rrw@naucse.cse.nau.edu (Robert Wier) (04/26/91)
Many thanks to those who responded to my message of about
a week ago about decoding weather satellite transmissions.
Most suggested some type of phase - locked loop detection.
In starting to check on this, I ran across Application Note
AN-46 from National (1986 Linear Applications Databook), and
guess what? On page 153, they have a circuit for a "Weather
Satellite Picture Demodulator" which uses a LM565 PLL and a
LM1596 double balanced demodulator. Talk about hitting the
nail on the head!
It should be pretty stable, since it was designed with the
application in mind of taking the 2.4Khz subcarrier and
recording it onto audio tape. On playback, the PLL should
track the carrier and "...will track any flutter and instability
in the recorder, and effectively filter out noise..."
They also have a divide by 600 circuit so that the 2.4Khz
subcarrier will produce the horizontal sync frequency of
4 Hz...
Again, many thanks!
- Bob Wier
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Northern Arizona University / Flagstaff, Arizona
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