I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Check out http://gpsinformation.net/main/gpstime.htm
The short answer is, the internal GPS clock for position is very accurate or it could not make to calculations needed as to where you are at, but there are many factors that might delay what time it gives to you on a display panel or through a serial cable.
73 Kevin WA6FWF
On 2/2/2012 7:28 AM, Vince Fiscus, KB7ADL wrote:
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
I'm not sure about GPS,but I have noticed that the clock on our cable box is off by up to 4 seconds at times.Customer service was not aware or concerned when I let them know.
-----Original Message----- From: Vince Fiscus, KB7ADL Sent: Thursday, February 02, 2012 10:28 AM To: [email protected] Subject: [amsat-bb] GPS Time observation
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
You will find that most handheld GPS receivers sold for casual use have a displayed time error that varies from 0 to 4 seconds. The receiver software was designed with an emphasis on computing position and performing other tasks, such as routing, more than on displaying time. Hence the presentation of time is some times delayed. If time is of higher importance, then a specialized GPS timing receiver is needed. Look for one that outputs a 1PPS (one pulse per second) signal and comes with timing software.
John WA4WDL
-------------------------------------------------- From: "George and Cheryl Abbott" [email protected] Sent: Thursday, February 02, 2012 11:57 AM To: [email protected]; "Vince Fiscus, KB7ADL" [email protected] Subject: [amsat-bb] Re: GPS Time observation
I'm not sure about GPS,but I have noticed that the clock on our cable box is off by up to 4 seconds at times.Customer service was not aware or concerned when I let them know.
-----Original Message----- From: Vince Fiscus, KB7ADL Sent: Thursday, February 02, 2012 10:28 AM To: [email protected] Subject: [amsat-bb] GPS Time observation
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
I think this has something to do with "GPS Time" vs "Earth Time".
IIRC, GPS time doesn't take into account the Leap Seconds that have been added to Earth time since the first GPS satellites have been launched. I think some of the newer receivers can compensate for this, but I'm not sure.
It's been about 14 years since I last worked in the GPS industry, and I'm a bit rusty on all the new stuff!
73, Jim KQ6EA
On 02/02/2012 04:57 PM, George and Cheryl Abbott wrote:
I'm not sure about GPS,but I have noticed that the clock on our cable box is off by up to 4 seconds at times.Customer service was not aware or concerned when I let them know.
-----Original Message----- From: Vince Fiscus, KB7ADL Sent: Thursday, February 02, 2012 10:28 AM To: [email protected] Subject: [amsat-bb] GPS Time observation
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
The difference between GPS time and UTC is adjusted as necessary. The adjustments come in the form of leap seconds and are added when needed at the end of June or December. The difference between GPS time and UTC is currently 15 seconds. There will be a leap second added this coming June 30. What is being seen is the casual user GPS receiver software does not put a high priority on time display.
John WA4WDL
-------------------------------------------------- From: "Jim Jerzycke" [email protected] Sent: Thursday, February 02, 2012 3:18 PM To: [email protected] Subject: [amsat-bb] Re: GPS Time observation
I think this has something to do with "GPS Time" vs "Earth Time".
IIRC, GPS time doesn't take into account the Leap Seconds that have been added to Earth time since the first GPS satellites have been launched. I think some of the newer receivers can compensate for this, but I'm not sure.
It's been about 14 years since I last worked in the GPS industry, and I'm a bit rusty on all the new stuff!
73, Jim KQ6EA
On 02/02/2012 04:57 PM, George and Cheryl Abbott wrote:
I'm not sure about GPS,but I have noticed that the clock on our cable box is off by up to 4 seconds at times.Customer service was not aware or concerned when I let them know.
-----Original Message----- From: Vince Fiscus, KB7ADL Sent: Thursday, February 02, 2012 10:28 AM To: [email protected] Subject: [amsat-bb] GPS Time observation
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Ahhh...., yes. "UTC". That's what I meant by "Earth Time".
Need...more...coffee...
73, Jim
On 02/02/2012 08:44 PM, jmfranke wrote:
The difference between GPS time and UTC is adjusted as necessary. The adjustments come in the form of leap seconds and are added when needed at the end of June or December. The difference between GPS time and UTC is currently 15 seconds. There will be a leap second added this coming June 30. What is being seen is the casual user GPS receiver software does not put a high priority on time display.
John WA4WDL
From: "Jim Jerzycke" [email protected] Sent: Thursday, February 02, 2012 3:18 PM To: [email protected] Subject: [amsat-bb] Re: GPS Time observation
I think this has something to do with "GPS Time" vs "Earth Time".
IIRC, GPS time doesn't take into account the Leap Seconds that have been added to Earth time since the first GPS satellites have been launched. I think some of the newer receivers can compensate for this, but I'm not sure.
It's been about 14 years since I last worked in the GPS industry, and I'm a bit rusty on all the new stuff!
73, Jim KQ6EA
On 02/02/2012 04:57 PM, George and Cheryl Abbott wrote:
I'm not sure about GPS,but I have noticed that the clock on our cable box is off by up to 4 seconds at times.Customer service was not aware or concerned when I let them know.
-----Original Message----- From: Vince Fiscus, KB7ADL Sent: Thursday, February 02, 2012 10:28 AM To: [email protected] Subject: [amsat-bb] GPS Time observation
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
At 03:44 PM 2/2/2012 -0500, you wrote:
The difference between GPS time and UTC is adjusted as necessary. The adjustments come in the form of leap seconds and are added when needed at the end of June or December. The difference between GPS time and UTC is currently 15 seconds. There will be a leap second added this coming June 30. What is being seen is the casual user GPS receiver software does not put a high priority on time display.
John WA4WDL
From: "Jim Jerzycke" [email protected] Sent: Thursday, February 02, 2012 3:18 PM To: [email protected] Subject: [amsat-bb] Re: GPS Time observation
I think this has something to do with "GPS Time" vs "Earth Time".
IIRC, GPS time doesn't take into account the Leap Seconds that have been added to Earth time since the first GPS satellites have been launched. I think some of the newer receivers can compensate for this, but I'm not sure.
It's been about 14 years since I last worked in the GPS industry, and I'm a bit rusty on all the new stuff!
73, Jim KQ6EA
On 02/02/2012 04:57 PM, George and Cheryl Abbott wrote:
I'm not sure about GPS,but I have noticed that the clock on our cable box is off by up to 4 seconds at times.Customer service was not aware or concerned when I let them know.
Thanks everyone for educating me on GPS. I wasn't concerned that it didn't display the exact time, but I was kind of curious as to why it didn't.
73 KB7ADL
At 11:57 AM 2/2/2012 -0500, "George and Cheryl Abbott" [email protected] wrote:
I'm not sure about GPS,but I have noticed that the clock on our cable box is off by up to 4 seconds at times.Customer service was not aware or concerned when I let them know.
Well the clock on my VCR constantly flashes 12:00.
;-)
KB7ADL
Interesting question, Vince...am sure someone on here will be able to answer it. I know at one time the civilian population was restricted from the most accurate location, and as I also remember the military accuracy was within a centimeter if several observations were taken...Nice to see your smiling face on here, my friend...
Anyone?
73 Dave
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
73, Dave, WB6LLO [email protected]
Disagree: I learn....
Pulling for P3E...
Well the most likely explanation would seem to be related to your GPS display routine. If you are getting accurate position information the timing from the satellites must be within a few nanoseconds. The satellite time currently differs from UTC by plus 15 seconds because UTC is retarded by one leap second on a regular basis but the satellite time is not altered. The satellites broadcast this offset from UTC but only every 12.5 minutes. It is not unusual for a GPS display to have a relatively low priority compared to the intensive position calculations and give a time display that differs by a second or two from UTC.
73 Alan ZL2BX
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Dave Guimont Sent: Thursday, 2 February 2012 18:29 To: Vince Fiscus, KB7ADL Cc: [email protected] Subject: [amsat-bb] Re: GPS Time observation
Interesting question, Vince...am sure someone on here will be able to answer it. I know at one time the civilian population was restricted from the most accurate location, and as I also remember the military accuracy was within a centimeter if several observations were taken...Nice to see your smiling face on here, my friend...
Anyone?
73 Dave
I have an old GPS unit, a Magellan explorist 210. It's fairly accurate determining position. After it has acquired about eight to ten satellites the position error averages between 20 to 35 feet. Now the question, the other day I was looking at one of the information pages the unit can display and on it, it gives the time in UTC. Just for fun I thought I would see how close the time was to WWV. I was surprised to see the unit was between one to four seconds off over various tests compared to WWV. IS this typical of all GPS units or do some display the time of day more accurately?
KB7ADL
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
73, Dave, WB6LLO [email protected]
Disagree: I learn....
Pulling for P3E... _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
At 10:28 AM 2/2/2012 -0800, Dave Guimont [email protected] wrote:
Interesting question, Vince...am sure someone on here will be able to answer it. I know at one time the civilian population was restricted from the most accurate location, and as I also remember the military accuracy was within a centimeter if several observations were taken...Nice to see your smiling face on here, my friend...
Anyone?
73 Dave
Hello again my friend, Nice to see you around too. I used the military units when I was in the army. The units could be loaded with crypto to remove the selective availability skew. That was back in the 90's.
73 KB7ADL
participants (7)
-
Alan Cresswell -
Dave Guimont -
George and Cheryl Abbott -
Jim Jerzycke -
jmfranke -
Vince Fiscus, KB7ADL -
WA6FWF