A system includes a sampling module, a counter module, and a frequency characteristic module. The sampling module samples radio frequency (RF) signals on a first channel for a first predetermined period and a second predetermined period that is subsequent to the first predetermined period. The counter module increments first and second counts when the samples collected during the first and second predetermined periods reverse polarity, respectively. The frequency characteristic module determines a frequency of the RF signal based on at least one of the first and the second counts and determines frequency variation of the RF signal based on the first and second counts.