Superheterodyne Receiver

In this lecture, we are going to learn about the most important radio receiver called Superheterodyne Receiver. We will the basic function of it, a block diagram of the Superheterodyne Receiver, advantages of the Superheterodyne Receiver. So let’s discuss getting the basic concept of Superheterodyne Receiver.

Introduction of Superheterodyne Receiver

• All the drawbacks in the TRF receiver have been removed in Superheterodyne Receiver. This basic Superheterodyne Receiver is most widely used in most communication.

• This means that the Superheterodyne principle is used in all types of receivers like television receivers, radar receivers, etc.

Superheterodyne Receiver Block Diagram

• The below figure shows the Superheterodyne Receiver Block Diagram.

• In a superheterodyne receiver, the incoming RF signal frequency is combined with the local oscillator signal frequency through a mixer and is converted into a signal of lower fixed frequency. This lower fixed frequency is known as an intermediate frequency (I.F.).

• However, the intermediate frequency signal contains the same modulation as the original signal. This intermediate frequency signal is now amplified and demodulated to reproduce the original signal.

• The word heterodyne stands for mixing. Here we gave mixed the incoming signal frequency with the local oscillator frequency. Therefore this receiver is called the superheterodyne receiver.

• Thus, in a superheterodyne receiver, a constant frequency difference is maintained between the local oscillator signal frequency and incoming RF signals frequency through capacitance tunning in which the capacitances are ganged together and operated by a common control knob The intermediate frequency (IF) amplifier generally contains a number of transformers each consisting of a pair of mutually coupled tuned circuits. Thus, with this large number of double-tuned circuits, operating at a specially chosen frequency, the IF amplifier provides most of the gain (i.e. sensitivity) and bandwidth requirements (i.e. selectivity) of the receiver. This means that the IF amplifier determines the sensitivity and selectivity of the superheterodyne receiver.

• Also, since the characteristics of the IF amplifier are independent of the incoming frequency to which the receiver is tuned, the selectivity and sensitivity of the superheterodyne receiver are quite uniform throughout its tunning range and not subject to the variations like a TRF receiver. Further, since the I.F. amplifier works at a fixed I.F. frequency, the design of this system is quite easy to provide high gain and constant bandwidth.

• Because of its narrow bandwidth, the I.F. amplifier rejects all other frequencies except intermediate frequency (I.F.). Actually, this rejection process reduces the risk of interference from other stations or sources. In fact, this selection process is the key to the superheterodyne receiver’s exceptional performance.

• After the I.F. amplifier, the signal is applied at the input of the demodulator which extracts the original modulating signal (i.e. audio signal). This audio signal is amplified by an audio amplifier to get a particular voltage level. This amplified audio signal is further amplified by a power amplifier to get a specified power level so that it may activate the loudspeaker. The loudspeaker is a transducer that converts this audio electrical signal into an audio sound signal and thus the original signal is reproduced i.e. the original transmission is received.

Advantages of Superheterodyne Receiver

• The advantages of the superheterodyne receiver make it the most suitable for the majority of radio receiver applications like AM, FM, communications, single-sideband, television, and even radar receivers; all use the superheterodyne principle. This means that it can be considered today’s standard form of a radio receiver.

1. No variation in bandwidth. The BW remains constant over the entire operating range.
2. High sensitivity and selectivity.
3. High adjacent channel rejection.

Frequency Parameters of AM Superheterodyne Receiver

• The AM receiver has the following frequency parameters:

• Two frequency bands: Medium wave (MW) band and short wave (SW) band
• RF carrier range (MW) range: 535 kHz to 1650 kHz (SW band) : 5 to 15MHz
• Intermediate frequency IF: 455kHz
• IF bandwidth B: 10 kHz

Frequently Asked Question on Superheterodyne Receiver