[Phys-l] measure phasors and plot them using your very own lock-in amplifier

[John Denker <jsd@av8n.com>]

Hi --

I wrote up some documentation on my computer-based lock-in amplifier.
  http://www.av8n.com/physics/lockin.htm

This includes a screenshot showing the phasor diagram for an RC lowpass
at the half-power point:
  http://www.av8n.com/physics/lockin.htm#fig-lockin-ex1


  It must be emphasized that this is real data, obtained by 
  connecting my lockin to a real resistor and a real capacitor. 
  It is not an “artist’s conception”. My lock-in amplifier is 
  not a software simulation, but rather a real implementation 
  using the hardware of a real PC plus some software.


Assuming you have a Linux box with an ordinary audio interface, you 
can download the software and have your very own lockin.
  http://www.av8n.com/physics/lockin.htm#sec-download

This is not highly polished software.  It is in the "alpha" (evaluation)
phase.  If it looks like it was thrown together by somebody who had never
used Qt before, that's because it was.  The list of not-yet-implemented
features is quite long.  OTOH ... I find it useful as-is.  It's better
than nothing.

If anybody wants to collaborate on making it fancier, please let me know.

=============

There is also a brief review of how phasors are defined and how they are
used:
  http://www.av8n.com/physics/lockin.htm#sec-phasor-review