Characterizing the number and type of transmitters occupying a given frequency band is a critical aspect of spectrum sensing specifically and cognitive radio generally. We present an analytical framework based on probability to identify the number of frequency hopping transmitters of one specific type in a band of interest, and show that the probability mass functions associated with the different potential number of transmitters quickly becomes Gaussian as the number of channel observations increases. Simulation results confirm that the approach can lead with high probability to a correct decision regarding the number of interferers. Thus, the methods here can serve as a valuable complement to other spectrum sensing approaches.