The Big Idea
QAM takes two separate data streams and combines them into one signal that travels on a single frequency.
How? By using a clever trick with phase.
Watch It Happen
How It Works (Simply)
1. Two inputs: I and Q
These are amplitude values representing your data. For 16-QAM, each can be -3, -1, +1, or +3.
2. Two carriers that are 90° apart
The oscillator generates a carrier wave. The same wave is also shifted by 90° to create a second carrier.
- The original is called In-phase (I carrier)
- The shifted one is called Quadrature (Q carrier)
3. Multiply each input by its carrier
- I input × In-phase carrier = I signal
- Q input × Quadrature carrier = Q signal
4. Add them together
The two signals combine into one output. This is your QAM signal.
Why Does This Work?
Because the two carriers are 90° apart, they don’t interfere with each other.
Think of it like two lanes on the same road. At the receiver, you can separate them back out because of that 90° difference.
The clever bit: You’re sending TWO data streams using ONE frequency. QAM doubles the data capacity without needing more spectrum.
The Block Diagram
This is how engineers draw a QAM modulator:
The circles with × are mixers (they multiply signals together).
The + box is a summer (it adds the signals together).