GPS Inaccuracy in Cell Phones

After trying to use these cell phone apps that us GPS to give distance traveled I've looked up data trying to discover why these apps are so far out of kilter.

This isn't just my assessment, before when my friend still lived in Castro Valley he was using some app that always had noticeably less mileage than my or his wife's speedometers.

As I said before, Strava was consistently 6% shorter than my speedo. MapMyRide wasn't even in the same ballpark. At first I attempted to explain the 6% loss on the climbing and descending but this course is so flat that there isn't a total of 100 feet change in altitude over the entire course. This would make a maximum error of about a 1/10th of a percent.

Then I figured that it had to do with latitude corrections not being properly made. While that may be part of the problem it isn't very likely since rather than the old geosynchronous orbits that were originally used, they are using an entire spate of GPS satellites that are in all sorts of orbits and at a distance that allows them to make complete orbits twice a day. They sent out their precise point in the orbit and if you have exact time and several satellites you can calculate (triangulate if you will) your position.. The best GPS units can handle 20 satellites at once and can get your position down to mm.

Question: could this error be due to time since the time of the GPS apps is derived not internally but from the cell phone center which can be several miles from you and transferred through several cell towers?

This seems pretty likely to be the problem to me. Being just one microsecond off could increase the error band to 1131 feet on a single satellite and it is unlikely that that apps track more than two or three satellites at a time. On a 3 satellite lock this would interestingly enough give an error band of about 6%.

Since this ride is local it would always be using the same cell CPU to be getting the time and so you would expect a pretty consistent error always in the same direction while on a long distance ride the errors would be divided between plus and minus errors and would average out to little or no discernable errors.

Likewise the error on my friend's app for the Palomares ride always gave approximately the same sort of error relatively reliably.

Military grade GPS that has an entirely different approach to getting time. I have designed clocks that lost one microsecond in a week. This requires a crystal oven that can regulate crystal oscillator temperatures to within a tenth of a degree C or better per 24 hour time period. The crystal is cut on a particular bias of the grain which I cannot remember. Crystals grow like a tree with a grain. This high accuracy crystal is frequency controlled by its size, the placement of the electrodes and temperature. The highest accuracy ones are extremely wasteful of these crystal structures. If you have precise location of where your position is you can use this to get precise time from your transmissions from the satellites and set the time precisely the first time. From that point you can find your exact position and then again with multiple satellites reset your timer as often as you find a significant timing error. These GPS systems use up to 20 satellites encoded in a manner that commercial devices cannot unlock. This is how you can target any location from any other location with mm distance errors. This means that the ONLY accurate means of touching that spot is from perfectly vertical from the target. Also since all of these satellites pass an un-named precisely known point at a precisely known distance you can reset the satellite timers which are necessary for this system.

This is the sort of thing I was paid to know and use. This was why I could get a quarter of a million bucks a year and have people standing in line for my services. Too bad about the concussion which caused me a couple of years out of the field at just exactly the wrong time - when one generation of managers that knew me were retiring and another which didn't took over. Resume's mean very little in the immediate area you're looking, because most of the hiring is done from recommendations of high level managers. But the resume alone is enough to get me jobs in Illinois or Texas or Arizona or Florida (???) were I willing to relocate. Last week I had two offers from aerospace firms in San Diego but I can't get the wife to move away from her children and grandchildren. And I really don't care to go back through the effort of showing boards of directors and CEO's what I can do. When I first recovered I should have immediately taken the jobs I was offered as some of these managers were still working and wanted me at places like Lawrence Labs in Berkeley and Sandia in Livermore. But quite frankly with my spotty memory I didn't think I still had it. Finally I was talked into taking a job for a friend and I told him that I would not allow him to pay me. But as soon as I sat down with the schematic and idiot code that the previous programmer had made it was all as fresh as yesterday. My total pay for 8 months was gas money to the job location and a $2,000 H-P laptop which I haven't even opened since the end of that job.

Tom Kunich wrote:
After trying to use these cell phone apps that us GPS to give distance
traveled I've looked up data trying to discover why these apps are so far out of kilter.

This isn't just my assessment, before when my friend still lived in
Castro Valley he was using some app that always had noticeably less
mileage than my or his wife's speedometers.

As I said before, Strava was consistently 6% shorter than my speedo.
MapMyRide wasn't even in the same ballpark. At first I attempted to
explain the 6% loss on the climbing and descending but this course is so
flat that there isn't a total of 100 feet change in altitude over the
entire course. This would make a maximum error of about a 1/10th of a percent.

Then I figured that it had to do with latitude corrections not being
properly made. While that may be part of the problem it isn't very likely
since rather than the old geosynchronous orbits that were originally
used, they are using an entire spate of GPS satellites that are in all
sorts of orbits and at a distance that allows them to make complete
orbits twice a day. They sent out their precise point in the orbit and if
you have exact time and several satellites you can calculate (triangulate
if you will) your position. The best GPS units can handle 20 satellites
at once and can get your position down to mm.

Question: could this error be due to time since the time of the GPS apps
is derived not internally but from the cell phone center which can be
several miles from you and transferred through several cell towers?

No. GPS predates cell phone systems that send out time. GPS receivers get
their time signal from the satellites themselves.

This seems pretty likely to be the problem to me. Being just one
microsecond off could increase the error band to 1131 feet on a single
satellite and it is unlikely that that apps track more than two or three
satellites at a time. On a 3 satellite lock this would interestingly
enough give an error band of about 6%.

Since this ride is local it would always be using the same cell CPU to be
getting the time and so you would expect a pretty consistent error always
in the same direction while on a long distance ride the errors would be
divided between plus and minus errors and would average out to little or
no discernable errors.

Likewise the error on my friend's app for the Palomares ride always gave
approximately the same sort of error relatively reliably.

Military grade GPS that has an entirely different approach to getting
time. I have designed clocks that lost one microsecond in a week. This
requires a crystal oven that can regulate crystal oscillator temperatures
to within a tenth of a degree C or better per 24 hour time period. The
crystal is cut on a particular bias of the grain which I cannot remember.
Crystals grow like a tree with a grain. This high accuracy crystal is
frequency controlled by its size, the placement of the electrodes and
temperature. The highest accuracy ones are extremely wasteful of these
crystal structures. If you have precise location of where your position
is you can use this to get precise time from your transmissions from the
satellites and set the time precisely the first time. From that point you
can find your exact position and then again with multiple satellites
reset your timer as often as you find a significant timing error. These
GPS systems use up to 20 satellites encoded in a manner that commercial
devices cannot unlock. This is how you can target any location from any
other location with mm distance errors. This means that the ONLY accurate
means of touching that spot is from perfectly vertical from the target.
Also since all of these satellites pass an un-named precisely known point
at a precisely known distance you can reset the satellite timers which
are necessary for this system.

This is the sort of thing I was paid to know and use. This was why I
could get a quarter of a million bucks a year and have people standing in
line for my services. Too bad about the concussion which caused me a
couple of years out of the field at just exactly the wrong time - when
one generation of managers that knew me were retiring and another which
didn't took over. Resume's mean very little in the immediate area you're
looking, because most of the hiring is done from recommendations of high
level managers. But the resume alone is enough to get me jobs in Illinois
or Texas or Arizona or Florida (???) were I willing to relocate. Last
week I had two offers from aerospace firms in San Diego but I can't get
the wife to move away from her children and grandchildren. And I really
don't care to go back through the effort of showing boards of directors
and CEO's what I can do. When I first recovered I should have immediately
taken the jobs I was offered as some of these managers were still working
and wanted me at places like Lawrence Labs in Berkeley and Sandia in
Livermore. But quite frankly with my spotty memory I didn't think I still
had it. Finally I was talked into taking a job for a friend and I told
him that I would not allow him to pay me. But as soon as I sat down with
the schematic and idiot code that the previous programmer had made it was
all as fresh as yesterday. My total pay for 8 months was gas money to the
job location and a $2,000 H-P laptop which I haven't even opened since the end of that job.

On Saturday, April 11, 2020 at 6:49:59 PM UTC-7, Ralph Barone wrote:
Tom Kunich wrote:
After trying to use these cell phone apps that us GPS to give distance
traveled I've looked up data trying to discover why these apps are so far out of kilter.

This isn't just my assessment, before when my friend still lived in
Castro Valley he was using some app that always had noticeably less
mileage than my or his wife's speedometers.

As I said before, Strava was consistently 6% shorter than my speedo.
MapMyRide wasn't even in the same ballpark. At first I attempted to
explain the 6% loss on the climbing and descending but this course is so
flat that there isn't a total of 100 feet change in altitude over the
entire course. This would make a maximum error of about a 1/10th of a percent.

Then I figured that it had to do with latitude corrections not being
properly made. While that may be part of the problem it isn't very likely
since rather than the old geosynchronous orbits that were originally
used, they are using an entire spate of GPS satellites that are in all
sorts of orbits and at a distance that allows them to make complete
orbits twice a day. They sent out their precise point in the orbit and if
you have exact time and several satellites you can calculate (triangulate
if you will) your position. The best GPS units can handle 20 satellites
at once and can get your position down to mm.

Question: could this error be due to time since the time of the GPS apps
is derived not internally but from the cell phone center which can be
several miles from you and transferred through several cell towers?

No. GPS predates cell phone systems that send out time. GPS receivers get
their time signal from the satellites themselves.

This seems pretty likely to be the problem to me. Being just one
microsecond off could increase the error band to 1131 feet on a single
satellite and it is unlikely that that apps track more than two or three
satellites at a time. On a 3 satellite lock this would interestingly
enough give an error band of about 6%.

Since this ride is local it would always be using the same cell CPU to be
getting the time and so you would expect a pretty consistent error always
in the same direction while on a long distance ride the errors would be
divided between plus and minus errors and would average out to little or
no discernable errors.

Likewise the error on my friend's app for the Palomares ride always gave
approximately the same sort of error relatively reliably.

Military grade GPS that has an entirely different approach to getting
time. I have designed clocks that lost one microsecond in a week. This
requires a crystal oven that can regulate crystal oscillator temperatures
to within a tenth of a degree C or better per 24 hour time period. The
crystal is cut on a particular bias of the grain which I cannot remember.

Tom Kunich wrote:
On Saturday, April 11, 2020 at 6:49:59 PM UTC-7, Ralph Barone wrote:
Tom Kunich wrote:
After trying to use these cell phone apps that us GPS to give distance
traveled I've looked up data trying to discover why these apps are so far out of kilter.

This isn't just my assessment, before when my friend still lived in
Castro Valley he was using some app that always had noticeably less
mileage than my or his wife's speedometers.

As I said before, Strava was consistently 6% shorter than my speedo.
MapMyRide wasn't even in the same ballpark. At first I attempted to
explain the 6% loss on the climbing and descending but this course is so
flat that there isn't a total of 100 feet change in altitude over the
entire course. This would make a maximum error of about a 1/10th of a percent.

Then I figured that it had to do with latitude corrections not being
properly made. While that may be part of the problem it isn't very likely
since rather than the old geosynchronous orbits that were originally
used, they are using an entire spate of GPS satellites that are in all
sorts of orbits and at a distance that allows them to make complete
orbits twice a day. They sent out their precise point in the orbit and if
you have exact time and several satellites you can calculate (triangulate
if you will) your position. The best GPS units can handle 20 satellites
at once and can get your position down to mm.

Question: could this error be due to time since the time of the GPS apps
is derived not internally but from the cell phone center which can be
several miles from you and transferred through several cell towers?

No. GPS predates cell phone systems that send out time. GPS receivers get
their time signal from the satellites themselves.

This seems pretty likely to be the problem to me. Being just one
microsecond off could increase the error band to 1131 feet on a single
satellite and it is unlikely that that apps track more than two or three
satellites at a time. On a 3 satellite lock this would interestingly
enough give an error band of about 6%.

Since this ride is local it would always be using the same cell CPU to be
getting the time and so you would expect a pretty consistent error always
in the same direction while on a long distance ride the errors would be
divided between plus and minus errors and would average out to little or
no discernable errors.

Likewise the error on my friend's app for the Palomares ride always gave
approximately the same sort of error relatively reliably.

Military grade GPS that has an entirely different approach to getting
time. I have designed clocks that lost one microsecond in a week. This
requires a crystal oven that can regulate crystal oscillator temperatures
to within a tenth of a degree C or better per 24 hour time period. The
crystal is cut on a particular bias of the grain which I cannot remember.
Crystals grow like a tree with a grain. This high accuracy crystal is
frequency controlled by its size, the placement of the electrodes and
temperature. The highest accuracy ones are extremely wasteful of these
crystal structures. If you have precise location of where your position
is you can use this to get precise time from your transmissions from the
satellites and set the time precisely the first time. From that point you
can find your exact position and then again with multiple satellites
reset your timer as often as you find a significant timing error. These
GPS systems use up to 20 satellites encoded in a manner that commercial
devices cannot unlock. This is how you can target any location from any
other location with mm distance errors. This means that the ONLY accurate
means of touching that spot is from perfectly vertical from the target.
Also since all of these satellites pass an un-named precisely known point
at a precisely known distance you can reset the satellite timers which
are necessary for this system.

This is the sort of thing I was paid to know and use. This was why I
could get a quarter of a million bucks a year and have people standing in
line for my services. Too bad about the concussion which caused me a
couple of years out of the field at just exactly the wrong time - when
one generation of managers that knew me were retiring and another which
didn't took over. Resume's mean very little in the immediate area you're
looking, because most of the hiring is done from recommendations of high
level managers. But the resume alone is enough to get me jobs in Illinois
or Texas or Arizona or Florida (???) were I willing to relocate. Last
week I had two offers from aerospace firms in San Diego but I can't get
the wife to move away from her children and grandchildren. And I really
don't care to go back through the effort of showing boards of directors
and CEO's what I can do. When I first recovered I should have immediately
taken the jobs I was offered as some of these managers were still working
and wanted me at places like Lawrence Labs in Berkeley and Sandia in
Livermore. But quite frankly with my spotty memory I didn't think I still
had it. Finally I was talked into taking a job for a friend and I told
him that I would not allow him to pay me. But as soon as I sat down with
the schematic and idiot code that the previous programmer had made it was
all as fresh as yesterday. My total pay for 8 months was gas money to the
job location and a $2,000 H-P laptop which I haven't even opened since
the end of that job.



Palph, what in the hell are you talking about? If you don't understand
how GPS works please don't tell me how you think it works. There is a
large difference between a commercial GPS that has an internal reference
clock and a military grade GPS which can derive its time in several ways.


OK, let me try this in more detail. GPS satellites send out a data packet
which contains the satellite’s x, y and z position, as well the the time
from the satellite’s internal atomic clock. If your receiver can get
signals from four satellites, then it can solve the equations to determine
the receiver’s x, y, z and t. If you can see more than four satellites, the
receiver then does a weighted least squares type of fit to get a more
accurate position signal. Look it up if you don’t believe me. The main
difference between civilian and military GPS units is that the military
units have the capability of using the SA (selective availability) signal,
which is a higher accuracy code which is broadcast along with the regular
“low accuracy� signal. There are numerous other small, but important
differences between the two, but SA is the big one.


While talking about how GPS predates cell phones explain my Sony watch
which always has the correct time which I bought in the 70's and is still working today.


Your Sony watch probably receives a WWVB signal (transmitted at 60 kHz)
containing time code, so it is not a GPS device (nor a cell phone, which
makes it a weak counter argument to a statement about GPS and cell phones).
Secondly, my statement was not that GPS predates cell phones. It was that
GPS predates cellular services which transmitted accurate time. TDMA
required (by definition), the receiver to switch at accurate times,
therefore a time signal was added to the protocol to sync the receivers.
TDMA rolled out circa 1990. Civilian GPS receivers came out in the 80s.

PS: I used to sit next to the guy who rolled out GPS enabled fault location
in our utility, and who also tested the accuracy of GPS time receivers
using our own cesium clock.

On Sunday, April 12, 2020 at 9:50:47 AM UTC-7, Ralph Barone wrote:

OK, let me try this in more detail. GPS satellites send out a data packet
which contains the satellite’s x, y and z position, as well the the time
from the satellite’s internal atomic clock. If your receiver can get
signals from four satellites, then it can solve the equations to determine
the receiver’s x, y, z and t. If you can see more than four satellites, the
receiver then does a weighted least squares type of fit to get a more
accurate position signal. Look it up if you don’t believe me. The main
difference between civilian and military GPS units is that the military
units have the capability of using the SA (selective availability) signal,
which is a higher accuracy code which is broadcast along with the regular
“low accuracy� signal. There are numerous other small, but important
differences between the two, but SA is the big one.

Cesium "clocks" are not clocks at all. They are an extremely accurate frequency standard. You still have to use digital electronics around it to make it into a clock.

And every single satellite has to have synchronized clocks. This accuracy has to be so accurate that not only to you have to take into account the distance that the signal has to travel at the speed of light, but the actual location in its orbit which gives you relative speed hence giving you the ability to measure the shift in time due to relativity.

In the normal speed regimes it isn't much but it is enough that military GPS must account for it.

With a somewhat faulty memory I don't believe that they send X,Y, and Z because they don't know it. Then send a satellite ID and their time. Your GPS looks up that satellite and its supposed location at that time (with all of the time corrections) which gives you their position. Comparing that distance with your clock give you a distance.

So now you have a satellite and its distance from you. That circumscribes and entire circle that is that distance from that satellite at that time.

Doing this for at least three satellites up to I believe as many as 20 gives you and increasingly accurate position.

Remember not only do you have to correct for speed and distance but actual processing time in the electronics which includes counting actual operations.

I remember actually writing this stuff but damned if I can remember who for or when.

I also remember that the satellites have to have their clocks corrected because their orbits are not stable because of atmospheric drag and a change in relative velocities.

This crap can get so complicated that you could spend your entire life on nothing else but GPS. There is a lot more that comes into play such as updating GPS files which hold the exact position at the exactly time. This is most easily done on ground files. I can't remember if a GPS receiver keeps the data in files or perhaps like you said that they are transmitted with the time signal and ID. There would be a hell of a lot of problems with that. It would mean updating satellite position files virtually twice a day to keep the satellite correct.

Normal GPS probably doesn't need an accuracy of better than 10 feet or so.

Tom Kunich wrote:
On Sunday, April 12, 2020 at 9:50:47 AM UTC-7, Ralph Barone wrote:

OK, let me try this in more detail. GPS satellites send out a data packet
which contains the satellite’s x, y and z position, as well the the time
from the satellite’s internal atomic clock. If your receiver can get
signals from four satellites, then it can solve the equations to determine
the receiver’s x, y, z and t. If you can see more than four satellites, the
receiver then does a weighted least squares type of fit to get a more
accurate position signal. Look it up if you don’t believe me. The main
difference between civilian and military GPS units is that the military
units have the capability of using the SA (selective availability) signal,
which is a higher accuracy code which is broadcast along with the regular
“low accuracy� signal. There are numerous other small, but important
differences between the two, but SA is the big one.

Cesium "clocks" are not clocks at all. They are an extremely accurate
frequency standard. You still have to use digital electronics around it
to make it into a clock.

And every single satellite has to have synchronized clocks. This accuracy
has to be so accurate that not only to you have to take into account the
distance that the signal has to travel at the speed of light, but the
actual location in its orbit which gives you relative speed hence giving
you the ability to measure the shift in time due to relativity.

In the normal speed regimes it isn't much but it is enough that military
GPS must account for it.

With a somewhat faulty memory I don't believe that they send X,Y, and Z
because they don't know it. Then send a satellite ID and their time. Your
GPS looks up that satellite and its supposed location at that time (with
all of the time corrections) which gives you their position. Comparing
that distance with your clock give you a distance.

So now you have a satellite and its distance from you. That circumscribes
and entire circle that is that distance from that satellite at that time.

Doing this for at least three satellites up to I believe as many as 20
gives you and increasingly accurate position.

Remember not only do you have to correct for speed and distance but
actual processing time in the electronics which includes counting actual operations.

I remember actually writing this stuff but damned if I can remember who for or when.

I also remember that the satellites have to have their clocks corrected
because their orbits are not stable because of atmospheric drag and a
change in relative velocities.

This crap can get so complicated that you could spend your entire life on
nothing else but GPS. There is a lot more that comes into play such as
updating GPS files which hold the exact position at the exactly time.
This is most easily done on ground files. I can't remember if a GPS
receiver keeps the data in files or perhaps like you said that they are
transmitted with the time signal and ID. There would be a hell of a lot
of problems with that. It would mean updating satellite position files
virtually twice a day to keep the satellite correct.

Normal GPS probably doesn't need an accuracy of better than 10 feet or so.


So to summarize, GPS location from your phone does does not depend on the
clock in the phone (although in urban areas where view of the GPS
satellites may be spotty, phones can get a position fix by triangulation
from (known location) cell phone towers.

On Sun, 12 Apr 2020 13:27:46 -0700 (PDT), Tom Kunich
wrote:

On Sunday, April 12, 2020 at 9:50:47 AM UTC-7, Ralph Barone wrote:

OK, let me try this in more detail. GPS satellites send out a data packet
which contains the satellite’s x, y and z position, as well the the time
from the satellite’s internal atomic clock. If your receiver can get
signals from four satellites, then it can solve the equations to determine
the receiver’s x, y, z and t. If you can see more than four satellites, the
receiver then does a weighted least squares type of fit to get a more
accurate position signal. Look it up if you don’t believe me. The main
difference between civilian and military GPS units is that the military
units have the capability of using the SA (selective availability) signal,
which is a higher accuracy code which is broadcast along with the regular
“low accuracy” signal. There are numerous other small, but important
differences between the two, but SA is the big one.

Cesium "clocks" are not clocks at all. They are an extremely accurate frequency standard. You still have to use digital electronics around it to make it into a clock.

And every single satellite has to have synchronized clocks. This accuracy has to be so accurate that not only to you have to take into account the distance that the signal has to travel at the speed of light, but the actual location in its orbit which gives you relative speed hence giving you the ability to measure the shift in time due to relativity.

In the normal speed regimes it isn't much but it is enough that military GPS must account for it.

With a somewhat faulty memory I don't believe that they send X,Y, and Z because they don't know it. Then send a satellite ID and their time. Your GPS looks up that satellite and its supposed location at that time (with all of the time corrections) which gives you their position. Comparing that distance with your clock give you a distance.

So now you have a satellite and its distance from you. That circumscribes and entire circle that is that distance from that satellite at that time.

Doing this for at least three satellites up to I believe as many as 20 gives you and increasingly accurate position.

Remember not only do you have to correct for speed and distance but actual processing time in the electronics which includes counting actual operations.

I remember actually writing this stuff but damned if I can remember who for or when.

I also remember that the satellites have to have their clocks corrected because their orbits are not stable because of atmospheric drag and a change in relative velocities.

This crap can get so complicated that you could spend your entire life on nothing else but GPS. There is a lot more that comes into play such as updating GPS files which hold the exact position at the exactly time. This is most easily done on ground files. I can't remember if a GPS receiver keeps the data in files or perhaps like you said that they are transmitted with the time signal and ID. There would be a hell of a lot of problems with that. It would mean updating satellite position files virtually twice a day to keep the satellite correct.

Normal GPS probably doesn't need an accuracy of better than 10 feet or so.

A delusion is a false belief that is not subject to reason or
contradictory evidence which may be firmly maintained in the face of
incontrovertible evidence that it is false. Delusions are common
psychotic disorders and can also be a feature of brain damage or
disorders.Examples of delusions include the sufferer believing that
one has an unusual power or talent.
--
cheers,

John B.

On Sun, 12 Apr 2020 08:08:57 -0700 (PDT), Tom Kunich
wrote:

On Saturday, April 11, 2020 at 6:49:59 PM UTC-7, Ralph Barone wrote:
Tom Kunich wrote:
After trying to use these cell phone apps that us GPS to give distance
traveled I've looked up data trying to discover why these apps are so far out of kilter.

This isn't just my assessment, before when my friend still lived in
Castro Valley he was using some app that always had noticeably less
mileage than my or his wife's speedometers.

As I said before, Strava was consistently 6% shorter than my speedo.
MapMyRide wasn't even in the same ballpark. At first I attempted to
explain the 6% loss on the climbing and descending but this course is so
flat that there isn't a total of 100 feet change in altitude over the
entire course. This would make a maximum error of about a 1/10th of a percent.

Then I figured that it had to do with latitude corrections not being
properly made. While that may be part of the problem it isn't very likely
since rather than the old geosynchronous orbits that were originally
used, they are using an entire spate of GPS satellites that are in all
sorts of orbits and at a distance that allows them to make complete
orbits twice a day. They sent out their precise point in the orbit and if
you have exact time and several satellites you can calculate (triangulate
if you will) your position. The best GPS units can handle 20 satellites
at once and can get your position down to mm.

Question: could this error be due to time since the time of the GPS apps
is derived not internally but from the cell phone center which can be
several miles from you and transferred through several cell towers?

No. GPS predates cell phone systems that send out time. GPS receivers get
their time signal from the satellites themselves.

This seems pretty likely to be the problem to me. Being just one
microsecond off could increase the error band to 1131 feet on a single
satellite and it is unlikely that that apps track more than two or three
satellites at a time. On a 3 satellite lock this would interestingly
enough give an error band of about 6%.

Since this ride is local it would always be using the same cell CPU to be
getting the time and so you would expect a pretty consistent error always
in the same direction while on a long distance ride the errors would be
divided between plus and minus errors and would average out to little or
no discernable errors.

Likewise the error on my friend's app for the Palomares ride always gave
approximately the same sort of error relatively reliably.

Military grade GPS that has an entirely different approach to getting
time. I have designed clocks that lost one microsecond in a week. This
requires a crystal oven that can regulate crystal oscillator temperatures
to within a tenth of a degree C or better per 24 hour time period. The
crystal is cut on a particular bias of the grain which I cannot remember.
Crystals grow like a tree with a grain. This high accuracy crystal is
frequency controlled by its size, the placement of the electrodes and
temperature. The highest accuracy ones are extremely wasteful of these
crystal structures. If you have precise location of where your position
is you can use this to get precise time from your transmissions from the
satellites and set the time precisely the first time. From that point you
can find your exact position and then again with multiple satellites
reset your timer as often as you find a significant timing error. These
GPS systems use up to 20 satellites encoded in a manner that commercial
devices cannot unlock. This is how you can target any location from any
other location with mm distance errors. This means that the ONLY accurate
means of touching that spot is from perfectly vertical from the target.
Also since all of these satellites pass an un-named precisely known point
at a precisely known distance you can reset the satellite timers which
are necessary for this system.

This is the sort of thing I was paid to know and use. This was why I
could get a quarter of a million bucks a year and have people standing in
line for my services. Too bad about the concussion which caused me a
couple of years out of the field at just exactly the wrong time - when
one generation of managers that knew me were retiring and another which
didn't took over. Resume's mean very little in the immediate area you're
looking, because most of the hiring is done from recommendations of high
level managers. But the resume alone is enough to get me jobs in Illinois
or Texas or Arizona or Florida (???) were I willing to relocate. Last
week I had two offers from aerospace firms in San Diego but I can't get
the wife to move away from her children and grandchildren. And I really
don't care to go back through the effort of showing boards of directors
and CEO's what I can do. When I first recovered I should have immediately
taken the jobs I was offered as some of these managers were still working
and wanted me at places like Lawrence Labs in Berkeley and Sandia in
Livermore. But quite frankly with my spotty memory I didn't think I still
had it. Finally I was talked into taking a job for a friend and I told
him that I would not allow him to pay me. But as soon as I sat down with
the schematic and idiot code that the previous programmer had made it was
all as fresh as yesterday. My total pay for 8 months was gas money to the
job location and a $2,000 H-P laptop which I haven't even opened since the end of that job.



Palph, what in the hell are you talking about? If you don't understand how GPS works please don't tell me how you think it works. There is a large difference between a commercial GPS that has an internal reference clock and a military grade GPS which can derive its time in several ways.

While talking about how GPS predates cell phones explain my Sony watch which always has the correct time which I bought in the 70's and is still working today.

A delusion is a false belief that is not subject to reason or
contradictory evidence which may be firmly maintained in the face of
incontrovertible evidence that it is false. Delusions are common
psychotic disorders and can also be a feature of brain damage or
disorders.Examples of delusions include the sufferer believing that
one has an unusual power or talent.
--
cheers,

John B.

Tom Kunich writes:

On Sunday, April 12, 2020 at 9:50:47 AM UTC-7, Ralph Barone wrote:

OK, let me try this in more detail. GPS satellites send out a data packet
which contains the satellite’s x, y and z position, as well the the time
from the satellite’s internal atomic clock. If your receiver can get
signals from four satellites, then it can solve the equations to determine
the receiver’s x, y, z and t. If you can see more than four satellites, the
receiver then does a weighted least squares type of fit to get a more
accurate position signal. Look it up if you don’t believe me. The main
difference between civilian and military GPS units is that the military
units have the capability of using the SA (selective availability) signal,
which is a higher accuracy code which is broadcast along with the regular
“low accuracy� signal. There are numerous other small, but important
differences between the two, but SA is the big one.

Cesium "clocks" are not clocks at all. They are an extremely accurate
frequency standard. You still have to use digital electronics around
it to make it into a clock.

Pendulum "clocks" are not clocks at all. They are a moderately accurate
frequency standard. You still have to use mechanical parts around it to
make it into a clock.

Sorry, no opinion on GPS, just had to point that out.

On Sun, 12 Apr 2020 08:08:57 -0700, Tom Kunich wrote:


Palph, what in the hell are you talking about? If you don't understand
how GPS works please don't tell me how you think it works. There is a
large difference between a commercial GPS that has an internal reference
clock and a military grade GPS which can derive its time in several
ways.

Wow, how is your foot little Tommy.