How MC1496 Balanced Modulator Works?(DSB-SC AM)

 Here it is illustrated with circuit animation of how the MC1496 Balanced Modulator Demodulator can be used to produce Double Sideband Suppressed Carrier(DSB-SC) signal. Modulator/demodulators are used in RF circuits. RF circuits are used in all wireless communication electronics circuits from cell phones, mobile towers, WiFi routers, anything that is used in wireless equipment.

MC1496 is old but still usefully used in RF circuits by HAM radio hobbyist and professionals and is useful for teaching purpose to electronics student graduates. It can be used in application like generating DSB-SC AM, SSB AM signal, as a RF frequency mixer, as RF frequency multiplier or RF frequency doubler, RF detector circuit, Phase detector etc. Here is a demonstration of how we can generate double sideband suppressed carrier AM signal using the MC1496(LM1496) modulator/demodulator IC(Integrated Circuit). 

MC1496 modulator/demodulator IC

The MC1496 IC is 14 pin RF modulator/demodulator whose pin diagram is shown below.

MC1496 pin connection

The following shows the circuit schematic of MC1496 when used to generate Double Sideband Suppressed Carrier signal(for AM transmitter). 

MC1496 balanced modulator circuit diagram

In the above circuit implementation, dual power supply(+12V and -8V) are used. The input pin are 1 and 4 for the modulating signal, 8 and 10 for the carrier signal and the output pin for the output are the pins 6 and 12. All the resistors connected to these input and output pins are for voltage biasing the internal differential amplifiers inside the chip. The pin 5 is used to bias current for DC operating. The pin 2 and 3 is for setting the linear dynamic range for the modulating signal(information signal) and for setting the gain of the modulator.

For maximum modulation, the recommended carrier amplitude is 300mV rms. The frequency used in this example is 500KHz. This is applied to the Vc input in the above circuit diagram using function generator.

Similarly, a 1KHz 300mV rms modulating signal is applied to Vs in the above circuit diagram with function generator.

On the virtual oscilloscope we can see that the output shown in pink color is DSB-SC signal.

The yellow waveform is the high frequency carrier signal and the blue waveform is the modulating signal.

We can use spectrum analyzer(Fourier Transform) to see the frequency spectrum of the output signal which is shown below.

frequency spectrum

From the spectrum we can see that this is indeed double sideband suppressed carrier signal at 500KHz. In the spectrum we can see that double sideband having more magnitude then the center 500KHz signal, that is the carrier at 500KHz is suppressed.

See the following video demonstration of how MC1496 balanced modulator works.

So in this tutorial we showed how the MC1496 can be used to generate DSB-SC signal for making AM transmitter

See next how to build AM modulator using MC1496 modulator.

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