Advantages of FM over AM for Sound Signal Transmission

Frequency modulation has the following advantages over amplitude modulation- Noise Reduction, Transmitter Efficiency, Less adjacent Channel and co-channel Interference etc.

The greatest advantage of FM is its ability to eliminate noise interference and thus increase the signal to noise ratio. In FM, amplitude variations of the modulating (message) signal cause frequency deviations and not a change in the amplitude of the carrier. Noise interference results in amplitude variations of the carrier and thus it can be easily removed by the use of amplitude limiters. The amplitude limiter in the FM section of the receiver works on the principle of passing the stronger signal and eliminating the weaker. In this manner, a relatively weak interfering signal (as sound signals  generated at nature has low frequency) or any pick-up from a co-channel station (a station operating at the same carrier frequency) gets eliminated in a FM system.

In an FM receiver, if two signals are being received simultaneously, the weaker signal will be eliminated almost entirely if it possesses less than half the amplitude of the other stronger signal. However, in AM the interfering signal or station can be heard or received even when a 100 : 1 relationship exists between their amplitudes.

The amplitude of the FM wave is independent of the depth of modulation, whereas in AM it is dependent on this parameter. This means that low level modulation can be used in FM and all succeeding amplifiers can be class ‘C’ which are more efficient. Thus, unlike AM, all amplifiers handle constant power and this results in more economical FM transmitters.

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The Evolution and Impact of Television: From its Origins to Modern Applications

The name 'Television' comes from the Greek word 'tele' (= far) and the Latin word 'visionis' (from videre = to see) which means 'to see from a distance'. The fundamental aim of a television system is to extend the sense of sight beyond its natural limits, along with the sound associated with the scene being televised. Essentially, then, a TV system is an extension of the science of radio communication with the additional complexity that besides sound, the picture details are also to be transmitted.

The first demonstration of actual television was given by J.L. Baird in the UK and C.F. Jenkins in the USA around 1927. However, the real breakthrough occurred with the invention of the cathode ray tube and the success of V.K. Zworykin of the USA in perfecting the first camera tube

In the absence of any international standards, three monochrome ( black and white) systems grew independently. These are the 525 line American, the 625 line European and the 819 line French systems. When both the quality of reproduction and the cost of equipment are taken into account, it is difficult to definitely establish the superiority of any one of these systems over the other two. This naturally prevents direct exchange of programme between countries using different television standards. Committee on radio and television (CCIR) efforts for changing to a common 625 line system by all concerned proved ineffective and thus all the three systems have apparently come to stay. The inability to change over to a common system is mainly due to the high cost of replacing both the transmitting equipment and the millions of receivers already in use. The three different standards of black and white television have resulted in the development of three different systems of color television such as - SECAM, PAL and NTSC.

Each television broadcast station is assigned a channel bandwidth of 7 MHz (6 MHz in the American, 8 MHz in the British and 14 MHz in the French systems).In the earlier days TV broadcast was confined to assigned VHF bands of 41 to 68 MHz and 174 to 230 MHz. Later additional channel allocations have been made in the UHF band between 470 and 890 MHz. 

Applications of Television:

Impact of television is far and wide and has opened new avenues in diverse fields like public entertainment, social education, mass communication, newscasts, weather reports, political organization and campaigns, security(CCTV), live streaming, announcements and guidance at public places like airport terminals, sales promotion and many others.

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An Introduction to Oscillators: Their Functionality, Types, and Application

Oscillator is the basic element of ac signal sources and generates ac signals of known frequency and amplitude. The main applications of oscillators are as sinusoidal waveform sources in electronic measurement work. To generate ac voltage, the circuit is supplied energy from a dc source. That is why, although an oscillator can be considered as generating sinusoidal signal, it is to be noted that it merely acts as an energy converter, It converts a dc source of supply to alternating current of desired frequency. 

Oscillators are generally an amplifier with positive feedback. An oscillator has a gain equal to or slightly greater than unity. In the feedback path of the oscillator, capacitor, inductor or both are used as reactive components. In addition to these reactive components, an operational amplifier or bipolar transistor is used as amplifying device. No external ac input is required to cause the oscillator to work as the dc supply energy is converted by the oscillator into ac energy.

Oscillators can be classified in a number of ways. They can be classified based on:
   (a) the design principle used 
   (b) the frequency range over which they are used and
   (c) the nature of generated signals.

1. Classification According to Design Principle
   (a) Positive feedback oscillators 
   (b) Negative feedback oscillators

2. Classification According to Frequency Band of the Signals
  (a) Audio Frequency (AF) oscillators—frequency rage is 20 Hz to 20 kHz
  (b) Radio Frequency (RF) oscillators—frequency range is 20 kHz to 30 MHz
  (c) Video Frequency oscillators—frequency range is dc to 5 MHz
  (d) High Frequency (HF) oscillators—frequency range is 1.5 MHz to 30 MHz
  (e) Very High Frequency (VHF) oscillators—frequency range is 30 MHz to 300 MHz

3. Classification According to Types of Generated Signals

  (a) Sinusoidal Oscillators: These are known as harmonic oscillators and are generally LC tuned-feedback or RC tuned-feedback type oscillator that generates a sinusoidal waveform which is of constant amplitude and frequency.

  (b) Non-sinusoidal Oscillators: These are known as relaxation oscillators and generate complex non-sinusoidal waveforms that changes very quickly from one condition of stability to another such as square-wave, triangular-wave or sawtooth-wave-type waveforms.

The oscillators have a variety of applications. In some applications we need voltages of low frequencies, in others of very high frequencies. For example to test the performance of a stereo amplifier, we need a signal of variable frequency in the audio range (20 Hz-20 KHz). Next to amplifiers, oscillators are the most important analog circuit block. Oscillators can be found in almost every imaginable electronic system. For example all radio receiving systems must have a local oscillator. All transmitting systems require oscillators to define the carrier frequency. Similarly, most digital systems are clocked and require a master clock oscillator to operate. Signal sources, which are essential for testing electronic systems are also precise oscillators whose frequency and amplitude can be accurately set according to the requirement. A working knowledge of oscillators, their construction and operating characteristics is therefore essential to analog electronics. This module is intended to introduce the reader to oscillator types, their characteristics and considerations for their behaviour.

A few basic requirements for an oscillatory circuit are:

1. The circuit should contain a reactive or frequency dependent component—either an Inductor (L) or a Capacitor (C) and a dc supply voltage.

2. Overall gain of the amplifier circuit must be at least unity.

3. Self-regenerative or positive feedback results oscillations.

4. Oscillations of the circuit become damped due to circuit losses.

5. To overcome these circuit losses, voltage amplification is necessary.

6. Desired oscillations can be maintained by using some part of the output voltage as feedback to the tuned circuit that is of the correct amplitude and in-phase (0°).

7. To keep the output signal in phase with the input, the overall phase shift of the circuit must be zero.

In conclusion, oscillators are a crucial component in the field of electronics. They are used to generate AC signals of known frequency and amplitude and have a wide range of applications, from testing electronic systems to defining the carrier frequency in transmitting systems. A working knowledge of oscillators, their construction, and operating characteristics is essential to analog electronics.

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