This is a tutorial on how the AM Detector Demodulator with MC1496 works and how to build it. AM detector(demodulator) is a circuit that translates AM signals to baseband signal by mixing the AM signal with local oscillator signal. This is done to recovers the transmitted message signal from AM carrier signal. AM detector also called AM demodulator are used in AM RF receivers. The AM detector/demodulator uses RF mixer circuits. There are couples of circuit design methods to build AM demodulator. Among them are diode RF mixers, BJT and FET transistor based RF mixers and they are can arranged in different typologies to create more efficient RF mixers. More efficient means mixers better port isolation between the carrier signal port and modulating signal port and output port. RF mixers which produces isolation between these signals are called RF balanced mixers. MC1496 is a balanced modulator demodulator which can be used as AM modulator or demodulator. Here MC1496 is used to build AM detector.
To make AM modulator using MC1496 see the following previous tutorials.
- MC1496 Balanced Modulator Demodulator(MC1496 Introduction)
- How MC1496 Balanced Modulator Works? (DSB-SC AM)
- AM modulator using MC1496 modulator(standard AM)
- Single Supply MC1496 AM modulator(standard AM)
The MC1496 based AM detector circuit design is shown below.
In the above diagram the local oscillator carrier signal is fed in the port named Vc. The local oscillator signal amplitude should be in the 300mV range and the frequency should be in AM band frequency like 500KHz. The received AM signal from the antenna goes into the port named Vs in the above am detector block diagram. The local oscillator carrier signal is connected to the pin 8 and 10. The AM received signal is connected to pin 1 and 4. The output is connected to pin 6 and 12. The resistors connected at these input and output pins are for biasing the transistors(differential amplifiers). The power supply used here is +5V. The voltage level at the output and input should be such that the output pins are connected to the highest voltage(+5V), then the carrier signal input should have lower than highest voltage which is in this case 2.9V and the AM signal input should have the lowest voltage which is 1.6V in this case. The resistor connected at pin 2 and 3 is for making the differential amplifier inside the chip operate in the linear region for the input AM signal. At the output pin 12 an RC filter is used having value 1KOhm(here a 10KOhm potentiometer was used for adjusting the cutoff frequency of the filter) and 5nF capacitance. The capacitors C1 and C5 which are 0.1uF are input coupling capacitors and the capacitor C8 is output coupling capacitor. The capacitors C4, C3 and C6 are bypass capacitors. The capacitor C2 is for reducing power supply noise. So in this way we can build a AM Detector Demodulator with MC1496.
The following shows the transmitted message input signal, the input received AM signal signal, the carrier input signal and the received message output signal from the MC1496 detector.
Watch the following video demonstration of the AM Detector Demodulator with MC1496 works.
So in this tutorial we showed how the AM Detector Demodulator with MC1496 works. AM detector can also be build using diodes. For diodes see the tutorials How to design AM modulator circuit using transistor and How does Single Diode Modulator Circuit work?.
