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Factors affecting doppler Shift.

Discussion in 'Electronic Basics' started by thejim, Dec 29, 2005.

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  1. thejim

    thejim Guest

    Suppose we have a raddar that works on Doppler principle.As an object
    comes closer to the radar there will be a change in frequency(doppler
    shift).What i am asking to know is if the object comes closer at a
    greater speed is there going to be a change in the magnitude of the
    frequency shift in comparison if it was coming slower or just the the
    rate of change of magnitude will be faster.

    Thank you.
     
  2. PeteS

    PeteS Guest

    Doppler shift is dependent on the relative velocity between the target
    and the receiver, and the frequency shift is proportional to the
    relative velocity.

    Doppler shift is given as (for a generating source moving relative to
    an independent receiver):

    f' = f( 1 / [ 1+ (v / Co)] ) where f' is the received frequency, f the
    transmitted frequency, v the relative velocity between source and
    receiver and Co the medium velocity. For free space and electromagnetic
    radiation, that's 3 X 10^8 m/s to a close approximation.

    For a target of a radar gun, the solution is f' = 2{f( 1 / [ 1+ (v /
    Co)] )} because the doppler effect occurs both on the outbound and
    return trips.

    These equations are for targets moving much less than the speed of
    light (beyond that relativistic effects become significant).

    Note that the relative velocity is |v| x cos theta where |v| is the
    absolute velocity of the target + receiver and theta the angle between
    the target motion and the direct line between target and receiver. For
    a stationary radar gun, it is the velocity of the target times the
    cosine of the angle involved.

    A rate change of frequency will occur is the target accelerates
    relative to the receiver. (Acceleration may be positive or negative)

    Cheers

    PeteS
     
  3. Jasen Betts

    Jasen Betts Guest

    the frequecy shift of the reflected signal will be greater for greater speed
    of aproach.

    the magnitude of the reflected signal depends on the surface of the object
    and it's distance etc.

    Bye.
    Jasen
     
  4. Rich Grise

    Rich Grise Guest

    That's why the train horn goes: "BWAAAAAAP! BWAAAAAAAP! BWAP BWOWWWWWWWW....."

    Cheers!
    Rich
     
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