The main purpose of a radio receiver is to intercept and decode the radio waves. All radio receivers MUST contain at least these, 1.Antenna system,
2.Tuned circuit,
3.Detector
4.Transducer When the sound signal is mixed with the carrier frequency then the frequency of the carrier wave remains the same but the amplitude of the carrier changes with the amplitude of the signal. In this case when the amplitude of the carrier waves changes with the amplitude of the sound signals, then the modulation is said to be the Amplitude Modulation or AM. This type of amplitude modulation is characterized by a lot of disturbance and noise. Consequently, the quality and clarity of the transmitted sound is not quite good. When these AM signal is received on the radio receivers then the quality of the sound reproduced also remains poor. The main objective of the Super heterodyne receiver is to produce an intermediate frequency (IF) by the process of heterodyne or beating. This can be accomplished when two frequencies are mixed to produce the beat frequency .In superhets, the IF is usually 455 kHz which is selected because the broadcast band begins above that frequency. So if we imagine a situation when the RF amplifier is tuned to receive a 800KHz broadcast signal the local oscillator must be tuned to 1255 kHz which will result in an IF of 455KHz(1255-800 kHz). Since we have to tune the RF amplifier section throughout the entire broadcast band, the frequency of the local oscillator must also vary in a manner that it always maintains a gap of 455kHz. To achieve this condition, the local oscillator and the RF amplifier section are “ganged “, i.e., their tuning condensers are connected /ganged mechanically in such a way that when we tune the variable capacitor in the RF section, the variable capacitor in the local oscillator also changes its value it ‘tracks’ the frequency to which the ‘aerial circuit ‘is tuned and remain separated from the tuned frequency by 455kHz up. The intermediate frequency (IF), which is considerably low frequency is being used, because it is a suitable The demonstrator has several test points for observations. Using these test points, waveforms of incoming signals can be observed using a high frequency oscilloscope. The test points brought out for observations are: - Modulated RF waveform
- Output of the mixer stage
- RF amplifier stage
- Second intermediate frequency stage
- Detector stage
- Input of the Power amplifier stage
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