Date: Thu, 1 Mar 2012 09:20:00 +

Author: --- Urs Lauterburg

Subject: Re: How to Measure Doppler Shift


Dear Jerry man,

Well, not so long ago we actually designed, developed, built and
implemented a nice Doppler lab experiment. The idea was to also get a
feel for some of the measuring techniques which are required to
detect exosolar planets. In fact some of these detection methods also
look at the Doppler shift of the emitted light caused by the periodic
motion of the center stars.

I am just about to present this lab experiment along with a new piece
of apparatus that demonstrates an other universal physical aspect to
a crowd of educators next week.

In our case we have audible and ultrasonic sound sources we can
interchange and attach to the periphery of a spinning wheel. The
signal is then picked up by a stationary receiver in order to be
processed by a piece of dedicated LabVIEW software.

There are several strategies to go about and the students are made to
think about the various constraints and what method would be best
applied to a given situation. We are actually looking at periodic
signals with a sine modulated Doppler shift frequency content. The
straight forward approach is to record the signal of the rotating
source for some time and look at the frequency distribution
calculated by the FFT. Another method is to trigger measurements at
the points of maximal and minimal velocity in respect to the
receiver. In any case it is appropriate to use FFT algorithms for
good precision.

Maybe I get invited to give a PIRA talk some time again and you will
be able to see in all details how we actually do it ;-).

Muchos regardos


Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern

Am 29.02.2012 um 18:48 schrieb Zani, Gerald:

> Tapplers,
> How do you measure the Doppler shift on the oscilloscope?
> Does anyone do it with a beat between two identical sources, one
> stationary and one moving?
> Thanks,
> - Jerry
> --
> Gerald Zani
> Demonstration Manager
> Physics
> Brown University
> (401) 863-3964