I find totally rare that these devices works at 5kHz. instead of 5MHz or 500Khz (for example). At 5kHz you would need in theory huge antennas to being able to t

I find totally rare that these devices works at 5kHz. instead of 5MHz or 500Khz (for example). At 5kHz you would need in theory huge antennas to being able to transmit and receive the signal correctly, and hundreds of kHz frequencies are totally achievable even with the most basics mid 1900s telecom systems. If you know the data to send, and you are totally sure the data is sent electromagnetically at 5kHz, you can modulate in as sound in a computer and play it in a PA system connected to a long cable,