AM index improvement

Mar 21, 2006 2 Replies
R

Hi,



I'm a software engineer and not really comfortable with electronics. May be some of you could help me with the following problem.



A have an AM signal, the carrier is about 250 volt (ca 100 kHz) and the modulated (digital) block wave (ca 1 kHz) is about 1 mVolt. That is an AM index of about 1:250,000! I'd like to (under)sample it with an ADC and then demodulate it (Hilbert transform). Because of the enourmous difference in amplitudes it is not possible to do this in one go. So I'm looking for an analogue way to enhance the modulation index before digitizing the signal.



Does anyone of you out there have a suggestion how to improve the modulation index of an AM signal?



Rutger


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J

That amplitude difference corresponds to about 108dB, and being two decades apart in frequency,
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J

Aarghhh!!! Hit transmit too quickly... Sorry about that. I was starting to think along the same line as Larkin about using a notch. With enough diddling you can get a _very_ deep notch (to infinity if you\'ve got perfect parts. ;) and if you make it active you can get the Q up high enough to keep the skirts well away from the 1000Hz (sideband???) National\'s got a nice write-up at: http://www.national.com/ms/LB/LB-5.pdf
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