Abstract
The characteristics of the decision feedback carrier recovery loop (DFL) and the Costas carrier recovery loop (Costas Loop) for a conventional QPSK signaling were compared and evaluated experimentally. The DFL and the Costas Loop was respectively applied to the experimental QPSK system where the carrier frequency is 10.7 MHz and the simbol rate is 64 kS/s. The performance of the DFL and the Costas Loop was investigated through measurements of the signal-to-noise ratio of the recovered carrier, the lock range, the capture range and the bit error rate. A result was obtined that the capture range of the DFL did not exist due to the false lock, while the signal-to-noise ratio and the bit error rate showed more excellent performance than those of the Costas Loop. Therefore a circuit for avoiding the false lock in the DFL was proposed. With the proposal circuit, it was showed that the false lock in the DFL could be avoided.
