This program uses a interface box to the PC's RS-232 COM port and counts signal enhancements via an FM radio tuned to an unused channel. I use it on 88.7 MHz.
Software is free.
He provides a schematic for the simple one IC interface which can be built from Radio Shack parts. It is powered by the COM port. Here's a great sound card audio spectrum program that I use to display meteor returns. A must for any work with signals that are fed into your sounds card. You can save incoming signals to WAV files for later analysis.