Abstract: To enhance the detection of a desired signal in the presence of interference, the degree of modulation of a received input signal is amplified. In the preferred embodiments, this is accomplished by amplifying the degree of amplitude modulation. This works especially well in situations where constant or substantially constant envelope jamming is employed. However, the arrangement is also effective in some cases where the jamming signal has a rapidly fluctuating envelope. The success of the technique in cases of rapidly fluctuating envelopes depends upon the probability distribution of the envelope.

Abstract: A code tracking loop for a spread spectrum receiver includes a pair of mixer circuits to which phase offset or relatively delayed pseudo noise code signals are applied and combined with an incoming IF spread spectrum signal. The output of the mixers are coupled to a sum and difference hybrid. The hybrid produces a sum signal corresponding to the sum of the mixer outputs and a difference signal corresponding to the difference between the mixer outputs. These sum and difference signals are separately filtered, amplified and then coupled to a further mixer or phase detector. Appropriate AGC circuitry is controlled by the envelope of the sum signal to adjust the gains of the respective amplifiers. The output of the phase detector is proportional to the difference between the squares of the outputs of the hybrid and represents the phase of the sum signal relative to the difference signal.