Spread spectrum long loop receiver

摘要

A Long Loop GPS receiver converts the pseudo random noise code bi-phase modulated input signal to a first IF frequency. The first IF is correlated against a duplicate of the pseudo random noise code that modulates the input signal. The correlator output is converted to a last IF having a frequency of one-half the pseudo random noise code sequence repetition rate. Local oscillator leakage into the receiver input is spread in spectrum by the correlator into spectral lines that do not lie on the received signal. A bandpass filter in the last IF removes the leakage spectral lines. A hard limiter converts the last IF to digital format. A digital phase detector adjusts the local oscillator to lock the local oscillator signal to the receive signal. The correlator pseudo random noise code signal is clocked by the local oscillator.