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Analog / Digital conversion for DSP

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Member level 4
Sep 6, 2007
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I'm new to DSP and also don't speak english that good, so please forgive me if my questions somehow sound dumb ;)

At the output of a receiver, I have a 25KHz rectangular signal which is AM-modulated with a 125kHz sine. The modulated signal only has two amplitudes, 0 and 1 (see attached picture from a simulation I made - 010010). Though there are also some intermodulation products of (unwanted) higher frequencies (MHz) at the receiver output.

Now I want to demodulate this signal as I somehow want to convert the 25kHz rectangular signal into a digital signal (1 0 0 0 1 1 0...or whatever). To get rid of the higher frequencies I need a lowpass filter. Also, I want to do several other things with it (e.g. measurement of signal level).

My system would look like this:

| Receiver | - - -> | Amplifier | - - -> | Analog/Digital-Converter fs= ca.500kHz | - - -> | DSP |

I'd like to use the DSP most importantly for
- lowpass filtering (getting rid of all frequencies > 25kHz)
- measurement of signal level

A few questions about that, would be great if someone would be able to answer:
1. Do I need another (analog) lowpass filter before the ADC (sample theorem)?
2. What could be used as an ADC - would a simple Schmitt-Trigger do the job (I just need 1 bit as there are only two amplitudes)?
3. Do you think DSP is the best way to do this at all...are there alternatives maybe?

Thanks in advance for your answers! is wat i think may help u....

1. a filter before the a/d is always advisable.... but u need to know abt the carrier freq to filter it.

2. schmith trigger can be used only if u can make up with certain u need to clearly know the delay wid whcih the signal is comin to ur samplin point and even the sampling freq.....

3...i am sorry, i am not well acquainted wid this subject to help u in that....

but go through simon comm book...its will surely help u....


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