Presented by: Laxman Ram Suthar

Submitted to :Ms. Laxmi Choudhary(Training seminar

coordinator)

History of ALL INDIA RADIO

In British India broadcasting started in June 1923 with programs by the Radio Club of Bombay. Then, by an agreement of 1926 the private Indian Broadcasting Company (IBC) was granted permission to operate two radio stations; the Bombay station was inaugurated on July 23, 1927, the Calcutta station followed on August 26, 1927. But already on March 1, 1930 the Company went into liquidation. Thus the Government took over the broadcasting facilities, starting the Indian State Broadcasting Service (ISBS) on April 1, 1930 (on experimental basis for two years, but continued in May 1932). On June 8, 1936 the ISBS was renamed All India Radio (AIR; also known as Akashvani since 1956).

Principles Of All India Radio Transmitting A radio wave carries information

signal; Signals are converted into electrical signals. A carrier wave is then produced from the modulation. The wave is then amplified, and sent to the antenna that then converts signal into an E.M. wave.

Receiving An antenna on receiving the signal

send it to the receiver this then converts the electrical signal sends it to the amplifier either a speaker/headphones jack this is then converted into a sound wave.

In Realty it works like this:

Phase 1:

Baseband Or the Original signal message signal

Phase 2 : After

carrier being sent then modulating siganl

•Studio center•Broadcast station•Mixing•Control room•Recording room•Dubbing room

Microphone

Microphone is a device which converts acoustical energy into electrical energy. In the professional broadcasting field microphones have primarily to be capable of giving the highest fidelity of reproduction over audio bandwidth.•The first type of studio microphone is the condenser microphone.•The second type of studio microphone is dynamic microphone. •The third major type of studio microphone is the ribbon microphone.

Classification of microphone

Pressure Operated Type: In such microphones only one side of the diaphragm is exposed to the sound wave. The output voltage is proportional to the sound pressure on the exposed face of the diaphragm with respect to the constant pressure on the other face. Moving coil, carbon, crystal and condenser microphones are mostly of this type. In their basic forms, the pressure operated microphones are Omni-directional.

Velocity or Pressure Gradient Type: In these microphones both sides of the diaphragm are exposed to the sound wave. Thus the output voltage is proportional to the instantaneous difference in pressure on the two sides of the diaphragm.

Design of Microphone

Microphones can be designed either to respond equally to sounds from an angle or to discriminate those arriving from specific directions. Microphones which respond equally at all angles are called Omni-directional. The microphones which pick up equally from front and rear and have very little pick up equally from sides are called Bi-directional and have a polar diagram as figure of eight. The microphones which pick up maximum from the front with slight reduction in the sides and very less pick up from the rear are called C

ardioids (means heart shape).

Condenser Microphone. This is the simplest type of all

studio microphones. They work by converting signals caused by acoustic energy to electrical energy resulting in a stronger signal.

Condenser microphones use energy from the studio’s mixing station or from a battery supply to operate.

Dynamic Microphone

These are the kind of microphones that generate signals by a conductor which is in magnetic field being in motion.

The majority of microphones that fall under the dynamic microphone category have a light, very thin diaphragm that gets in motion responding to the pressure of the sound it is exposed to. The motion creates voice coils which are suspended to magnetic fields, making the fields to move which in turn creates electric currents in small quantities.

Majority of dynamic studio microphone can operate without external power supply.In many occasions dynamic microphones are used in studios to record drums, electric guitars and the like.

Ribbon Microphone: a velocity microphone, which means that such usually respond to the velocity of the air that is produced by the sound rather than the level of the pressure caused by the sound which many other microphones respond to.

Ribbon microphones operate by suspending loosely small elements in a magnetic field that is quite strong. The “ribbon” is put to motion by the moving air thus cutting through the magnetic fields which in turn creates audio signals. Typically, have pick up patterns making a figure 8.

Frequency Response . Frequency response of a microphone depends on:-

Direction of arrival of sound, and

Distance between the source and the microphone

Directivity

Termination Impedance and sensitivity

Termination Impedance The microphone must have proper impedance and

a balanced or unbalanced output suited to the pre-amplifier. In the broadcast chain the microphone lines cover long distances, therefore, the impedance is chosen in the range of 50 ohms to 60 ohms at the microphone terminals

Sensitivity: The ability to pick up weak sound and to deliver more electrical signal determines the sensitivity. It is measured in dBs below 1 volt as the electrical output from a microphone when a standard sound pressure of one microbar i.e. 1 dyne per sqr. cm. is applied at the diaphragm of the microphone

Placement of Microphone

Placement of microphone has important bearing on the quality of its output. A few general guidelines given in the following paragraphs should help in improvement of programme production.

Microphones should be placed with its 0o axis facing the source of sound to avoid off axis coloration.

Phasing of Microphone: Whenever two or more microphones are used with their outputs mixed together, it should be ensured that their outputs are in phase.

Working Distance: Whenever a directional microphone is kept fairly close to the source of sound low frequencies in the output of the microphone may get disproportionately boosted thereby giving rise to boom sound. This effect known as proximity effect. This effect should be normally avoided by placing the microphones fairly away (30-45 cm) from the source of sound.

Electronic System

The Recording Chain: A correct amount of HF boost is provided to pre compensate for the HF record process losses as described earlier. It converts constant voltage input into constant current output. This is required because the record head is a current operated device and the magnetic flux is proportional to the current flowing in the record head coil.

The Playback Chain: The output of the PB head is rather low and rising with frequency. Great care is taken in electrically and magnetically shielding the P.B. Head to avoid hum pick up.

Antenna system of FM transmitter

Antenna system of FM Transmitter

A tower of good height is required for mounting the FM antenna since the coverage of the transmitter is proportional to the height of the tower. For a 100 m height, the coverage is about 60 km. Wherever new towers were to be provided, generally they are of 100 m height since beyond this height; there is steep rise in their prices because of excessive wind load on the top of the tower.

The main requirements of the antenna to be used for FM transmitters are :

  Wide-band usage from 88 to 108 MHz range. Omni-directional horizontal pattern of field strength. Circular polarization for better reception. High gain for both vertical and horizontal signals. Two degrees beam tilt below horizontal Sturdy design for maintenance-free service.

Basic Components of AM receiver

1) An antenna, to receive the electromagnetic waves and convert them back to electrical signals

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

3) A detector (diode) , to get rid of the high-frequency signal but keep the low-frequency part.

4) An amplifier, to make the signal bigger 5) A speaker, to produce the sound that we can hear

Amplification part

The signals that we pick up with the antenna and tuner are very small -- maybe only a few thousandths of a volt. (A regular flashlight battery is 1 ½ volts). So, the amplifier makes the signal bigger. In our radios, we will two little things called “integrated circuits”, or “chips”, to make the signal bigger. There are a lot of different kids of integrated circuits. The kind that we will use are called “op-amps”, or “operational amplifiers”. Each op-amp looks like little spiders with 8 legs! We will use 2 of them in each radio. It simply produces a more powerful version of the audio signal.

Advantage OF FM over AM•AM is much looser than the FM signal meaning that less data can be sent at one time as it isn’t compressed. •All the transmitted power in FM is useful whereas in AM most of it is in the carrier which contains no useful information. •Better Noise Performance•Less adjacent- channel interference•FM broadcasts operate in the VHF and UHF ranges in which there happens to be less noise than in the MF and HF ranges occupied by AM bands.

•Stereo transmission is possible with FM due to its wider bandwidth

Advantage Of Radio station

o This is only means which can provide multi access two way communication.

o The cost of transmitting information through satellite is independent of

distance involved.o Satellites are capable of handling

very high bandwidth.o It is possible to provide large

coverage using satellite.

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QUERIES ??? (if any..)

Thank you