Abstract: Methods and apparatus for detecting the presence of a particular signal among all the channels of interest in a cellular or similar type system are disclosed. A first method detects CDPD signals, and a second method detects DQPSK signals used in digital control channels in accordance with the IS-136 standard. These methods include the steps of sampling a received signal in at least one channel to obtain a predetermined number of samples for the at least one channel; computing an error value for each sample; determining a minimum error value; determining a ratio of the minimum error value to a reference value; and making a decision as to whether the received signal is the prescribed signal on the basis of at least the ratio, wherein the decision is made by comparing the ratio to a threshold value.