The AN/GSC-10 (KATHRYN) Variable Rate Data Modem for HF Radio

The AN/GSC-10 (KATHRYN) is a new modem equipment for digital data transmission on HF radio circuits. Its unique modulation technique provides a wide range of signal redundancy and data rate to allow optimum performance over the correspondingly wide range of propagation conditions characteristic of HF radio. Efficient detection is achieved at all levels of redundancy by utilizing a fully coherent correlation detection technique. The detector is a continually self-adjusting matched filter to the timevarying ionospheric transfer function. The fine grain propagation data derived for detection allow continuous observation of parameters such as multipath delay and coherence time. As a variable data rate modem with channel measurement capabilities, it can serve in future fully adaptive communication nets.