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1. INTRODUCTION

Wireless communication is the transfer of information over a distance without the use of

enhanced electrical conductors or "wires". The distances involved may be short (a few meters as in

television remote control) or long (thousands or millions of kilometers for radio communications)

When the context is clear, the term is often shortened to "wireless". Wireless communication is

generally considered to be a branch of telecommunications.

.The term "wireless" has become a generic and all-encompassing word used to describe

communications in which electromagnetic waves or RF (rather than some form of wire) carry a

signal over part or the entire communication path. Common examples of wireless equipment in use

today include:

  Professional LMR (Land Mobile Radio) and SMR (Specialized Mobile Radio) typically used

by business, industrial and Public Safety entities.

  Consumer Two Way Radio including FRS (Family Radio Service), GMRS (General Mobile

Radio Service) and Citizens band ("CB") radios.

  The Amateur Radio Service (Ham radio).

  Consumer and professional Marine VHF radios. 

  Cellular telephones and pagers: provide connectivity for portable and mobile applications, both

personal and business.

  Global Positioning System (GPS): allows drivers of cars and trucks, captains of boats and

ships, and pilots of aircraft to ascertain their location anywhere on earth.

  Cordless computer peripherals: the cordless mouse is a common example; keyboards and

printers can also be linked to a computer via wireless.

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  Cordless telephone sets: these are limited-range devices, not to be confused with cell phones.

  Satellite television: allows viewers in almost any location to select from hundreds of channels.

  Wireless gaming: new gaming consoles allow players to interact and play in the same game

regardless of whether they are playing on different consoles. Players can chat, send text

messages as well as record sound and send it to their friends. Controllers also use wireless

technology. They do not have any cords but they can send the information from what is being

pressed on the controller to the main console which then processes this information and makes

it happen in the game. All of these steps are completed in milliseconds.

1.1 MODES OF WIRELESS COMMUNICATION

  radio frequency communication,

  microwave communication, for example long-range line-of-sight via highly directional

antennas, or short-range communication, or

  infrared (IR) short-range communication, for example from remote controls or via Infrared

Data Association (IrDA).

1.2 DIFFERENCE BETWEEN WIRELESS AND CORDLESS

The term "wireless" should not be confused with the term "cordless", which is generally used to

refer to powered electrical or electronic devices that are able to operate from a portable power

source (e.g. a battery pack) without any cable or cord to limit the mobility of the cordless device

through a connection to the mains power supply. Some cordless devices, such as cordless

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telephones, are also wireless in the sense that information is transferred from the cordless telephone

to the telephone's base unit via some type of wireless communications link . 

1.3 HISTORY

The world's first, wireless telephone conversation occurred in 1880, when Alexander Graham

Bell and Charles Sumner Tainter invented and patented the photophone, a telephone that conducted

audio conversations wirelessly over modulated light beams (which are narrow projections

of  electromagnetic waves). In that distant era when utilities did not yet exist to provide electricity

and lasers had not even been conceived of in science fiction, there were no practical applications

for their invention, which was highly limited by the availability of both sunlight and good weather

Similar to free space optical communication, the photophone also required a clear line of sight

between its transmitter and its receiver. It would be several decades before the photophone's

principles found their first practical applications in military communications and later in fiber-optic

communications. 

1.3.1 EARLY WIRELESS WORK

David E. Hughes, eight years before Hertz's experiments, transmitted radio signals over a few

hundred yards by means of a clockwork keyed transmitter. As this was before Maxwell's work was

understood, Hughes' contemporaries dismissed his achievement as mere "Induction". In 1885, T

A. Edison used a vibrator magnet for induction transmission. In 1888, Edison deployed a system of

signaling on the Lehigh Valley Railroad. In 1891, Edison obtained the wireless patent for this

method using inductance (U.S. Patent 465,971) 

.In the history of wireless technology, the demonstration of the theory of  electromagnetic

waves by Heinrich Hertz in 1888 was important. The theory of electromagnetic waves was

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predicted from the research of  James Clerk Maxwell and Michael Faraday. Hertz demonstrated tha

electromagnetic waves could be transmitted and caused to travel through space at straight lines and

that they were able to be received by an experimental apparatus.

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2. METHODOLOGY

2.1 VHF COMMUNICATION

VHF (Very high frequency) is the radio frequency range from 30 MHz to 300 MHz. Frequencies

immediately below VHF are denoted High frequency(HF), and the next higher frequencies are

known as Ultra high frequency (UHF). The frequency allocation is done by ITU. 

These names referring to high-end frequency usage originate from mid-20th century, when regular

radio service used MF, Medium Frequencies, better known as "AM" in USA, below the HF

Currently VHF is at the low-end of practical frequency usage, new systems tending to use

frequencies in SHFand EHF above the UHF range. See Radio spectrum for full picture.

Common uses for VHF are FM radio broadcast, television broadcast, land mobile stations

(emergency, business, and military), long range data communication with radio modems, Amateur

Radio, marine communications, air traffic control communications and air navigation systems

(e.g. VOR,DME & ILS).

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2.1.1 Propagation characteristics 

VHF propagation characteristics are ideal for short-distance terrestrial communication, with a

range generally somewhat farther than line-of-sight from the transmitter (see formula below).

Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus

transmissions are restricted to the local area (and don't interfere with transmissions thousands of

kilometres away). VHF is also less affected by atmospheric noise and interference from electrical

equipment than lower frequencies. Whilst it is more easily blocked by land features than HF and

lower frequencies, it is less affected by buildings and other less substantial objects than UHF

frequencies.

Two unusual propagation conditions can allow much farther range than normal. The

first, tropospheric ducting, can occur in front of and parallel to an advancing cold weather front

especially if there is a marked difference in humidities between the cold and warm air masses. A

duct can form approximately 250 km (155 mi) in advance of the cold front, much like a ventilation

duct in a building, and VHF radio frequencies can travel along inside the duct, bending or

refracting, for hundreds of kilometers. For example, a 50 watt Amateur FM transmitter at 146 MHz

can talk from Chicago, to Joplin, Missouri, directly, and to Austin, Texas, through a repeater. In a

July 2006 incident, a NOAA Weather Radio transmitter in north central Wisconsin was blocking

out local transmitters in west central Michigan, quite far out of its normal range. In midsummer

2006, central Iowa stations were heard in Columbus, Nebraska and blocked out Omaha radio and

TV stations for several days, while WBNX-TVin Akron, Ohio, a television station on Channel 55

in the analog age, was noted for bleeding over other Channel 55 stations in Wausau and Kenosha

Wisconsin as far west as the Wisconsin Rivervalley for hours at a time. Similar propagation effects

can affect land-mobile stations in this band, rarely causing interference well beyond the usual

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coverage area. The second type, much more rare, is called Sporadic E, referring to the E-layer of

the ionosphere. Phenomena still not completely understood (as of 2010) may allow the formation

of ionized "patches" in the ionosphere, dense enough to reflect back VHF frequencies the same

way HF frequencies are usually reflected (skywave). For example, KMID (TV Channel 2; 54 –

60 MHz) from Midland, Texas was seen around Chicago, pushing out Chicago's WBBM-TV.[citation

needed ] These patches may last for seconds, or extend into hours. FM stations from Miami

Florida; New Orleans, Louisiana; Houston, Texas and even Mexico were heard for hours in

central Illinois during one such event.

2.1.2 Line-of-sight calculation

For analog TV, VHF transmission range is a function of transmitter power, receiver sensitivity, and

distance to the horizon, since VHF signals propagate under normal conditions as a near line-of-

sightphenomenon. The distance to the radio horizon is slightly extended over the geometric line of

sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere.

An approximation to calculate the line-of-sight horizon distance (on Earth) is:

  distance in miles = where A f is the height of the antenna in feet

  distance in kilometres = where Am is the height of the antenna in metres.

These approximations are only valid for antennas at heights that are small compared to the radius

of the Earth. They may not necessarily be accurate in mountainous areas, since the landscape may

not be transparent enough for radio waves.

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In engineered communications systems, more complex calculations are required to assess the

probable coverage area of a proposed transmitter station.The accuracy of these calculations

for digital TV signals is being debated. 

2.1.3 VHF Stations at HAZIRA PLANT

  Security section

  Main fire station(CISF)

  Plant main gate (CISF)

  Additional fire station

  LPG C/r plant

  CO-GEN C/R plant

  Radio room satellite building

  Umbhrat valve station

  CISF control room

  Jeep DC fire

  Jeep fire

  Jeep DC

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2.2 HF COMMUNICATION

High frequency (HF) radio frequencies are between 3 and 30 MHz. Also known as the decameter

band or decameter wave as the wavelengths range from one to ten decameters (ten to one hundred

metres). Frequencies immediately below HF are denoted Medium-frequency (MF), and the nex

higher frequencies are known as Very high frequency (VHF). Shortwave (2.310 - 25.820 MHz)

overlaps and is slightly lower than HF.

ICOM M700Pro marine SSB radiotelephone

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2.2.1 Propagation characteristics

Since the ionosphere often refracts HF radio waves quite well (a phenomenon known as skywave

propagation), this range is extensively used for medium and long range radio communication

However, suitability of this portion of the spectrum for such communication varies greatly with a

complex combination of factors:

  Sunlight/darkness at site of transmission and reception

  Transmitter/receiver proximity to terminator 

  Season 

  Sunspot cycle 

  Solar activity 

  Polar aurora 

These and other factors contribute, at each point in time for a given communication path, to a

  Maximum usable frequency (MUF)

  Lowest usable high frequency (LUF) and a

  Frequency of optimum transmission (FOT)

When all factors are at their optimum, worldwide communication is possible on HF. At many other

times it is possible to make contact across and between continents or oceans. At worst, when a

band is 'dead', no communication beyond the limited groundwave paths is possible no matter what

powers, antennas or other technologies are brought to bear. When a transcontinental or worldwide

path is open on a particular frequency, digital, SSB and CW communication is possible using

surprisingly low transmission powers, often of the order of tens of watts, provided suitable

antennas are in use at both ends and that there is little or no  man-made or natural interference. On

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such an open band, interference originating over a wide area affects many potential users. These

issues are significant to military, safety and amateur radio users of the HF bands.

2.2.2 Uses

The high frequency band is very popular with amateur radio operators, who can take advantage of

direct, long-distance (often inter-continental) communications and the "thrill factor" resulting from

making contacts in variable conditions. International shortwave broadcasting utilizes this set of

frequencies, as well as a seemingly declining number of "utility" users (marine, aviation, military,

and diplomatic interests), who have, in recent years, been swayed over to less volatile means of

communication (for example, via satellites), but may maintain HF stations after switch-over for

back-up purposes. However, the development of  Automatic Link Establishment technology based

on MIL-STD-188-141A and MIL-STD-188-141B for automated connectivity and frequency

selection, along with the high costs of satellite usage, have led to a renaissance in HF usage among

these communities. The development of higher speed modems such as those conforming to MIL-

STD-188-110B which support data rates up to 9600 bit/s has also increased the usability of HF for

data communications. Other standards development such as STANAG 5066 provides for error free

data communications through the use of  ARQ protocols.

CB radios operate in the higher portion of the range (around 27 MHz), as do some studio-to-

transmitter (STL) radio links. Some modes of communication, such as continuous wave morse

code transmissions (especially by amateur radio operators) and single sideband voice transmissions

are more common in the HF range than on other frequencies, because of their bandwidth-

conserving nature, but broadband modes, such as TV transmissions, are generally prohibited by

HF's relatively small chunk of  electromagnetic spectrum space.

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Noise, especially man-made interference from electronic devices, tends to have a great effect on

the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over

"broadband over power lines" (BPL) Internet access, which is believed to have an almos

destructive effect on HF communications. This is due to the frequencies on which BPL operates

(typically corresponding with the HF band) and the tendency for the BPL "signal" to leak from

power lines. Some BPL providers have installed "notch filters" to block out certain portions of the

spectrum (namely the amateur radio bands), but a great amount of controversy over the deployment

of this access method remains. Some radio frequency identification (RFID) tags utilize HF. These

tags are commonly known as HFID's or HighFID's (High Frequency Identification).

2.2.3 Round the clock from/to Hazira plant following locations-

1.  BPA Offshore platform

2.  BPB Offshore platform

3.  Tapti Offshore platform

4.  Panna Field

5.  Juhu Helibase

6.  Vasudhara Bhavan

7.  Trombay

8.  Uran

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2.3 SATELLITE COMMUNICATIONS

In satellite communication , I have studied on ICNET( Integrated communication network) and

INMARSET Telephone. In ICNET there are two parts DAMA and PAMA.

1.  Satellite- INSAT – 3E

2.  Location – 550 East

3.  Transponder no.- 15

4.  Transponder Band width - 36 MHz

5.  Transponder center frequency – 6050/3825MHz

6.  Polarisation – Linear

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2.3.1 ICNET ( Integrated communication Network)- 

1.  Satellite based communication network 

2.  Network Control center at Uran Earth station.

3.  Data channels are operating in Permanent assigned Multiple Access (PAMA Mode).

4.  Voice channels are operating in Demand assigned multiple access modes (DAMA Mode).

This is broadly divided in two parts , DAMA and PAMA

2.3.1.1 DAMA

Demand Assigned Multiple Access (DAMA) is a technology used to assign a channel to clients

that don't need to use it constantly. DAMA systems assign communication channels based on

requests issued from user terminals to a network control system. When the circuit is no longer in

use, the channels are then returned to the central pool for reassignment to other users.

Channels are typically a pair of carrier frequencies (one for transmit and one for receive), but can

be other fixed bandwidth resources such as timeslots in a TDMA burst plan or even physical party

linechannels. Once a channel is allocated to a given pair of nodes, it is not available to other users

in the network until their session is finished.

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It allows utilizing of one channel (radio or baseband frequency,  timeslot, etc.) by many users

sequentially at different times. This technology is mainly useful with sparsely used networks of

transient clients, as opposed to PAMA (Permanently Assigned Multiple Access). By using DAMA

technology the number of separate nodes that can use a limited pool of circuits can be greatly

increased at the expense of no longer being able to provide simultaneous access for all possible

pairs of nodes. A five-channel DAMA network can only have five simultaneous conversations but

could have any number of nodes. A five-channel PAMA network permanently supports five

simultaneous conversations, with channel ownership remaining with their permanently-assigned

nodes even when idle.

DAMA and PAMA are related only to channel/resource allocation and should not be confused

intended to divide a single communication channel into multiple virtual channels. These systems

typically use resource allocation protocols that allow a more rapid (although often less

deterministic, consider CDMA collisions) near-real-time allocation of bandwidth based on demand

and data priority. However, in sparsely allocated multiple-access channels, DAMA can be used to

allocate the individual virtual channel resources provided by the multiple-access channel. This is

most common in environments that are sufficiently sparsely utilized that there is no need to add

complexity just to recover "conversation gap" idle periods.

DAMA is widely used in satellite communications, especially in VSAT systems. It is very effective

in environments comprising multiple users each having a low to moderate usage profile.

DAMA is often used in military environments due to the relative simplicity of implementation,

ease of modeling, and the fact that military usage profiles are a very good fit. In

military SATCOM, it has the added advantage that it can function in a  bent pipe environment, thus

requires no special security or coordination hardware on the satellite. This allows the master and

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slave ground stations to be upgraded repeatedly to change or improve security and compression

without requiring an expensive satellite replacement.

2.3.1.2 PAMA-

Permanently assigned multiple accesses (PAMA) is a permanently assigned frequency

channel that provides dedicated bandwidth, through which one can send data, voice or video. This

illustrates the concept of dedicated but the basic satellite resource is shared by many.

2.3.2 INMARSAT TELEPHONE

INMARSAT is an international telecommunication company found in 1979, originally as an

intergovernmental organization. It operates a fleet of 13 geosynchronous telecommunication

satellites. The company is publicly traded on the London Stock Exchange as of June 2005.

It provides telephony and data services to users worldwide via special digital radios called

‗terminals‘. These terminals contact the satellite and communicate to a ground station through a

satellite. It provides reliable communication services to a range of governments, old agencies,

media outlets and business companies which need reliable communication on their remote regions.

Inmarsat plc (LSE: ISAT) is a British satellite telecommunications company, offering global

mobile services. It provides telephony and data services to users worldwide, via portable or mobile

terminals which communicate to ground stations through

eleven geosynchronous telecommunications satellites. Inmarsat's network provides

communications services to a range of governments, aid agencies, media outlets and businesses

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with a need to communicate in remote regions or where there is no reliable terrestrial network. The

Company is listed on the London Stock Exchange and is a constituent of the FTSE 100 Index from

September 2008.

2.3.2.1 History

The company was originally founded in 1979 as the International Maritime Satellite

Organization (Inmarsat), a not-for-profit international organization, set up at the behest of

the International Maritime Organization (IMO), a United Nations body, for the purpose of

establishing a satellite communications network for the maritime community It began trading in

1982. From the beginning, the acronym "Inmarsat" was used. The intent was to create a self-

financing body which would improve safety of life at sea. The name was changed to " International

Mobile Satellite Organization" when it began to provide services to aircraft and portable users, but

the acronym "Inmarsat" was kept. When the organisation was converted into a private company in

1999, the business was split into two parts: The bulk of the organisation was converted into the

commercial company, Inmarsat plc, and a small group became the regulatory body, IMSO.In

2005 Apax Partners and Permira bought shares in the Company. The Company was also first listed

on the London Stock Exchange in that year. In March 2008 it was disclosed that U.S. hedge

fund Harbinger Capital owned 28% of the company. In July 2009, Inmarsat completed the

acquisition of a 19-per-cent stake in SkyWave Mobile Communications Inc., a provider of

Inmarsat D+/IsatM2M network services which in turn purchased the GlobalWave business from

TransCore.[7] On 15-04-2009 Inmarsat completed the acquisition of satellite communications

provider Stratos Global Corporation (Stratos) 

Inmarsat won the 2010 MacRobert Award for its Broadband Global Area Network  (BGAN)

service[8]

, overcoming the three other shortlisted companies[9]

  –  Chas. A. Blatchford & Sons Ltd

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for the Echelon hydraulic ankle-foot for amputees, Cobham Technical Services for the Minehound

dual sensor land mine detector, and Lucite International UK Ltd for the Alpha process for methyl

methacrylate. 

INMARSAT TELEPHONE

2.3.2.2 Operations

Aside from its commercial services, Inmarsat provides global maritime distress and safety

services (GMDSS) to ships and aircraft at no charge, as a public service.Services include

traditional voice calls, low-level data tracking systems, and high-speed Internet and other data

services as well as distress and safety services. The most recent of these provides GPRS-type

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services at up to 492 kbit/s via the Broadband Global Area Network (BGAN) IP satellite modem

the size of a notebook computer.Other services provide mobile Integrated Services Digital

Network (ISDN) services used by the media for live reporting on world events via videophone .The

price of a call via Inmarsat has now dropped to a level where they are comparable, and in many

cases favorable, to international roaming costs, or hotel phone calls. Voice call charges are the

same for any location in the world where the service is used. Tariffs for calls to Inmarsat country

codes vary, depending on the country in which they are placed. Inmarsat primarily uses country

code 870 (see below).

Newer Inmarsat services use an IP technology that features an always-on capability where the users

are only charged for the amount of data they send and receive, rather than the length of time they

are connected.This applies specifically to BGAN and MPDS.

The satellites are digital transponders that receive digital signals, reform the pulses, and then

retransmit them to ground stations. Ground stations maintain usage and billing data and function as

gateways to the public switched telephone network  and the Internet. 

The first (F1) and second (F2) of Inmarsat's most recent series of satellites, known as the "I4"

satellites, were launched in June and November 2005. The third and final satellite (F3) was

launched from the Cosmodrome in Kazakhstan on the 18th August 2008.These were the largest

commercial telecommunications satellites ever launched. Each satellite is equipped with a global

beam, 19 regional spot beams, and over 200 narrow spot beams.

In addition to its own satellites, Inmarsat has a collaboration agreement with ACeS regarding

handheld voice services

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2.3.2.3 Coverage

There are 3 types of coverage related to each Inmarsat satellite.  

Global beam coverage

Each satellite is equipped with a single global beam that covers up to one-third of the

Earth's surface, apart from the poles. Overall, global beam coverage extends from latitudes

of −82 to +82 degrees regardless of longitude. 

Regional spot beam coverage

Each regional beam covers a fraction of the area covered by a global beam, but collectively

all of the regional beams offer virtually the same coverage as the global beams. Use of

regional beams allow user terminals (also called mobile earth stations) to operate with

significantly smaller antennas. Regional beams were introduced with the I-3 satellites. Each

I-3 satellite provides four to six spot beams; each I-4 satellite provides 19 regional beams.

Narrow spot beam coverage

Narrow beams are offered by the three Inmarsat-4 satellites. Narrow beams vary in size

tend to be several hundred kilometers across. The narrow beams, whilst much smaller than

the global or regional beams, are far more numerous and hence offer the same global

coverage. Narrow spot beams allow yet smaller antennas and much higher data rates. They

form the backbone of Inmarsat's handheld (GSPS) and broadband services (BGAN). This

coverage was introduced with the I-4 satellites. Each I-4 satellite provides around 200

narrow spot beams.

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2.4 Non-directional beacon

A non-directional (radio) beacon (NDB) is a radio transmitter at a known location, used as an

aviation or marine navigational aid. As the name implies, the signal transmitted does not

include inherent directional information, in contrast to other navigational aids such as low

frequency radio range, VHF omnidirectional range (VOR) and TACAN. NDB signals follow the

curvature of the earth, so they can be received at much greater distances at lower altitudes, a major

advantage over VOR. However, NDB signals are also affected more by atmospheric conditions

mountainous terrain, coastal refraction and electrical storms, particularly at long range.

NDBs used for aviation are standardised by ICAO Annex 10 which specifies that NDBs be

operated on a frequency between 190 kHz and 1750 kHz,although normally all NDBs in North

America operate between 190 kHz and 535 kHz. Each NDB is identified by a one, two, or three-

letter Morse codecallsign. In Canada, some of the identifiers include numbers. North American

NDBs are categorized by power output, with low power rated at less than 50watts, medium from

50 W to 2,000 W and high being over 2,000 W.

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2.4.1 Automatic direction finder equipment

NDB navigation consists of two parts — the automatic direction finder  (or ADF) equipment on the

aircraft that detects an NDB's signal, and the NDB transmitter. The ADF can also locate

transmitters in the standard AM medium wave broadcast band (530 kHz to 1700 kHz at 10 kHz

increments in the Americas, 531 kHz to 1602 kHz at 9 kHz increments in the rest of the world).

ADF equipment determines the direction to the NDB station relative to the aircraft. This may be

displayed on a relative bearing indicator (RBI). This display looks like a compass card with a

needle superimposed, except that the card is fixed with the 0 degree position corresponding to the

centreline of the aircraft. In order to track toward an NDB (with no wind) the aircraft is flown so

that the needle points to the 0 degree position, the aircraft will then fly directly to the NDB

Similarly, the aircraft will track directly away from the NDB if the needle is maintained on the 180

degree mark. With a crosswind, the needle must be maintained to the left or right of the 0 or 180

position by an amount corresponding to the drift due to the crosswind.

When tracking to or from an NDB, it is also usual that the aircraft track on a specific bearing. To

do this it is necessary to correlate the RBI reading with the compass heading. Having determined

the drift, the aircraft must be flown so that the compass heading is the required bearing adjusted for

drift at the same time as the RBI reading is 0 or 180 adjusted for drift. An NDB may also be used

to locate a position along the aircraft track. When the needle reaches an RBI reading corresponding

to the required bearing then the aircraft is at the position. However, using a separate RBI and

compass, this requires considerable mental calculation to determine the appropriate relative

bearing.

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To simplify this task a compass card is added to the RBI to form a "Radio Magnetic Indicator"

(RMI). The ADF needle is then referenced immediately to the aircraft heading, which reduces the

necessity for mental calculation.

The principles of ADFs are not limited to NDB usage; such systems are also used to detect the

location of a broadcast signal for many other purposes, such as the location of emergency beacons.

2.4.2 Use of non-directional beacons

Airways

A bearing is a line passing through the station that points in a specific direction, such as 270

degrees (due West). NDB bearings provide a charted, consistent method for defining paths aircraft

can fly. In this fashion, NDBs can, like VORs, define "airways" in the sky. Aircraft follow these

pre-defined routes to complete a flight plan. Airways are numbered and standardized on charts

colored airways are used for low to medium frequency stations like the NDB and are charted in

brown on sectional charts. Green and red airways are plotted east and west while amber and blue

airways are plotted north and south. There is only one colored airway left in the continental United

States. It is located off the coast of North Carolina and is called G13 or Green 13. Alaska is the

only other state in the United States to make use of the colored airway systems. Pilots follow these

routes by tracking radials across various navigation stations, and turning at some. While most

airways in the United States are based on VORs, NDB airways are common elsewhere, especially

in the developing world and in lightly-populated areas of developed countries, like

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the Canadian Arctic, since they can have a long range and are much less expensive to operate than

VORs.

All standard airways are plotted on aeronautical charts, such as U.S. sectional charts, issued by

the National Oceanographic and Atmospheric Administration (NOAA).

The ability to intercept fixes is a long-used application of NDBs. A fix is a point on the surface of

the Earth. These fixes are computed by drawing lines through navigation stations until they

intersect (called "triangulation"), creating a triangle with the fix as one vertex:

Plotting fixes in this manner allows a pilot to roughly determine his horizontal location. This usage

is important in situations where other navigational equipment, such as VORs with distance

measuring equipment (DME), have failed.

2.4.3 Determining distance from an NDB station

To determine the distance in relation to an NDB station in nautical miles, the pilot uses this simple

method:

1.  Turns the aircraft so that the station is directly off one of the wingtips.

2.  Flies that heading, timing how long it takes to cross a specific number of NDB bearings.

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3.  Uses the formula: Time to station = 60 x number of minutes flown / degrees of bearing

change

4.  Uses the flight computer to calculate the distance the aircraft is from the station; time *

speed = distance.

Some NDBs have co-located DME facilities to simplify this determination.

Aeronautical chart pictogram of a non-directional beacon

2.4.4 Instrument landing systems

NDBs are most commonly used as markers for an instrument landing system (ILS) approach and

standard approaches. NDBs may designate the starting area for an ILS approach or a path to follow

for a standard terminal arrival procedure, or STAR. In the United States, an NDB is often

combined with the outer marker beacon in the ILS approach (called a Locator Outer Marker, or

LOM); in Canada, low-powered NDBs have replaced marker beacons entirely. Marker beacons on

ILS approaches are now being phased out worldwide with DME ranges used instead to delineate

the different segments of the approach. A runway which is equipped with NDB or VOR (or both)

as the only Navigation aid is called Non Precision Approach Runway and if it is equipped with ILS

is called Precision Approach Runway.

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2.4.5 Technical

NDBs typically operate in the frequency range from 190 kHz to 535 kHz (although they are

allocated frequencies from 190 to 1750 kHz) and transmit a carriermodulated by either 400 or

1020 Hz. NDBs can also be colocated with DME in a similar installation for the ILS as the outer

marker, only in this case, they function as the inner marker. NDB owners are mostly governmental

agencies and airport authorities.

Antennas have as part of their makeup a segment that consists of an inductor and a capacitor in

series "tuned" to the particular frequency or frequencies assigned to that antenna. NDB's tuned

segment is part of the antenna itself. What is viewed as the Vertical part of the antenna tends to be

the supporting pylon for the capacitive element. At low frequencies the antenna itself is capacitive.

(functions as the capacitor in the system). There is often a counterpoise (or bottom section of the

capacitor) buried in the ground underneath the antenna. The inductive section is the feedline, and

the vertical antenna element itself.

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2.5 Walkie-talkie

A walkie-talkie, or handie talkie, (more formally known as a handheld transceiver) is a hand-

held, portable, two-way radio transceiver. Its development during the Second World War has been

variously credited to Donald L. Hings, radio engineer Alfred J. Gross, and engineering teams

atMotorola. Similar designs were created for other armed forces, and after the war, walkie-talkies

spread to public safety and eventually commercial and jobsite work. Major characteristics include

a half-duplex channel (only one radio transmits at a time, though any number can listen) and a

"push-to-talk" (P.T.T) switch that starts transmission. Typical walkie-talkies resemble

a telephone handset, possibly slightly larger but still a single unit, with an antenna sticking out of

the top. Where a phone's earpiece is only loud enough to be heard by the user, a walkie-talkie's

built-in speaker can be heard by the user and those in the user's immediate vicinity. Hand-held

transceivers may be used to communicate between each other, or to vehicle-mounted or base

stations.

2.5.1 History

The first radio receiver/transmitter to be widely nick-named "Walkie-Talkie" was

the backpacked Motorola SCR-300, created by an engineering team in 1940 at the Galvin

Manufacturing Company (fore-runner of Motorola). The team consisted of Dan Noble, who

conceived of the design using frequency modulation, Raymond Yoder, Henryk Magnuski who was

the principal RF engineer, Marion Bond, Lloyd Morris, and Bill Vogel.

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SCR 320 HANDIE TAKIE

Motorola also produced the hand-held AM SCR-536 radio during World War II, and it was called

the "Handie-Talkie" (HT). The terms are often confused today, but the original walkie talkie

referred to the back mounted model, while the handie talkie was the device which could be held

entirely in the hand (but had vastly reduced performance). Both devices ran on vacuum tubes and

used high voltage dry cell batteries. (Handie-Talkie became a trademark of Motorola, Inc. on May

22, 1951. The application was filed with the U.S. Patent and Trademark Office, and the trademark

registration number is 71560123.)

Radio engineer Alfred J. Gross also worked on the early technology behind the walkie-talkie

between 1934 and 1941, and is sometimes credited with inventing it. Gross had developed and

tested a small portable high-frequency radio with two-way communications features which he

dubbed a "walkie-talkie". The device caught the attention of the U.S. Office of Strategic Services

(now the Central Intelligence Agency), which recruited him to develop the Joan-Eleanor system, a

two-way, air-to-ground radio system for covert use by troops behind enemy lines during World

War II. Also credited with the invention of the walkie talkie is Canadian inventor Donald

Hings who created a portable radio signaling system for his employer CM&S in 1937 which he

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called a "packset", but which later became known as the "walkie talkie". Hings was formally

decorated for its significance to the war effort Hing's model C-58 "Handy-Talkie" was in military

service by 1942, the result of a secret R&D effort that began in 1940.

Following World War II, Raytheon developed the SCR-536's military replacement, the AN/PRC-6

The AN/PRC-6 circuit uses 13 tubes (receiver and transmitter); a second set of 13 tubes is supplied

with the unit as running spares. The unit is factory set with one crystal and may be changed to a

different frequency in the field by replacing the crystal and re-tuning the unit. It uses a 24 inch

whip antenna. There is an optional handset H-33C/PT that can be connected to the AN/PRC-6 by a

5 foot cable. A web sling is provided.

In the mid-1970s the Marine Corps initiated an effort to develop a squad radio to replace the

unsatisfactory helmet-mounted AN/PRR-9 receiver and receiver/transmitter hand-held AN/PRT-4

(both developed by the Army). The AN/PRC-68 was first produced in 1976 by Magnavox, was

issued to the Marines in the 1980s, and was adopted by the US Army as well.

The abbreviation HT, derived from Motorola's "Handie Talkie" trademark, is commonly used to

refer to portable handheld ham radios, with "walkie-talkie" often used as a layman's term or

specifically to refer to a toy. Public safety or commercial users generally refer to their handhelds

simply as "radios". Surplus Motorola Handie Talkies found their way into the hands of ham radio

operators immediately following World War II. Motorola's public safety radios of the 1950s and

1960s, were loaned or donated to ham groups as part of the  Civil Defense program. To avoid

trademark infringement, other manufacturers use designations such as "Handheld Transceiver" or

"Handie Transceiver" for their products.

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2.5.2 Developments

Some cellular telephone networks offer a push-to-talk handset that allows walkie-talkie-like

operation over the cellular network, without dialling a call each time.

Walkie-talkies for public safety, commercial and industrial uses may be part of  trunked radio

systems, which dynamically allocate radio channels for more efficient use of limited radio

spectrum. Such systems always work with a base station that acts as a repeater and controller

although individual handsets and mobiles may have a mode that bypasses the base station.

RADIO HANDELED RECIEVER

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Walkie-talkies are widely used in any setting where portable radio communications are necessary

including business, public safety, military, outdoor recreation, and the like, and devices are

available at numerous price points from inexpensive analog units sold as toys up to ruggedized

(i.e. waterproof or intrinsically safe) analog and digital units for use on boats or in heavy industry.

Most countries, at the very least, will allow the sale of walkie-talkies for business,  marine

communications, and some personal uses such as CB radio, as well as amateur radio designs

Walkie-talkies, thanks to increasing use of miniaturized electronics, can be made very small, with

some personal two-way UHF radio models being smaller than a pack of cigarettes (though VHF

and HF units can be substantially larger due to the need for larger antennas and battery packs). In

addition, as costs come down, it is possible to add advanced squelch capabilities such

as CTCSS (analog squelch) and DCS (digital squelch) (often marketed as "privacy codes) to

inexpensive radios, as well as voice scrambling and trunking capabilities. Some units (especially

amateur HTs) also include DTMF keypads for remote operation of various devices such

as repeaters. Some models include VOX capability for hands-free operation, as well as the ability

to attach external microphones and speakers.

Consumer and commercial equipment differ in a number of ways; commercial gear is generally

ruggedized, with metal cases, and often has only a few specific frequencies programmed into it

(often, though not always, with a computer or other outside programming device; older units can

simply swap crystals), since a given business or public safety agent must often abide by a specific

frequency allocation. Consumer gear, on the other hand, is generally made to be small, lightweight

and capable of accessing any channel within the specified band, not just a subset of assigned

channels.

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Military organizations of most countries continue to use handheld radios for a variety of purposes.

Modern units such as the AN/PRC-148 Multiband Inter/Intra Team Radio (MBITR) can

communicate on a variety of bands and modulation schemes and include encryption capabilities.

Amateur radio

Walkie-talkies (also known as HTs or "handheld transceivers" ) are widely used among  amateur

radio operators. While converted commercial gear by companies such as Motorola are not

uncommon, many companies such as Yaesu, Icom, and Kenwood design models specifically for

amateur use. While superficially similar to commercial and personal units (including such things as

CTCSS and DCS squelch functions, used primarily to activate amateur radio repeaters), amateur

gear usually has a number of features that are not common to other gear, including:

  Wide-band receivers, often including radio scanner functionality, for listening to non-amateur

radio bands.

  Multiple bands; while some operate only on specific bands such as 2 meters or 70 cm, others

support several UHF and VHF amateur allocations available to the user.

  Since amateur allocations usually are not channelized, the user can dial in any frequency

desired in the authorized band.

  Multiple modulation schemes: a few amateur HTs may allow modulation modes other than FM

including AM, SSB, and CW, [4][5]

 and digital modes such as radioteletype or PSK31. Some

may have TNCs built in to support packet radio data transmission without additional hardware.

A newer addition to the Amateur Radio service is Digital Smart Technology for Amateur Radio

or D-STAR. Handheld radios with this technology have several advanced features, including

narrower bandwidth, simultaneous voice and messaging, GPS position reporting, and callsign

routed radio calls over a wide ranging international network.

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As mentioned, commercial walkie-talkies can sometimes be reprogrammed to operate on amateur

frequencies. Amateur radio operators may do this for cost reasons or due to a perception that

commercial gear is more solidly constructed or better designed than purpose-built amateur gear.

Personal use

The personal walkie-talkie has become popular also because of the U.S. Family Radio

Service (FRS) and similar unlicensed services (such as Europe's PMR446 and Australia's UHF CB)

in other countries. While FRS walkie-talkies are also sometimes used as toys because mass-

production makes them low cost, they have propersuperheterodyne receivers and are a useful

communication tool for both business and personal use. The boom in unlicensed transceivers has,

however, been a source of frustration to users of licensed services that are sometimes interfered

with. For example, FRS and GMRS overlap in the United States, resulting in substantial pirateuse

of the GMRS frequencies. Use of the GMRS frequencies (USA) requires a license; however most

users either disregard this requirement or are unaware. Canada reallocated frequencies for

unlicensed use due to heavy interference from US GMRS users. The European PMR446 channels

fall in the middle of a United States UHF amateur allocation, and the US FRS channels interfere

with public safety communications in the United Kingdom. Designs for personal walkie-talkies are

in any case tightly regulated, generally requiring non-removable antennas (with a few exceptions

such as CB radio and the United States MURS allocation) and forbidding modified radios.

Most personal walkie-talkies sold are designed to operate in UHF allocations, and are designed to

be very compact, with buttons for changing channels and other settings on the face of the radio and

a short, fixed antenna. Most such units are made of heavy, often brightly colored plastic, though

some more expensive units have ruggedized metal or plastic cases. Commercial-grade radios are

often designed to be used on allocations such as GMRS or MURS (the latter of which has had very

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little readily available purpose-built equipment). In addition, CB walkie-talkies are available, but

less popular due to the propagation characteristics of the 27 MHz band and the general bulkiness of

the gear involved.

Personal walkie-talkies are generally designed to give easy access to all available channels (and, if

supplied, squelch codes) within the device's specified allocation.

Personal two-way radios are also sometimes combined with other electronic devices; Garmin's

Rino series combine a GPS receiver in the same package as an FRS/GMRS walkie-talkie (allowing

Rino users to transmit digital location data to each other) Some personal radios also include

receivers for AM and FM broadcast radio and, where applicable, NOAA Weather Radio and

similar systems broadcasting on the same frequencies. Some designs also allow the sending of text

messages and pictures between similarly equipped units.

While jobsite and government radios are often rated in power output, consumer radios are

frequently and controversially rated in mile or kilometer ratings. Because of the line of

sight propagation of UHF signals, experienced users consider such ratings to be wildly

exaggerated, and some manufacturers have begun printing range ratings on the package based on

terrain as opposed to simple power output.

While the bulk of personal walkie-talkie traffic is in the 27 MHz area and in the 400-500 MHz area

of the UHF spectrum, there are some units that use the 49 MHz band (shared with cordless phones

baby monitors, and similar devices) as well as the 900 MHz band; in the US at least, units in these

bands do not require licenses as long as they adhere to FCC power output rules. A company

called TriSquare is, as of July 2007, marketing a series of walkie-talkies in the United States based

on frequency-hopping spread spectrumtechnology operating in this frequency range under the

name eXRS (eXtreme Radio Service — despite the name, a proprietary design, not an official

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allocation of the US FCC). The spread-spectrum scheme used in eXRS radios allows up to 10

million virtual "channels" and ensures private communications between two or more units.

Recreation

Low-power versions, exempt from licence requirements, are also popular children's toys. Prior to

the change of  CB radio from licensed to "permitted by part" (FCC rules Part 95) status, the typical

toy walkie-talkie available in North America was limited to 100 milliwatts of power on transmit

and using one or two crystal-controlled channels in the 27 MHzcitizens' band using amplitude

modulation (AM) only. Later toy walkie-talkies operated in the 49 MHz band, some

with frequency modulation (FM), shared with cordless phones and baby monitors. The lowest cost

devices are very simple electronically (single-frequency, crystal-controlled, generally based on a

simple discrete transistor circuit where "grownup" walkie-talkies use chips), may

employ superregenerative receivers, and may lack even a volume control, but they may

nevertheless be elaborately decorated, often superficially resembling more "grown-up" radios such

as FRS or public safety gear. Unlike more costly units, low-cost toy walkie-talkies may not have

separate microphones and speakers; the receiver's speaker sometimes doubles as a microphone

while in transmit mode.

An unusual feature, common on children's walkie-talkies but seldom available otherwise even on

amateur models, is a "code key", that is, a button allowing the operator to transmit  Morse code or

similar tones to another walkie-talkie operating on the same frequency. Generally the operator

depresses the PTT button and taps out a message using a Morse Code crib sheet attached as a

sticker to the radio; however, as Morse Code has fallen out of wide use outside amateur radio

circles, some such units either have a grossly simplified code label or no longer provide a sticker at

all.

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In addition, personal UHF radios will sometimes be bought and used as toys, though they are not

generally explicitly marketed as such (but seeHasbro's ChatNow line, which transmits both voice

and digital data on the FRS band).

2.5.3 Specialized uses

In addition to land mobile use, walkie-talkie designs are also used for marine

VHF and aviation communications, especially on smaller boats and aircraft where mounting a

fixed radio might be impractical or expensive. Often such units will have switches to provide quick

access to emergency and information channels.

Intrinsically safe walkie-talkies are often required in heavy industrial settings where the radio may

be used around flammable vapors. This designation means that the knobs and switches in the radio

are engineered to avoid producing sparks as they are operated.

2.5.4 Accessories

There are various accessories available for walkie talkies such as rechargeable batteries, drop in

rechargers, multi-unit rechargers for charging as many as six units at a time, and an audio

accessory jack that can be used for headsets or speaker microphones.[6]

 

When headsets are used with voice activation (VOX) capability the user can talk with hands free

operation. Several types of audio accessories are available such as speaker microphones that clip

near the ear, security type earpieces with a pendant push-to-talk switch and a built-in microphone,

a headset that has a push-to-talk switch earbud that looks more like what you would find on a

music player, or a single-ear lightweight behind-the-head headset with boom microphone and

pendant push-to-talk switch similar to that worn by a telephone call center agent.

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2.5.5 Facilities at Hazira plant- 

1.  VHF Fixes – 11 sets

2.  VHF Mobile – 3 sets

3.  Walkie Talkie sets – 65 sets

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2.6 RADIO PAGING

2.6.1 Paging

Paging is a means of sending a digital coded signal to a radio receiver known as a Pager which

is carried by a service user. The signal can be simple causing the pager to just beep, or more

complex, transmitting numeric characters or even more complex to show alphanumeric text

messages on pager up to 400 characters at a time.

The pager contains a digital radio receiver permanently tuned in to a single radio

frequency. When the unit is manufactured, it is given a unique identity called the Radio

Identification Code (RIC). This code is transmitted to alert the pager which responds when it

recognizes its own identity.

Radio paging can be considered as a subset of paging. It is a pocket sized

radio receiver capable of alerting its holder of a phone call, either from a displayed number or to a

predestined number.

2.6.2 Facility in Hazira Plant-

1.  The system is Motorola ―People Finder LT/PLUS‖. 

2.  Capacity- 999 individuals or maximum 75 in a group/subgroup.

3.  Two groups are operational, GP no. 700(gen) and GP no. 100(DMP). One way

alphanumeric communication through operator no. 5515.

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4.  Paging can be done through telephone set by dialing 5525 along with pager number and

numeric message (i.e. contact number), then press #1 (voice guided).

5.  It is being used as an emergency communication in the plant.

RADIO PAGER

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2.7 CONCLUSION

Hence the term "wireless" has become a generic and all-encompassing word used to describe

communications in which electromagnetic waves or RF (rather than some form of wire) carry a

signal over part or the entire communication path. Common examples of wireless equipment in use

today include:

  Professional LMR (Land Mobile Radio) and SMR (Specialized Mobile Radio) typically used

by business, industrial and Public Safety entities.

  Consumer Two Way Radio including FRS (Family Radio Service), GMRS (General Mobile

Radio Service) and Citizens band ("CB") radios.

  The Amateur Radio Service (Ham radio).

  Consumer and professional Marine VHF radios. 

  Cellular telephones and pagers: provide connectivity for portable and mobile applications, both

personal and business.

  Global Positioning System (GPS): allows drivers of cars and trucks, captains of boats and

ships, and pilots of aircraft to ascertain their location anywhere on earth.

  Cordless computer peripherals: the cordless mouse is a common example; keyboards and

printers can also be linked to a computer via wireless.

  Cordless telephone sets: these are limited-range devices, not to be confused with cell phones.

  Satellite television: allows viewers in almost any location to select from hundreds of channels.

  Wireless gaming: new gaming consoles allow players to interact and play in the same game

regardless of whether they are playing on different consoles. Players can chat, send text

messages as well as record sound and send it to their friends.

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  2.8 REFERENCES 

  http://en.wikipedia.org/wiki/Inmarsat  

  http://en.wikipedia.org/wiki/Very_high_frequency  

  http://en.wikipedia.org/wiki/High_frequency  

  http://en.wikipedia.org/wiki/Non-directional_beacon  

  http://en.wikipedia.org/wiki/Pager  

  http://en.wikipedia.org/wiki/Walkie-talkie