Patent ID: 7548735

Claim:
A radio apparatus comprising: a frequency agile radio receiver including an antenna for collecting electromagnetic energy, a bandpass filter connected to the antenna and having a pass band passing radio frequencies within a first range of radio frequencies, and rejecting frequencies outside the first range of frequencies; receiver circuits for processing radio frequency signals received through the antenna and producing an output, a radio frequency preamplifier amplifying a radio frequency signal received from the antenna through the bandpass filter; and a microprocessor controlling tuning of the frequency agile radio receiver; and a frequency determining apparatus for determining the frequency of a radio frequency signal received from the antenna and through the bandpass filter and supplying the frequency determined to the microprocessor, wherein the microprocessor tunes the frequency agile radio receiver to the frequency determined, wherein the frequency determining apparatus includes a counter for counting zero amplitude transitions of a radio frequency signal in each of a plurality of time periods of identical duration; a first register for storing counted zero amplitude transitions for a selected one of the time periods; a second register for storing an accumulated count of zero amplitude transitions counted during a total counting time including the plurality of time periods; and comparing means for comparing counted zero amplitude transitions for each time period other than the selected time period with the counted zero amplitude transitions for the selected time period, the second register discarding the accumulated count if the counted zero amplitude transitions for any of the time periods other than the selected time period are different from the counted zero amplitude transitions for the selected time period by more than a quantization error, wherein the frequency of the radio frequency signal is indicated by the accumulated count stored in the second register when the total counting time ends.