SUPER HETERODYNE

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hi, plz allow me to downlaod this

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4/1/2012 1 Presentation on… Super Heterodyne D K Borah STS BSF Bangalore

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Introduction:- Word heterodyne is the combination of two words i.e. Hetero and Dyne The word heterodyne is derived from the Greek roots Hetero – “different” and Dyne – “power 4/1/2012 2

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History:- The original heterodyne technique was pioneered by Canadian inventor Reginald Fessenden. But it was not pursued far because local oscillators available at the time were unstable in their frequency output The superheterodyne principle was revisited in 1918 by U.S. Army Major Edwin Armstrong in France during world war-I. 4/1/2012 3

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What heterodyning is:- To heterodyne means to mix two frequencies together so as to produce a beat frequency , namely IF, the difference between the two. Normally the beat frequency is associated with the lower side-band, the difference between the two. 4/1/2012 4

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What super heterodyning is:- When we use the lower side-band (the difference between the two frequencies), it means we are superheterodyning . Strictly speaking, the term superheterodyne refers to creating a beat frequency that is lower than the original signal. 4/1/2012 5

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Superheterodying purposely mix two frequencies in the receiver, so as to reduce the signal frequency for further processing. It is a type of receivers, in where the received signal is transformed into a fixed intermediate frequency signal for further amplification. 4/1/2012 6

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Different stages of super heterodyne receiver:- 4/1/2012 7 RF Amplifier Mixer or 1 st Detector Local oscillator IF Amplifier 2 ND Detector or demodulator &1 st AF Amplifier AF Power Amplifier

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4/1/2012 8 How it works

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4/1/2012 9 Ant. RF Amplifier Mixer Filter IF Amplifier AF Amplifier and Demodulator AF Power amplifier speaker Local oscillator Radio Frequency (RF) Amplifier section: This section performs two major tasks: It couples the antenna voltage to the converter of the of the receiver. It accepts only desired frequency and reject all other spurious signal It amplify the desired signals and increase the signal to noise ratio for efficient operation.

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4/1/2012 10 Ant. RF Amplifier Mixer Local oscillator To filter Mixer or 1 st Detector stage:- The main objective of the superheterodyne receiver is to produce a constant Intermediate Frequency most commonly used frequency is 455 kHz in commercial broadcast band radio sets which is suitable for:- gaining efficiency of the electronic circuit as far as its amplification is concerned providing uniform sensitivity

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4/1/2012 11 Ant. RF Amplifier Mixer Local oscillator To filter So a Local Oscillator and a Mixer circuit are combined, where, by the process of 'heterodyning', the 'Intermediate Frequency (IF)' is obtained. If the RF Amplifier section selects and amplify a signal of 800 kHz, then the local oscillator produces a frequency of 1255 kHz. By mixing both the frequencies at the mixer stage, a difference of frequency of the value 455 kHz is obtained (1255-800=455 kHz). 800khz 1255khz

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4/1/2012 12 Fixed Filter Of 455 khz Mixer Local oscillator Ant. RF Amplifier 1.Vividh bharti 800khz 2.Akashwani Jaipur 1000khz 1255khz 1455khz 1255khz – 800khz = IF 455khz 1455khz – 1000khz= IF 455khz Concept behind the superheterodyne .

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4/1/2012 13 IF 455KHZ Mixer Fixed narrow band Filter Local oscillator Ant. RF Amplifier TO IF Amplifier Filter stage :- Here a fixed narrow band IF filter is used or design not only to filter 455khz IF but also to eliminate distortions, harmonics or undesired information presents in signal before amplification. Just because of this we can get true replica in audio out put.

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4/1/2012 14 4/1/2012 Ant. RF Amplifier Mixer Filter IF Amplifier AF Amplifier or Demodulator Local oscillator IF Amplifier:- To The 455 kHz IF is fed to the IF amplifier IF amp. section is designed and tuned i n such a way so that it gives the optimum gain at that particular IF IF 455Khz

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4/1/2012 15 4/1/2012 o Ant. RF Amplifier Mixer Filter IF Amplifier AF Amplifier & Demodulator AF Power amplifier Local oscillator To Now the level of AF (audio frequency) is low. So we have to amplify it. Because of this reason 1 st AF Amp is placed and f ed to AF power amplifier stage Demodulator & 1 st audio amp. stage:- The main function of demodulator is demodulate the signal to detect intelligence (AF )or information from IF (carrier).

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4/1/2012 16 4/1/2012 Ant. RF Amplifier Mixer Filter IF Amplifier AF Amplifier or Demodulator AF Power amplifier speaker Local oscillator This section further amplifies the audio signals and finally fed to the speaker for final reception AF power amp. stage:-

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4/1/2012 17 Why super heterodyne

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4/1/2012 18 Early Tuned Radio Frequency Operation The Tuned Radio Frequency (TRF) receiver is one of the oldest receiver designs that was popular in the 1910s to 20s Basic idea was to simply use a LC tuner to select a station, and triodes vacuum tubes are used. There are many problems with this approach. At the time, triodes did not have very good amplification gain. LC circuit in practice is generally a broad bandpass filter and will pass few adjacent stations

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4/1/2012 19 Triodes vacuum tube look like

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4/1/2012 20 Animated demonstration and find the difference Disadvantages:- Poor rejection of strong signals at adjacent frequencies. Increased noise or interference and there is no selectivity against the undesired sideband .

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4/1/2012 21 reducing to lower frequency, resulting lower frequency components can be used, superior sensitivity Further advantage is that many components can be designed for a fixed frequency which is easier and cheaper than designing wideband components. stability and selectivity. Compared with the TRF design , Advantages:-

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4/1/2012 22 For single conversion superheterodyne AM receivers designed for medium wave (AM broadcast) the IF is commonly 455 kHz. Most superheterodyne receivers designed for broadcast FM (88 - 108 MHz) use an IF of 10.7 MHz. TV receivers often use intermediate frequencies of about 40 MHz.

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