A false lock detector for Costas loops with integrate and dump arm filters

The acquisition of frequency and phase of a suppressed carrier BPSK signal with a Costas loop is inhibited by a phenomenon known as 'false lock' or lock to data related sidebands. This troublesome effect becomes important when the total frequency uncertainty exceeds one half the data rate. For Costas loops implemented with passive arm filters the data may be turned off during acquisition and the false lock effect is eliminated. This option is not available to the users of links implemented with integrate and dumps; in fact, the false lock effect in loops with I&D's is independent of the data. This paper discusses a lock detector that can differentiate between false lock and true lock in Costas loops with I&D's and an unmodulated signal input.