Difference Bw Product & Diode Detector

Q-What is the DSB SC? ANSDSB SC (double sided band suppressed-carrier) the modulation process which does not introduce a sinusoid at fc. The term suppressed carrier does not necessarily mean absence of the spectrum at the carrier frequency fc. It means that there is no discrete component of the carrier frequency. The carrier signal is removed or suppressed by the balanced modulators.

Difference between AM Modulation and DSB SC Modulation: DSB SC modulated signal contains no carrier. Carrier frequency and amplitude always remains constant while side bands constantly vary in frequency and in amplitude. Thus carrier contains no information; this means that carrier power is pure dissipation. Transmitting efficiency of amplitude modulation is lower than DSB SC modulation. Amplitude demodulator circuit is simple.

Demodulation

Synchronous Detector (Product Detector)

Asynchronous Detector (Diode Detector)

Difference between Product and Diode Detector: Product Detector

Diode Detector

1- Rather than converting the envelope of the signal into the decoded waveform, the product detector takes the product of the modulated signal and a local oscillator.

1- A diode detector is simply a diode between the input and output of a circuit, connected to a resistor and capacitor in parallel from the output of the circuit to the ground. The output is a voltage-shifted version of the original (baseband) signal.

2- The product demodulator can decode over modulated AM, AM with suppressed carrier, and SSB.

2- If the signal is over modulated , distortion will occur

3- A signal demodulated with a product 3- It is more susceptible to noise than a detector will have a higher signal to product detector. noise ratio than the same signal demodulated with an envelope detector. 4- Filter is not used.

4- A simple filter can then be applied to filter out the DC component.

5- Product detector quality is excellent but the circuit is complicated. Carrier signal must exactly synchronize with AM signal.

5-Diode detector circuit is simple but quality is bad.

A more sophisticated product detector A more sophisticated product detector can be constructed in a way much like a single-sideband modulator. I. II. III. IV.

Two copies of the modulated input signals are created. The first copy is mixed with a local oscillator and low-pass filtered. The second copy is mixed with a 90° phase-shifted copy of the oscillator and the output of this mixer is also 90° phase-shifted and then low-pass filtered. These copies are then combined to produce the original message.