Communication Systems Sandbox
Visualizing the fundamentals of signal processing and transmission.
Amplitude Modulation (AM)
Encoding a low-frequency message onto a high-frequency carrier wave.
The Concept
To transmit low-frequency information (like audio) over long distances, it must be encoded onto a high-frequency carrier wave. In Amplitude Modulation, the amplitude of the carrier wave is varied in proportion to the instantaneous amplitude of the message signal. The resulting wave carries the original message in its "envelope".
How to Use the Lab
- Adjust the Message and Carrier frequencies to see the two base signals.
- Change the Modulation Index ($m_a$). This critical parameter controls how strongly the message affects the carrier.
- Observe the final AM wave. Notice its envelope has the same shape as the message signal.
- Try setting the Modulation Index above 100% to see "over-modulation" and distortion.
Controls
What's Happening?
Message Signal
Carrier Wave
Resulting AM Wave
Elements of a Communication System
Visualizing the journey of a signal from source to destination.
Controls
1. Transmitter
The transmitter converts the original message into a suitable form for transmission. This often involves modulation and amplification.
2. Channel
The channel is the physical medium. The signal inevitably gets weaker (**Attenuation**) and can be corrupted by unwanted signals (**Noise**). Adjust the sliders to see these effects!
3. Receiver
The receiver's job is to intercept the signal, amplify it, and decode it (demodulation) back into its original form so it can be understood.
Signal Bandwidth
Visualizing a signal in the frequency domain to understand the space it occupies.
The Concept
An AM signal doesn't just exist at the carrier frequency. It's composed of the carrier ($f_c$) plus two **sidebands**: an Upper Sideband (USB) at $f_c + f_m$ and a Lower Sideband (LSB) at $f_c - f_m$. The **bandwidth** is the total range of frequencies occupied by the signal, which for AM is $2 \times f_m$.
How to Use the Lab
- The graph shows the signal in the **frequency domain**.
- Adjust the Message Frequency to see the sidebands move.
- Change the Carrier Frequency to shift the entire group.
- Notice how the bandwidth (the shaded region) depends only on the message frequency.
Controls
Calculated Values
Frequency Spectrum
Propagation of EM Waves
See how radio waves travel through the atmosphere based on their frequency.
Ground Wave
Low-frequency waves (< 2 MHz) that follow the Earth's curvature. Used for AM radio broadcasts.
Sky Wave
Medium-frequency waves (3-30 MHz) that reflect off the ionosphere, enabling long-distance communication.
Space Wave
High-frequency waves (> 30 MHz) that pass through the ionosphere. Used for TV, FM radio, and satellite links.