[DonRotolo]

Your audio equipment should do just fine, the data can't be much more than 2400 or 4800 baud (transitions per second), probably much slower than that. If you are finding high-frequency carrier waves on the signal, you can demodulate it (ASK) with a simple diode (use germanium fo low loss) - google "AM demodulator". A small (several picofarads) capacitor from signal to ground will shunt any stray RF as well.