Draw the block diagram for an AM super heterodyne receiver and describe its operation and the primary function of each stage. Discuss the filter method of sideband suppression with the help of a block diagram.
The Correct Answer and Explanation is :
AM Superheterodyne Receiver Block Diagram and Explanation
Block Diagram:
+----------------+ +----------------+ +----------------+ +-----------------+ +----------------+
| RF Amplifier | --> | Mixer (Mixer | --> | Intermediate | --> | IF Amplifier | --> | Detector (AM |
| | | Frequency) | | Frequency (IF) | | | | Demodulator) |
+----------------+ +----------------+ +----------------+ +-----------------+ +----------------+Operation and Functions of Each Stage:
- RF Amplifier:
- The first stage of the superheterodyne receiver is the RF amplifier. It receives the weak AM signal from the antenna and amplifies it. The RF amplifier filters out unwanted signals, thus improving the signal-to-noise ratio before it is passed to the mixer.
- Mixer:
- The mixer receives both the amplified RF signal and a signal from the local oscillator. The mixer combines these signals and generates two new frequencies: the sum and difference of the RF signal and the local oscillator frequency. The difference frequency is called the Intermediate Frequency (IF).
- Intermediate Frequency (IF) Filter:
- This filter isolates the desired IF signal, removing the unwanted sum frequency generated by the mixer. The filtered IF signal typically has a fixed frequency (e.g., 455 kHz for AM) and is sent to the next stage.
- IF Amplifier:
- The IF amplifier boosts the IF signal to a level suitable for demodulation. Since the IF signal is at a constant frequency, the IF amplifier is designed to optimize the gain for this specific frequency range.
- Detector (AM Demodulator):
- The detector demodulates the IF signal, extracting the audio or baseband information (e.g., speech, music) encoded in the AM wave. Common demodulation methods include envelope detection, where the amplitude variations of the IF signal are converted back into the original audio signal.
Sideband Suppression Method (Filter Method):
In AM transmission, the signal contains two sidebands: the upper and lower sidebands, which carry redundant information. To suppress these sidebands and improve the efficiency of the receiver, a bandpass filter can be used.
Block Diagram for Sideband Suppression:
+-------------------+ +-------------------+ +-------------------+ +-------------------+
| RF Amplifier | --> | Mixer | --> | Bandpass Filter | --> | IF Amplifier |
| | | (Local Oscillator | | (Sideband Supp.) | | |
+-------------------+ +-------------------+ +-------------------+ +-------------------+Explanation:
In this method, a bandpass filter is placed after the mixer to allow only the desired intermediate frequency (IF) to pass while rejecting the unwanted sidebands generated during the mixing process. This ensures that only the relevant part of the signal (the IF) reaches the amplifier and the detector for demodulation. This method reduces interference and improves the overall performance of the receiver.