My 7400 contest entry is an AM Radio Transmitter, which nicely complements another entry. The TX frequency is digitally tunable from 520kHz – 1.6MHz, although this part of the circuit is open loop, so tuning to a specific frequency may require a slight adjustment on a potentiometer. The RF section is strong enough to broadcast across a room, but weak enough that it shouldn’t interfere with anything important. Here is a screen shot of a 1kHz audio signal on a 930 kHz (approx) carrier. Full circuit information, including the theory of operation, is outlined on my website.
Via the forum.
Check out the video of his entry below.