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An Anonymous Coward writes:

https://stdw.github.io/cm-sdr/ [github.io]

A few weeks ago I got curious about an old cable modem sitting in my closet, a Motorola MB7220. Initially I was interested in what kind of hardware it had and if it was running Linux. Some quick searching brought me to a thread on a web forum where people were discussing the built in spectrum analyzer feature used for diagnostics. Someone mentioned that they could see spikes corresponding to FM radio stations. This sparked a thought: if a cable modem and a digital TV tuner dongle are fundamentally doing the same thing (receiving and demodulating QAM signals), could a modem be turned into an SDR (software-defined radio) a la RTL-SDR?

Going into this project, I knew next to nothing about RF and had no idea if this goal was even feasible at all for the hardware. I found an SDR project based on an Analog Devices cable modem chip, as well as a forum thread where someone else was wondering about the same thing a few years ago.

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