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*Subject*: Re: [amsat-bb] Aircraft Doppler?*From*: "Dave G." <dmg@xxxxxxxxxx>*Date*: Sat, 19 Nov 2005 13:26:11 -0800*In-reply-to*: <011201c5ed42$4c9f2610$af89fd18@youre7075dc078>

John. Beautiful exposition --- I appreciate it, even tho' I did not ask the question :-\ Dave KK7SS On 19 Nov 2005 at 14:49, jmfranke wrote: > The maximum Doppler shift would be when the aircraft was > moving direct towards or away from the tranceiver. When the > aircraft is approaching, the shift would be to a higher > frequency, when moving away, the shift would be to a lower > frequency. One cycle of Doppler occurrs for every half > wavelength of change of distance. This is because the > transmitter to receiver path changes one wavelength when the > aircraft moves a half wavelength. For a direct approach or > departure, the Doppler shift is independent of distance. For > other angles, just multiply the direct approach valus by the > Cosine of the approach or departure angle. > > The Doppler shift "D" is found by starting with calculating > the wavelength L: > > L(in feet) = 984,000,000/F(in Hz) > > D = V/(L/2) > > But V is in mph and it must be converted to feet/sec. An easy > convesion to remember is 60mph = 88 ft/sec > > Or, D(in Hz) = F(in MHz) times V(in mph) times 88 divided by > ((984/2) times 60) > > Running the number for a police traffic radar using 10.525 GHz > and a speed of 1mph: > > D = (10525*88)/((984/2)*60) = 926200/29520 = 31.375 Hz/mph > which is correct > > Now, returning to your problem; > F = 144, let V = 1mph > > D = (144*88)/((984/2)*60) = 12672/29520 = 0.429 Hz/mph > > So: > for 200mph, the maximum shift is 200* 0.429 = 85.8 Hz > for 300 mph, the maximum shift is 300* 0.429 = 128.7 Hz > for 500 mph, the maximum shift is 500* 0.429 = 214.5 Hz > > One resuly of the calculation is that it shows that aircraft > talking to each other do not need to worry about the Doppler > shift moving the signals more than the channel bandwidth. ---- 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**:**Re: Aircraft Doppler?***From:*Roger Kolakowski

**References**:**Re: Aircraft Doppler?***From:*jmfranke

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