Low‐cost 1‐Hz resolution bandwidth spectrum analyzer in the 0.1–1000‐MHz frequency range

We present a very effective, low‐cost spectrum analyzer, built entirely from commercially available standard laboratory equipment. A broadband radio frequency synthesizer is used as the local oscillator input of a double‐balanced diode mixer to convert the high‐frequency input signal into the intermediate‐frequency output of the mixer, a lower‐frequency signal which is analyzed in an audio‐frequency spectrum analyzer. The overall performance depends on the specifications of the frequency synthesizer, the mixer, and the spectrum analyzer. Our instrument has a resolution bandwidth of 1 Hz in the 0.1–1000‐MHz frequency range with a −139‐dBm sensitivity for the smallest bandwidth. Especially the single‐hertz resolution bandwidth is an essential feature of our spectrum analyzer, not yet commercially available.