Time-Diversity Modem for Tactical Hf Teletype Circuits. On-the-Air Tests Verify that Time Diversity Provided by NELC Five-Tone Modem Significantly Improves BER of Tactical HF TTY Link.

摘要

A full-duplex FSK time-diversity modem using five tones was constructed in a unit requiring only 5.5 inches of rack space. Hf tests over a 750-km circuit showed that the time-diversity modem has error rates 100 times lower than those of a URA-17C modem for 70% of the test period. For 90% of the test time the time-diversity modem had a measured bit error rate at least 10 times better than those of the URA-17C. Greatest improvement occurred when the circuit was experiencing large fades. (Author)