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Interactive Digital Modulation Demonstration

Digital Modulation — Interactive Demonstration

ASK • FSK • PSK | Digital bits → Modulator → Modulated carrier → Receiver

1. What is Digital Modulation?

Digital modulation is the process of using a carrier signal to transmit digital information such as 0s and 1s through a communication channel. The digital information changes one or more characteristics of a carrier wave.

Digital Data
10110010

→

Digital
Modulator

→

Modulated
Carrier

→

Communication
Channel

→

Receiver

ASK changes amplitude, FSK changes frequency, and PSK changes phase according to the digital data.

2. Interactive Controls

Digital Modulation Type

Digital Bit Pattern

Use only 0 and 1

Carrier Amplitude

1.0

Carrier Frequency

7 cycles/bit

FSK Low Frequency

4 cycles/bit

FSK High Frequency

9 cycles/bit

3. Digital Input Data

The transmitter receives this digital sequence. Each bit occupies one time slot. The modulator changes the carrier according to whether the current bit is 0 or 1.

4. Carrier Signal

5. Modulated Output

Invalid bit pattern. Please enter only 0 and 1.

6. Output Information

Modulation

ASK

Number of Bits

Bit Rate

1 bit/time slot

Output

Amplitude

7. How Does Each Method Work?

ASK — Amplitude Shift Keying

In ASK, the amplitude of the carrier changes according to the digital bit. For example, a bit 1 can transmit a carrier with full amplitude, while a bit 0 can transmit a carrier with little or no amplitude.

FSK — Frequency Shift Keying

In FSK, the amplitude remains approximately constant but the frequency changes. One frequency represents bit 0 and another frequency represents bit 1.

PSK — Phase Shift Keying

In PSK, the carrier phase changes according to the digital bit. In simple BPSK, a bit 0 and bit 1 can be represented by carrier phases separated by 180°.

8. Equipment Needed for a Practical Experiment

💻

Computer

Simulation software or signal-processing software.

〰️

Function Generator

Produces the carrier signal.

📡

Modulator

ASK, FSK or PSK modulation circuit/module.

📺

Oscilloscope

Displays the carrier and modulated waveform.

🔌

Power Supply

Provides DC power to electronic circuits.

📟

Digital Data Source

Microcontroller, pattern generator or digital source.

🔗

Communication Channel

Cable, RF link or optical link.

📥

Demodulator

Recovers the original digital data.

9. Practical Demonstration Procedure

Generate a digital sequence such as 10110010.
Generate a high-frequency carrier using a function generator.
Connect the digital data source to the digital modulator.
Select ASK, FSK or PSK modulation.
Observe the carrier on an oscilloscope.
Observe the modulated output.
Change the digital bit sequence and observe how the waveform changes.
Send the modulated signal through the communication channel.
Use a demodulator at the receiving end.
Compare the recovered data with the original digital sequence.

Learning experiment: First select ASK and observe how the amplitude changes. Then select FSK and observe the frequency change. Finally select PSK and look for the phase reversal at bit transitions.

10. Effects You Can Observe

ASK: Changing amplitude produces different signal levels.
FSK: Changing frequency produces different numbers of carrier cycles within each bit.
PSK: Changing phase produces a phase reversal between digital states.
Changing the bit pattern: Immediately changes the output waveform.
Increasing carrier amplitude: increases the overall signal amplitude.
Changing carrier frequency: changes the number of carrier cycles represented in each bit.