Too late to edit, but per Wikipedia[1] once the quenched-spark transmitters were widespread, transoceanic transmissions were VLF and LF, marine were MF, and ama

Too late to edit, but per Wikipedia[1] once the quenched-spark transmitters were widespread, transoceanic transmissions were VLF and LF, marine were MF, and amateur was high MF (above 1.5MHz). 1: https://en.wikipedia.org/wiki/Spark-gap_transmitter#The_%22spark%22_era https://en.wikipedia.org/wiki/Spark-gap_transmitter#The_%22s...