An experimental new digimode: EbNaut

Pieter-Tjerk de Boer, PA3FWM web@pa3fwm.nl

(This is an adapted version of part of an article I wrote for the Dutch amateur radio magazine Electron, August 2016.)

Earlier [11] I wrote about the use by a few amateurs of slow BPSK modulation with a strong error-correcting code to send messages on VLF with weak signals, in which the Shannon limit is nearly achieved. With less than 10 microwatt effectively radiated power about 1000 km was crossed from Germany to England on 8.27 kHz, and in December 2014 in the same way the Atlantic ocean was crossed using about 150 microwatt.

Since then, Paul Nicholson further developed this technique and implemented it in software that anyone can run on a PC, thus creating a new digital mode for amateurs, called EbNaut [7]. However, it is not really a mode for normal QSOs. One needs a propagation path of which the phase shift does not change too much during the entire transmission, practically limiting it to LF and VLF. Lots of computational power is needed at the receiving side. But mostly, the receiver must know rather precisely on what frequency, at what time, and with what parameters, a transmission is to be expected. The software cannot search for the signal by itself, and usually the signal is also too weak to be seen on e.g. a waterfall display. This is a conscious design choice; otherwise, part of the transmitted energy would have to be "wasted" to help the receiver recognize the signal and synchronize to it; and that energy is then no longer available for the actual message. Pratically, EbNaut is therefore mostly used for experiments and tests, coordinated via the rsgb_lf_group mailing list.

References:

[7] http://www.abelian.org/ebnaut/
[11] PA3FWM: Signal/noise ratio of digital amateur modes. Electron, February 2015; and on this website.