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GPS Speed Measurement Using Doppler Shift

09/23/2009 8:00 AM

Hi, From what i read as of today active speed measurement is done by measuring the doppler shift in the carrier wave.Any guidance as to how one can go about this?The sources in the internet suggest that this is a highly accurate method to measure speed using GPS.Any idead how i should go about it ?

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#1

Re: GPS Speed Measurement Using Soppler Shift

09/23/2009 9:01 AM

"Any guidance as to how one can go about this?"

."Any idead how i should go about it ?"

Go about what? What's the question?

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#4
In reply to #1

Re: GPS Speed Measurement Using Soppler Shift

09/23/2009 1:05 PM

sorry ...should not have left the question open ended....the question is how is one supposed to go about measuring the speed using doppler shift of the carrier wave..

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#5
In reply to #4

Re: GPS Speed Measurement Using Soppler Shift

09/23/2009 1:18 PM

The carrier wave is electromagnetic radiation...which will go at the speed of light.
Ok it will slow down in some media.
Light doesn't go so fast in water or brick for that matter.
Hmmm, still not sure what you are after...
Or am I missing something? Help me out some one quick.
Del

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#2

Re: GPS Speed Measurement Using Doppler Shift

09/23/2009 10:02 AM

Sounds a bit unlikely to me unless speeds are high.
Position and time are probably more accurate.
You don't say what you want to measure the speed of...a man shambling along to buy his newspaper isn't going to give much doppler shift.

So my guidance would be 'don't do it that way'
Del
(I reserve the right to be completely wrong...)

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#3
In reply to #2

Re: GPS Speed Measurement Using Doppler Shift

09/23/2009 11:41 AM

"(I reserve the right to be completely wrong...)"

Hmmm.... Thats looks like a really good signiture to me...

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#6

Re: GPS Speed Measurement Using Doppler Shift

09/23/2009 10:51 PM

You are not going to get much better info from this forum than you can get from a good google search result like this...

http://nujournal.net/HighAccuracySpeed.pdf

Good luck with your project.

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#7

Re: GPS Speed Measurement Using Doppler Shift

09/24/2009 9:57 AM

As I said to you via PM and on your previous thread....

You don't have to worry about the mixing requirement of the transmitted wave and the received wave to get the doppler frequency...

This is all done for you in the microwave module... there is a transmitter section at 10.7 GHz and next to it is a receiving section with a gunn diode demodulator, built in and tuned to the same frequency.

Because the transmitted frequency leaks into the receiving section you automatically have a mixed signal picked up by the gunn diode....

This IS the doppler frequency....

John.

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#8

Re: GPS Speed Measurement Using Doppler Shift

09/24/2009 1:19 PM

As I understand GPS, the satellite(s) are moving at high (orbital) velocity. How do you distinguish your speed (using doppler effect) without knowing your relationship to the transmitted GPS signal? Sounds a bit to difficult to get reasonable accuracy. Try using delta between (2) samples of the same signal and calculate speed that way.

MRH

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