Learn the fundamentals of software-defined radio
Figure 5: The spectrogram view of a CW Morse code
signal. Image source: Digi-Key Electronics
National Weather Service carries only voice and uses narrowband FM (Figure 4). The National Weather Service station is received using a bandwidth of only 11.2 kHz because the program content is only voice.
the radio controls in the upper left of the display. The signal spectrum consists of the analog signal about the center frequency. This carries the analog radio program. Outside of that are dual sub-bands that contain other program material and digital information. The program information content is decoded
and appears immediately above the spectrum analyzer display. As well as the spectrum display, the radio station’s audio components are available through the host computer for listening. Wideband FM has a large bandwidth because it is expected to carry high fidelity stereophonic music. A radio service such as the
Again, the audio program material is available as well as the spectrum displays. The SDR receiver adds all of these services to the host computer. The spectrum history or spectrogram display is useful for seeing changes in the received signals spectrum over time. A
Figure 6: The spectrogram of a remote weather station transmitter at 433.92 MHz that sends data in bursts. The spectrogram captures and displays transmitted bursts roughly 50 seconds apart. Image source: Digi-Key Electronics
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