karn@eagle.UUCP (Phil Karn) (08/22/83)
This morning between about 05:00 and 06:20, three stations took part in packet radio experiments via Amsat-Oscar-10: ZL1AOX in Auckland, New Zealand; W3IWI in Clarksville, MD; KA9Q in New Providence, NJ. Limited HDLC frames were successfully exchanged despite the use of non-optimal noncoherent FSK modems (namely the XR chips provided with the TAPR TNCs). A major problem was frequency errors between stations due to the doppler shift caused by the different relative velocities to the satellite. The signal-to-noise ratio was also marginal for this modulation technique. It appears clear that simple FSK (F1) is certainly not very good for satellite use but that PSK modems now under development in AMSAT should work very well under the observed conditions. PSK modems will automatically track changes in carrier frequency due to doppler shift and work well with typical signal-to-noise ratios on Oscar-10. Phil Karn, KA9Q