[time-nuts] Is possible precise 1pps?
I have GPS without position hold, I wonder how precise 1PPS, which I want to use for disciplined OCXO. You do not know how GPS with position hold calculates the measured coordinates vs know the real coordinates of the expected error timestamps 1 pps? Thansk for information ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
Hi A GPS that uses position hold gets it's coordinates from one of two possible sources: 1) You measure the actual antenna location with a precision survey grade GPS and enter them. --or-- 2) The GPS does a survey for some amount of time. It averages it's own reasonable location estimates over this time period. With 48 hour averaging and a good sky view the location estimate can be pretty good. The position hold function allows the GPS to come up with a time estimate from a small number of satellites. This is useful when the sky view is not very good. A position error of one meter can translate into a time error of about 3 ns. Most GPS engines are rated for a 3 meter error, so that would be roughly 9 or 10 ns. Since the exact error depends on the stat's location relative to the error vector, the actual error will vary a bit (= it looks like noise). Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of hutt...@seznam.cz Sent: Wednesday, March 13, 2013 9:04 AM To: time-nuts@febo.com Subject: [time-nuts] Is possible precise 1pps? I have GPS without position hold, I wonder how precise 1PPS, which I want to use for disciplined OCXO. You do not know how GPS with position hold calculates the measured coordinates vs know the real coordinates of the expected error timestamps 1 pps? Thansk for information ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
On 3/13/13 7:06 AM, Bob Camp wrote: Hi A GPS that uses position hold gets it's coordinates from one of two possible sources: 1) You measure the actual antenna location with a precision survey grade GPS and enter them. --or-- 2) The GPS does a survey for some amount of time. It averages it's own reasonable location estimates over this time period. With 48 hour averaging and a good sky view the location estimate can be pretty good. The position hold function allows the GPS to come up with a time estimate from a small number of satellites. This is useful when the sky view is not very good. A position error of one meter can translate into a time error of about 3 ns. Most GPS engines are rated for a 3 meter error, so that would be roughly 9 or 10 ns. Since the exact error depends on the stat's location relative to the error vector, the actual error will vary a bit (= it looks like noise). I was just reminded of an interesting observation.. The satellites are all moving, so whether your receiver is moving or not doesn't really change the inherent time accuracy possible, as long as you can accurately (!) estimate your position. Otherwise, the time uncertainty is some combination of the position uncertainty of the satellites and your own position uncertainty. i.e. there's no reason why you can't determine the position of a LEO satellite to centimeters, even though it's zipping along at 7km/sec. In fact it's potentially easier than on the earth's surface: less ionosphere, less multipath, less high frequency variation in position and velocity vectors. What position hold really buys you is a reduction in own position uncertainty and the ability to use fewer satellites to get a time fix. Think of it as solving for 4 unknowns (x,y,z,t) (i.e. your position and time). And, as a practical matter, you need to solve for their derivatives as well. Using inputs that are the (multiple) satellites' (x,y,z,t and derivatives). Position hold essentially says xdot,ydot,zdot =0, so you have fewer things to solve for (t and tdot). Fewer things to solve for with the same number of observables means, hopefully, smaller uncertainty on the resulting solution. There's also a basic issue with some receivers... if they were intended for an application that didn't need precise timing (e.g. they just time stamp things to the nearest millisecond or something), then the internal receiver architecture and software may not bother to actually try to solve for time to a higher level of precision. Maybe 1 microsecond is good enough to produce position and time outputs with the required accuracy. I recall seeing a patent (or maybe a paper) for a low precision attitude determination system (1 or 0.1 degree, as I recall) and it didn't need very good time or position accuracy at all.. what it needed to know was the direction of arrival of the GPS signal, so they could compare carrier phase between two antennas. And they didn't need precise measurement of carrier frequency either. To a first order, to get 1 degree knowledge, you need to know your position to within 1/57th of the distance to the satellite, or some hundreds of km. That's pretty crummy in GPS terms, but it works. I don't recall if that system even solved for own position, or if it used an estimate from somwhere else, or whether it just acquired and tracked the carrier and PN code, without doing a nav solution. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] 3 volt/ 5 volt antenna
I have a Thunderbolt and a Zypher Nanosync II GPSDO, both of which put out 5 V. The typical EBAY Marine GPS Antenna is not voltage labeled, but since it died after a few hours, I assume it was 3 volt. Any suggestions on a mod to either unit to change the feed to 3 volt, or suggestions on a reasonable cost 5 volt antenna. Do not really need a survey grade antenna. Thanks 73 Les Lester B Veenstra MØYCM K1YCM W8YCM les...@veenstras.com US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.33675 N 78.9823527 W Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 UK cell +44-(0)7849-248-749 Guam Cell: +1-671-929-8141 Jamaica: +1-876-456-8898 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 3 volt/ 5 volt antenna
Hi There are a ton of timing GPS antennas on the usual auction sites. Cone shaped or mushroom shaped white plastic enclosures. Mast mount with a coax connector on the bottom (occasionally a pigtail). They generally sell for less than $30. I've never seen one of the sub $30 ones that wanted anything other than 5 volts. Even the 5 volt ones seem to survive long term (days) exposure to +12. I'm not sure I'd count on that with every single one of them though. No I didn't test that feature on purpose Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Lester Veenstra Sent: Wednesday, March 13, 2013 11:04 AM To: 'Discussion of precise time and frequency measurement' Subject: [time-nuts] 3 volt/ 5 volt antenna I have a Thunderbolt and a Zypher Nanosync II GPSDO, both of which put out 5 V. The typical EBAY Marine GPS Antenna is not voltage labeled, but since it died after a few hours, I assume it was 3 volt. Any suggestions on a mod to either unit to change the feed to 3 volt, or suggestions on a reasonable cost 5 volt antenna. Do not really need a survey grade antenna. Thanks 73 Les Lester B Veenstra MØYCM K1YCM W8YCM les...@veenstras.com US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.33675 N 78.9823527 W Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 UK cell +44-(0)7849-248-749 Guam Cell: +1-671-929-8141 Jamaica: +1-876-456-8898 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 3 volt/ 5 volt antenna
Well of course you are correct. My mushroom is fine, Wish I could say the same for the connector/adaptors I used on the way to the mushroom. All is fine now after reseating connectors. Lester B Veenstra MØYCM K1YCM W8YCM les...@veenstras.com US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.33675 N 78.9823527 W Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 UK cell +44-(0)7849-248-749 Guam Cell: +1-671-929-8141 Jamaica: +1-876-456-8898 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Wednesday, March 13, 2013 11:33 AM To: les...@veenstras.com; 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] 3 volt/ 5 volt antenna Hi There are a ton of timing GPS antennas on the usual auction sites. Cone shaped or mushroom shaped white plastic enclosures. Mast mount with a coax connector on the bottom (occasionally a pigtail). They generally sell for less than $30. I've never seen one of the sub $30 ones that wanted anything other than 5 volts. Even the 5 volt ones seem to survive long term (days) exposure to +12. I'm not sure I'd count on that with every single one of them +though. No I didn't test that feature on purpose Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Lester Veenstra Sent: Wednesday, March 13, 2013 11:04 AM To: 'Discussion of precise time and frequency measurement' Subject: [time-nuts] 3 volt/ 5 volt antenna I have a Thunderbolt and a Zypher Nanosync II GPSDO, both of which put out 5 V. The typical EBAY Marine GPS Antenna is not voltage labeled, but since it died after a few hours, I assume it was 3 volt. Any suggestions on a mod to either unit to change the feed to 3 volt, or suggestions on a reasonable cost 5 volt antenna. Do not really need a survey grade antenna. Thanks 73 Les Lester B Veenstra MØYCM K1YCM W8YCM les...@veenstras.com US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.33675 N 78.9823527 W Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 UK cell +44-(0)7849-248-749 Guam Cell: +1-671-929-8141 Jamaica: +1-876-456-8898 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
On Wed, Mar 13, 2013 at 6:03 AM, hutt...@seznam.cz wrote: I have GPS without position hold, I wonder how precise 1PPS, which I want to use for disciplined OCXO. THere is more difference between brands and models of GPS receivers. Accuracy of the pPS can vary over a factor of 1000.But the good news is that you can buy a good one for under $20 on eBay so there is not much reason to make do and one that does not work well. Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Russian Timing Geosync Sats?
Hi Peter: I've been told that the 150 and 400 MHz signals are still active and that in the past week or so the timing signals on those frequencies from geostationary satellites (not the low orbit nav sats) are being used by some hacked Chinese cell phones to determine position to about 1 meter, but so far have not been able to confirm that. Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Peter Bell wrote: Tsikada was (maybe still is?) the Russian version of TRANSIT - it used 150MHz and 400MHz carriers, but I'm pretty sure the orbits were (like TRANSIT) low polar rather than Geosynchronous. You may also run into the name Parus - which was the name of the system before it was released to civilian use. The same satellites also carried the receivers for the original COSPAS system (aka SARSAT in english) - they also apparently had some sort of datalink capability, although the exact details are not clear - my guess is that now GLONASS is fully operational this datalink is the main reason for retaining them in operational status. It's also interesting that even after both the Tsikada and COSPAS programs were public knowledge the satellites were still given a cosmos-xxx designation which was normally only used for soviet military satellites (and launch failures). This strongly suggests that there was more stuff on board that they weren't talking about. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
Hutta, to sum up for you: as you have read, position hold doesn't mean precise PPS, only the ability to determine the PPS (the time) with less than 4 satellites, downto only one. Timing grade receivers have better internal oscillators and give better PPS always, either in position hold or not. Best to use a timing grade receiver but to move the first step towards the OCXO disciplining, a navigation receiver will do. Then you will start to appreciate things that will lead you to a timing receiver with the sawtooth correction. I say this because I have travelled this way over the years. On Wed, Mar 13, 2013 at 3:30 PM, Jim Lux jim...@earthlink.net wrote: On 3/13/13 7:06 AM, Bob Camp wrote: Hi A GPS that uses position hold gets it's coordinates from one of two possible sources: 1) You measure the actual antenna location with a precision survey grade GPS and enter them. --or-- 2) The GPS does a survey for some amount of time. It averages it's own reasonable location estimates over this time period. With 48 hour averaging and a good sky view the location estimate can be pretty good. The position hold function allows the GPS to come up with a time estimate from a small number of satellites. This is useful when the sky view is not very good. A position error of one meter can translate into a time error of about 3 ns. Most GPS engines are rated for a 3 meter error, so that would be roughly 9 or 10 ns. Since the exact error depends on the stat's location relative to the error vector, the actual error will vary a bit (= it looks like noise). I was just reminded of an interesting observation.. The satellites are all moving, so whether your receiver is moving or not doesn't really change the inherent time accuracy possible, as long as you can accurately (!) estimate your position. Otherwise, the time uncertainty is some combination of the position uncertainty of the satellites and your own position uncertainty. i.e. there's no reason why you can't determine the position of a LEO satellite to centimeters, even though it's zipping along at 7km/sec. In fact it's potentially easier than on the earth's surface: less ionosphere, less multipath, less high frequency variation in position and velocity vectors. What position hold really buys you is a reduction in own position uncertainty and the ability to use fewer satellites to get a time fix. Think of it as solving for 4 unknowns (x,y,z,t) (i.e. your position and time). And, as a practical matter, you need to solve for their derivatives as well. Using inputs that are the (multiple) satellites' (x,y,z,t and derivatives). Position hold essentially says xdot,ydot,zdot =0, so you have fewer things to solve for (t and tdot). Fewer things to solve for with the same number of observables means, hopefully, smaller uncertainty on the resulting solution. There's also a basic issue with some receivers... if they were intended for an application that didn't need precise timing (e.g. they just time stamp things to the nearest millisecond or something), then the internal receiver architecture and software may not bother to actually try to solve for time to a higher level of precision. Maybe 1 microsecond is good enough to produce position and time outputs with the required accuracy. I recall seeing a patent (or maybe a paper) for a low precision attitude determination system (1 or 0.1 degree, as I recall) and it didn't need very good time or position accuracy at all.. what it needed to know was the direction of arrival of the GPS signal, so they could compare carrier phase between two antennas. And they didn't need precise measurement of carrier frequency either. To a first order, to get 1 degree knowledge, you need to know your position to within 1/57th of the distance to the satellite, or some hundreds of km. That's pretty crummy in GPS terms, but it works. I don't recall if that system even solved for own position, or if it used an estimate from somwhere else, or whether it just acquired and tracked the carrier and PN code, without doing a nav solution. __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
On 3/13/2013 13:15, Azelio Boriani wrote: Then you will start to appreciate things that will lead you to a timing receiver with the sawtooth correction. For what it's worth: I have been evaluating the NEO-6M, a navigation receiver, for use in a NTP server which I have posted here in the past. It seems to perform quite well. It *does* have sawtooth correction, probably because it has a timing cousin (NEO-6T), and is stable enough to get RMS jitter to sub-10ns where the noise floor of my input capture is. It does not, however, have position hold (they have to have *some* reason to charge triple the price for a 6T) so over moderate timescales it might wander slightly more. Would I use 6M in a GPSDO? Probably not. But the PPS is pretty good, and some navigation receivers *do* have sawtooth correction, which I guess was really the point I was getting at. -- m. tharp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
Good, so we can see that position hold - can use down to one satellite, sawtooth correction - we can squeeze the most out of the PPS precision, whatever receiver (navigation/timing/other) we have. Good to know that the NEO-6M navigation receiver has the sawtooth correction. On Wed, Mar 13, 2013 at 7:42 PM, Michael Tharp g...@partiallystapled.comwrote: On 3/13/2013 13:15, Azelio Boriani wrote: Then you will start to appreciate things that will lead you to a timing receiver with the sawtooth correction. For what it's worth: I have been evaluating the NEO-6M, a navigation receiver, for use in a NTP server which I have posted here in the past. It seems to perform quite well. It *does* have sawtooth correction, probably because it has a timing cousin (NEO-6T), and is stable enough to get RMS jitter to sub-10ns where the noise floor of my input capture is. It does not, however, have position hold (they have to have *some* reason to charge triple the price for a 6T) so over moderate timescales it might wander slightly more. Would I use 6M in a GPSDO? Probably not. But the PPS is pretty good, and some navigation receivers *do* have sawtooth correction, which I guess was really the point I was getting at. -- m. tharp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Voltage on antennas
Some of the little magnetic attached antennas on eBay will operate on 3-5V. More problematic is using the older antennas which require 5V with the newer chips such as the LEA-5,6,7 series which run on 3.3V. There is an internal Bias T, but I haven't tried to bring in 5V through the Vant pin as I'm not sure how to make the device use the T. Perhaps someone can enlighten me. Off topic for this list: I'm playing with RTKLib with two LEA-4T in Tupperware boxes outside with the puck antennas inside the box and using 'Monoprice USB RJ45' USB extension adapters on 100 ft of Cat6 cables. Completely blows the timing delay, but 40 dB signals on U-center with 6 or more birds. Now to get the wireless link going for rover positioning! Building a small hobby planter. Need position accuracy to some extent, but not nanosecond timing of when each seed was dropped! N0UU ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Is possible precise 1pps?
NEO-6M buy for less than $ 10 including shipping from China, NEO-6T is unfortunately expensive, and frankly I do not know who sells it for at least a little reasonable prices. Difference between M and T - T supports fixed position - T has TXO Finally, the price at T version comes inadequate I find the possibilities to use the cheaper M module and achieve accuracy to T. I use MV89A OCXO, In addition, I have derived from the 10MHz frequency 100MHz (10th harmonic) So considering using something like http://goo.gl/LiakP(http://goo.gl/LiakP) and thus precise 1PPS used to disciplined OCXO. What do u think about it? I welcome any idea, it's certainly been discussed. Thanks On 3/13/2013 13:15, Azelio Boriani wrote: Then you will start to appreciate things that will lead you to a timing receiver with the sawtooth correction. For what it's worth: I have been evaluating the NEO-6M, a navigation receiver, for use in a NTP server which I have posted here in the past. It seems to perform quite well. It *does* have sawtooth correction, probably because it has a timing cousin (NEO-6T), and is stable enough to get RMS jitter to sub-10ns where the noise floor of my input capture is. It does not, however, have position hold (they have to have *some* reason to charge triple the price for a 6T) so over moderate timescales it might wander slightly more. Would I use 6M in a GPSDO? Probably not. But the PPS is pretty good, and some navigation receivers *do* have sawtooth correction, which I guess was really the point I was getting at. -- m. tharp ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Voltage on antennas
On 3/13/2013 6:40 PM, lstosk...@cox.net wrote: Some of the little magnetic attached antennas on eBay will operate on 3-5V. More problematic is using the older antennas which require 5V with the newer chips such as the LEA-5,6,7 series which run on 3.3V. Some distribution amps will all you to inject the voltage you need. I have an HP 58516A (an inexpensive eBay purchase) which passes the voltage from port 1 to the antenna. That also powers the amp. So, I put clean 5 V into port 1, and connect GPS receivers to the other 3. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Voltage on antennas
On 3/13/2013 5:19 PM, Mike S wrote: On 3/13/2013 6:40 PM, lstosk...@cox.net wrote: Some of the little magnetic attached antennas on eBay will operate on 3-5V. More problematic is using the older antennas which require 5V with the newer chips such as the LEA-5,6,7 series which run on 3.3V. Some distribution amps will all you to inject the voltage you need. I have an HP 58516A (an inexpensive eBay purchase) which passes the voltage from port 1 to the antenna. That also powers the amp. So, I put clean 5 V into port 1, and connect GPS receivers to the other 3. You can also put a 5-volt GPS on port 1 to match your 5-volt antenna and GPSs with other voltages, e.g. 3.3 or even 12 volts, on the other ports. This way, you don't lose the use of one port. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
On Wed, 13 Mar 2013 10:17:30 -0700, Chris Albertson albertson.ch...@gmail.com wrote: On Wed, Mar 13, 2013 at 6:03 AM, hutt...@seznam.cz wrote: I have GPS without position hold, I wonder how precise 1PPS, which I want to use for disciplined OCXO. THere is more difference between brands and models of GPS receivers. Accuracy of the pPS can vary over a factor of 1000.But the good news is that you can buy a good one for under $20 on eBay so there is not much reason to make do and one that does not work well. Chris Albertson Redondo Beach, California This brings up something that I have wondered about for a while. The Garmin GPS18x (and many other receivers) specify the PPS output as within 1uS but does that mean it wanders around over say 12 or 24 hours within 1uS of GPS Time or does it mean something else? I can easily see the granularity of the PPS output but that is obviously not what the specification refers to. I guess I need to pickup a real timing receiver or good oscillator to run a comparison with to see what is going on. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
On 03/13/2013 09:05 PM, David wrote: This brings up something that I have wondered about for a while. The Garmin GPS18x (and many other receivers) specify the PPS output as within 1uS but does that mean it wanders around over say 12 or 24 hours within 1uS of GPS Time or does it mean something else? I can easily see the granularity of the PPS output but that is obviously not what the specification refers to. If it's anything like the ancient Motorola receivers I purchased off fleabay on the mistaken assumption that they were UT+, it might have a 1uS phase skip every 20s or so. In other words, after a random number of seconds the PPS (and all subsequent PPS) will be exactly 1uS early. The idea being that it loosely tracks UTC/GPS, but jumps whenever it gets too far away. Totally useless for timing but at least they were cheap. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is possible precise 1pps?
On Wed, 13 Mar 2013 23:07:01 -0400, Michael Tharp g...@partiallystapled.com wrote: On 03/13/2013 09:05 PM, David wrote: This brings up something that I have wondered about for a while. The Garmin GPS18x (and many other receivers) specify the PPS output as within 1uS but does that mean it wanders around over say 12 or 24 hours within 1uS of GPS Time or does it mean something else? I can easily see the granularity of the PPS output but that is obviously not what the specification refers to. If it's anything like the ancient Motorola receivers I purchased off fleabay on the mistaken assumption that they were UT+, it might have a 1uS phase skip every 20s or so. In other words, after a random number of seconds the PPS (and all subsequent PPS) will be exactly 1uS early. The idea being that it loosely tracks UTC/GPS, but jumps whenever it gets too far away. Totally useless for timing but at least they were cheap. I have watched the output pretty carefully on my repaired Racal-Dana 1992 reliably to the nanosecond and I have never seen a jump like that and I doubt I would have missed it. At least for the Garmin 18x, the output pulse is definitely synchronous to the basic 16 MHz internal clock which is expected and I can see the sawtooth error change frequency as the GPS unit's temperature changes. It actually makes a pretty good temperature sensor. My 1992 lacks GPIB so I can not use it for logging unfortunately and I lack a better timebase for comparison purposes anyway. Those are on my list of things to take care of. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
