Spectrum Analyzer Audio Demodulation Tips for AM/FM

October 17, 2018

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 to1.

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 radio2.

station channels have bandwidths < 1 MHz.

Set the RBW > the modulation bandwidth of the signal. For most radio transmissions, this is > 203.

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. This4.

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 volume5.

as you slowly raise the volume to an acceptable level.

Remember that the bandwidth of human voice audio is 4k and radio broadcast transmissions are6.

often 20 kHz. So an RBW larger than 40 kHz is required (Nyquist Sampling).

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