Slide 1

Name #ateeq ur rehmanElectronic engineering email ateequrrehman1604@gmail.com

COMMUNICATION SYSTEMS USED IN RADIO STATIONThe points we have to discuss is given below: 1. Radio communication Radio broadcasting2. Communication process used in radio stationInformation source Transmission equipmentReceiving equipmentAntennas4. AM Vs FM5. Difference between AM and FM

3

RADIO COMMUNICTIONRadio or radio communication means any transmission, emission, or reception of signs, signals, writing, images, sounds or intelligence of any nature by means of electromagnetic waves of frequencies lower than three thousand gigacycles per second (3000 GHz) propagated in space without artificial guide.Examples of radio communication systems:Radio broadcasting.TV broadcasting.Satellite communication.Mobile Cellular Telephony.Wireless LAN.Multimedia communication & Mobile Internet

4

HISTORY1864: Maxwell describes radio wave mathematically1888: Hertz generates radio waves1890: Detection of radio waves1896: Marconi makes the first radio transmission1915: Radio tubes are invented1948: Shannons law1948: Transistor1960: Communication Satellites1981: Cellular technology

COMMUNICATION PROCESSThe process of sharing information between the transmitter and receiver is called communication process.The combination of different equipments required for communication is called communication system.Types of communication systems Radio , TV broadcasting Satellite system Cellular phones Computer networks(LANs , WANs)

BLOCK DIAGRAM OF COMMUNICATION PROCESSInput transducertransmitterchannelreceiverOutputtransducer

noise

Speech picture/data

Information in Electrical form

Informationsource

INFORMATION SOURCEThe source which is responsible for originating the information or message signal is called information source.In radio broadcasting system the information source is the person setting in the control room of radio station.

TRANSMISSION EQUIPMENTS

Input transducerAudio processorOscillator Amplifierantennas

INPUT TRANSDUCERA transducer is a device which convert energy from one form to another formUsually our message signal is not in electrical form .so we must have to convert it to electrical form for efficient communication.In radio broadcasting system a microphone is a transducer which convert sound signal into electrical signal.

INPUT TRANSDUCER conti..

AUDIO PROCESSOR

The audio processor ensures that the amplitude of the audio signal does not exceed a certain limit. Without a processor the signal can become over- modulated Which decreases the quality of the resulting radio signal and can cause splatter on other frequencies.

AN OSCILLATOR

provides a source of repetitive A.C. signal across its output terminals without needing any input (except a D.C. supply). The signal generated by the oscillator is usually of constant amplitude.The frequency of the output wave may be fixed or variable, depending on the oscillator design.

Frequency of oscillations

Here we require a frequency between

88 MHz to 108 MHz

Tank circuit

PRE-AMPLIFIER electronicamplifieror (informally) amp is an electronic device that can increase thepowerof a signal (a time-varying voltage or current). Anamplifierfunctions by takingpowerfrom apower supply and controlling the output to match the input signal shape but with a larger amplitude.Input Output

WHYPRE-AMPLIFIER? when source and destination are far away from each other. In this situation a pre-amp can be helpful so that the noise that is picked up on the line to the power amp is minimum compared to the signal itself.Another situation is if you were going to be performing some filtering on a signal. All of the filtering elements can add noise to your system and by adding a preamp the noise in the filtering is minimized compared to the signalYou may still wonder why not just use a power amp? Power amps are more difficult to directly change the volume on while a preamp is much easier. So you can change your volume on the pre amp and have a fixed gain on the power amp.

PRE-AMPLIFIER OUTPUT

Input audio signal

Amplified output

ANTENNAAn antenna (or aerial) is an electrical device which converts electric power into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiverTypes of AntennasWire Antennas Half-wave dipole antenna. Short Dipole Antenna Monopole Antenna Loop AntennaTravelling Wave AntennasMicrowave AntennasReflector Antennas

WIRE ANTENNAS

Wire antennas are also known as linear or curved antennas. These antennas are very simple, cheap and are used in a wide range of applications.The dipole antenna is cut and bent for effective radiation. The length of the total wire, which is being used as a dipole, equals half of the wavelength (i.e., l = /2). Such an antenna is called ashalf-wave dipole antenna. This is the most widely used antenna because of its advantages. It is also known asHertz antenna.

ADVANTAGES & DISADVANTAGES

advantagesdisadvantagesInput impedance is not sensitive.Matches well with transmission line impedance.Has reasonable length.Length of the antenna matches with size and directivity.

Not much effective due to single element.It can work better only with a combination

WIRE ANTENNAS conti.. loop antenna

Half wave dipole

Dipole antenna

NOISENoise is typically narrow spikes of voltage with lots of harmonics and other high frequency components that add to a signal, interferes with it and sometimes, completely damages the signal information. Techniques for noise overcoming:Limiter circuits

USE OF LIMITER CIRCUITS:Limiter circuits can be embedded into FM transmitters to deliberately restrict the amplitude of received signals. This is based on the fact that FM signals have constantmodulated carrier amplitude. Any amplitude variations occurring on the FM signal areeffectively clipped by these circuits. This amplitude variation in turn does not affect the information content of the FM signal, since it is contained solely within the frequencyvariations of the carrier.

PRE-EMPHASIS:Noise can interfere with an FM signal and particularly with the high-frequency components of the modulating signal. This technique is used to overcome these high frequency noises. A simple high-pass filter can serve as a transmitters pre-emphasiscircuit.

RECEIVER EQUIPMENT An antenna A tuner A detector (diode) An amplifier A speaker

AN ANTENNA

to receive the electromagnetic waves and convert them back to electrical signals

TUNER

to select out the particular carrier frequency that we want, corresponding to a particular radio station that we are interested in listening to

variable tuningcapacitor (150pF)

DETECTOR (DIODE)to get rid of the high-frequency signal but keep the low-frequency part

AN AMPLIFIER

electronicamplifieror (informally) amp is an electronic device that can increase thepowerof a received signal.The incoming radio signal from the antenna is passed through a tenable RF band pass filter to attenuate some unwanted signals, amplified in a radio frequency amplifier, and mixed with a sine wave produced by a local oscillator.

A SPEAKER

speaker (output transducer) an electronic device which convert electrical signal back to sound signal which we ca hear.

AM vs. FM

AM requires a simple circuitvery easy to generate It is simple to tune is used in almost all short wave broadcasting. The area of coverage of AM is greater than FM However, it is quite inefficient, and is susceptible to static and other forms of electrical noise.

The main advantage of FM is its audio quality and immunity to noise. Most forms of static and electrical noise are naturally AM, and an FM receiver will not respond to AM signals.

AM VS. FM conti

The audio quality of a FM signal increases as the frequency deviation increases (deviation from the center frequency), which is why FM broadcast stations use such large deviation. The main disadvantage of FM is the larger bandwidth it requires

Difference between AM and FM

FM can be filtered out when the tune received by receiver but in AM not.The AM signal can be changed And difficult to get information form it but in FM is constant. AM is taken In low Frequency and not stereo but FM taken in high frequency and its stereo.AM can received as a analog but FM can be received as Digital.The Amplitude of Income will be muted in FM if its not that much strong enough, but in AM whether its strong or not.