From: whit3rd@gmail.com   
      
   On Monday, October 2, 2017 at 4:53:37 PM UTC-7, gghe...@gmail.com wrote:   
   > On Monday, October 2, 2017 at 7:06:01 PM UTC-4, Mike S wrote:   
   > > On 10/2/2017 8:29 AM, ggherold@gmail.com wrote:   
   > >    
   > > > Someone pointed me to the DT35 distance measuring device.   
      
   > > > And I was wondering how it worked.  (What's inside.)   
      
   > I'm guessing they are modulating the laser beam.   
      
   Isn't it a lidar set?  Frequency-swept outgoing chirps, and receiver that   
   mixes down against the transmitter signal, so you get a low difference   
   frequency   
      
   F_difference =  dF/dt * 2X/c   
      
   ... that shows up on an FFT   
   AGC is allowed (it's not an intensity-dependent signal).   
   The receiver can be relatively low-gain, and AC coupled, which   
   gets rid of lots of stray light issues, even if your (iight) filtering is   
   sloppy.   
      
   Looks like there's a lens, maybe collimator with a retroreflector for a target.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)