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*Subject*: [amsat-bb] Re: A doppler 2.4GHz question*From*: James R Miller <g3ruh@xxxxxxxxxxxxxxxxxxxx>*Date*: Wed, 22 Dec 2004 00:41:02 +0000

To Graham, G3VZV You asked about maximum rates of change of doppler -------------------------------------------------- Assuming the satellite is in a circular orbit, and passes overhead then, with a little bit of (easy) manipulation of Pythagorus' theorem, you find: RangeRate_Max = Re W km/s at the horizon (1) Re Rs RateOfRangeRate_Max = ----- W^2 km/s^2 at overhead (2) Rs-Re where: Re is Earth radius 6378.140 km Rs is satellite orbital radius km W is satellite mean motion rad/s And Re^2 W^2 = g ------ where g = 9.81 m/s^2 (3) Rs^3 Plugging in some numbers, taking care with units: Norad 2-line elements for the ISS give mean motion 15.716 rev/day which equates to W = 1.143E-3 rad/s. Using (3) this leads to a value for Rs = 6735 km. Substituting into (1) and into (2) we find: RangeRate_Max = 7.290 km/s at the horizon RateOfRangeRate_Max = 157 m/s/s at overhead To convert these to frequency shift, divide by the wavelength, which at S-band is 0.125 m. Thus: RangeRate_Max = +/-58.3 kHz at the horizons RateOfRangeRate_Max = -1257 Hz/s at overhead The minus sign is because doppler shift is -ve for a +ve velocity. [The above also assumes that the Earth is non-rotating]. 73 de James G3RUH -- ========================================================================== James R Miller WWW/PGP: http://www.jrmiller.demon.co.uk/ Cambridge, England Stardate: 2004 Dec 21 [Tue] 1732 utc ========================================================================== ---- Sent via amsat-bb@amsat.org. Opinions expressed are those of the author. Not an AMSAT member? Join now to support the amateur satellite program! To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**Follow-Ups**:**AO-51 38k4 on 2.4GHz--reports?***From:*Mark L. Hammond

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