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Old 11th Jan 2018, 12:17 pm   #11
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 1,454
Default Re: Ultra VLF signals?

There are no speech signals below the LW AM band. I suspect what you are hearing are images or intermod products. There are a number of data and 'time & frequency' transmissions in the sub 150 KHz band though, and many of them sound like RTTY. I've attached a 0 to 200KHz grab from my SDR. There's a group of data sigs around 20 KHz (not sure where they originate) and 60 KHz and 81 KHz from Anthorn are clearly visible, as is DCF77. There are plenty of others, including the tele-switching EFR signals around 140 KHz which when decoded simply send time & date info. The big hump at 100 KHz is LORAN.
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Andy G1HBE.
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