k9iu@iuvax.UUCP (05/17/84)
What does someone with a Bell 202 modem have to do to receive the telemetry? We have hardware and software expertise available. k9iu - Indiana University Amateur Radio Club uucp: ...ihnp4!inuxc!iuvax!k9iu csnet: k9iu@Indiana ARPA: k9iu.Indiana@CSnet-Relay
karn@mouton.UUCP (Phil Karn) (05/17/84)
Receiving UO-11 telemetry is much like UO-9, except that there are some important differences. 1. The deviation of the data subcarrier is considerably higher. This makes for much improved copy in my experience. 2. THE MARK AND SPACE TONES ARE REVERSED relative to UO-9 (and to the Bell 202 modem standard.) If you cannot hack up your modem to invert data, you'll have to do it externally. My own solution to this problem was to add a 7486 exclusive-OR gate to the serial/parallel I/O card on my computer. A bit from the parallel port controls whether the 7486 inverts the incoming data stream that is fed to the UART. 3. The resulting data stream is conventional 1200 baud asynchronous ASCII, and may be displayed directly on a terminal. However, the telemetry mode that the spacecraft is currently in produces page after page of hexadecimal digits, so the best way to see what's going on is with a decoding program. Since each channel is checksummed this time, decoding is much more reliable. I have written a C program to do this which works pretty well, and even regains "synchronization" with the data stream quickly after a noise burst. I can post this program here or on net.sources if anyone is interested. On the pass that just ended at my QTH, UO-11 is still transmitting strong telemetry on 145.825. 73, Phil, KA9Q