Last week I looked at 54 sferics to make a sanity check
of the antenna at 3kHz.   Here is the average spectrum

 http://abelian.org/vlf/tmp/170203a.gif

Peak is at 8.6 kHz with amplitude 0.11 and the
dip is at 2.5 kHz amplitude 0.012 so about a 20dB
difference.

The source of these daytime sferics was about 1200 to
1300 km distant.

Sferic blanking at 8270 usually makes up to 20dB S/N
improvement, but only a few dB at 2970.  There is not
so much sferic energy to remove at the lower frequency.

--
Paul Nicholson
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