Over on YouTube user MrCircuitMatt has uploaded a video where he explains the concepts of FM deviation, modulation index and sidebands using an RTL-SDR dongle as the receiver, and a function generator connected to a Kenwood TM-D700 transceiver as the transmitter.
In the video he transmits a modulated signal and uses a GNU Radio flowgraph to demonstrate and visualize what happens when the modulation frequency is changed. Later in the video he moves to pen and paper to explain the theory behind the results he saw.
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