A certain run of very inexpensive tv tuner cards can be used for software defined radios. The tuner cards that are reported to work the best for SDR usage are the Realtek RT 2832/E4000 USB units. The prices seem to run from around $20 to $60 for these chip sets. Other SDR radios can cost hundreds more. Free software programs for both Windows and Linux are readily available. I used SDR# for my testing today.
After a friend ordered one of these units I had to have one. The one I picked up was from an Amazon seller in Hong Kong. Within a very short period of time and after a little tweaking of the software I was picking up all kinds of signals. This is a fun little quirky project that I'm looking forward to playing with. Anyone who likes tinkering should pick one or two of these up. As a side note, some folks have even gotten these units to trunk track with two units working as a set; one is used as the control channel and the other as the scanner. I haven't played with that yet but perhaps down the road. Anyhow, it's a fun little project.