I added the relative background noise at 6470 Hz to
the error map,

 http://abelian.org/vlf/tmp/161102b.gif

Tried some further settings of blanker but no
improvement over the +1.7 dB.

> Start time: 03.11.2016   06:00:00 UTC
> Symbol length: 30 s
> Characters: 11

Should have a good chance if we have another quiet
day.  I think that 15 chars with 25 second symbols
is probably within reach (at about -0.4 dB) but
let's try 11 chars first.

The error map is useful for planning transmissions.
Even though the signal is too weak to plot its
amplitude, the error map reveals when the signal
is strong enough.

--
Paul Nicholson
--