GPS Inaccuracy in Cell Phones

On Sun, 12 Apr 2020 16:50:43 +0000 (UTC), Ralph Barone
wrote:

Tom Kunich wrote:
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,

Probably not an "atomic clock".
"Radio Controlled Clocks"
https://tf.nist.gov/general/pdf/1877.pdf
It gives a tolerable history of radio clocks.
"Laboratory type receivers for the LF signals appeared in
both the United States and Europe during the 1960s and 1970s..."
From about 1973 to 1981, I was working for a marine radio
manufacturer. Some of my tinkering included Loran C, NAVSAT (early
doppler), NAVSTAR (now GPS). The 100KHz Loran C receiver morphed into
a 60KHz WWVB receiver. However, the project died when we discovered
that a rather complicated decoder was required, and that a rather high
(at the time) license fee would need to be paid to the license holder.
Incidentally, the same thing happened in 2010, when WWVB added BPSK
modulation. No chips, no license, no service, and one giant step
backwards:
WWVB BPSK Modulation Remover - the "Dephaser"
http://www.californiahistoricalradio.com/wp-content/uploads//2017/02/CHRS-Construction-BPSK-Dephaser-John-Staples.pdf

Anyway, back on topic, Sony or any other Japanese company would have
little reason to produce a LF wris****ch without a domestic market.
See table 1 in the NIST document above, Pg 5 for the dates that
various transmitter were put into service:
WWVB US 1965
MSF UK 1974
DCF Germany 1973
JJY Japan 1999 (and 2001 for 60KHz)
BPC China 2002
We were watching the radio clock market during the 1970's. All I saw
were very large "instruments" made for laboratories and scientific
expeditions. The NIST article above mentions some of the early
devices which includes LF watches starting in 1990:
"The first radio controlled wrist watch is believed to be
the Junghans MEGA 1, which debuted in 1990, an introduction
that was hailed by one reviewer as 'one of the most momentous
horological events ever'. This digital watch synchronized to
signals from station DCF77 in Germany. Figure 9 shows the
watch and its internal clockwork, including the antenna
embedded inside the wrist band."
In other words, there were no consumer wris****ch atomic clocks in the
1970's.

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.

Sorta-maybe. GPS was first used in 1.9GHz PCS (TDMA) base stations to
synchronize the SONET clocks starting in 1995. GPS deployment
starting in 1978. The full 24 satellite constellation was ready for
general consumption in 1993. There were also some GPS modules crammed
into trunk mounted analog cellular phones and in some analog "bag
phones". However, these were rare and lacking a suitable display,
were only used for tracking.

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.

I was the guy who, after seeing an early GPS receiver, declared that
such a receiver would never be smaller or weigh less than two bricks.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

snip


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

snip
....not trying to be troll here, but x, y and z relative to WHERE?

What is the standard origin used with a rotating ball traveling through space?
Does it go back to the Prime Meridian and Greenwhich Main Time in some manner?

url to some basic primer appreciated.

pH in Aptos

pH wrote:
snip


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

snip
...not trying to be troll here, but x, y and z relative to WHERE?

What is the standard origin used with a rotating ball traveling through space?
Does it go back to the Prime Meridian and Greenwhich Main Time in some manner?

url to some basic primer appreciated.

pH in Aptos

I’ll be honest here. I’ve got no clue. I can only imagine that the math
would be easier if the satellites broadcast their position in the same
coordinate system that the GPS eventually outputs. It can’t be more than
two Google searches away.

And it’s probably not x, y, z, t, but altitude, longitude, latitude, t, or
some similar spherical coordinate system