Hi all,

Thanks to Bob Reise for pointing out that ringing voltage is a lot higher
than S9.  A high pass filter would be a useful precaution for connecting to
a telephone line.  For checking LF harmonic content it should be connected
to an LF receiver, not directly to a sound card.  Further, the higher
frequency content may propagate in unbalanced mode, rather than in
"pushpull", in which case radio sampling could be via a low value capacitor,
to either leg of the telephone line.

But the practical result is still there, that amateurs should avoid
multiples of 8 kHz for weak signal LF DX work.

73, Bob ZL2CA