Turnstile / Reflector antenna - or - Quadrifilar Helix antenna

137 MHz GaAsFET masthead Preamplifier

137 MHz Dual conversion Receiver

A DSP synchronous demodulator using a Texas Instruments DSP Starter Kit module

A DSP software weather satellite demodulator program

A custom program that reads from COM 2 and writes the data to disk as a raw file, while displaying a preview picture in a window

The satellite signal is transmitted as FM with a 2400 Hz AM subcarrier. The subcarrier is modulated by the video signal corresponding to the brightness in the scanned image. The receiver recovers the 2400 Hz audio signal. This is then fed to the DSP, which locks to the signal, demodulates it to an 8 bit value, synchronizes the serial data rate to the 2400 Hz incoming signal, and sends it to the PC for display, at 57600 baud, 4800 bytes per second. By using the original 2400 Hz tone from the satellite as a reference, it avoids the annoying doppler shift curve often seen in these type of pictures . In fact, the DSP demodulator works so well, it stays locked during very deep signal fades as can be seen in some of the pictures.

Another page explaining how it works.

- The 1995 ARRL Handbook

- Digital Signal Processing Applications with the TMS320 Family - Theory, Algorithms, and Implementations Volume 2 - "Theory and Implementation of a Splitband modem Using the TMS32010"

- AMSAT/TAPR DSP WEFAX demodulator - Code by Bob McGwier N4HY.