AN920 Posted September 26, 2006 Report Share Posted September 26, 2006 I am building a FM stereo transmitter from a kit and need to measure my modulation or also called deviation when on air. Where can I find a circuit to do this? The only thing I found was here http://www.edmdesign.com/mic.htm where they use a small radio. Any idea what the "additional electronics" would be and how they do it? If I use the VU meters on a FM receiver, how can I calibrate it at 75kHz modulation? Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 26, 2006 Report Share Posted September 26, 2006 Hi AN920,I think the "additional electronics" takes the audio signal before de-emphasis and peak detects it with a peak detector like in the datasheet for the LM3915. You can add your two stereo channels and it probably doesn't need to be before the de-emphasis because high audio frequencies usually aren't loud. Your VU meter is probably not a peak detector.They say that rock stations frequently peak at 80kHz so measure a few stations and average their outputs. Quote Link to comment Share on other sites More sharing options...
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