In fact there are lower-frequency signals that carry more data, generally used for submarine communication - the wikipedia article says "uo tp 300bps" using VLF

In fact there are lower-frequency signals that carry more data, generally used for submarine communication - the wikipedia article says "uo tp 300bps" using VLF (30KHz or so). Fun fact: sound cards in PC's are now fast enough that it's possible to receive many of these signals (including WWWV, DCF77 and MSF) directly with a sound card - basically connect a long wire (or tuned circuir) to the sound card input and do a bit of DSP. Sampling at 192KHz makes reception of any of these easy. [0] https://en.wikipedia.org/wiki/Communication_with_submarines https://en.wikipedia.org/wiki/Communication_with_submarines