Analog / Digital conversion for DSP

[arefeidi]

Hi,

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!

 

[rakesh_vnit]

hey...here 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 constrains...like 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 haykin...digital comm book...its will surely help u....