[time-nuts] GLONASS receiver
Hi there! I currently have 2 embedded machines connected to a Garmin 18 LVC and a Sure GPS board. They are NTP servers for my company's LAN and I, at the moment, I get sub-ms accuracy over the LAN. Everything is fine but I am a bit worried about the GPS reliability because GPS is ruled by the USA. Would a GPS disciplined oscillator solve any potential problems? A receiver for GLONASS, even though I did not find any at a reasonable price, would be better? An iridium oscillator calibrated, regularly by GPS? Too many questions... but in the end I would like to know what is the best path that I could follow after these GPS receivers. Many thanks! Regards, Miguel ___ 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] Clock Correction Algorithm
Hi! I am building a clock that fetches its time from a local NTP server (GPS synched machine). I am using a timer based on a 16 bit interrupt on an Arduino (ATmega328 clocked at 16 MHz). I am implementing an algorithm to steer the this clock (nothing as complicated as the NTP algorithms) and wanted your opinion regarding this. The clock is set by sending an NTP packet and setting the clock with the replied timestamp plus half of the round trip time. In a local LAN this seems a good solution. I am not after micro-second accuracy as this is a clock and our eyes don't recognize anything faster than 50 ms. Even then I am aiming for 1-10 ms maximum offset with the NTP server. So, I am thinking about this algorithm (1-4 are done once and then it will jump to a): 1. interval = 64 2. ncorrections = 0 3. lastcorrection = 0 4. lastset = now a. while (lastset - now) interval do nothing b. fetch time from NTP c. compute offset from local clock d. compute correction to be added/subtracted to each second for this interval (offset/interval) e. reset clock with time fetched from NTP and apply correction to clock (making the second longer or shorter as appropriate) f. lastset = now g. if lastcorrection = 0 then go to i h. if abs(lastcorrection - correction) max then go to r i. lastcorrection = correction j. ncorrections = ncorrections + 1 k. if ncorrections 3 go to a l. if interval = 1024 go to m l. interval = interval x 2 m. ncorrections = 0 n. lastcorrection = 0 r. interval = 64 s. ncorrections = 0 t. lastcorrection = 0 u. go to a What's your take regarding this matter? Any help will be appreciated. Cheers, Miguel ___ 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] Clock Correction Algorithm
On 24/11/2011, at 11:42, Attila Kinali att...@kinali.ch wrote: On Thu, 24 Nov 2011 10:14:17 + Miguel Gonçalves m...@miguelgoncalves.com wrote: The clock is set by sending an NTP packet and setting the clock with the replied timestamp plus half of the round trip time. In a local LAN this seems a good solution. I am not after micro-second accuracy as this is a clock and our eyes don't recognize anything faster than 50 ms. Even then I am aiming for 1-10 ms maximum offset with the NTP server. if you want to be better than 10ms, you can just use the value you get from the NTP server, raw, without any processing. The usuall RTT values in a LAN (light or moderate load) is around 100-200us. Ie if your NTP server doesn't take an exuberant amount of time to respond (which it should not anyways) and your LAN is not heavily loaded, you will be below 1ms in 99% of the time. Right! That is what I am doing. The problem is the drift between adjustments. Arduino's clock is slow 25 ms every minute and if temperature changes it will surely be different. The proposed algorithm wants to correct that. Cheers, Miguel ___ 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] Clock Correction Algorithm
Hi Javier! Thanks for your help. On 24/11/2011, at 13:16, Javier Herrero jherr...@hvsistemas.es wrote: El 24/11/2011 13:56, Miguel Gonçalves escribió: Right! That is what I am doing. The problem is the drift between adjustments. Arduino's clock is slow 25 ms every minute and if temperature changes it will surely be different. That is more than 400ppm error, that sounds quite high. Is the clock frequency of the Arduino so drifted? I would try first to check (and correct a bit) the source of that error. If the crystal frequency is ok, perhaps there is an error in the programming of the timer that generates the timing interrupt. I am using an Arduino Uno that presumably is running at 16 MHz. I am using a 16 bit timer with a 256 pre-scaler: 1600 / 256 = 62500 Hz 1 / 62500 = 16 us 65536 - 62500 = 3036 I am setting the counter to 3036 and let it overflow after 65535. If I check the error every second I see the clock getting behind correct time and after 60 seconds it's 25 ms apart from UTC. Perhaps I should increase the initial value from 3036 to 3036+25E6/(60/16). I will make the second shorter this way. What do you think? Cheers, Miguel Regards, Javier ___ 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] Clock Correction Algorithm
Hi!! On 24/11/2011, at 13:48, Attila Kinali att...@kinali.ch wrote: On Thu, 24 Nov 2011 12:56:31 + Miguel Gonçalves m...@miguelgoncalves.com wrote: Right! That is what I am doing. The problem is the drift between adjustments. Arduino's clock is slow 25 ms every minute and if temperature changes it will surely be different. The proposed algorithm wants to correct that. Oh.. sorry.. i misunderstood your question. Yes the algorithm would work, though i'd rather use a pll style sytem. Ie, measure the differnce in time between your clock and your refrence. Calculate from this a correction value for the clock frequency (should be a simple multiplication by a constant factor). Low pass filter that correction value. I will investigate PLL. I don't want something overly complicated because this is a time display. I want less that 10 ms error and this goal is much better than needed for a clock. This should also do away with all those special cases in your algorithm, as a PLL style algo is self stabilizing (unless you got the loop gain too high*). You will get at most a constant difference between your clock and the reference. This difference can be minimized by using a higher gain in the feedback loop (at the cost of stability). This is exactly what I wanted. I really need to read about PLL. Also as Javier said, 400ppm is a quite high offset for a crystal. Or are you using a RC oscillator based RTC? (a lot of on chip RTCs are build that way) I am using the oscillator that comes with the Arduino. On the other hand, i once used a Atmel SAM7 RTC (or RTT in Atmel lingo) that is based on a RC Oscillator with +/- 30% accuracy. Using a simple calibration step (powering up the crystal oscillator every hour and using the crystal to measure the RTT frequency, setting this as new correction value, then going back to sleep for an hour) got me below 100ppm over a day in my tests (office enviroment, temperature variation probably below 2°C over a day, definitly less than 5°C, 30ppm crystal) I have a RTC that I am not using for this project that has 3.5ppm between -40C and 85C but I don't intend to use it because I want to keep this simple. Thanks a lot Atilla for your help. Cheers, Miguel ___ 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] Clock Correction Algorithm
Hi Atilla!
On 24/11/2011, at 14:42, Attila Kinali att...@kinali.ch wrote:
On Thu, 24 Nov 2011 14:21:37 +
Miguel Gonçalves m...@miguelgoncalves.com wrote:
I am using an Arduino Uno that presumably is running at 16 MHz.
I am using a 16 bit timer with a 256 pre-scaler:
1600 / 256 = 62500 Hz
1 / 62500 = 16 us
65536 - 62500 = 3036
I am setting the counter to 3036 and let it overflow after 65535.
I'm not quite sure i understood you correctly, and i dont know anything
about the arduino and the avr32. But usually, you set a timer to do a
certain repetition rate. Ie raises an interrupt ever x clock cycles.
Or to put it differently, you let the timer run freely, but let it call
you when it's time to do something.
It's really easy: the timer counter is increased 62500 times per second so on
each increase 16 us have passed. I set the start of the counter to 3036 to let
it run to 65535. From 3036 to 65535 one second has passed at the 62500 Hz rate
When it overflows a routine is called that simply updates a global boolean flag.
In my main loop I just have something like
while (true) {
while (!flag) {}
/* a second has passed... this code is executed between seconds */
flag = false;
}
How do you check for the overflow? If you check a flag in your main loop,
this would explain the huge difference, as this polling will add a
(not so) constant delay each time the timer overflows, until you start
your timer again.
I have to check this flag. I do all the processing between seconds. I believe
the interrupt service routine should be kept as short as possible.
Also I checked with a simple counter and the above loop (the inner one) is
executed 48 times per second. I also know that if I don't measure this it
will run much more. Right?
Thanks for your help!
Cheers,
Miguel
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Re: [time-nuts] Clock Correction Algorithm
Hi Javier! On 24/11/2011, at 15:15, Javier Herrero jherr...@hvsistemas.es wrote: El 24/11/2011 15:21, Miguel Gonçalves escribió: I am using an Arduino Uno that presumably is running at 16 MHz. I am using a 16 bit timer with a 256 pre-scaler: 1600 / 256 = 62500 Hz 1 / 62500 = 16 us 65536 - 62500 = 3036 I am setting the counter to 3036 and let it overflow after 65535. If I check the error every second I see the clock getting behind correct time and after 60 seconds it's 25 ms apart from UTC. Perhaps I should increase the initial value from 3036 to 3036+25E6/(60/16). I will make the second shorter this way. Hi! Can you check the real frequency of the oscillator? If it is too far from 16MHz, there are two options: trim the capacitors that are in the crystal oscillator circuit (I'm not familiarized with the Arduino... but I suppose they will be there), or... software trim changing the counter reload value as you suggest :) The software way is probably the best idea as it would account for small differences in different oscillators. I have 3 Arduino boards and will make 3 time displays. Does the counter needs reloading every overflow or it is automatically reloaded? depending on how you are done this, it can also provide some delays that apparently slows the clock. It's manually reloaded with the 3036 value every time the routine is called. If I load it with a bigger value I will make a faster second. If with a small value the second will be longer. Thanks for your help! Cheers, Miguel Regards, Javier ___ 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] Clock Correction Algorithm
Hi! On 24/11/2011, at 15:16, Bob Camp li...@rtty.us wrote: Hi How about simply adding 1 ms every other second? You could then fine tune it by picking a small number of seconds to not add a ms to. An idea but I am searching for a more global and elegant solution. In fact, after reading about PLL (as someone suggested) I noticed that my algorithm is a simple PLL. Cheers, Miguel Bob On Nov 24, 2011, at 7:16 AM, Javier Herrero jherr...@hvsistemas.es wrote: El 24/11/2011 13:56, Miguel Gonçalves escribió: Right! That is what I am doing. The problem is the drift between adjustments. Arduino's clock is slow 25 ms every minute and if temperature changes it will surely be different. That is more than 400ppm error, that sounds quite high. Is the clock frequency of the Arduino so drifted? I would try first to check (and correct a bit) the source of that error. If the crystal frequency is ok, perhaps there is an error in the programming of the timer that generates the timing interrupt. Regards, Javier ___ 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] iPhone keeping better time?
On 16 November 2011 12:27, Jim Palfreyman jim77...@gmail.com wrote: Folks, Is it my imagination or is the iPhone under IOS 5 keeping way better time? Mine (3 GS running 5.0.1) is apparently within 1 second of UTC which is good. By the way... is it possible to build a custom receiver to send this information to a computer? I live in Europe so there's only GSM available... Do the US CDMA receivers work here? Cheers, Miguel ___ 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] iPhone keeping better time?
On 16 November 2011 12:47, David J Taylor david-tay...@blueyonder.co.ukwrote: Folks, Is it my imagination or is the iPhone under IOS 5 keeping way better time? I assume it's contacting the mobile towers more often for reading time. Jim Palfreymam Lucky Jim! Certainly doesn't apply to my iPad2. Currently 40.8 seconds out under 5.0.1. Sinful it doesn't use NTP ( I suppose you know who didn't approve of NTP, since it wasn't under Apple's firm grip). I own a Mac Mini and a MacBook. Their NTP implementation is simply a joke. Even with a local stratum 1 I can't get decent accuracy. :-( David, weren't you interested in a LED clock I was going to build? Cheers, Miguel ___ 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] iPhone keeping better time?
Hi David! On 16 November 2011 16:18, David J Taylor david-tay...@blueyonder.co.ukwrote: Yes, Miguel, someone did mention an NTP synched clock some time back, and I thought it might be a fun project. Based on an Arduino board IIRC? Although I don't think it had Wi-Fi by default I have it running at the moment. Have to build a case tough. See attached picture. It looks very smart! I have a small plate of frosted plexiglass in front of the display to diffuse the strong light of the LED. I am about 4 meters away from it and it looks great. The digits are 29 mm tall while with 5 mm LED they would be 50 mm tall. Too big for my office but perhaps some might want larger digits. It syncs at the 9th, 19th, 29th, ... second mark from a local GPS based NTP server. On every sync, the timestamp returned from the NTP server is on the 6 ms mark this means that the local clock of the Arduino drifts a lot. 6 ms per 10 s. Outside the 500 ppm allowed for NTP! G A bit too much... The RTC will help a lot. Actually, the RTC performance is great. 2 ppm means 0.02 ms every 10 seconds (0.12 ms every minute). Not bad! With 3 local GPS stratum 1 servers peered together I can pool them every 10 seconds and maintain sub ms accuracy. Inova clocks talk about 200 ms accuracy. Even with Internet NTP servers and pooling every 5 minutes the accuracy of this RTC would be 0.6 ms. 200 times better than the commercial product. I don't understand why a company like Meinberg sells these clocks! I am installing a realtime clock (Chronodot) this weekend that has an accuracy of +/- 3.5 ppm from -40C to 85C (I read somewhere that between 0 and 40C it is 2 ppm). This RTC can output a square wave signal at 1 Hz and Arduino can read that and use it to update the display at the exact second mark. With the RTC and synching every 10 minutes (9th, 19th, 29th, 39th, 49th and 59th of every hour) I expect a maximum error of 1.2 ms (based on 2 ppm). My eyes can't read that :-) Nor mine! On my PC, the radio pips, and the hands on the analogue clock I wrote, appear to be precisely in sync, but I expect that means within a few tens of milliseconds. :-) Perhaps we both need to wear glasses :-) A neat feature I added is that when the clock can't synch it won't show a time. It will show -- : --. Shouldn't that be the classic video recorder display? A flashing 00:00 or whatever? 00:00 flashing... done! I'll post a video for you to see soon. You'll tell me if you like it or not. You'll be my beta tester :-) Yes, I would be interested, but others might as well, so perhaps put it up on the Web somewhere? I'll do that as soon as possible. Cheers, Miguel ___ 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] iPhone keeping better time?
On 16 November 2011 18:21, David J Taylor david-tay...@blueyonder.co.ukwrote: It's even worse on the WiFi iPad - there is no way to automatically set the time. You can only do it via the Settings page and that only gives you minute resolution. The Emerald-Sequoia app is nice, but since it can't actually fix the time, every app that has time constraints has to do its own NTP. Criminal, really! Even SNTP would be better. I had hoped it would be fixed in iOS 5.0 as I'd seen it discussed in the beta groups. IMHO, in Mac OS X it is worse to have a bad NTP client installed by default than no NTP client at all. Cheers, Miguel ___ 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] Precisione GPS based led clock
Hi Paolo! On 03/11/2011, at 10:44, paolo.mart...@alice.it paolo.mart...@alice.it wrote: Dear all I am an amateur astronomer working in the field of minor planet occultation. To arrange a precise reference time I am looking for a 1/100 sec LED dispaly clock GPS based. (LED is usefull for night vision) My idea is to use a ebay used master clock such as ThunderBolt GPS disciplined clock to drive a timecode display. Particulary I wish to realize a PIC based LED clock to display hour min sec and use the 10 MHz reference to arrange an 1/10 and 1/100 sec disaply. Can anyone help me in finding schemes or any more flexible idea? thanks I am, at the moment, developing a led clock with an Arduino board that synchronizes its clock with the use of a NTP GPS server in my LAN. The clock can be configured through telnet and it syncs with the NTP server every 8 seconds. I expect to have it ready next week. I can send you the schematic if you so desire. Cheers, Miguel ___ 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] Subject: Listening to the List Owner
I really find it funny (to say the least) that in the XXI century people concentrate on form rather than content when using such an informal medium as e-mail. This resembles professional and academic titles that people insist on appending to their names. These human beings are all about appearance. When you squeeze then there's little juice. It's ridiculous! Regarding HTML mail it's like still using, today, a text based console e-mail client on a VAX/VMS! Fortunately punch cards went away a while ago! By the way, HTML is a standard and I find it perfectly acceptable to have it used to format content of an e-mail. Are you against standards? I bet you use MIME or do you attach the links to an FTP server for large files? Not an HTTP server as HTTP was not designed to transfer files. I believe we have to be flexible and open in the world we live today. Cheers, Miguel PS: Sorry for any typos as English is not my main language. On 21/09/2011, at 13:07, Peter Gottlieb n...@verizon.net wrote: Here, I'll top post this, and explain why. It is frequently very difficult to follow a complex thread due to different indentings, split up messages, some groups not accepting HTML (like Yahoo's intermittent problems), and just plain efficiency. I have frequently missed points because I didn't spend time to comb through a long thread to see a few words of response buried deep in the message. I also get a rather large volume of mail, much of which has a pretty low SNR. The quickest, most efficient method in my experience is to top post when there is a single point to communicate. Obviously, if you want to cover many points of a long message, then it makes sense to be inserting the comments in the proper locations, so you will see me doing that when appropriate. Besides, what is more important: the ideas someone has, or their posting style? When the posting style becomes more important in a group than the ideas, I find that's usually not the place for me (and I know there are many others who share that sentiment, it's far from original). I suspect we can all easily adapt to either, both, or an as-appropriate mix of posting styles. Peter On 9/21/2011 7:43 AM, Rob Kimberley wrote: David, I appreciate the subtle humour here, but virtually all people I communicate with top post, and I've been using email since the early 90s. It is only groups like this where it seems to be a problem. Maybe it is a function of the mail reader that is being used, (not sure on that one), but I think you will find that you are in the minority. Rob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David J Taylor Sent: 21 September 2011 10:42 AM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Subject: Listening to the List Owner Nothing wrong with top posting my friend! Rob K Please see: http://www.html-faq.com/etiquette/?toppost Cheers, David -- ___ 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] Subject: Listening to the List Owner
I might have missed but has the owner of the list said anything yet about this?? Cheers, Miguel On 21/09/2011, at 20:09, Robert Darlington rdarling...@gmail.com wrote: I'm not replying to anybody in particular, just hit the reply key on the last email. Guys, this is rather off topic, dontchathink? Get over it. Whining won't change how I post, but perhaps asking nicely might. -Bob On Wed, Sep 21, 2011 at 12:05 PM, Don Latham d...@montana.com wrote: What he said!! Don Max Robinson Bottom posting is anathema to those of us who use screen readers. We can't skim, we have to read every line or risk the possibility of missing something. In extreme cases I often give up before getting to the poster's message. If you must bottom post summarize instead of quoting every word of every preceding message on the subject. This will be my only post on this subject. Regards. Max. K 4 O D S. Email: m...@maxsmusicplace.com Transistor site http://www.funwithtransistors.net Vacuum tube site: http://www.funwithtubes.net Music site: http://www.maxsmusicplace.com To subscribe to the fun with transistors group send an email to. funwithtransistors-subscr...@yahoogroups.com To subscribe to the fun with tubes group send an email to, funwithtubes-subscr...@yahoogroups.com - Original Message - From: David J Taylor david-tay...@blueyonder.co.uk To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Wednesday, September 21, 2011 4:41 AM Subject: Re: [time-nuts] Subject: Listening to the List Owner Nothing wrong with top posting my friend! Rob K Please see: http://www.html-faq.com/etiquette/?toppost Cheers, David -- SatSignal software - quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ 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] Averaging Location for Position Hold
Thank you all for all the good advice! Cheers, Miguel On 16 September 2011 00:10, li...@lazygranch.com wrote: I have a program called Expertgps that seems to be accurate, but uses old bw imagery. I think they fixed the bug, but it used to be that the windows and linux version of google earth would show different dates for the imagery. ___ 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] Averaging Location for Position Hold
Hi! On 14 September 2011 05:36, Mark Sims hol...@hotmail.com wrote: Lady Heather's precision (nominal 48 hour) survey collects data over multiple 1 hour periods. With 48 hours of data, multipath and transient disturbances are minimized. It applies weighted median filters to the data and does other statistical analysis to arrive at a final location. With a good choke-ring antenna you can get within under a foot. With a crappy patch antenna without a ground plane maybe 6 feet. Simple averaging of the survey samples does not perform nearly as well. Will do. Thanks! As far as Lady Heather not working with other GPSDO's... well, She has good taste. The Trimble Thunderbolt is far and away the best time-nut GPSDO out there. It is highly configurable and controllable, comes with a very good OCXO, and is dirt stinkin' cheap. If you dot all your i's and cross all your t's and pay very close attention to the details you can coax ridiculously high performance out of the tiny little box... rivaling the best cesium references made for under $200. This is why I am looking at some units on eBay. :-) One, perhaps, silly question: when it looses lock it continues to issue the PPS (hold-over mode) but does the second numbering continues also through RS-232? This is going to be used for an NTP server. Cheers, Miguel ___ 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] Averaging Location for Position Hold
Hi all! I am installing a timing GPS unit over a new location where I already have a NMEA GPS with PPS (let's call it unit A). The NMEA GPS is logging every 16 seconds its GPGGA string. I have a log with around 213400 samples. Each line is similar to this one 55817 48494.500 127.127.20.0 $GPGGA,132814.000,4055.2142,N,00829.6071,W,2,9,1.06,278.9,M,51.2,M,,*4E I averaged the minutes of latitude and longitude, the MSL (278.9) and the Geoid Separation (51.2) and got the following 40º 55.2155' N 8º 29.6044' W (MSL 268.195m and Geoid Separation 51.2m) (for unit A) I entered this location on Google Maps I got a position that is in the middle of a close street (see footer for image; real location is the red dot). I also have another GPS unit (let's call it unit B) that is on the roof and did the same calculations (36500 samples): 40º 55.2228' N 8º 29.6103' W (MSL 262.66m and Geoid Separation 51.7m) (for unit B) When I plot this with Google Maps I get the exact location of the antenna (within 1 meter; see footer for image; real location is the red dot). I am assuming the first unit has some kind of internal error. Or, does Google Maps has an offset? I need this information to enter the precise location in the Oncore UT+ unit I will be using at this location. I will be using the location of unit A. Cheers, Miguel The images available here: http://dl.dropbox.com/u/11210443/GPS%20A.JPG and http://dl.dropbox.com/u/11210443/GPS%20B.JPG. I did not attach these to the message to reduce traffic on the mailing list server. ___ 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] Averaging Location for Position Hold
Thanks! I believe then that is best to rely on SynTac position averaging or the auto-survey feature? Regards, Miguel On 13 September 2011 20:24, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message CAEdntmtEcC=_N1uwvNb2GZqVX8r-AXO81hw+SXF6= p+kegb...@mail.gmail.com , =?ISO-8859-1?Q?Miguel_Gon=E7alves?= writes: I have a log with around 213400 samples. Each line is similar to this one [...] I averaged the minutes of latitude and longitude, the MSL (278.9) and the Geoid Separation (51.2) and got the following That doesn't work very well, because the variation in your samples is not a random distribution: Echos and other multipath is the same every day, the buildings that cause it do not move. A much better strategy is to weigh the filtering by DOP quality or even better, if you have the actual residuals from each of the satelites used. You may find some inspiration here: http://phk.freebsd.dk/raga/sneak/ -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] Averaging Location for Position Hold
Hi Chris! The problem with auto-survey is that it doesn't report the averaged position in the log file. I haven't checked if the binary protocol enables access to this but if it does it's just a matter of patching the driver IMHO. If I use auto-survey should I continue using mode 1 in ntp.oncore? I believe that the first time it will auto-survey but for the next start-ups it won't. Right? PHK: you had your hands on this driver I believe. Am I saying something stupid? :-) Google Maps reports WGS84. Google Earth reports WGS84 and altitude is MSL (Mean Sea Level) that is easily converted to GPS altitude using the Geoid Correction. Regarding Google Maps accuracy just look at the images I sent in my previous message. The GPS that sits on the roof is giving coordinates that are 1 meter away max from the truth. Cheers, Miguel On 13 September 2011 22:03, Chris Albertson albertson.ch...@gmail.comwrote: 2011/9/13 Miguel Gonçalves m...@miguelgoncalves.com: Hi all! I am installing a timing GPS unit over a new location where I already have a NMEA GPS with PPS (let's call it unit A). The NMEA GPS is logging every 16 seconds its GPGGA string. The Oncore UT+ can does it's own site survey automatically. That's the best way. You can only compare the GPS location with Google if both are using the same system. The most common one today is WPS84 but you need to check. The problem is that the Earth is not a Sphere and different systems assume non-sphere shapes. Getting this wrongs gives about the size error you observed, more or less. Also, can you really trust Google Earth as an authoritative source? I'm not sure.An interesting test would be to go find a USGS benchmark or a section marker near you then enter it's location into Google. See if Google hits the marker. -- 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. ___ 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] Averaging Location for Position Hold
Hi David! Same here. I discussed this matter with a friend that did some GIS work a few years back and we both believe that the unit reporting the wrong position might be doing this because it's only seeing half of the sky (it is near a window facing SE) while the other one sees the entire sky. My friend pointed out that Google Maps are used today in navigation systems and while the software might have some corrections algorithms built in he believes that the maps should be reasonably accurate. Cheers, Miguel On 13 September 2011 22:25, David VanHorn d.vanh...@elec-solutions.comwrote: Also, can you really trust Google Earth as an authoritative source? I'm not sure.An interesting test would be to go find a USGS benchmark or a section marker near you then enter it's location into Google. See if Google hits the marker. -- For what it's worth, my Thunderbolts here did a 48 hour survey, and the position they report, fed into google earth, hits the north side of the 3' x 3' skylight they are in. Roughly 18 error. Maybe luck, but they both report almost identical positions. I'm north of Denver, so I'm a bit off the spherical average. ___ 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] Averaging Location for Position Hold
On 13/09/2011, at 23:10, gary li...@lazygranch.com wrote: Google maps/earth is sometimes on the money, and sometimes not. Remember, these are orthorectified images pieced together. That can't be easy. [They are also on my fecal matter list since they trespassed on my land (undeveloped) to place a satellite cross mark for a shoot. Needless to say I was pissed to see the big X on google earth, though now I have free pointers for NEWS. The while paper had mostly rotted away.] What is the location?? I am curious. I guess the other question is what do you get with Lady Heather? That is, how does it average your position? I will try it over this weekend. I have to get a Windows PC. Only Macs and FreeBSD boxes here. Thanks for your ideas! Cheers, Miguel ___ 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] Averaging Location for Position Hold
Upon further investigation I learned that Lady Heather is only for Trimble units... I could borrow a Windows laptop from my company for a couple of days. That's how I surveyed my window (current location of the GPS antenna) using SynTac (formerly WinOnCore). Cheers, Miguel On 14 September 2011 01:43, Chris Albertson albertson.ch...@gmail.comwrote: 2011/9/13 Miguel Gonçalves m...@miguelgoncalves.com: I guess the other question is what do you get with Lady Heather? That is, how does it average your position? I will try it over this weekend. I have to get a Windows PC. Only Macs and FreeBSD boxes here. I thought Lady Heather. If so do you really have to get a Windows box to run it? Can't it be build on any other platform? Maybe using Wine. Sorry to have to ask but I've not looked at the source code. -- 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. ___ 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] GPS Antenna
Hi all! First let me introduce myself: I am a time nut since 1996 (former admin of a stratum 2 server: bug.fe.up.pt) but college and other priorities kept me away from my obsession. The other day I happened to buy a Garmin 18 LVC unit and installed it in the roof in my company. It has been working great and it handled the hot days of August quite well. It shares it's time with the entire network through NTP. Here it is: tick# ntpq -pn remote refid st t when poll reach delay offset jitter == *127.127.20.0.GPS.0 l1 16 3770.0000.010 0.004 10.0.2.9.GPS.1 u4 16 3770.1610.012 0.007 194.117.9.130 194.117.9.1292 u 33 64 377 14.8101.154 0.886 194.117.9.136 194.117.9.1382 u 62 64 377 14.307 -2.253 3.324 193.136.5.7 193.136.250.246 2 u 18 64 377 11.7191.549 0.811 193.136.5.15193.136.250.246 2 u 43 64 377 15.9221.166 0.819 178.79.160.159 217.20.44.6 2 u 51 64 377 43.315 -0.816 0.666 BTW, it's an embedded machine (ALIX 1D) running FreeBSD 7.4 out of a Compact Flash card. I am looking at other stratum 2 servers to see if my time is off. I also added another stratum 1 server (tock, 10.0.2.9) using the same FreeBSD/CF configuration but on a more powerful machine (an old server laying around). This time I used a Sure GPS Evaluation Board. Here it is: tock# ntpq -pn remote refid st t when poll reach delay offset jitter == o127.127.20.0.GPS.0 l6 16 3770.000 -0.009 0.001 10.0.2.10 .GPS.1 u3 16 3770.176 -0.015 0.004 194.117.9.130 194.117.9.1382 u 29 64 377 14.4580.837 2.336 194.117.9.136 194.117.9.1382 u 22 64 377 14.073 -2.361 2.371 193.136.5.7 193.136.250.246 2 u 20 64 377 12.4251.420 0.377 193.136.5.15193.136.250.246 2 u 26 64 377 16.5941.651 0.924 178.79.160.159 217.20.44.6 2 u 23 64 377 44.289 -0.722 1.819 I've also installed, at home, a FreeBSD machine (same software as before) but this time I hooked it with a Motorola Oncore UT+ (great unit by the way) and configured it to resolve only time (averaged the antenna location for 24 hours). This machine is also running NTP: oncore# ntpq -p remote refid st t when poll reach delay offset jitter == oGPS_ONCORE(0) .GPS.0 l 12 16 3770.0000.002 0.001 canon.inria.fr .GPSi. 1 u 30 64 377 56.2183.469 0.261 ptbtime1.ptb.de .PTB.1 u 23 64 377 65.3950.225 0.355 ntp.inrim.it.CTD.1 u7 64 377 50.8400.185 0.314 ntp02.oal.ul.pt 194.117.9.1382 u 61 64 377 10.703 -0.811 2.863 ntp04.oal.ul.pt 194.117.9.1382 u 46 64 377 10.361 -3.673 0.401 Router7.Lisboa. 193.136.250.246 2 u 17 64 3778.313 -0.189 0.390 Router15.Porto. 193.136.250.246 2 u 65 64 377 13.0520.040 0.280 li298-159.membe 217.20.44.6 2 u 64 64 377 40.719 -2.208 0.385 The Oncore machine has the antenna indoors (near the window) and after looking at the clockstats file I have this oncore# /var/tmp/sats.sh 8 satellites:0 7 satellites:0 6 satellites: 870 5 satellites: 7941 4 satellites: 7313 3 satellites: 6385 2 satellites: 575 1 satellites:0 The machine has been running for 6 hours and it has been seeing a good number of satellites for most of the time. Do you think I should buy an external antenna like this one: http://www.ebay.co.uk/itm/Panasonic-NAis-VIC-100-TNC-Timing-GPS-L1-Active-Antenna-/180721168817?pt=LH_DefaultDomain_0hash=item2a13d231b1or my current antenna ( http://www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItemitem=330464866792) is good enough used indoors? Thanks for your help. Cheers, Miguel ___ 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] GPS Antenna
Hi Chris! Here and on ntp-questions always helping me out! Thanks! Moving it up to the roof would be difficult. Would have to talk to all neighbours to ask permission to run a cable to the roof. I'll have to keep it at this location. Anyway, in position hold I would assume that using 2 satellites will give me good time. Right? Thanks again! Cheers, Miguel On 12 September 2011 16:03, Chris Albertson albertson.ch...@gmail.comwrote: 2011/9/12 Miguel Gonçalves m...@miguelgoncalves.com:.. oncore# /var/tmp/sats.sh 8 satellites:0 7 satellites:0 6 satellites: 870 5 satellites: 7941 4 satellites: 7313 3 satellites: 6385 2 satellites: 575 1 satellites:0 The machine has been running for 6 hours and it has been seeing a good number of satellites for most of the time. Do you think I should buy an external antenna . It looks like your current antenna can only see about 1/2 of the sky. The reason to replace it is so you can see the entire sky. the Panasonic would be ideal because it has enough gain to drive a long cable. THere is no resin to replace the antenna unless you intend to place it in a better location. A higher gain at the same location will not give you a better view of the sky. Any outdoor antenna needs to be pointed or have a dome shape so that whatever falls on it rolls off. -- 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. attachment: satellites.svg___ 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] GPS Antenna
Hi! It's an apartment. I'll check today where south is to see what I can do. Two last questions about clockstats 55816 60529.233 127.127.30.0 3524834928.99971 2011 255 16 48 49 48 rstat 08 dop 0.0 nsat 12,4 traim 1,0,0 sigma 54 neg-sawtooth 13 sat 38808008 I was wondering what does sigma 54 mean... Is it the One Sigma Timing error? Meaning 54 ns? What about sat 38808008? I assume this is the status of the tracked satellites. 8 means is being tracked while 3 is about to be tracked. Am I right? Thanks for your patience and help. Cheers, Miguel On 12 September 2011 17:41, Chris Albertson albertson.ch...@gmail.comwrote: 2011/9/12 Miguel Gonçalves m...@miguelgoncalves.com: Hi Chris! Here and on ntp-questions always helping me out! Thanks! Moving it up to the roof would be difficult. Would have to talk to all neighbours to ask permission to run a cable to the roof. I'll have to keep it at this location. Anyway, in position hold I would assume that using 2 satellites will give me good time. Right? I think you have already proved that it can work.This is an apartment or condo? If so then all you can do is either indoors or at best a pole that hangs out the window or maybe a south facing balcony rail mount. If it's not your building then you can't even drill a hole through the wall so you are stuck with indoors. 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. ___ 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.
