On Saturday June 7th I gave a talk at SeaPac 2014. You can download the PowerPoint presentation here: Download Sea-Pac 2014 Presentation . I should add that the Flex Radio 1500 and 6000 series SDR's can transmit on 630m. I spoke with the K3 folks and while the K3 will not operate directly that low in frequency they have modified the software to be compatible with transverters.
For true LF operation read this: http://www.arrl.org/news/radio-amateur-s-sub-9-khz-vlf-signal-detected-across-the-atlantic .