Re: Ultra VLF signals?
Curious- could they be intermod products? I'd be surprised if there was much speech transmission below 153kHz (the bottom edge of LW broadcast) as that would seem to be anti-socially greedy of bandwidth, if nothing else. RTTY of one form or another is entirely understandable, though.
This brings us to definition pedantry- formally, VLF is 3-30kHz, though there's probably a fair amount of sloppiness in usage, I've even seen US references to the aeronautical beacon band (between LW and MW broadcasting allocation) as VLF!
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