Having a look on that site, is shows how to make radio receivers, so you could try one of these, and fix the frequency to 1MhZ. Or just find a cheap AM radio, take it apart, use the circuitry in there. Just tune it to the correct frequency, and fix it, and the volume will probably be a variable resistor, so take it out and replace with a fixed one, then use the wires to the speakers for the signal. Although you may want the un-amplified signal so find that before it goes through the amplifier circuitry (this might cut out the variable resistor anyway).
I once made a radio transmitter and a receiver on an ‘electronic playground’ I can upload the schematics if you want.
A variable capacitor most probably controls the tuning as in: http://sci-toys.com/scitoys/scitoys/radio/three_penny/three_penny.html I don’t know if it is possible to measure what the capacitance is set to, and find a capacitor of that value to replace it. It might be easier to use a variable one and fix it in place.
one other thing to add is that using the frequency band for radio stations to transmit data is probably not a good idea, as you will get alot of interference, and it might be illegal depending on where you are.
