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*Subject*: Re: Predicting Doppler Shift*From*: "Kenneth J. Ernandes" <n2wwd@xxxxxxxxxxxxxx>*Date*: Thu, 12 Mar 1998 08:02:51 -0500

Matt - The easiest way to compute Doppler shift is using vectors. The orbit propagation algorithm takes the Keplerian data and converts it to position and velocity vectors as a function of time. These vectors are in an inertial (non-rotating; non-accelerating) frame-of-reference. You can do a simple coordinate transformation to respresent position and velocity in an Earth-fixed (i.e., rotating) coordinate frame. You can then compute a slant range vector (observer to satellite) as a vector subtraction (satellite position vector minus observer position vector). If you normalize the slant range vector, you have unit direction vector pointing from the observer to the satellite which gives you a basis for computing the azimuth and elevation antenna pointing angles. Once you have position and velocity in an Earth-fixed frame-of-reference, you can compute the velocity with respect to any observer on the surface of the Earth (i.e., range rate). This is done by computing the dot product of the satellite's velocity in the Earth-fixed frame with the normalized slant range vector. The range rate is the relative speed between the satellite and the observer used in the standard Doppler shift formulas. BTW, vector computations may sound intimidating, but if you use cartesian (X,Y,Z) reference frames, they're straight forward. 73, Ken N2WWD n2wwd@amsat.org http://www.mindspring.com/~n2wwd At 00:42 3/12/98 -0500, you wrote: > Name here is Matt the call is AB8AF. I have a guestion regarding > doppler shift, I would like to set up my tracking software to recognize > > the amount of shift at a given time. I need to get attitude latitude > and longitude for RS-12 or any OSCAR sat. available. Any suggestions ? > Thanks for your help! de Matt AB8AF > > Ken Ernandes n2wwd@amsat.org http://www.mindspring.com/~n2wwd

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