their land/mobile communications networks:

Oil Central

Oil South

Drilling

Gas Central

The following are some of the organizations that use a simplex networked configuration for

their land/mobile communications networks:

Utilities

Construction

Drilling

Industrial Security

Frequencies

Several frequency allocations in both the VHF and UHF frequency bands are used for

land/mobile communications systems. The Consultif Committee for International Radio(CCIR) has allocated frequencies for use by land/mobile communication systems. The

Ministry of Post, Telephone, and Telegraph (MOPTT) further allocates frequencies for use

within Saudi Aramco. The 50 MHz to 70 MHz and 150 MHz to 174 MHz frequency bands

are the VHF bands that are used by Saudi Aramco land/mobile systems. The 406.1 MHz to

420 MHz frequency bands and the 450 MHz to 470 MHz frequency bands are the UHF

frequency bands that are used by Saudi Aramco land/mobile systems. Most of the UHF

land/mobile systems use frequencies between 460 MHz and 470 MHz; however, frequencies

between 407 MHz and 414 MHz are used for security and emergency types of land/mobile

systems.


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The frequency response of all land/mobile communications systems, with the exception of the

paging system, is a nominal voice channel. The nominal voice channel ranges from .3 kHz to

3.4 kHz. In narrowband radio systems, the voice channel typically is limited to .3 kHz to 3

kHz. This frequency band is sufficiently large to provide an intelligible speech output;

however, the frequency band is kept small to minimize the bandwidth of the transmitted

carrier. The reduced carrier frequency bandwidth allows closer channel spacing. A small

transmitter frequency deviation (_ 5 kHz) is required to maintain the close spacing between

land/mobile radio channels.

The power output of transmitters depends on the coverage requirements of the system. A

typical base station transmitter is rated for a 100-watt output power. Typical fixed

transceivers, such as a desk-top transceiver and vehicular-mounted transceivers, are rated fora 40-watt output power. The hand-held transceivers usually are rated for a 5-watt output

power.

Beyond the transmitter output power, the range of the transmitters depends on the transmit

antenna gain, the antenna height, and the propagation conditions in the area. As an example,

the coverage area of the Power Distribution Department/Gas Central Network base station in

Shedgum extends from Abqaiq to Uthmaniyah. The coverage area is the area in which the

signal from a transmitter is of sufficient amplitude to be detected by a receiver. The size of

the coverage area also depends on the following receiver characteristics:

Receiver antenna gain Antenna height

Receiver sensitivity

Obviously, the coverage range of fixed transceivers, vehicular-mounted transceivers, and

hand-held transceivers is smaller than the typical coverage range of a base station transmitter.

Many of the base stations that are used by Saudi Aramco use omni-directional antennas to

provide a relatively circular coverage area. Areas with difficult propagation conditions and

areas along a coast or border may require an offset or directional antenna. These types of

antennas concentrate the radiated power in one direction. Because extended subscriber

installations are point-to-point communications systems, extended subscriber installations alsouse directional antennas.


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Figure 2 shows an overview of the Power Distribution Department (PDD)/Gas Central Local

Network. This network employs many of the features that are found in other land/mobile

communications systems. The Gas Central portion of this network is a system that employs

networked base stations. These base stations extend from Zuluf in the north to Haradh in the

south. The PDD local portion of the network only provides for mobile-to-mobile

communication. All of the base stations that are shown in Figure 2, with the exceptions of the

Dhahran Tower and the Uthmaniyah base stations, have both Gas Central and Local Base

stations. The Dhahran Tower and Uthmaniyah local base stations are used in the Local

Network.

The Gas Central Network is configured for half-duplex operation. Because the coverage

areas of adjacent base stations may overlap, two separate pairs of frequencies are used by thenetwork. Interference could result from base stations that transmit at the same frequency and

that have overlapping coverage areas; therefore, the frequency pairs, red and green, are

alternately used by the narrowband base stations. For example, the Dhahran and the

Shedgum base stations use the green frequencies, but the Abqaiq base station, which has a

coverage area that overlaps the coverage area of the Dhahran and Shedgum base stations, uses

the red frequencies.

The following frequencies are used by the Gas Central Network:

Red (transmit) - 464.800 MHz

Red (receive) - 469.800 MHz Green (transmit) - 464.850 MHz

Green (receive) - 469.850 MHz

The transmit frequencies are the frequencies of the base station transmitters; the receive

frequencies are the frequencies of the mobile station transmitters.

The PDD Gas Local Network is configured for half-duplex operation (red and green).

Additionally, a gas local base station is located at the Dhahran tower and Uthmaniyah tower.

The frequencies are alternated between coverage areas (red and green). Because the PDD

local network only provides for local communication, two separate frequencies are used; the

network is not used as a wide area network. With two sets of frequencies, the transmissionsfrom one coverage area will not interfere with the transmissions from another coverage area.


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PDD/Gas Central/PDD Local Network

Figure 2


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Marine Radio

The following topics that pertain to marine radio systems are covered in this section:

Purposes

Frequencies



Purposes

The purpose of marine radio systems is to provide for communications among shore facilities

and nearby ships. These communications may be from ship to ship, from ship to shore, or

from shore to shore, and they are used for docking, loading, or unloading activities and for

general administrative functions.

Frequencies

Marine radio operates in both the UHF and VHF frequency bands. The majority of the

marine systems operate in the VHF frequency band. Saudi Aramco systems operate on the

following marine frequencies:

Channel 10 - 156.50 MHz












The Ras Tanura Mooring System is a four-channel system that operates between 165 and 167

MHz. The Juaymah Mooring System is the only half-duplex UHF system that is used for

Saudi Aramco marine activities, and most of the frequencies in this system are around 408

MHz and 419 MHz; however, at Berth 51 and Berth 52, the frequencies are around 469 MHz

and 466 Mhz.


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The marine communications systems essentially are push-to-talk systems, and the

configuration of the Saudi Aramco marine communications systems is very similar to the

configuration of the land/mobile push-to-talk systems. Because these systems share the same

configuration, the performance characteristics of the marine systems are very similar to the

performance characteristics of the land/mobile push-to-talk systems.


Figure 3 is a diagram of the Marine Channel 16 System. This system is typical of a number

of the Saudi Aramco marine systems. The system is configured for simplex operation, and it

employs a number of stand-alone base stations. Base stations are located at the Juaymah

Platform, the Juaymah Tressel, the Ras Tanura (RT) Terminal, and Dhahran. A receive- only

station is located at Ras Tanajib Comm, and a transmit-only station is located at Tanajib

Marine. The frequency that corresponds to channel 16 is 156.80 MHz.


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Marine Channel 16

Figure 3


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Aviation Radio

The following topics that pertain to aviation radio systems are covered in this section:

Purposes

Frequencies



Purposes

The purpose of the aviation radio systems is to provide for communications between the

crews of both fixed-wing/helicopter aircraft and ground control personnel.

Frequencies

VHF frequencies are used for the aviation air-to-ground communication systems. The

frequencies that are used for communications between helicopters and ground stations are

138.225 MHz and 138.250 MHz. The frequencies that are used for communications between

fixed-wing aircraft and ground stations are 138.200 MHz and 138.250 MHz.


The aviation communications systems essentially are push-to-talk systems, and the

configuration of the Saudi Aramco aviation communications systems is very similar to the

configuration of the land/mobile push-to-talk systems. Because these systems share the same

configuration, the performance characteristics of the aviation systems are very similar to the

performance characteristics of the land/mobile push-to-talk systems.


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Figure 4 shows the configuration of the various Saudi Aramco aviation air-to-ground

communications systems. The following are the locations of the stand-alone aviation base

stations that are used for communications with fixed-wing aircraft:

Udhailiyah

Khurais

Dhahran

Safaniyah

Ras Tanura (RT)

Abu Ali

Shedgum

Haradh-G2

Stand-alone base stations that are used for communications with helicopters are located at

airstrips at Ras Tanura (RT), Abu Ali, Ras Tanajib Support, and Marjan G1. These stand-

alone base stations provide for local communications between ground support personnel and

aircraft that are within range of a base station.

A separate aviation system that employs networked base stations is in place along the

East/West Pipeline. The locations of these networked base stations are as follows:

Km 82 to Km 402

Yanbu NGL to PS 6 PS 3 to PS 10

Because these base stations are networked, ground control personnel can communicate with

aircraft over a larger area than would be possible if stand-alone base stations were used.


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Aviation Air-to-Ground

Figure 4


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INMARSAT

The following topics that relate to the INMARSAT system are covered in this section:

Purposes

Frequencies



Purposes

The purpose of the INMARSAT system is to provide communications for individuals who

cannot be served by any other communications system. The INMARSAT system is a satellite

system that provides narrowband communications services to the subscribers of the service.

Originally, the INMARSAT system was conceived for maritime use; the INMARSAT system

is replacing the conventional HF communications systems that have been used for maritime

service. In Saudi Aramco, INMARSAT supplements existing HF systems. The INMARSAT

system can provide communications for operations, such as deep desert exploration, that

originally were provided through use of HF systems.

Frequencies

With respect to satellite systems, two frequencies are specified: the uplink frequency and the

downlink frequency. The uplink frequency is for transmissions from the ground station to the

satellite; the downlink frequency is for transmissions from the satellite to the ground stations.

With the INMARSAT system, two sets of uplink frequencies and downlink frequencies are

specified: one frequency for the link between the coast earth stations (CESs) and the satellite

and one frequency for the link between the satellite and the transportable stations. The CESs

transmit in the 6 GHz band, and they receive in the 4 GHz band. The transmissions between

the portable stations and the satellite occur in the L band. The L band extends between 1 GHz

and 2 GHz.


Three standards have been developed for the INMARSAT system: A, B, and C. Basically,

the standards specify items, such as the required frequencies, bit rates, and error performance,

that must be met by the equipment that is designed to conform with a standard.


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Although the equipment that is manufactured by different companies may have slightly

different transmitter power levels or antenna sizes, all of the equipment that is manufactured

to conform with one of the standards will have virtually the same performance characteristics.

The A standard is designed for use on larger ships, and it requires a large amount of

equipment. The A standard is impractical for portable stations.

To overcome these problems, the B and C standards have been developed. The B standard

provides telephone services that employ digital speech processing and coding. Basically, the

speech is converted to a digital signal. This digital signal is then encoded. The encoding

allows the system to employ error correction. The use of error correction improves the

quality of the output audio signals. As with standard telephone systems, a typical 300 Hz to

3400 Hz voice channel is transmitted over the B standard systems.

Data may also be transmitted through B standard systems. The user may select between twodata rates: 9600 bits per seconds and 16000 bits per second. These data rates are comparable

to the data rates that can be achieved over conventional analog telephone systems.

The C Standard provides for low bit rate data transmissions. The power and size

requirements for C standard applications are very low; however, the C standard only provides

a 600 bits per second data transmission rate.


Figure 5 shows a typical Saudi Aramco INMARSAT system application. The Saudi Aramcotransportable satellite terminals are used in locations such as a deep desert rig. The terminal

communicates with the Indian Ocean INMARSAT satellite, which in turn communicates with

the Jeddah ground station. The Jeddah ground station is connected to the Saudi Arabian

National Telephone Network. The Saudi Aramco Telephone Network also is connected to the

Saudi Arabian National Telephone Network. A call between the transportable satellite

terminal and a telephone that is connected to the Saudi Aramco Telephone Network passes

through the Saudi Arabian National Telephone Network, the Jeddah ground station, and the

Indian Ocean INMARSAT satellite.


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INMARSAT

Figure 5


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MAJOR SAUDI ARAMCO SYSTEM CONFIGURATIONS

In the previous section, the purposes and applications of the various narrowband

communications systems that are used by Saudi Aramco were reviewed. The following topics

that pertain to the configurations of the major Saudi Aramco systems are covered in this

section:

Improved Mobile Telephone Service (IMTS) System

Paging System

Push-to-Talk Systems

Extended Subscribers

INMARSAT Satellite System

Improved Mobile Telephone Service (IMTS) System

The purpose or function of the IMTS system is to provide mobile telephone service for

designated individuals. The following topics that pertain to the configuration of the IMTS

system are covered in this section:

Configuration

Call Scenario

Configuration

Figure 6 is a block diagram of the UHF IMTS system. An IMTS system consists of the

following major components:

Central Office

IMTS Terminal

Base Stations

Mobile Telephones

Centr al Office - Central offices are components of telephone switching systems. Each

telephone within a telephone network is connected into the telephone network througha central office. The central office provides two basic functions: call routing and call

supervision.

Call routing is required to route both incoming and outgoing calls to the correct location. Call

supervision is required to establish the talking path between the parties that are involved in the

call and to provide the necessary control signals that are used by the telephone network to

establish, monitor, and break connections. All incoming and outgoing UHF IMTS calls are


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routed through the Dhahran central office, whereas all incoming and outgoing VHF IMTS

calls are routed through the Abqaiq central office.


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IMTS System

Figure 6


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IMTS Terminal - The IMTS terminal is the heart of the IMTS system, and it is the

interface between the telephone network and IMTS radio base stations. The following

functions are performed by the IMTS terminal:

Selects the channel for idle tone transmissions.

Recognizes when a mobile telephone attempts to seize a channel or has

answered a call.

Stores mobile telephone identification numbers.

Stores valid numbers for outgoing IMTS calls.

Makes and breaks connections between base stations and the central

office.

Provides receiver voting.

A 2 kHz idle tone is transmitted on one channel by each base station. The purpose of

the idle tone is to provide the mobile telephones with the identification of the channel

to monitor. The UHF IMTS system has eight channels: F1 through F8. Each mobile

telephone scans the eight channels until the channel that contains the idle tone is

received. After the channel that contains the idle tone is received, the mobile

telephone will monitor that channel.

Seizures and call answers must be recognized so that the IMTS terminal can connect

the appropriate telephone to the central office. The recognition of these actions is

performed with the transmission and reception of various acknowledge tones.

The mobile telephone identification numbers are used to identify which mobile

telephone has an incoming or an outgoing call. The mobile telephone identification

number (ANI) is analogous to a conventional telephone number. The IMTS system

only allows outgoing calls to be placed to telephones that are within a particular

calling area; therefore, each time an outgoing call attempt occurs, the IMTS terminal

determines whether the called telephone number is located within the allowable calling

area. Those telephone numbers that are valid for each mobile telephone are stored bythe IMTS terminal.


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The IMTS terminal is illustrated in Figure 7. The IMTS terminal provides the

connections between the base stations and the central office (C.O.) so that dialed

numbers, conversations, busy signals, and other information can be transmitted

between the central office and the mobile telephones. The receiver voter panelprovides the best received signal from the mobile telephone to the central office.

The computer work station that is shown in Figure 7 provides the processing and

storage functions for the IMTS terminal. The channel inputs/outputs (I/Os) provide

the interface between the work station and the control equipment for each channel and

the central office.

DID and DOD are acronyms for Direct Inward Dialing and Direct Outward Dialing,

respectively. The DID and the DOD units provide the interface between the IMTS

terminal and the central office. The base unit provides the interface between the IMTS

terminal, the voter panel, and the transmitter steering (bridge). Telephone calls fromthe telephone network that are to be routed to mobile telephones are routed through the

DID unit. Telephone calls from mobile telephones are routed to the central office

through the DOD unit. All of the information that is transmitted between the central

office and a mobile telephone is routed through the base unit.

Because the IMTS system is a four-wire system and the trunks that connect the CO to

the IMTS terminal are two-wire circuits, a hybrid is required. The hybrid performs the

conversions between two-wire circuits and four-wire circuits. A two-wire circuit is a

circuit in which both transmission directions are carried over a single wire pair or radio

channel. A four-wire circuit is a circuit that employs two wire pairs or channels for the

two-transmission directions. The trunk selector selects between the DID trunks and

the DOD trunks, dependent upon whether the call is from land to a mobile unit or from

a mobile unit to land.


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IMTS Terminal

Figure 7


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The purposes of the voter panel are to determine which receiver provides the highest

quality received signal and to connect the output of that receiver to the base unit.

Figure 8 shows a block diagram of a voter panel. The voter panel consists of receiver

modules and an audio module. The output of each receiver is connected to a receivermodule. The receiver module amplifies and squelches (as required) the receiver input.

The amplified signals from each receiver module are alternately applied by the select

and hold switches on the receiver modules to a select and hold timer that is located in

the audio module. The select and hold timer provides an input to the select circuit on

the receiver module for the channel that has the best received signal. The select circuit

provides a gate signal for the selected audio gate that allows the selected audio gate to

connect the amplified received signal to the audio amplifiers on the audio module.

The received signal is then output from the audio module to the base unit.


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Voter PanelFigure 8


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The transmitter steering (bridge) that was shown in Figure 7 connects the signals to be

transmitted to the correct transmitter. The transmitter that is to broadcast the signals is

the transmitter that is associated with the receiver that has been selected by the voter

panel. The transmitter steering (bridge) consists of three transmitter selectors and twoaudio splitter units. Each transmitter selector is associated with several of the base

stations. If the receiver for a given base station has been selected by the voter panel, a

signal from an associated receiver module is output to the associated transmitter

selector. The transmitter selector then signals the associated base station transmitter to

transmit. The audio splitters split the audio signals that are received from the IMTS

base unit into separate signals for each base station transmitter. During a call, the only

transmitter that transmits is the transmitter at the base station with the receiver that has

been selected by the voter panel.

Base Stations - The base stations are basically UHF transmitters and receivers. The

locations of the base stations are as follows:

Safaniyah

Abu Hadriyah

Berri

Ras Tanura

Dhahran

Abqaiq

Shedgum

Surge Tank

Udhailiyah

The base stations are linked to the IMTS terminal through the fiber optic and/or

microwave backbone communications systems. Figure 9 is a table that provides the

frequencies that are used for the different IMTS channels.


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IMTS Channel Frequencies

Figure 9

Mobile Telephones - The mobile telephones that are used by the IMTS system contain a

transmitter, a receiver, and control circuits. The transmitter and the receiver provide

the link between the IMTS system subscriber and the base stations. The control

circuits are required to ensure that the transmitter and the receiver are tuned to the

correct frequency.

Call Scenario

Figure 10 shows a simplified block diagram of the IMTS system; this block diagram is

referenced throughout the descriptions of the call scenarios. The following call scenarios will

be examined in this section:

From Land to Mobile Call

From Mobile to Land Call

Fr om Land to Mobile Call - Initially, all of the IMTS base stations transmit the idle toneon one of the channels, provided that there is at least one channel that is free of traffic.

Each mobile telephone that is activated (turned on) monitors the channel that

broadcasts the idle tone. The following sequence is followed when a call is placed

from a land telephone to a mobile telephone:


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The central office routes the call to the IMTS terminal. Because all

IMTS mobile telephone numbers begin with 87704 and 87705, the

IMTS terminal discards the first three digits of the called telephone

number, and it passes the last four digits to the SUB FILES (subscriberfiles). The subscriber files are stored in the computer work station.

If the four digits correspond to a mobile telephone number, the

computer work station provides the ANI that corresponds to the digits of

the base stations for transmission. The IMTS terminal also removes the

idle tone.

All mobile telephones that are activated receive the transmitted ANI;

however, only the mobile telephone that is assigned that ANI can

decode the ANI. After the ANI has been decoded, the mobile telephone

that is assigned the ANI transmits an acknowledge tone. The othermobile telephones begin to scan for the next idle channel.

After receipt of the acknowledge tone, the IMTS terminal switches on

ringing for the called telephone. The ringing signal is transmitted by all

of the base stations. If the base station does not receive an acknowledge

tone, a recorded announcement that states that the dialed telephone is

not available is returned to the calling telephone.

In response to the ringing signal, the called telephone goes off-hook.

"Off-hook" is the telephone terminology that describes when the

telephone handset is removed from its cradle. The called telephone

begins to broadcast as soon as the telephone has gone off-hook.

For 400 milliseconds, the voter panel determines which receiver

provides the best signal. This site initially is selected to handle the call;

the other transmitters stop transmitting.

With the site selected, the IMTS terminal connects the call through to

the central office.

The voter panel continues to monitor the quality of the received signalfrom each site. If the quality of the received signal from another site

becomes better, that site is selected, and the transmitter at the original

site drops off.


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IMTS Block Diagram

Figure 10


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Fr om Mobile to Land C all - Initially, all of the IMTS base stations that are on a single

channel transmit the idle tone. Each mobile telephone that is activated monitors the

channel that broadcasts the idle tone. The following sequence occurs when a call is

placed from a mobile telephone to a land telephone:

The mobile telephone that is to place the call goes off-hook. When the

mobile telephone goes off-hook, the mobile telephone transmits a seize

tone.

The seize tone is received by the IMTS terminal, and it is acknowledged

by the IMTS terminal by means of the transmission of an acknowledge

tone. The voter panel selects the site based on the quality of the signals

that are received from the various sites. The other transmitters cease to

transmit on this channel.

When the IMTS terminal acknowledges the seizure, the IMTS terminalswitches the idle tone to the next available channel. The other mobile

telephones that are activated scan the channels until the channel that

contains the idle tone is received. The mobile telephones then monitor

this new channel.

When the calling mobile telephone receives the acknowledge tone, the

mobile telephone transmits its ANI.

The IMTS terminal determines whether the ANI is valid. If the ANI is

valid, the IMTS terminal connects the central office to the mobile

telephone, and the central office applies a dial tone for the mobile

telephone.

Upon receipt of the dial tone, the telephone number is dialed.

The IMTS terminal monitors the dialed number to determine whether

the dialed number is valid. Those calling areas that may be reached by

each mobile telephone are programmed into the IMTS terminal

computer work station. Generally, the mobile telephones may be

restricted to a particular local calling area or to the Eastern Province.


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Paging System (464.3 MHz)

The purpose/function of the paging system is to notify designated personnel through portable

radio receiving units that there is a message for the designated personnel. The radio receiving

units are referred to as pagers. Pagers are used by personnel who spend considerable time in

the field or away from their office telephones. The paging system is a tone and voice system

that employs transmitters at various major communications sites. The following topics that

pertain to the paging system are covered in this section:

Configuration

Call Scenario

Configuration

Figure 11 is a block diagram of the paging system. The paging system consists of the

following major components: the paging terminal, networked base stations, modems, and the

pagers.

The paging terminal is located at the Dhahran telephone central office. The terminal

processes the calls to pagers, and it stores messages. All calls to a pager are routed through

the paging terminal.

When a call is placed to a pager, the terminal converts the dialed telephone number to a pager

identification number, and it provides a recorded message to the caller to leave a message forthe called party. The pager identification number is analogous to the IMTS ANI. Dependent

on the telephone number that was dialed, the paging signal will be transmitted from either one

of three areas or a combination thereof: the Northern Area, the Central Area, or the Southern

Area. The paging terminal routes a signal that corresponds to the pager identification number

of the pager that was called to the base stations in the appropriate area or areas.

When prompted by the recorded message, the caller leaves a message for the called party.

The paging terminal stores these messages. The nominal message length that can be stored by

the paging terminal is 15 seconds. The paging terminal provides a queue to store multiple

messages that have been left for a single individual. A group call feature that allows one

individual to leave a message to a group of paging system subscribers also is available. Atelephone access number is assigned to each individual who is assigned a pager. The

telephone access number allows these individuals to access their messages that are stored by

the paging terminal.

The base stations broadcast the signal that corresponds to the pager identification number of

the pager that was called. This signal is broadcast from all of the base stations in the

appropriate area. The Northern Area base stations are those base stations that are north of


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Dhahran. The Southern Area base stations are those base stations that are south of Dhahran.

The Dhahran base station is the only Central Area base station.

The pagers are simply radio receivers that contain a decoder and an alerting device. Whenturned on, the pagers receive the 464.300 MHz signals that are transmitted from the paging

base stations. A signal to a pager that is transmitted by the base stations is received by all of

the pagers that are turned on and within the range of a base station; however, because the

pager identification number is transmitted, only the pager for which the transmission is

intended can decode the signal. When the signal is decoded, the decoder signals the alerting

device to inform the wearer that a message has been left for that individual.


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Paging System

Figure 11


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Call Scenario

The following sequence occurs when a call is placed from a telephone to a pager telephone

number:

The caller dials the telephone number for the desired pager.

The paging terminal "answers" the call. After a recorded message and at the

"beep" prompt, the caller leaves the desired message.

The paging terminal stores the message.

The paging terminal converts the telephone number to a paging identification

number that corresponds to the dialed number.

A signal that corresponds to the called paging identification number is routed to

the area that corresponds to the dialed number.

Each transmitter in the appropriate area transmits a signal that can be decoded

only by the pager that is assigned to the called individual.

The called pager notifies the wearer that a message has been left for that

individual.

The "beeped" individual dials his telephone access number and retrieves anymessages that are queued for that individual.

Push-to-Talk Systems

The vast majority of Saudi Aramco's narrowband communication systems consists of push-to-

talk systems. The purposes/functions of the push-to-talk systems vary with the application

and the configuration of the systems. Generally, push-to-talk systems can be classified as

either repeatered systems or as non-repeatered systems. The purpose of a repeatered system

is to provide wide area communications. The purpose of a non-repeatered system is to

provide communications in a local area.


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The Northern Remote Division Security System will be used to describe the operation of both

repeatered and non-repeatered push-to-talk (PTT) systems. This system has three channels.

The first channel is used on a half-duplex repeatered system. The second channel is used

for a simplex non-repeatered system. The third channel is used for simplex non-repeateredcommunications between personal radios and from personal radios to mobile radios and fixed

transceivers. The following topics that pertain to push-to-talk systems are covered in this

section:

Non-Repeatered Systems

Repeater Systems

Non-Repeatered Systems

The following topics that pertain to non-repeatered push-to-talk systems are covered in thissection:

Configuration

Call Scenario

Configuration - Figure 12 is a block diagram of the Local Channel for the Northern

Remote Division Security System. The radio system consists of a console, base

stations, fixed transceivers, personal radios, and mobile radios. The console is located

at the Ras Tanajib ISD building. The base stations are located at Ras Tanajib, Berri,

Nariyah, Wariyah, and Khursaniyah. The base stations are configured for remote

control. Both transmission and reception are alone on 410.450 MHz.

The console is a remote controller that allows an individual at the Ras Tanajib ISD

building to transmit to and receive information from the base stations. The console

provides the microphone, the speaker, and the controls that are required for an

individual at the console to transmit to and to receive information from the base

stations. Voice signals to be transmitted and control tones are transmitted from the

console to hub equipment at Ras Tanajib communications site. The control tones are

used by the base station line equalization and control equipment to control the base

station transmitters. Received voice signals are transmitted from all Ras Tanajib

communications sites to the console.

The Ras Tanajib hub contains a voter, line equalization and control equipment, transmitter

and receiver, transmission line components, and an antenna. Each base station receiver

transmits to the voter either the received audio signal or, if the receiver is squelched, a 1950

Hz tone. The voter selects the best received signal for transmission to the console. The

operation of the voter is similar to the operation of the voter that was discussed in the IMTS

section.


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Local Channel

Figure 12


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The line equalization and control equipment performs three functions: the equipment

equalizes the lines to the various base stations, and it inserts the correct amount of

delay into the transmitted audio signals as is required for simulcast operation, and it

interprets the control tones from the console to control the keying of the base stationtransmitters.

Because the system is a simulcast system, the line equalization and delay function is

required. A simulcast system is a system that simultaneously transmits the same

information from more than one base station on the same frequency. Interference and

degraded system performance result from simulcast base station transmissions that are

not simultaneous, of equal amplitude, and in phase. Because each base station

simultaneously transmits the same information, the signals from the console must

simultaneously reach each base station.

Interpretation of control tones is required to key the base station transmitters. Whenan individual at the console depresses the PTT switch, the transmitters are keyed, and

the voice signals are transmitted to the base stations for transmission. Control tones

are used to indicate to the control equipment that the PTT switch has been depressed.

Two tones are used: a 2175 Hz tone and a 1950 Hz tone. The 2175 Hz tone is first

transmitted for 125 milliseconds to alert the control equipment. After the 2175 Hz

tone, the 1950 Hz tone is transmitted for 40 milliseconds. The 1950 Hz tone is the

signal to key the base station transmitters. After the 1950 Hz tone has been

transmitted, the 2175 Hz tone is transmitted as long as the PTT switch is depressed.

This tone is the transmitter holding tone; the tone ensures that the transmitters remain

keyed as long as the PTT switch is depressed.

In order for the line equalization and control equipment to perform these two

functions, two signal paths are present through the line equalization and control

equipment: a transmit audio signal path and a keying signal path. The components

through which the transmit audio signals pass are as follows:

From the ISD BLDG Industrial Security Console

TX/RX Audio and Control Interface

Keying Control Assembly

Bridging Amplifiers

Delay Lines Equalizers

To the Base Station Transmitters


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A block diagram of the line equalization and control equipment is shown in Figure13.

In the transmit audio signal path, the TX/RX audio and control interface processes the

signals from the console to separate the transmit audio signals from the keying signals.The transmit audio signals pass through the keying control assembly to the bridging

amplifiers. The bridging amplifiers compensate for the losses that are inserted by the

delay lines and equalizers and ensure that the level to each destination is correct. The

delay lines ensure that the transmit audio signals from the console simultaneously

reach each base station. Also, the amplitude and phase of the transmit audio signals

must be equal. The transmit audio signals may be transmitted to the base stations over

either a microwave system or a twisted wire pair; however, only signals to the Ras

Tanajib Comms base station are transmitted over a twisted wire pair.

In the keying signal path, the control tones are connected to the TX/RX Audio and

Control Interface from the console. This interface removes the control signals fromthe voice signals, and it transmits each control signal to the keying control assembly.

The keying control assembly routes the voice signals to be transmitted to the base

station transmitters through the delay and equalization circuitry. The keying signals

are routed to the transmitter keying control assembly. The transmitter keying control

assembly provides the transmitter keying signals that are transmitted to the base station

transmitters through the keying relay assemblies. The transmitter keying signals are

transmitted to the Ras Tanajib base station through a twisted wire pair and to the other

base stations through microwave systems.


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Line Equalization and Control Equipment


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Figure 13


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Figure 14 shows a block diagram of the remainder of the base station components: the

transceiver rack and the antenna. The transceiver rack contains the transmitter (TX1),

the receiver (RX1), the cavity filter, the RF patch panels, the low noise amplifier

(LNA), and the transmit/receive relay.

The transmitter receives an audio input, a transmitter keying input, and a master

frequency reference oscillator input. The keying input (TX key) causes the transmitter

to begin to transmit. The keying relay assembly was discussed in the previous section.

The audio input (TX audio) provides the information that frequency modulates the

transmitted carrier. The TX key and TX audio inputs are outputs from the line

equalization and control equipment through the terminal blocks. The terminal blocks

simply provide a connection point. The master frequency reference is used by the

transmitter to ensure that the correct carrier frequency is maintained. The importance

of the base station transmitter frequency stability is increased in simulcast systems.

Because the system is a simulcast system, any variation between the transmitterfrequencies of the various base stations will introduce distortion and decrease system

performance.

The output of the transmitter is connected to a cavity filter through a transmission line

and RF patch panel. The cavity filter ensures that no unwanted signal components are

transmitted. When the transmitter transmits, the transmit/receive relay connects the

cavity filter output to the antenna. The transmit/receive relay also connects the

receiver to the antenna when transmission stops. The relay is also activated by the

keying relay assembly. The base station transmitters that are used in this system are

rated at 100 watts.

Received signals are coupled from the antenna to a cavity filter through a transmission

line and the transmit/receive relay. The cavity filter ensures that no frequencies that

could interfere with the received signal are coupled to the receiver. An LNA

compensates for the losses that are inserted by the filter, and it boosts signal strength

for the receiver. The audio output from the receiver (RX audio) is sent to the voter

through the terminal blocks.

Several different types of antennas are used for the base station antennas. The type of

antenna that is used depends on the desired coverage area for the base station. For

example, the Ras Tanajib and Wariyah base stations are located near the edge of thenorthern remote division coverage area; therefore, directional antennas are used to

focus the transmitted energy within the desired coverage area. Two directional

antennas are used at the Nariyah base station to form an effective bi-directional

antenna that provides a long, narrow coverage area. More omni-directional types of

antennas are used at the Berri and Khursaniyah base stations.


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Mobile radios, personal radios, and fixed transceivers are self-contained transceivers.

The fixed transceiver's transmit power is 50 watts, the personal radio's transmit power

is 5 watts, and the mobile radio's transmit power is 40 watts. The mobile radios and

fixed transceivers are configured for two-channel operation over the local channel andthe division channel. The personal radios are configured for three-channel operation.

The third channel is for personal radio to personal radio communications; however, the

mobile radios and fixed transceivers can monitor this communication on the division

channel.


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Base Station

Figure 14


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Call Scenar io - The following scenario occurs when an individual at the console

depresses the PTT switch and speaks into the microphone:

The console sends the 2175 Hz tone, which is followed by the 1950 Hztone and another 2175 Hz tone, to the line equalization and control

equipment. After the tones have been transmitted, voice signals are

transmitted.

The line equalization and control equipment removes the control tones

from the voice signals. The voice signals are split into five signals for

the five base stations, amplified, and sent to the delay lines. The delay

lines insert the correct amount of delay for each base station. The voice

signals then are equalized and transmitted to each base station

transmitter.

The line equalization and control equipment simultaneously transmits

the transmitter keying signal to each base station transmitter to key the

transmitters.

Each keyed transmitter simultaneously transmits the voice signals. The

transmitted carrier frequency is 410.450 MHz.

Any fixed transceiver, mobile radio, or personal radio that is turned on

within the range of the transmitters and that is selected to the correct

channel will receive the transmitted voice signals, and it will provide an

audio output through a speaker.

The following scenario occurs when an individual with a personal or other mobile

radio transmits:


within the range of the personal radio and that is selected to the correct

channel will receive the transmitted voice signals, and it will provide an

audio output through a speaker.

The transmitted signal is received at varying levels by the receivers atone or more of the base stations. The received level at a base station

depends on the proximity of the personal radio, the propagation

conditions, and the radiation pattern of the base station antenna.


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The received voice signals are transmitted from the base station

receivers to the voter at the Ras Tanajib Comms site.

The voter selects the highest-quality received signal, and it transmits thesignal to the console in the ISD building. The console provides an

audio output through the console speaker.

Repeatered Systems

The following topics that pertain to a repeatered system are covered in this section:

Configuration

Call Scenario

Configuration - Figure 15 is a block diagram of the Division Channel for the Northern

Remote Division Security System. The radio system consists of a console, base

stations, fixed transceivers, personnel radios, and mobile radios. The location of the

components is the same location as the local channel; however, the base stations can

be configured as remotes or as repeaters. A repeater is a base station that transmits the

signals that are received from the console and the signals that are received by the base

station receiver. The base station transmit frequency is 408.875 MHz, and its receive

frequency is 413.875 MHz.

The console is the same console that is used by the local channel. The console

performs the same functions for the division channel as the functions that weredescribed for the local channel.


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Block Diagram of the Division Channel for the

Northern Remote Division Security SystemFigure 15


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Figure 16 is a block diagram of the voter and the line equalization and control

equipment that are used for the division channel. The voter receives the received

audio signals from the base station receivers, and it selects the best signal for

transmission to the console. The signal is transmitted to the console through theTX/RX audio and control interface. The voter also transmits the selected audio signal

and a keying signal to the keying control assembly. The TX/RX audio and control

interface receives both the audio signals to be transmitted and the control tone signals

from the console. The audio signals to be transmitted and the transmitter keying

signals are transmitted from the TX/RX audio and control interface to the keying

control assembly.

The keying control assembly routes the audio signals to be transmitted to the base

station transmitters through the delay and equalization circuitry. The division channel

delay and equalization circuitry is identical to the circuitry that is used for the local

channel. The keying signals are routed to the transmitter keying control assembly.The transmitter keying control assembly provides the transmitter keying signal that is

transmitted to the base station receivers through the keying relay assemblies. The

audio and transmitter keying signals are transmitted to the Ras Tanajib base station

through a twisted wire pair. The audio and transmitter keying signals are transmitted

to the other base stations through wideband systems.

Because the division channel is a repeatered network, the base station transmitters can

be keyed by either keying signals from the console or by the selected audio signals

from the voter. If desired, the repeater function can be suspended by the repeat disable

switch at the console. The repeat disable command is transmitted as a control tone

from the console to the TX/RX audio and control interface. The repeat disable control

tone is interpreted by the TX/RX audio and control interface, which, in turn, provides

the repeat disable command to the voted repeat disable control. When the repeat

disable command is present, the voted repeat disable control signals the keying control

assembly. This signal prevents the voter keying signal from signaling the keying

control assembly to key the base station transmitters.


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Line Equalization and Control

Figure 16


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Figure 17 shows the base station transmitter (TX2), the receiver (RX2), the

transmission lines, and the antenna. The division channel base station transmitters,

receivers, and antennas are very similar to those transmitters, receivers, and antennas

that are used by the local channel. The transmit frequency is 408.875 MHz. Thereceive frequency is 413.875 MHz. Several different components are located between

the antenna and the transmitter/receiver. An isolator is used between the transmitter

and the antenna. The isolator prevents energy from being reflected back to the

transmitter. The duplexer performs a function that is similar to that of the

transmit/receive relay. The duplexer couples energy from the transmitter to the

antenna, and it prevents the transmitter energy from being coupled to the receiver.

The duplexer also couples the energy from the antenna to the receiver, and it prevents

the energy that is received by the antenna from being coupled to the transmitter.

Because two receivers share the same antenna, a multicoupler is required. The

multicoupler couples the received 413.875 MHz signals to the division channel

receiver and the received 408.275 MHz signals to the auxiliary receiver (RX5). Theauxiliary receiver is used for medical services.

The same fixed transceivers, mobile radios, and personal radios are used for the

division channel as are used for the local channel.


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Base Station

Figure 17


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Call Scenar io - The following scenario occurs when an individual at the console

depresses the PTT switch and speaks into the microphone:

The console sends the 2175 Hz tone, which is followed by the 1950 Hztone and another 2175 Hz tone, to the line equalization and control

equipment. After the tones have been transmitted, voice signals are

transmitted.

The line equalization and control equipment removes the control tones

from the voice signals. The voice signals are split into five signals for

the five base stations, amplified, and sent to the delay lines. The delay

lines insert the correct amount of delay for each base station. The audio

signals then are equalized and transmitted to each base station

transmitter.

The line equalization and control equipment simultaneously transmits

the transmitter keying signal to each base station transmitter, which keys

the transmitters.

Each keyed transmitter simultaneously transmits the voice signals. The

transmitted carrier frequency is 408.875 Mhz.



channel receives the transmitted audio signals, and it provides an audio

output through a speaker.

The following scenario occurs when an individual with a personal radio transmits and

the repeat disable function is not selected:

The signal is transmitted from the personal radio at 413.875 MHz.

The transmitted signal is received at varying levels by the receivers at

one or more of the base stations. The received level at a base station

depends on the proximity of the personal radio, the propagation

conditions, and the radiation pattern of the base station antenna. Thereceived voice signals are transmitted from the base station receivers to

the voter at the Ras Tanajib Comms site.

The voter selects the highest-quality received signal, and it transmits the

signal to the console in the ISD building and to the keying control

assembly.


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When repeater operation is enabled, the keying control assembly routes

both the received audio to the base station transmitters and keys the base

station transmitters.

The base station transmitters re-transmit the received audio at 408.875

MHz.



channel receives the transmitted audio signals, and it provides an audio

output through a speaker.

Extended Subscriber

The purpose/function of the extended subscriber system is to allow individuals at remote

locations to have access to the Saudi Aramco Telephone Network. The following topics that

pertain to the extended subscriber system are covered in this section:

Configuration

Call Scenario

Configuration

Figure 18 is a block diagram of an extended subscriber system installation. An extendedsubscriber installation consists of a conventional telephone, a subscriber radio, and a central

office radio. Generally, extended subscriber facilities are designated as either central office

end or subscriber end.

A conventional full-duplex transceiver is used for the central office and subscribes radios of

an extended subscriber installation. A highly directional antenna is connected to the

transceiver. Because all transmissions between the central office end and the subscriber end

are point-to-point, directional antennas are used. Also, the use of directional antennas helps

to minimize interference between the extended subscriber installation and any other radio

systems utilizing the same frequency.

Calls that are routed to an extended subscriber telephone are processed through the central

office in the same manner as are other calls; however, instead of the twisted wire pair that

connects conventional telephones to a central office, the extended subscriber connection is

through a radio. The signaling and voice signals for the extended subscriber telephone are

routed through the central office to the central office end transmitter. The signaling and voice

signals that are outputs of the extended subscriber telephone are routed from the central office


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end receiver to the central office. The subscriber radio is connected to a conventional

telephone.


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Extended Subscriber

Figure 18


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Call Scenario

The following call scenarios will be examined in this section:

To an Extended Subscriber Telephone

From an Extended Subscriber Telephone

To an Extended Subscriber Telephone - The following sequence occurs when a call is

placed from a telephone to an extended subscriber telephone:

The call is routed to the central office that serves the extended

subscriber.

The central office routes the call to the central office end transmitter.The transmitter transmits an alerting tone to the subscriber end receiver.

The subscriber-end receiver processes the alerting tone, and its

transmitter returns an acknowledge tone.

After receipt of the acknowledge tone, the central office switches on the

ringing signal for the called telephone. The ringing signal is transmitted

by the central office end transmitter.

In response to the ringing signal, the called telephone goes off-hook.

The subscriber-end transmitter begins to transmit as soon as thetelephone has gone off-hook.

In response to the off-hook condition of the called telephone, the central

office end transmitter begins to transmit. To the individuals who are

engaged in the telephone call, the call proceeds in the same manner as a

conventional call.

When one of the telephones returns to an on-hook condition, the call is

terminated.

Fr om an Extended Subscriber Telephone - The following sequence occurs when a call isplaced from an extended subscriber telephone:

The extended subscriber telephone that is to place the call goes off-

hook. When the extended subscriber telephone goes off-hook, the

subscriber end transmitter transmits a seize tone.


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The seize tone is received by the central office end receiver, and it is

acknowledged by the central office by means of the transmission of a

dial tone.

Upon receipt of the dial tone, the telephone number is dialed, and the

call proceeds as a conventional telephone call.

INMARSAT

The purpose/function of the INMARSAT system, as the system is used by Saudi Aramco, is

to provide a method for Saudi Aramco personnel outside existing communications

infrastructure to communicate with other Saudi Aramco personnel. The following topics that

relate to INMARSAT are covered in this section:

Configuration

Call Scenario

Configuration

Figure 19 is a block diagram of an INMARSAT communications link. The INMARSAT

communications link consists of a transportable INMARSAT terminal, the INMARSAT

satellite, the coastal earth station (CES), and the telephone network (PTT).

The INMARSAT terminal is a self-contained transmitter and receiver that includes atelephone interface (the voice card), a data interface, and an antenna. The transmitter and the

receiver share a single parabolic antenna. A duplexer separates and routes the transmitted and

received signals. Many INMARSAT terminals include a Global Positioning System (GPS)

receiver that is used to fix the position of the terminal. The GPS system uses reference

signals that are transmitted from satellites in known orbits in order to determine the position

of a GPS receiver. The location that has been determined by the GPS receiver is used by the

terminal to train the antenna toward the INMARSAT satellite.

The transmitter components include an up-converter and a high power amplifier (HPA). The

receiver components include a low noise amplifier (LNA) and a down-converter. The

transmitter and the receiver share a terminal control unit (TCU) and a central processing unit(CPU). The CPU receives inputs from the telephone and data interface, the TCU, the RF

card, the up-converter and the down-converter. It also provides outputs to the telephone and

data interface, the TCU, the RF card, the up-converter, and the down-converter. Basically,

the CPU performs the majority of the control functions that are required by the terminal. The

TCU receives and processes the operational commands from the terminal front panel controls.

These operational commands include requests for channels and commands to begin and end

transmissions.


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The RF card processes the voice and data signals that are output to the transmitter and that are

input from the receiver. The RF card also provides the data interface. The voice card

provides the telephone interface with the RF card.

The output to the transmitter from the RF card is converted to the transmit frequency by the

up-converter. The HPA amplifies the upconverted signal to the transmit power. The uplink

frequency from the terminal is approximately 1.6 GHz. The downlink frequency to the

terminal is approximately 1.5 GHz. The LNA amplifies the received signals, and the

downconverter converts the received frequency to an intermediate frequency signal that is

output to the RF card.

The INMARSAT system employs three geo-synchronous satellites. A geo-synchronous

satellite is a satellite that is positioned over the equator and orbits the earth exactly once per

day; therefore, geo-synchronous satellites appear to remain in a stationary position. TheIndian Ocean INMARSAT satellite is normally used by Saudi Aramco. The satellite receives

the transmitted signals from the terminal, and it retransmits those signals to a CES. The

downlink frequency from the satellite to the CES is approximately 4 GHz. The satellite also

receives the signals that are transmitted from the CES, and it retransmits those signals so that

the signals can be received by INMARSAT terminals. The uplink frequency from the CES to

the satellite is approximately 6 GHz.

The CES provides the interface between the INMARSAT system and the telephone network.

The CESs utilize a 10 to 13 meter transmit/receive antenna on the satellite link. The CES that

is normally used by Saudi Aramco is located in Jeddah. The Jeddah CES is linked with the

Saudi Arabian National Telephone Network (PTT). Calls to an INMARSAT terminal are

routed to the Jeddah CES. The CES transmits the call to the Indian Ocean INMARSAT

satellite. Calls from an INMARSAT terminal are received by the Jeddah CES, and they are

routed through the Saudi Arabian National Telephone Network to the called telephone.


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INMARSAT Satellite Network

Figure 19


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Call Scenario

The following call scenarios are described in this section:

Call from an INMARSAT Terminal

Call to an INMARSAT Terminal

Call from an INMARSAT Terminal - This call scenario assumes that the INMARSAT

terminal is energized and that the antenna has been trained to the correct orientation.

The following scenario occurs when a call is placed from an INMARSAT terminal:

Voice is selected on the front panel controls.

The telephone handset is removed from the hookswitch and the SelectChannel pushbutton is pressed. The hookswitch is the device that holds

the handset and that signals either when a call is to be placed or when it

has been terminated. When the Select Channel pushbutton is depressed,

a signal that identifies the desired CES is transmitted from the terminal.

The terminal transmits a request for channel signal to the CES. If a

channel is available, the CES replies with a 2600 Hz tone. Upon receipt

of the 2600 Hz tone, the terminal acknowledges the 2600 Hz tone with

the transmission of its own 2600 Hz tone. If a channel is not available,

the busy indicator lights. If the busy indicator lights, another request for

a channel may be made after six seconds.

The CES responds to the 2600 Hz tone from the terminal with the

transmission of a 425 Hz "go ahead with dialing" tone. This tone is

analogous to the standard dial tone.

Upon receipt of the 425 Hz tone, the telephone number of the called

telephone is dialed. Standard dual-tone multi-frequency (DTMF)

signals are transmitted to represent the dialed digits. DTMF signals are

the normal tone signals that are transmitted from a standard tone

telephone to a central office.

For calls that are directed to company telephone numbers, the CES

routes the call to the Saudi Arabian National Telephone Network, and

the Saudi Aramco Telephone Network routes the call to the called

telephone.


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The called telephone rings, and the called party answers the telephone to

establish the connection. The call proceeds as a normal telephone call.

When desired, the call can be terminated through placement of thetelephone handset back on the hookswitch.

Call to an I NMARSAT Terminal - This call scenario assumes that the INMARSAT

terminal is energized and that the antenna has been trained to the correct orientation.

The following scenario occurs when a call is placed to an INMARSAT terminal:

When the calling telephone dials the telephone number for the

INMARSAT terminal, the call is routed to the Jeddah CES. The CES

transmits a tone that signals the called INMARSAT terminal that an

incoming call is present.

An intermittent audio tone is transmitted from an annunciator on the

TCU. The tone signifies the presence of an incoming call.

The call is answered, and the connection is established by removal of

the telephone handset from the hookswitch. The call proceeds as a

normal telephone call.

When desired, the call can be terminated through placement of the

telephone handset back on the hookswitch.


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FUNCTION AND CHARACTERISTICS OF SAUDI ARAMCO NARROWBAND

RADIO EQUIPMENT

Narrowband radio systems consist of transmitters, receivers, antennas, and control equipment.

It is important for the Communications Engineer to understand the function, characteristics,

and operation of these components. The following topics that pertain to the function and

characteristics of Saudi Aramco narrowband radio equipment are covered in this section:

Transceivers

Filters/Combiners/Multicouplers

Antennas/Transmission Lines

Control Equipment (Tone and DC Control)

Transceivers

A transceiver is a piece of equipment that combines a transmitter and a receiver. Figure 20 is

a block diagram of a typical General Electric transceiver. The transceiver consists of two

circuit boards: a synthesizer/interconnection circuit board and a transmitter/receiver circuit

board.

The synthesizer/interconnection circuit board contains a microprocessor, a synthesizer,

microphone audio amplifiers, a voltage-controlled oscillator (VCO), and control circuitry.

The control circuitry processes the inputs from the channel selector switch, the channel guard

switch, and the PTT switch. The microprocessor receives inputs from the PTT switch, thechannel guard switch, and the channel selector switch. The microprocessor controls the

operation of the synthesizer. The purpose of the synthesizer is to control the operation of the

VCO. Basically, the VCO is an oscillator whose frequency depends on the control signals

from the synthesizer and the audio signals from the microphone audio amplifiers. The

microphone audio amplifiers amplify the voice signals from the microphone. The output

from the VCO is used by the transmitter and the receiver.

When the transceiver receives, the output frequency of the VCO is determined by the channel

selector switch. The frequency for each channel that can be received by the transceiver is

stored in memory that is available to the microprocessor. Based on the posi

configuration of narrow band radio systems

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