Most efficient way to find single dominant frequency (without amplitude) in analog signal
One approach is to use a phase/frequency detector as the circuit determining error and to ensure that the initial loop bandwidth is wide enough to “see” both the weaker signal that would otherwise be a false acquisition as well as the strongest signal desired. The loop will lock onto the strongest signal within the loop bandwidth as long as it is 6 dB above the total power of the other tones (a phase vector diagram illustrates well the need for 6 dB margin as anything less causes abrupt 0/180 degree changes In phase such that a phase lock loop can’t converge to zero error). Once locked, the bandwidth can then be tightened for better SNR performance on the locked signal. This approach also leads to much faster acquisition time in general and is often referred to as “gear-shifting”.
If the signals are much wider than the acquisition bandwidth then more elaborate search and assessment methods are needed prior to setting the center frequency for acquisition. A separate frequency lock loop with wider bandwidth can be employed or other techniques that sweep over the entire bandwidth and access signal strength (such as the FFT or if processing time is available and resources scarce a linear frequency ramp can be employed). Note that the FFT approach can be significantly simplified since the number of bins (samples) needed in the FFT computation only need to be enough to ensure one bin for each step size equal to the loop acquisition bandwidth or less (so if the entire bandwidth of interest is ten times the loop bandwidth in its widest setting for acquisition or a real signal, then a 20 point FFT could be used to determine the location of the strongest bin).