Unfortunately SNR and time are interrelated. A very weak signal can be strengthened, by comparing it over time. The longer it is present, the less likely what

Unfortunately SNR and time are interrelated. A very weak signal can be strengthened, by comparing it over time. The longer it is present, the less likely what is being received is noise. But that process blurs things over time, unsure precisely when a change in the signal occurred. Depending on the power and speed, it could take many milliseconds, or even seconds, to say whether the signal has changed. HF also has variable propagation. It doesn't always take the same path. So timing can be all over the place. Much lower frequencies (around 100 kHz instead of 10000 kHz) hug the ground, and their timing can be very precise. Low frequency was once used by navigation systems with ground-based transmitters. Takes huge antennas and transmitters to broadcast a strong enough signal for that. They were some of the biggest ever constructed. High-power HF (in the kilowatt range) has been suggested before for high speed trading: https://spectrum.ieee.org/wall-street-tries-shortwave-radio-to-make-highfrequency-trades-across-the-atlantic https://spectrum.ieee.org/wall-street-tries-shortwave-radio-...