SR/GR use absolute time to synchronize the GPS clocks with the ground clock.
in [Relativity]
|
From: Michael Moroney on 24 Mar 2010 11:32 kenseto <kenseto(a)erinet.com> writes: >On Mar 23, 12:51 pm, moro...(a)world.std.spaamtrap.com (Michael Moroney) >wrote: >> kenseto <kens...(a)erinet.com> writes: >> >Hey idiot time dilation got nothing to do with this discussion. >> >> Time dilation has *everything* to do with this discussion. Time dilation >> would cause the GPS satellite to "transmit" at the wrong frequency (as >> far as a terrestial receiver is concerned), so they adjusted the frequency >> before launch so it would at the correct frequency on Earth. >Sigh...the discussion was about whether observed doppler shift will >effect the rate of a clock. The answer is no. The discussion is about how different physical effects cause a frequency shift, and these frequency shifts can be calculated in advance and compensated for so that a relatively moving target receives a correct frequency. The passengers aboard the train will sense the "A" horn as mistuned. But those on the platform will hear the correct tune due to Doppler and some physics math. Someone riding aboard a GPS satellite will think the cesium clock is mis-set, with an incorrect divisor. A GPS receiver on the ground gets the correct frequency due to SR, GR and precalculated physics math that set the "wrong" divisor before launch. Same effect, different causes.
From: Michael Moroney on 24 Mar 2010 12:02 kenseto <kenseto(a)erinet.com> writes: >On Mar 23, 12:57 pm, moro...(a)world.std.spaamtrap.com (Michael Moroney) >wrote: >> >> Yes, just like the train horn. The approaching train has to sound at a >> frequency lower than 440 Hz to be heard at the station as 440 Hz, while a >> departing train has to sound at a higher frequency to be heard as 440 Hz. >No it's not the same. The GPS sends a signal after N+4.15 perods of Cs >133 radiation elapsed....no matter if it is approaching the ground >clock or receding away from the ground clock. There are additional Doppler effects on the GPS signal as the satellites approach or recede, but I'm not talking about that. Don't try to confuse matters by mixing the Doppler of the GPS signals and the Doppler train example. Consider the signal from a satellite as it passes directly overhead, so that it is neither approaching nor receding. Doppler effect is zero. However since the satellite is not as deep in the earth's gravity well, there are GR effects. In addition the satellite is moving at a decent clip so that there are SR (NOT Doppler!) effects. With the cesium clock "mis-set" so that the divisor is N+4.15 periods of Cs, the received signal on earth's surface is absolutely correct. (remember, no Doppler in this case). >With your situation the audience at the platform will hear 440 Hz when >the train is approaching but they will hear a different frequency when >the train is receding away from the platform. Remember, I changed the concert so that the train is receding for the entire performance, just for you. The Doppler effect on the performance is constant. You could also argue that the SR and GR effects on the satellites would change as the satellites speed up and slow down in their orbits, or move into higher and lower orbits. However, the satellites don't do that, so the SR/GR compensation factor is constant. Once again, same effect (frequency shift), different causes (SR/GR vs. Doppler)
From: Michael Moroney on 24 Mar 2010 13:13 "Androcles" <Headmaster(a)Hogwarts.physics_w> writes: >"Michael Moroney" <moroney(a)world.std.spaamtrap.com> wrote in message >news:hodajj$i24$1(a)pcls4.std.com... >> Looks like there's some ADD in with your psychosis. If you reread the >> Doppler comparison, you'd notice that there is just one train station. >If you reread the Doppler comparison, you'd notice that there is just one >city. >Someone in San Francisco can't use the same GPS satellite as someone >in New York simultaneously, they have to wait until it adjusts its >frequency! >Good comparison, MORONey. Perhaps GPS satellites only rise, they never >set below the horizon in your world. It appears that you are as thoroughly confused as Seto, thinking I am using the Doppler comparison for the satellites. The Doppler comparison was of a train's audio, just to demonstrate the trivially simple concept of pre-adjusting a frequency for a known effect of physics on a target in relative motion. Yes the Doppler effect most certainly exists in GPS, but the net result is zero, it does not accumulate. The receiver design includes the Doppler effects. As satellites rise, the received freq. is higher, they pass, they recede, the freq. is now lower, the satellite sets, this is a temporary, but not cumulative effect. However, I am discussing the SR/GR effects, that are cumulative and constant. Since the GR (gravity well) effects are about 5 times the SR (motion) effects, let's ignore SR since you confuse it with the Doppler. The earthbound clock will tick slower than a satellite clock due to GR, so an earthbound receiver will see the satellite clock as running fast. So, they simply preset the satellite clock to run just slow enough before launch for the frequency to be correct, as received on earth. Is that too complicated for your senile old brain to comprehend? Now back to your rubber room, you miserable senile old man.
From: Androcles on 24 Mar 2010 14:12 "Michael Moroney" <moroney(a)world.std.spaamtrap.com> wrote in message news:hodh8f$k9r$1(a)pcls4.std.com... > "Androcles" <Headmaster(a)Hogwarts.physics_w> writes: > >>"Michael Moroney" <moroney(a)world.std.spaamtrap.com> wrote in message >>news:hodajj$i24$1(a)pcls4.std.com... > >>> Looks like there's some ADD in with your psychosis. If you reread the >>> Doppler comparison, you'd notice that there is just one train station. > >>If you reread the Doppler comparison, you'd notice that there is just one >>city. >>Someone in San Francisco can't use the same GPS satellite as someone >>in New York simultaneously, they have to wait until it adjusts its >>frequency! >>Good comparison, MORONey. Perhaps GPS satellites only rise, they never >>set below the horizon in your world. > > It appears that you are as thoroughly confused as Seto, thinking I am > using the Doppler comparison for the satellites. The Doppler comparison > was of a train's audio, Good comparison, MORONey. If you reread the Doppler comparison, you'd notice that there is just one city. Perhaps GPS satellites only rise, they never set below the horizon in your world. Someone in San Francisco can't use the same GPS satellite as someone in New York simultaneously, they have to wait until it adjusts its frequency! It appears you remain the idiotic fuckwit you always were.
From: Michael Moroney on 24 Mar 2010 17:24
"Androcles" <Headmaster(a)Hogwarts.physics_w> writes: >"Michael Moroney" <moroney(a)world.std.spaamtrap.com> wrote in message >news:hodh8f$k9r$1(a)pcls4.std.com... >> >> It appears that you are as thoroughly confused as Seto, thinking I am >> using the Doppler comparison for the satellites. The Doppler comparison >> was of a train's audio, >Good comparison, MORONey. If you reread the Doppler comparison, >you'd notice that there is just one city. If YOU reread the Doppler comparison, you'd notice NO cities were mentioned, just a train, a train platform and a weird composer. Do you agree or disagree that someone on the platform will hear a tone different from that produced by a moving train? Do you agree or disagree that, with known conditions (such as a fixed speed of the train), you can calculate a frequency for the train's horn such that someone on the platform will hear a selected frequency? Now, if you had bothered to read what you snipped unread, you'd learn that the GR corrections (which is most of what the GPS has to account for) is due to the gravity well effect, and would still be necessary even if the GPS satellites were somehow held stationary over the earth, with NO Doppler effect involved whatsoever. Now, who keeps letting you out of your padded room? |