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Re: doppler shift

-----Original Message-----
From: Mark Flanagan <markf@cshore.com>
To: amsat-bb@AMSAT.Org <amsat-bb@AMSAT.Org>
Date: Wednesday, September 30, 1998 6:26 PM
Subject: [amsat-bb] doppler shift

Sorry for the newbie question.  Please flame me directly, not on the amsat-bb.
Am I correct in stating that the doppler shift of a receive frequency starts higher than the actual frequency as it is approaching then continues lower as it going away? 
Yes if "it" means the approaching satellite.
 Does the frequency appear to stabilize when the distance from the satellite to the qth becomes constant, even if it is briefly?
Actually, the distance from the satellite to the qth never becomes constant (unless you are measuring a point on the curve of doppler shift) which means that it might seem constant for a moment, but is still actually changing. As the satellite approaches the nearest point to your qth, the doppler shift decreases with time until it reaches the point of minimum distance, at which the doppler shift is zero. Almost instantaneously, the doppler begins to change again, slowly at first and continues to increase with time until it drops beyond the horizon.
A common analogy is that of an approaching train whistle. The tone of the whistle appears high pitched at first, and slowly begins to decrease as the train approaches. When the train is at the nearest point to you, it appears to be the actual tone of the whistle, and almost immediately, it begins to fall in pitch as the train passes.
Bobbie  KD4LV
73 de Mark K. Flanagan
Amateur Radio Station K1MKF
e-mail:  markf@cshore.com