The SIGLENT SSA and SVA series of spectrum analyzers feature the ability to demodulate AM or FM transmissions and then play the audio output using an external spe Spectrum-Analyzer-Audio-Demodulation-Tips-for-AM-FM.pdfaker or earphone.
Here are some tips to optimizing the audio quality:
- Set the center frequency to the match the channel of interest. For example, if you wish to monitor/demodulate a signal at 100.7 MHz, set the center frequency to 100.7 MHz
- Set the span to fully capture the entire transmission bandwidth. Most North American Am/FM radio station channels have bandwidths < 1 MHz.
- Set the RBW > the modulation bandwidth of the signal. For most radio transmissions, this is > 20 kHz. An RBW setting of 100 kHz or greater should be a good starting point.
- Set the demodulation time to 10 s or so. The analyzer will update the signal trace every 10 s. This decreases the audio interruptions that occur during a sweep update but still provides some signal information
- Turn the volume to 1 before enabling the demodulation. Enable demodulation and check the volume as you slowly raise the volume to an acceptable level.
- Remember that the bandwidth of human voice audio is 4k and radio broadcast transmissions are often 20 kHz. So an RBW larger than 40 kHz is required (Nyquist Sampling).