On Monday, April 7, 2014 6:55:28 AM UTC-4, sgpopt...@gmail.com wrote:   
   > Lock-in is a great idea but these are very slow filters. I must make a   
   decision within 100usec or so. At my frequencies, they take a very long time.   
   I experimented with Lock-in before and gave up. I already have a pretty   
   complex signal processing back    
   end to sanitize the data, I can push up the frequency 2x to get more data and   
   speed up the back end processing so that I get more dB. If I 2x the frequency,   
   I expect to get about another 2-3dB, this I also will try.    
      
   OK I'm as "in the dark" as the rest here.  But if you've got short pulses of   
   signal and longish dead times, then sometimes a box-car averager (also called   
   a gated integrator) can be a win in terms of signal to noise.  (The trick is   
   you only look at the    
   signal during the small window in time when the signal is present.. and then   
   you only get noise from that small time window too.)  Not at all sure it is   
   applicable here.     
      
   George H.   
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   > On Monday, April 7, 2014 1:58:17 AM UTC+8, haitic...@gmail.com wrote:   
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   > > On Saturday, April 5, 2014 8:12:13 AM UTC-4, sgpopt...@gmail.com wrote:   
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   > > > It is not reflectometry.. Actually, it is an AM modulated signal that I   
   am seeking. Revealing the details of the app would be difficult, as my   
   employer would not like that.    
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   > > > But in a nut shell, I have a very weak laser source, this source emits a   
   1MHz signal with low duty cycle and looks at the reflection of this signal.   
   The object in 400mm distance makes a motion and by analysing the reflection,   
   the system interprets    
   the motion and takes several decisions. Now the job is 10x the distance   
   without increasing the laser source.    
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   > > hmmm - If you want *definitive* advice, I would advise you to get more   
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   > > about the optics w/o telling the app.    
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   > > But from what you say, literally, you could try back-end signal   
   enhancement    
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   > > methods, like lock-in and signal averaging.   
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   > > A $5 microprocessor can do these.   
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   > > j.   
      
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