[G0HZU_JMR]

I put an aerial on the input to one of my spectrum analysers this evening and set it to capture about 20 seconds of the signal from a couple of FM broadcast stations. Reception isn't that great here as I don't have a proper aerial up for FM.

See below for the spectrum on a 200kHz span and the demodulated stereo signal from 0 to 100kHz. This shows the 19kHz pilot tone and the demodulated L+R up to 15kHz and also the L-R modulated on a suppressed 38kHz carrier. I think the strange modulation up at 57kHz is RDS.

The first image captures a quiet moment and this clearly shows the 19kHz pilot tone, the suppressed 38kHz carrier and the RDS waveform up at 57kHz. The second image shows a classic instrument and the third shows some pop music. The analyser works in real time so the screen display is very fluid in terms of update rate so it can be quite interesting to watch it whilst listening to the station at the same time.

It looks like the music has about 15kHz bandwidth although some modulation effects can be seen around the 19kHz carrier. I was expecting the demodulated signal to be a bit cleaner than this in this region.