The present invention relates to techniques for determining signal characteristics, and more particularly to a method for automatically identifying the carrier frequency of a pulsed signal using a spectrum analyzer for accurately counting the frequency of selected signals.
In the analysis and design of electronic devices it is important to determine the characteristics of various electrical signals which exist within the electronic devices. The two principal instruments which have been developed for this purpose are the oscilloscope, which displays the signal in terms of amplitude and time, and the spectrum analyzer, which displays the signal in terms of amplitude and frequency. By observing the displayed signals produced by these instruments the characteristics of the signals may be determined by a skilled operator. With the advent of microprocessor controlled instruments the goal is to make these instruments more "user friendly", i.e., make the instruments so easy to use that measurements can be made with little operator interaction or experience.
On a spectrum analyzer signals are displayed as a plurality of frequency components, each component having an amplitude corresponding to the strength of that component. Therefore, for pulse signals there is displayed a main lobe centered about a carrier frequency. This main lobe contains a plurality of spectral lines separated by the pulse repetition frequency of the pulsed signal. A plurality of side lobes representing the harmonic frequencies of the main lobe exist on either side of the main lobe separated by 1/PW, where PW is the pulse width of the pulsed signal. The frequency spectrum may become so complex that it is not easy to determine precisely by observation of the main lobe which spectral line represents the carrier frequency for the pulsed signal.
What is desired is a method for automatically identifying the carrier frequency of a pulsed signal with minimal operator interaction.