Superheterodyne Receiver Lab Report

NAME: CHRISTOPHER MBAH SID: 200964926

ELEC5451M Electronics Laboratory Session (3)

A SUPERHETERODYNE RECEIVER.

The objective of this lab session was to design a simple superheterodyne receiver and investigate the mixer circuit, the IF filter and the demodulator/audio output. The basic operation of the superheterodyne receiver revolves around the process of mixing. From last week’s experiment with mixers, I know that when two signals are multiplied together, the output is the product of the instantaneous level of the signal at one input and the instantaneous level of the signal at the other input. This output contains signals at frequency components other than the two input frequencies. These two new frequency components are the sum and difference of the two input signals, i.e. if the two input frequencies are f1 and f2, then new signals are seen at frequencies of

The lower frequency difference component fIF called the intermediate frequency (IF), is separated from the other components by fixed tuned amplifier and filter stages set to the intermediate frequency. The tuning of the local oscillator is linked to the tuning of the radio frequency (RF) stages so that the difference intermediate frequency is always the same fixed value. In this system, the IF stages need no tuning, consequently, detection takes place at intermediate frequency instead of at radio frequency as in tuned radio frequency (TRF) receivers.

The IF filter I worked with in this project was the ZTB 455E. Ideally, this is a bandpass filter that theoretically resonates at 455 KHz. But in practice, I discovered to my wild astonishment, that the ZTB 455E actually resonates at 450 KHz and attenuates signals above and below this value (including 455 KHz signals). The waveform of the output of the ZTB 455E at various frequencies is shown in Figure 1