Dear Iban,

Thank you for the timestamp, qth etc, and the info about the Spectravue
header format.

I examined the file anyway and worked out that a “stereo” signal was I and Q,
16-bits each, LSB first.

I confirm the signal as you found.  I averaged small and large numbers of
FFTs.  This showed that the signal strength varied, between approximately
11 to 16 dB-Hz.  The spacecraft is spinning at about 3 rpm, so this may be
the reason.

Attached is a typical plot from my my own software.  This is not the strongest
signal display; the largest I found was a signal = -45.7 dB over the
noisefloor = -53.8 dB, or SNR = 8.1 dB.

With a bin bandwidth of 0.124 Hz, this equates to a CNR of 16.4 dB-Hz.

Congratulations!

73 de James G3RUH

ISEE-3 signal processed by G3RUH