Operating principle of a superheterodyne (swept-tuned) spectrum analyzer
This instruments operates in accordance with the principle of super-heterodyne receiver.
It converts the input signal to an intermediate frequency (IF). This operation is carried out with the aid of a mixer and a local oscillator (LO).
The input frequency range is converted to a constant IF by varying the LO frequency.
In order to accomplish this result, a tunable LO is adopted and it is driven by a saw-tooth wave generator.
At IF it has a bandpass filter which bandwidth influences the resolution of the analysis.
It is worth to note that this instrument analyzes at each time instant only a frequency included in the frequency interval under analysis.