Re: [time-nuts] Faster than light of a different type
On Wed, May 09, 2012 at 06:11:22PM -0700, Jim Lux wrote: I'm not so sure about that, in general. (the access to the public, not the tax funding).. A lot of universities have put badge readers on a lot of areas that one might think are totally public access. Now, they might be wide open during the middle of the day, but at some point, you have to badge in to get access (so that my daughter studying at 3AM doesn't meet up with weirdness, probably). For what it's worth, I know of at least one large public university that does this, but you can get a card issued to you for library access with in-state ID and a credit card on file (for any resultant fees and as a deposit.) Try asking, it might be available to you, even off-hours. They tend not to advertise this option, but it's there in some cases. --msa ___ 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] Clocks for Audio gear
On Wed, 09 May 2012 14:25:34 -0700 Hal Murray hmur...@megapathdsl.net wrote: Back to technical stuff... As a practical matter, is clock jitter or phase noise from a typical low cost crystal and decent board layout a significant problem in audio gear? How hard is it to measure? Depends on how accurate it should be ;-) But for audio purposes, the crystal itself has low enough noise. The Problem is the oscillator circuit and the power supply. That's where most designs mess up. Video geeks solved their clock distribution problems by using frame buffers. Is there a similar trick for audio? Is there a need for it? Video is a lot less sensitive to jitter. An A/V desync starts to be noticable from 10ms upwards for most people. Trained people notice it even below 5ms. I guess that 1ms is beyond what anyone can notice. But imagine you've a 1ms gap in your audio... People will scream at the poor quality. Part of the problem is that they are doing magic down conversion in the ADC. (I can't think of the term.) Direct downconversion using sampling :-) Suppose you have a 100 MHz signal with a 1 MHz bandwidth. You don't have to sample at 200 MHz. You can sample at 2 MHz and your signal will alias down. It's turning what is normally a bug into a feature. It's not a bug. It's a feature of the sampling process itself. Think of sampling as multiplication of an comp of dirac pulses with your input signal. Now remember that mixing is a multiplication of two signalsAnd the idea doing that is actually quite old, but it wasn't feasible with main stream components until a few years back. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Clocks for Audio gear
Hearing tests showed the ability to discern jitter above a few hundred nanoseconds rms. http://amorgignitamorem.nl/Audio/Jitter/Detection%20threshold%20for%20distortions%20due%20to%20jitter%20on%20digital%20audio%2026_50.pdf Others claim the ability to detect jitter in the picoseconds range... It would be a conservative assumption that jitter in the range of tens-hundreds of picoseconds will be practically not discernible. Usually integrated oscillators are composed of the classical inverting gate oscillator, with external CQC, and selfbiasing R, which has practically no rejection (~6dB) of the power supply noise. As it's usually on the same die with noisy digital circuitry, the gate threshold will jump around, producing timing errors, also the slew-rate is quite low, which just worsens the situation. As most digital circuitry is less affected by jitter, the best solution is to place a clean oscillator near the D/A conversion, where the most critical timing point is, and through buffers clock the rest of the digital circuits - eventually galvanic isolation might be implemented, to pollute less the analog part with digital noise. To minimize jitter, digital clock inputs should be driven by fast slew-rate circuitry. On 5/10/2012 12:25 AM, Hal Murray wrote: was Subject: Re: [time-nuts] Faster than light of a different type (Probably my fault.) act...@hotmail.com said: What I found funny was that the Audiophlie and light thread drew such attacks when it hit home to me as exactly what the Time-Nuts mission is about. The Audio thread touched on some real world time and freq research ... I too enjoyed the technical discussions. Thanks for your contributions. It's the audiophool bashing that people are complaining about. Sure, it's fun, but only at the right time and it gets old quickly. The problem is that with large groups, there are different opinions of when and how much is appropriate. The long tail on opinions of reasonable can annoy a lot of people. --- Back to technical stuff... As a practical matter, is clock jitter or phase noise from a typical low cost crystal and decent board layout a significant problem in audio gear? How hard is it to measure? Is clock accuracy a practical problem? How good are people with perfect pitch? It wouldn't surprise me if there are a few that are much much better than others, but how good is that relative to 50 PPM which I can get in a low cost crystal? Video geeks solved their clock distribution problems by using frame buffers. Is there a similar trick for audio? Is there a need for it? I know clocking is a serious problem in fancy DSP systems. For example, modern radar has gone digital. In that context, clock jitter can be important. Standard procedure is don't run your clock through a FPGA because it will add jitter. Part of the problem is that they are doing magic down conversion in the ADC. (I can't think of the term.) Suppose you have a 100 MHz signal with a 1 MHz bandwidth. You don't have to sample at 200 MHz. You can sample at 2 MHz and your signal will alias down. It's turning what is normally a bug into a feature. The catch is that the errors/noise due to clock jitter happens at the high frequency, in this case multiplying the noise by 100. (Your sample/hold at the front end has to work at the high frequency and your anti-aliasing filter gets more interesting.) There has been an interesting change in the specs for ADCs and DACs over the past 20(?) years. They used to be specified using terms like DNL and INL and No-missing-codes. Modern high-speed ADCs are specified with terms like ENOB and SFDR. Data sheets often include several plots of a batch of samples run through a DFT so you can see the noise floor and such. Here is a reasonable glossary: http://pdfserv.maxim-ic.com/en/an/AN641.pdf I don't remember comments/specs about clock jitter in the data sheets but I haven't looked at one in a few years. I'll have to keep an eye out the next time I'm browsing. ___ 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] Clocks for Audio gear
In message 4fab74eb.1050...@medesign.ro, MailLists writes: Others claim the ability to detect jitter in the picoseconds range... It would be a conservative assumption that jitter in the range of tens-hundreds of picoseconds will be practically not discernible. We're probably talking about one of those tripple-blind experiments ? (http://www.cco.caltech.edu/~boyk/sdttest.htm) -- 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.
Re: [time-nuts] Clocks for Audio gear
Hal Murray wrote: As a practical matter, is clock jitter or phase noise from a typical low cost crystal and decent board layout a significant problem in audio gear? How hard is it to measure? The answer depends a lot on the circumstances (as usual). If you refer to jitter effects on a conversion between analog and digital (either way), and you're interested in whether these can be audible, you will want to measure the effect on the audio signal, and not necessarily the jitter itself. For example, you might want to use a high frequency sine wave close to the upper bandwidth limit as the audio signal, and measure the jitter-related distortions using an FFT analyzer. It may be hard to distinguish jitter-related artifacts from other distortions, but as you are interested in the overall signal fidelity, that's probably what you want anyway. The good thing about that is that you need no extra gear that you don't already have as an audio developer. No expensive phase noise analyzer, for example. If you refer to jitter effects on a digital transmission, you will be interested in what they do to the bit error probability, or whether you are still conformant to some standard that puts a limit to the allowable jitter. In that case you are more likely to find yourself looking at eye diagrams on an oscilloscope, or perhaps using a bit error analyzer. There is little use for a proper phase noise analyzer in audio, and RD labs of most manufacturers I know don't have one. Is clock accuracy a practical problem? How good are people with perfect pitch? It wouldn't surprise me if there are a few that are much much better than others, but how good is that relative to 50 PPM which I can get in a low cost crystal? Clock accuracy can be a problem, but not because of pitch perception. Crystal oscillators are easily accurate enough for human perception, even the crappy ones. Clock accuracy does matter in system applications, when pieces of gear need to lock to each other, or to a house clock. Here, the clock accuracy needs to match the lock range of downstream PLLs, or else you can't lock reliably. The AES11 standard has rules for that. Video geeks solved their clock distribution problems by using frame buffers. Is there a similar trick for audio? Is there a need for it? A sample buffer of at least one sample is contained in pretty much every S/P-DIF or AES/EBU receiver chip, so the answer to your question would be yes. Storing a sample is cheap, however, compared to storing a video frame. Cheers Stefan ___ 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] Trimble Resolution SMT - good/bad/indifferent?
As a GPS receiver (12 channel), it seems to be quite good. It is at least 6dB more sensitive than the Thunderbolt. You can also program the PPS output for PP2S (pulse per 2 seconds) ___ 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] question about Thunderbolt geo acuracy
Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. Thanks Tim ___ 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] question about Thunderbolt geo acuracy
How accurate do you need your height? Remember that height is the least accurate of GPS parameters due to the fact that you rarely have a GPS satellite directly overhead. Rob Kimberley -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of swingbyte Sent: 10 May 2012 13:50 To: Discussion of precise time and frequency measurement Subject: [time-nuts] question about Thunderbolt geo acuracy Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. Thanks Tim ___ 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] question about Thunderbolt geo acuracy
On 05/10/2012 02:50 PM, swingbyte wrote: Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. There are many sides to this issue. You will most definitely be best served by a choke-ring or similar antenna that suppresses multi-path reflections. In addition to that, you would want Lady Heather to do a 24 hour position averaging. This should give you an OK solution, but really not the best achievable. Accurate height data is complex, since besides the receiver and antenna issues, height data has more uncertainty than longitude and latitude measures, and also since even if precise WGS84 height is achieved, you would need to correct it to your datum, your sea-level etc. You would also like to have better ionspheric correction than a plain GPS solution gives you, but the Thunderbolt does not give you direct support for such corrections. Exactly how much effort you need to do depends on how accurate you need it, +/- 10 m, 1 m, 1 dm, 1 cm or 1 mm. Cheers, Magnus ___ 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] question about Thunderbolt geo acuracy
Not being able to receive signals from GPS satellites anywhere below the horizon is an even larger problem for vertical accuracy. On Thu, 10 May 2012 13:59:51 +0100, Rob Kimberley robkimber...@btinternet.com wrote: How accurate do you need your height? Remember that height is the least accurate of GPS parameters due to the fact that you rarely have a GPS satellite directly overhead. Rob Kimberley -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of swingbyte Sent: 10 May 2012 13:50 To: Discussion of precise time and frequency measurement Subject: [time-nuts] question about Thunderbolt geo acuracy Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. Tim ___ 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] question about Thunderbolt geo acuracy
On Thu, 10 May 2012 22:50:15 +1000 swingbyte swingb...@exemail.com.au wrote: Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. How fast do you need it? One project i'm involved with uses a LEA6-T with its phase data output and averaging over several hours to get x/y resolutions in the 2-4mm range. I'm quite sure you can do something similar with altitude as well. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] question about Thunderbolt geo acuracy
On 5/10/12 6:08 AM, Magnus Danielson wrote: On 05/10/2012 02:50 PM, swingbyte wrote: Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. There are many sides to this issue. You will most definitely be best served by a choke-ring or similar antenna that suppresses multi-path reflections. In addition to that, you would want Lady Heather to do a 24 hour position averaging. This should give you an OK solution, but really not the best achievable. Accurate height data is complex, since besides the receiver and antenna issues, height data has more uncertainty than longitude and latitude measures, and also since even if precise WGS84 height is achieved, you would need to correct it to your datum, your sea-level etc. You would also like to have better ionspheric correction than a plain GPS solution gives you, but the Thunderbolt does not give you direct support for such corrections. Exactly how much effort you need to do depends on how accurate you need it, +/- 10 m, 1 m, 1 dm, 1 cm or 1 mm. If you can get RINEX format files, you can post process them through GIPSY at JPL and get higher precision, using post determined ionospheric and other corrections. My friends in the GPS world say that getting to 1 meter absolute position is fairly straightforward but once you start getting finer than that, all the various factors start ganging up on you: ionosphere, solid earth tides, multipath, phase center shifts, etc.etc. Likewise, getting 1mm + 1 ppm of separation distance sorts of uncertainty in a differential measurement is fairly straightforward. ___ 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] question about Thunderbolt geo acuracy
A man with only one GPS Surveys from different receivers I have. All taken at the same height from prolonged surveys. WGS84 datum. Oncore UT+ A 207,62m Oncore UT+ B 209,24m Z3801A 180,72m Oncore VP A 229,95m TBolt 207.00m Le 10/05/2012 14:50, swingbyte a écrit : Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. Thanks Tim ___ 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] question about Thunderbolt geo acuracy
On 5/10/12 6:42 AM, mike cook wrote: A man with only one GPS Surveys from different receivers I have. All taken at the same height from prolonged surveys. WGS84 datum. Oncore UT+ A 207,62m Oncore UT+ B 209,24m Z3801A 180,72m Oncore VP A 229,95m TBolt 207.00m That's a pretty big variation (10s of meters), a lot more than I'd expect (I'd expect variations more like the difference between the two UT+s and the Tbolt). I wonder what about the VP and Z3801 fixes pushes them so far away. ___ 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] question about Thunderbolt geo acuracy
Le 10/05/2012 15:51, Jim Lux a écrit : On 5/10/12 6:42 AM, mike cook wrote: A man with only one GPS Surveys from different receivers I have. All taken at the same height from prolonged surveys. WGS84 datum. Oncore UT+ A 207,62m Oncore UT+ B 209,24m Z3801A 180,72m Oncore VP A 229,95m TBolt 207.00m That's a pretty big variation (10s of meters), a lot more than I'd expect (I'd expect variations more like the difference between the two UT+s and the Tbolt). I wonder what about the VP and Z3801 fixes pushes them so far away. May have an explanation for the Z3801A fix. I have just seen in my notes that the Z3801A was displaying MSL and not WGS84 . ___ 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] question about Thunderbolt geo acuracy
I've found significant altitude errors using a GPS and the following quotes found on the internet will explain why. From my experience of hiking in the mountains of New Hampshire an aneroid altimeter will vary with atmospheric pressure about 200 feet for a change of 0.2 of mercury so you have to continually set it at known waypoints, just like setting a frequency standard against a known reference, and then it will be 'accurate' for some length of time, and then you set it again. GPS altitude will be off but it should be fairly consistent in spite of the changing atmospheric pressure. The earth neither spins at a constant rate nor is it a perfect sphere. Maybe we need to trade it in for a newer model. ;-) GPS altitude measures the users' distance from the center of the SVs orbits. These measurements are referenced to geodetic altitude or ellipsoidal altitude in some GPS equipment. Garmin and most equipment manufacturers utilize a mathematical model in the GPS software which roughly approximates the geodetic model of the earth and reference altitude to this model. As with any model, there will be errors as the earth is not a simple mathematical shape to represent. What this means is that if you are walking on the seashore, and see your altitude as -15 meters, you should not be concerned. First, the geodetic model of the earth can have much more than this amount of error at any specific point and second, you have the GPS error itself to add in. As a result of this combined error, I am not surprised to be at the seashore and see -40 meter errors in some spots. We have to make some assumptions about the shape of the earth. WGS84 has defined that shape to be an ellipsoid, with a major and minor axis. The particular dimensions chosen are only an approximation to the real shape. Ideally, such an ellipsoid would correspond precisely to sealevel everywhere in the world. As it turns out, there are very few places where the WGS84 ellipsoid definition coincides with sealevel. On average, the discrepancy is zero, but that doesn't help much when you're standing at the water's edge of an ocean beach and your GPS is reading -100ft below sealevel. The deviation can be as large as 300ft in some isolated locations. When the National Marine Electronics Association came up with the NMEA standard, they decreed that altitudes reported via NMEA protocol, shall be relative to mean (average) sea level. This posed a problem for GPS manufacturers. How to report altitudes relative to mean sea level, when they were only calculating altitude relative to the WGS84 ellipsoid. Ignoring the discrepancy wasn't likely to make GPS users very happy. As it happens, there is actually a model of the difference between the WGS84 ellipsoid and mean sea level. This involves harmonic expansions at the 360th order. It's a very good model, but rather unusable in a handheld device. It was determined that this model could be made into a fairly simple lookup table included in the GPS receiver. The table is usually fairly coarse lat/lon wise, but the ellipsoid to mean sea level variation, known as geoidal separation, varies slowly as you move in lat/lon. -Arthur ___ 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] question about Thunderbolt geo acuracy
Hi Tim, The answer is NO. Even though decent accuracy can be had with long averaging. It was discussed a few years ago on this list. -- Björn Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. Thanks Tim ___ 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] question about Thunderbolt geo acuracy
Not for survey type accuracy (sub-meter, short measurement time). The average (over a 48 hour period) was pretty good (about 1.5 meters, RMS), but the reading over any 1 minute period can be off as much as 3-5 meters, satellite geometry dependent. I Have two units with good antennas, mounted roughly 40 meters apart, and after locating one of the antennas I use the second TBolt in a differential mode and get the 1-2 meter accuracy all the time. Michael / K7HIL On Thu, May 10, 2012 at 5:50 AM, swingbyte swingb...@exemail.com.au wrote: Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. Thanks Tim __**_ 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] question about Thunderbolt geo acuracy
Attilla, On Thu, 10 May 2012 22:50:15 +1000 swingbyte swingb...@exemail.com.au wrote: Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. How fast do you need it? One project i'm involved with uses a LEA6-T with its phase data output and averaging over several hours to get x/y resolutions in the 2-4mm range. I'm quite sure you can do something similar with altitude as well. Attila Kinali That is relative positions over a baseline of ca 100m. Not absolute positions. --- Björn ___ 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] Why 9,192,631,770 ??
Thanks, all ...this thread has helped me a lot. It reinforces my beliefs of what a 'second' is ...what we were taught from day 1 in school: One solar day/86,400 (A 'solar' day being an earth solar day) Hi Don, This was true until the 1960's. Hopefully the school curriculum has been updated since then. The definition of a pound, or a foot, or a second has progressed over centuries. We now have a very accurate and convenient definition of the second. And it is no longer 1/86400 of a day; it is no longer 1/31556925.9747 of a year either. The problem with day is you have to ask which one; each day has a different length when you measure down in the milli- or microsecond level; the earth doesn't spin very consistently. See: http://www.leapsecond.com/museum/earth/ So as I try to rationalize all this in my mind, ...a good cesium unit is just a sophisticated 'counter'. The counter gate is just the solar day. It's interesting to note (to ask?): When did someone get smart enough to start measuring 1/86thousthanth of a day, That starts needing a standard in itself. Exactly. A ~1-meter pendulum can conveniently be made to tick seconds. You can adjust the length until each day you count 86400 ticks. The earth is the standard and the pendulum clock is being measured. What was found in the early 1900's is that some precise pendulum clocks kept better time compared to themselves than to the earth. The conclusion was the earth is less stable than the best pendulum clocks. At that point the pendulum clocks became the standard and the earth became the thing to be measured. This was the beginning of the end for a second being 1/86400 of a day. The same thing is happening today with the cesium definition of the second. Optical clocks are so good that they are being used to measure the cesium clocks. So in years to come it is likely that the definition of the second will again be redefined; this time in terms of an optical frequency. /tvb ___ 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] question about Thunderbolt geo accuracy
Hi Just how accurate do you need? The local survey company will get you to ~ 1 cm in roughly an hour with real survey gear. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of swingbyte Sent: Thursday, May 10, 2012 8:50 AM To: Discussion of precise time and frequency measurement Subject: [time-nuts] question about Thunderbolt geo acuracy Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. Thanks Tim ___ 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] question about Thunderbolt geo acuracy
There is an error in your quoted text. The author must have though there was a difference between WGS84 and true sea level. No that is not true. If you paper map that you bought from US Gological Survey says WGS84 on it then THAT is the definition of sea level on that map. The altitudes of contour lines and peaks will be in WGS84 and should match what the GPS says. Many older maps use a different system so their saw level is defined differently. Almost all GPSes have away to select the elipoid. It defauls to WGS84 but you need to set it to match your paper map One problem is the geometry of the satellites in view. Unless the antenna can see to the horizon the sight lines up to the sats make a deep V and if you can see to the horizon there is 3X or 4X more atmosphere along the horizontal path On Thu, May 10, 2012 at 7:40 AM, Arthur Dent golgarfrinc...@yahoo.com wrote: I've found significant altitude errors using a GPS and the following quotes found on the internet will explain why. From my experience of hiking in the mountains of New Hampshire an aneroid altimeter will vary with atmospheric pressure about 200 feet for a change of 0.2 of mercury so you have to continually set it at known waypoints, just like setting a frequency standard against a known reference, and then it will be 'accurate' for some length of time, and then you set it again. GPS altitude will be off but it should be fairly consistent in spite of the changing atmospheric pressure. The earth neither spins at a constant rate nor is it a perfect sphere. Maybe we need to trade it in for a newer model. ;-) GPS altitude measures the users' distance from the center of the SVs orbits. These measurements are referenced to geodetic altitude or ellipsoidal altitude in some GPS equipment. Garmin and most equipment manufacturers utilize a mathematical model in the GPS software which roughly approximates the geodetic model of the earth and reference altitude to this model. As with any model, there will be errors as the earth is not a simple mathematical shape to represent. What this means is that if you are walking on the seashore, and see your altitude as -15 meters, you should not be concerned. First, the geodetic model of the earth can have much more than this amount of error at any specific point and second, you have the GPS error itself to add in. As a result of this combined error, I am not surprised to be at the seashore and see -40 meter errors in some spots. We have to make some assumptions about the shape of the earth. WGS84 has defined that shape to be an ellipsoid, with a major and minor axis. The particular dimensions chosen are only an approximation to the real shape. Ideally, such an ellipsoid would correspond precisely to sealevel everywhere in the world. As it turns out, there are very few places where the WGS84 ellipsoid definition coincides with sealevel. On average, the discrepancy is zero, but that doesn't help much when you're standing at the water's edge of an ocean beach and your GPS is reading -100ft below sealevel. The deviation can be as large as 300ft in some isolated locations. When the National Marine Electronics Association came up with the NMEA standard, they decreed that altitudes reported via NMEA protocol, shall be relative to mean (average) sea level. This posed a problem for GPS manufacturers. How to report altitudes relative to mean sea level, when they were only calculating altitude relative to the WGS84 ellipsoid. Ignoring the discrepancy wasn't likely to make GPS users very happy. As it happens, there is actually a model of the difference between the WGS84 ellipsoid and mean sea level. This involves harmonic expansions at the 360th order. It's a very good model, but rather unusable in a handheld device. It was determined that this model could be made into a fairly simple lookup table included in the GPS receiver. The table is usually fairly coarse lat/lon wise, but the ellipsoid to mean sea level variation, known as geoidal separation, varies slowly as you move in lat/lon. -Arthur ___ 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. -- 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] question about Thunderbolt geo accuracy
On Thu, May 10, 2012 at 9:07 AM, Bob Camp li...@rtty.us wrote: . Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. It will give pretty good height data. Within a few meters but you have to know how to translate between different definitions of sea level to make best use of the data. If you live in the USA you can now download for free the USGS topographic maps. I'm pretty sure thy have full coverage of all of the US. THese will have 20 foot contour intervals and you can interpolate to at least half that. So for most normal purposes you can find your elevation without a GPS. Just look on the topo map. Most of these maps where made with stereo camera pairs. They get relative elevation optically by matching the two images and then they sent survey teams to ground check some points. 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] question about Thunderbolt geo acuracy
On Thu, 10 May 2012 17:01:48 +0200 b...@lysator.liu.se wrote: On Thu, 10 May 2012 22:50:15 +1000 swingbyte swingb...@exemail.com.au wrote: Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. How fast do you need it? One project i'm involved with uses a LEA6-T with its phase data output and averaging over several hours to get x/y resolutions in the 2-4mm range. I'm quite sure you can do something similar with altitude as well. That is relative positions over a baseline of ca 100m. Not absolute positions. The Baseline is definitly larger than just 100m. the current testing field is spread over the side of a mountain... I haven't looked at the scale of the map, but i'd say it was somewhere in the range of 2-5km. I do not know whether they use fixed reference stations. I am not aware of any. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Clocks for Audio gear
On Thu, May 10, 2012 at 12:57 AM, MailLists li...@medesign.ro wrote: Hearing tests showed the ability to discern jitter above a few hundred nanoseconds rms. http://amorgignitamorem.nl/Audio/Jitter/Detection%20threshold%20for%20distortions%20due%20to%20jitter%20on%20digital%20audio%2026_50.pdf Others claim the ability to detect jitter in the picoseconds range... If we are to believe the above paper,then those guys who claim to hear pS jitter are wrong. Likely they can also here is a fuse is is place in the holder backwards. So by the above, no now can hear 250 nS of jitter.I really doubt any decent system other then the most low-cost consumer level junk has jitter at the 250 nS level. Even a TTL can oscillator is better than that. A TTL can that is marked 4.096 MHz costs about $2 and will make a square wave with a period of very close to 250 nS. Then they divide this down to the sample rate of 96KHz. In order to see a 250 nS jitter in the 96K signal the TTL can would have to skip a beat. 250 nS is is a huge error and you don't get there with digital noise 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] Clocks for Audio gear
In fact, I do believe the paper is a voice of rationality in an ocean oh hype. Very expensive hype, promoted by shameless hucksters. -John === On Thu, May 10, 2012 at 12:57 AM, MailLists li...@medesign.ro wrote: Hearing tests showed the ability to discern jitter above a few hundred nanoseconds rms. http://amorgignitamorem.nl/Audio/Jitter/Detection%20threshold%20for%20distortions%20due%20to%20jitter%20on%20digital%20audio%2026_50.pdf Others claim the ability to detect jitter in the picoseconds range... If we are to believe the above paper,then those guys who claim to hear pS jitter are wrong. Likely they can also here is a fuse is is place in the holder backwards. So by the above, no now can hear 250 nS of jitter.I really doubt any decent system other then the most low-cost consumer level junk has jitter at the 250 nS level. Even a TTL can oscillator is better than that. A TTL can that is marked 4.096 MHz costs about $2 and will make a square wave with a period of very close to 250 nS. Then they divide this down to the sample rate of 96KHz. In order to see a 250 nS jitter in the 96K signal the TTL can would have to skip a beat. 250 nS is is a huge error and you don't get there with digital noise 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] question about Thunderbolt geo acuracy
Chris Albertson albertson.chris at gmail.com There is an error in your quoted text. The author must have though there was a difference between WGS84 and true sea level. No that is not true. If you paper map that you bought from US Gological Survey says WGS84 on it then THAT is the definition of sea level on that map. The altitudes of contour lines and peaks will be in WGS84 and should match what the GPS says. Many older maps use a different system so their saw level is defined differently. Almost all GPSes have away to select the elipoid. It defauls to WGS84 but you need to set it to match your paper map. I'm not sure what point you're trying to make but it is a fact, as the OP pointed out, that there are differences between the empirical data of 'true elevation' and what various GPS receivers will indicate based on whatever model they are using. Elevation errors associated with GPS are well known and I have observed these errors and the 2 sources I quoted pointed them out as well. I've known the error between well-established landmarks and the GPS to be significantly off (over 200') and the error will vary from location to location but the error will be essentially constant for any single location. If you're saying that a GPS and a map based on the same model would agree and give the same incorrect elevation, then that is entirely possible but it would simply make both of them incorrect by the same amount. The example given in both references I quoted of having a GPS tell you are say 100 feet below the sea surface when you are standing on the beach high and dry is a situation where I'd believe my observations and doubt the model the GPS is using. The point of the 2 references is to explain why there could be a difference between two GPS receivers reporting elevation and not to get us mired in the weeds near MSL at the sea shore. -Arthur ___ 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] Clocks for Audio gear
Chris Albertson wrote: If we are to believe the above paper,then those guys who claim to hear pS jitter are wrong. Note that the jitter spectrum matters for its audibility. Ashihara et.al. used random jitter, and it is not very suprising that the sensitivity for random jitter is lower than for jitter that has specially been shaped to improve detectability by human ears. Thus the results by Ashihara are credible, but they are not the lower limit on jitter audibility. Benjamin and Gannon, the first reference in Ashihara's paper, come to lower figures for sinusoidal jitter with carefully selected frequencies relative to the main signal, which is also sinusoidal. Their results reach down to the single figure nanosecond range, and that can be regarded as the real limit of audibility. Of course, that still leaves those who claim to hear jitter in the picoseconds range out in fairy-tale land. And jitter of just a few nanoseconds is still quite easy to achieve with crystal oscillators. No need for special and expensive parts, then. Normal developer diligence is enough. Cheers Stefan ___ 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] Clocks for Audio gear
I've alway have thought that if nanosecond level jitter is bad then breathing while listening must be really bad. If you inhale the path length from your ear to the speaker changes at the microsecond level. You'd think the resulting doppler shift would drive these audiophiles nuts. All that pitch shifting. So my new product for this is the head vice It will have three wooden plates with lead screw clamps in a cast iron frame. The iron frame is to be bolted to a wall of other massive object. This will greatly reduce those annoying microsecond level audio path length variations that are caused by breathing, blood flow and eye blinks. For those sensitive to picosecond level jitter, the wood blocks can be removed and the steel clamp plate applied directly (wood after all is elastic and compressible) On Thu, May 10, 2012 at 10:03 AM, J. Forster j...@quikus.com wrote: In fact, I do believe the paper is a voice of rationality in an ocean oh hype. Very expensive hype, promoted by shameless hucksters. -John === On Thu, May 10, 2012 at 12:57 AM, MailLists li...@medesign.ro wrote: Hearing tests showed the ability to discern jitter above a few hundred nanoseconds rms. http://amorgignitamorem.nl/Audio/Jitter/Detection%20threshold%20for%20distortions%20due%20to%20jitter%20on%20digital%20audio%2026_50.pdf Others claim the ability to detect jitter in the picoseconds range... If we are to believe the above paper,then those guys who claim to hear pS jitter are wrong. Likely they can also here is a fuse is is place in the holder backwards. So by the above, no now can hear 250 nS of jitter. I really doubt any decent system other then the most low-cost consumer level junk has jitter at the 250 nS level. Even a TTL can oscillator is better than that. A TTL can that is marked 4.096 MHz costs about $2 and will make a square wave with a period of very close to 250 nS. Then they divide this down to the sample rate of 96KHz. In order to see a 250 nS jitter in the 96K signal the TTL can would have to skip a beat. 250 nS is is a huge error and you don't get there with digital noise 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. -- 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] question about Thunderbolt geo acuracy
On Thu, May 10, 2012 at 10:23 AM, Arthur Dent golgarfrinc...@yahoo.com wrote: Chris Albertson albertson.chris at gmail.com I'm not sure what point you're trying to make but it is a fact, as the OP pointed out, that there are differences between the empirical data of 'true elevation' and what various GPS receivers will indicate based on whatever model they are using. Sorry if not clear. My point was that (1) the wgs84 reference his GPS uses is not wrong. It can't be. It is the definition. It may not be the definition he wants and (2) GPS just is not good at altitude and he'd be better off using a paper map, they are free now so why not. mean sea level is not meaningful any more. What shape is the ocean and what if you live in Kanas? How to extrapolate the ocean level to Kanas? The answer is to use a model of some kind Here where I live I can walk down to the beach and pound a stake in the sand and mark the water level. People actually do that (in a more sophisticated way with tide misting stations up and down the coast) But in Kanas you need some kind of model that tell you what the ocean level would be if there were an ocean in Kanas. But BIG PROBLEM. No one knows how to do make such a model. So they simply DEFINE the height of the ocean in Kanas. One definition is wgs84. The trouble with a defining it is that it will not match what you measure with your stick in the sand.So there are any number of local definitions that are closer matches to measured heights The root of the problem is that the earch has a very complex shape. It is lumpy in random ways and you can't model this, you have to measure it and then look it up. 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] Clocks for Audio gear
Great dialog. The Time Nuts form can be very humbling and often has me questioning my own knowledge base. This thread is no exception. My take on the effect of jitter is when an d toA converter is reproducing a pure sine wave even a single point of slight jitter will show up in the FFT as false analog content. In a complex wave it can easily change the relationship between a fundamental and harmonics. This is a major problem in speaker crossovers design where drivers with different masses can only be aligned at one freq. It has been my experience this relationship between fundmentals and harmonics is noticeably audible at levels that are difficult to measure. To me, it is this difficulty to mathematically define certain aspects of audible distortion that makes audio design fascinating. (It also makes some voodoo science and snake oil products difficult to disprove, especially to those lacking an electronics or physics background) Will timing improvements affect sound quality, because of the complexity of human hearing it seems to me still worthy of investigation. Time will tell. Best Wishes; Thomas Knox From: albertson.ch...@gmail.com Date: Thu, 10 May 2012 09:48:21 -0700 To: time-nuts@febo.com Subject: Re: [time-nuts] Clocks for Audio gear On Thu, May 10, 2012 at 12:57 AM, MailLists li...@medesign.ro wrote: Hearing tests showed the ability to discern jitter above a few hundred nanoseconds rms. http://amorgignitamorem.nl/Audio/Jitter/Detection%20threshold%20for%20distortions%20due%20to%20jitter%20on%20digital%20audio%2026_50.pdf Others claim the ability to detect jitter in the picoseconds range... If we are to believe the above paper,then those guys who claim to hear pS jitter are wrong. Likely they can also here is a fuse is is place in the holder backwards. So by the above, no now can hear 250 nS of jitter.I really doubt any decent system other then the most low-cost consumer level junk has jitter at the 250 nS level. Even a TTL can oscillator is better than that. A TTL can that is marked 4.096 MHz costs about $2 and will make a square wave with a period of very close to 250 nS. Then they divide this down to the sample rate of 96KHz. In order to see a 250 nS jitter in the 96K signal the TTL can would have to skip a beat. 250 nS is is a huge error and you don't get there with digital noise 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] Clocks for Audio gear
albertson.ch...@gmail.com said: I've alway have thought that if nanosecond level jitter is bad then breathing while listening must be really bad. If you inhale the path length from your ear to the speaker changes at the microsecond level. You'd think the resulting doppler shift would drive these audiophiles nuts. All that pitch shifting. Perhaps the spectrum of the jitter matters. If the frequency is low enough, I call it wander rather than jitter. Audio doesn't need DC or low frequencies so wander is easy to filter out with a simple high-pass filter. Heartbeats may be more interesting than breathing. Does anybody know of spectrum domain data? It should be possible to collect position info while also monitoring heartbeat and chest diameter and then crunch some numbers do see how much of the position correlates with heartbeat vs breathing and then plot each part in the frequency domain. -- These are my opinions. I hate spam. ___ 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] question about Thunderbolt geo acuracy
On 5/10/12 7:40 AM, Arthur Dent wrote: I've found significant altitude errors using a GPS and the following quotes found on the internet will explain why. From my experience of hiking in the mountains of New Hampshire an aneroid altimeter will vary with atmospheric pressure about 200 feet for a change of 0.2 of mercury so you have to continually set it at known waypoints, just like setting a frequency standard against a known reference, and then it will be 'accurate' for some length of time, and then you set it again. GPS altitude will be off but it should be fairly consistent in spite of the changing atmospheric pressure. The earth neither spins at a constant rate nor is it a perfect sphere. Maybe we need to trade it in for a newer model. ;-) GPS altitude measures the users' distance from the center of the SVs orbits. Not precisely true. The SV orbits follow the usual Keplerian things so the focus of the ellipse is close to the barycenter of Earth, but of course, the moon and non uniform gravity of the Earth affect it too. GPS fixes are relative to WGS84 coordinate system (x,y,z) 0,0,0 in WGS84 is within a few cm of the center of mass of the Earth. WGS 84 also defines a datum for the surface (which is not, generally, the geoid) as an ellipsoid of revolution. (compare to the Clarke 1866 ellipsoid) These measurements are referenced to geodetic altitude or ellipsoidal altitude in some GPS equipment. This is a bit fuzzy... there are differences between geodetic and geocentric altitude for instance. And then there's the reference ellipsoid (e.g. Clarke 1866), or more generally the geoid Garmin and most equipment manufacturers utilize a mathematical model in the GPS software which roughly approximates the geodetic model of the earth and reference altitude to this model. Mmm.. I don't know that it roughly approximates.. WGS84 is precisely defined (that's the coordinate system). The geoid (in terms of the sea surface is defined in terms of spherical harmonics and varies some 100m or thereabouts from the reference datum. WHether your GPS uses the WGS84 datum (simple ellipsoid) or the fancier geoid, is something you'd have to look up. As with any model, there will be errors as the earth is not a simple mathematical shape to represent. What this means is that if you are walking on the seashore, and see your altitude as -15 meters, you should not be concerned. First, the geodetic model of the earth can have much more than this amount of error at any specific point and second, you have the GPS error itself to add in. As a result of this combined error, I am not surprised to be at the seashore and see -40 meter errors in some spots. Actually, no.. the geodetic model (e.g. the EGM96) should be VERY close to the actual sea surface (barring tides and local geographic effects.. the Gulf Stream sits several meters higher because it's warmer and less dense) The ellipsoid could easily be off by tens of meters. We have to make some assumptions about the shape of the earth. WGS84 has defined that shape to be an ellipsoid, with a major and minor axis. The particular dimensions chosen are only an approximation to the real shape. Ideally, such an ellipsoid would correspond precisely to sealevel everywhere in the world. As it turns out, there are very few places where the WGS84 ellipsoid definition coincides with sealevel. On average, the discrepancy is zero, but that doesn't help much when you're standing at the water's edge of an ocean beach and your GPS is reading -100ft below sealevel. The deviation can be as large as 300ft in some isolated locations. When the National Marine Electronics Association came up with the NMEA standard, they decreed that altitudes reported via NMEA protocol, shall be relative to mean (average) sea level. This posed a problem for GPS manufacturers. How to report altitudes relative to mean sea level, when they were only calculating altitude relative to the WGS84 ellipsoid. Ignoring the discrepancy wasn't likely to make GPS users very happy. As it happens, there is actually a model of the difference between the WGS84 ellipsoid and mean sea level. This involves harmonic expansions at the 360th order. It's a very good model, but rather unusable in a handheld device. It was determined that this model could be made into a fairly simple lookup table included in the GPS receiver. The table is usually fairly coarse lat/lon wise, but the ellipsoid to mean sea level variation, known as geoidal separation, varies slowly as you move in lat/lon. And that is a more accurate description.. The question really is what does YOUR receiver report.. if it's MSL in NMEA strings then I would imagine all modern receivers use some form of geoid model with error probably 1 meter. If it's WGS84, then it ignores the geoid. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
Re: [time-nuts] Trimble Resolution SMT - good/bad/indifferent?
Hi Holrum, how do you re-configure the SMT unit? Using Trimble GPS studio? Thanks, Said In a message dated 5/9/2012 15:17:21 Pacific Daylight Time, hol...@hotmail.com writes: I have it running now. It turns out that the units from fluke.l come shipped with TEP format messages enabled (it outputs @@Cf on power up). You have to re-configure them for TSIP protocol and save the configuration back to the unit. Hope to have Lady Heather taking to it. It does come up with several of the messages working. Sat info is not one of them. ___ 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] question about Thunderbolt geo accuracy
On 5/10/12 9:18 AM, Chris Albertson wrote: On Thu, May 10, 2012 at 9:07 AM, Bob Campli...@rtty.us wrote: . Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. It will give pretty good height data. Within a few meters but you have to know how to translate between different definitions of sea level to make best use of the data. If you live in the USA you can now download for free the USGS topographic maps. I'm pretty sure thy have full coverage of all of the US. THese will have 20 foot contour intervals and you can interpolate to at least half that. So for most normal purposes you can find your elevation without a GPS. Just look on the topo map. Most of these maps where made with stereo camera pairs. They get relative elevation optically by matching the two images and then they sent survey teams to ground check some points. And updated the elevation data with radar measurements from SRTM, as well. ___ 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] Trimble Resolution SMT - good/bad/indifferent?
Ok, I figured out that the unit fluke.l sells is running firmware to emulate the Motrola M12+ receiver or similar. So WinOncore 12 does work, and I can get the following receiver ID: COPYRIGHT 2008 Trimble Navigation Ltd. SFTW P/N # SOFTWARE VER # 0.03.0 SOFTWARE REV # 00 SOFTWARE DATE 04/27/2009 MODEL #3011 HDWR P/N # SERIAL # 20393136 MANUFACTUR DATE 06/05/2009 OPTIONS LIST Does anyone know what the command is to configure this for NMEA or TSIP? Thanks, Said In a message dated 5/10/2012 12:15:56 Pacific Daylight Time, saidj...@aol.com writes: Hi Holrum, how do you re-configure the SMT unit? Using Trimble GPS studio? Thanks, Said In a message dated 5/9/2012 15:17:21 Pacific Daylight Time, hol...@hotmail.com writes: I have it running now. It turns out that the units from fluke.l come shipped with TEP format messages enabled (it outputs @@Cf on power up). You have to re-configure them for TSIP protocol and save the configuration back to the unit. Hope to have Lady Heather taking to it. It does come up with several of the messages working. Sat info is not one of them. ___ 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] Clocks for Audio gear
One interesting note however. Years ago we had a standard old 4040 ripple counter in our shop that displayed a low occurrence of jitter of several times it's input frequency period at it's lowest frequency output (Sort of what you are describing below). I wish I had the numbers handy, but the output would be good for most of the time, then every once in a while it would jump to a longer delay. It was hard to catch with a scope, but when we measured every single pulse width it showed up fairly well. The high speed clock (A TTL OSC in a can) never skipped, as far as we know. We never did figure that one out. From what I remember we switched IC manufacturers, and the problem when away. Dan On 5/10/2012 1:49 PM, time-nuts-requ...@febo.com wrote: A TTL can that is marked 4.096 MHz costs about $2 and will make a square wave with a period of very close to 250 nS. Then they divide this down to the sample rate of 96KHz. In order to see a 250 nS jitter in the 96K signal the TTL can would have to skip a beat. 250 nS is is a huge error and you don't get there with digital noise 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] question about Thunderbolt geo acuracy
On 5/10/12 10:46 AM, Chris Albertson wrote: mean sea level is not meaningful any more. What shape is the ocean and what if you live in Kanas? How to extrapolate the ocean level to Kanas? The answer is to use a model of some kind mean sea level, these days, is a name for a particular height that matches the long term average of the ocean, where there is ocean to be measured, and which smoothly varies in between those points. The trouble with a defining it is that it will not match what you measure with your stick in the sand.So there are any number of local definitions that are closer matches to measured heights WGS84 won't match the stick in the sand, but one of the modern reference geoids most certainly will match it, within a few cm. It's important these days, where there are property boundaries referenced to things like mean high tide line. Measuring sea height (the actual height) to an accuracy of cm over a global scale is pretty straightforward these days (that's what TOPEX/JASON is all about). After that, it's a matter of choosing an appropriate averaging technique to remove the effect of tides (which you need to do on solid land, as well) WGS84, is pretty much the simplest model, and is more about defining the directions of X,Y, and Z (or lat/lon) than where the surface of the earth is. The root of the problem is that the earch has a very complex shape. It is lumpy in random ways and you can't model this, you have to measure it and then look it up. You CAN model it.. and that's what the EGM model is.. using multihundred order spherical harmonics. The model isn't simple, but neither is it just a table lookup of measured data. And, as mentioned in an earlier set of posts.. since the bumps aren't huge, if you're only interested in meter scale uncertainties, a fairly small table will give you the local variation between WGS84 ellipsoid (no bumps at all) and EGM. 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] Clocks for Audio gear
On 5/10/12 11:36 AM, Hal Murray wrote: albertson.ch...@gmail.com said: I've alway have thought that if nanosecond level jitter is bad then breathing while listening must be really bad. If you inhale the path length from your ear to the speaker changes at the microsecond level. You'd think the resulting doppler shift would drive these audiophiles nuts. All that pitch shifting. Perhaps the spectrum of the jitter matters. If the frequency is low enough, I call it wander rather than jitter. Audio doesn't need DC or low frequencies so wander is easy to filter out with a simple high-pass filter. Heartbeats may be more interesting than breathing. Does anybody know of spectrum domain data? It should be possible to collect position info while also monitoring heartbeat and chest diameter and then crunch some numbers do see how much of the position correlates with heartbeat vs breathing and then plot each part in the frequency domain. oddly, I happen to have just that data to hand, having been looking at ballistocardiography. If you put someone in a bed, suspended by 4 wires (one at each corner), your heart beat results in about 1mm displacement (head to foot). 1 degree phase shift at 1 kHz, or thereabouts. in terms of displacement in general, breathing is on the order of 1cm (at 0.1 Hz) and heartbeat is on the order of 0.1-1mm, depending on where you look. (look up microwave cardiography for instance) ___ 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] Clocks for Audio gear
On 5/10/12 12:44 PM, Chris Albertson wrote: On Thu, May 10, 2012 at 10:25 AM, Heinzmann, Stefan (ALC NetworX GmbH)stefan.heinzm...@alcnetworx.de wrote: Benjamin and Gannon, the first reference in Ashihara's paper, come to lower figures for sinusoidal jitter with carefully selected frequencies relative to the main signal, which is also sinusoidal. Their results reach down to the single figure nanosecond range, and that can be regarded as the real limit of audibility. Are there any real audio systems with sinusoidal jitter. powerline ripple on a signal going into a threshold detector that drive the sample clock would be a nice way to generate sinusoidal jitter. I've got a nice example where 66MHz processor clock modulates a 49MHz sample clock (well, it's not perfectly sinusoidal, but if you digitize a clean sine wave, you get nice aliases of the modulation frequency). I'd goes that it would all be random. I can see where I could build a system with that defect if I wanted to but are there any systems on the market like this? 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] Clocks for Audio gear
Don't forget the human mind can compensate for a lot of things. Think of how we can triangulate a sound source in realtime even with the included echos in a small room. The only thing that I can think of that messes with that system is a single tone setting up standing waves. It's impressive if you think about it. So, it's probably not much of a stretch to imagine the mind compensating for a little movement here and there (since we have controls and feedback to monitor that). It may just take a few thousand years for us to evolve to deal with distortion due to jitter in our digital recordings :) All fun aside. This has been a worth while thread in my opinion. I'm learning more this week, than others watching this list! On 5/10/2012 1:49 PM, time-nuts-requ...@febo.com wrote: I've alway have thought that if nanosecond level jitter is bad then breathing while listening must be really bad. If you inhale the path length from your ear to the speaker changes at the microsecond level. You'd think the resulting doppler shift would drive these audiophiles nuts. All that pitch shifting. ___ 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] Clocks for Audio gear
On Thu, May 10, 2012 at 1:09 PM, Jim Lux jim...@earthlink.net wrote: On 5/10/12 12:44 PM, Chris Albertson wrote: powerline ripple on a signal going into a threshold detector that drive the sample clock would be a nice way to generate sinusoidal jitter. I can think of other ways to design a defective system. But what I was wondering if there are in fact any audio systems on the market like this. The real reason that a recording studio will use a master clock is not because you can hear nS level jitter. It's that they like to use a sample accurate editor and they want to be able to over dub tracks recorded at different times, maybe months apart 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] Clocks for Audio gear
Are there any real audio systems with sinusoidal jitter. I'd goes that it would all be random. I can see where I could build a system with that defect if I wanted to but are there any systems on the market like this? I could easily imagine jitter with a significant sinusoidal component. Consider noise from the power supply leaking through. If you think of it as phase noise rather than jitter it would show up as a spike and harmonics. -- These are my opinions. I hate spam. ___ 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] Clocks for Audio gear
d...@irtelemetrics.com said: One interesting note however. Years ago we had a standard old 4040 ripple counter in our shop that displayed a low occurrence of jitter of several times it's input frequency period at it's lowest frequency output (Sort of what you are describing below). I wish I had the numbers handy, but the output would be good for most of the time, then every once in a while it would jump to a longer delay. It was hard to catch with a scope, but when we measured every single pulse width it showed up fairly well. The high speed clock (A TTL OSC in a can) never skipped, as far as we know. We never did figure that one out. From what I remember we switched IC manufacturers, and the problem when away. I expect ever old timer who did serious glitch chasing 25-30 years ago has similar stories. Mine involved a dual port RAM, 16x4. I think it was a 74S189. It was made by many companies. Chips from one vendor just occasionally screwed up. We were using them in FIFOs on ethernet boards. (They were probably used other other places too. I was worked on networking.) Back then, most large electronics companies had incoming inspection and qualification groups. I remember stories of somebody contacting that group for help and getting a response of roughly That's why we didn't qualify them. (We were a research group. We purchased small batches of chips wherever we could get them without going through the official qualified list.) -- These are my opinions. I hate spam. ___ 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] Trimble Resolution SMT - good/bad/indifferent?
The receivers from fluke.l are the TEP version that emulates Motorola protocols by default. I used Trimble GPS Monitor V1.05 to set it for TSIP. Select the Initialize Menu, Detect Receiver, click TEP protocol button. It then found the receiver and offered to enable it for TSIP. Then clicked SAVE CONFIG (so some such). I set it up for 9600,8,N,1 to make it easier to use with Lady Heather (default is 9600,8,Odd,1) using the Recever Configuration menu. ___ 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] Trimble Resolution SMT - good/bad/indifferent?
What's bad with the Motorola binary protocol? In my opinion it is superior to the NMEA one... On Thu, May 10, 2012 at 9:55 PM, saidj...@aol.com wrote: Ok, I figured out that the unit fluke.l sells is running firmware to emulate the Motrola M12+ receiver or similar. So WinOncore 12 does work, and I can get the following receiver ID: COPYRIGHT 2008 Trimble Navigation Ltd. SFTW P/N # SOFTWARE VER # 0.03.0 SOFTWARE REV # 00 SOFTWARE DATE 04/27/2009 MODEL #3011 HDWR P/N # SERIAL # 20393136 MANUFACTUR DATE 06/05/2009 OPTIONS LIST Does anyone know what the command is to configure this for NMEA or TSIP? Thanks, Said In a message dated 5/10/2012 12:15:56 Pacific Daylight Time, saidj...@aol.com writes: Hi Holrum, how do you re-configure the SMT unit? Using Trimble GPS studio? Thanks, Said In a message dated 5/9/2012 15:17:21 Pacific Daylight Time, hol...@hotmail.com writes: I have it running now. It turns out that the units from fluke.l come shipped with TEP format messages enabled (it outputs @@Cf on power up). You have to re-configure them for TSIP protocol and save the configuration back to the unit. Hope to have Lady Heather taking to it. It does come up with several of the messages working. Sat info is not one of them. ___ 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] question about Thunderbolt geo accuracy
Le 10/05/2012 21:50, Jim Lux a écrit : On 5/10/12 9:18 AM, Chris Albertson wrote: On Thu, May 10, 2012 at 9:07 AM, Bob Campli...@rtty.us wrote: . Hi all, Hope this isn't too chat roomy, however, I have need of a survey precise geolocation type gps. I was wondering if the precise timing abilities extend to its precision in position output? I have a thunderbolt and one of those conical white aerials from china and would like to know if this combination will give me accurate height data. It will give pretty good height data. Within a few meters but you have to know how to translate between different definitions of sea level to make best use of the data. I found an online WGS84-MSL converter at: http://earth-info.nga.mil/GandG/wgs84/gravitymod/wgs84_180/intptW.htm however for my location this gives the geoid height at 51,89m wrt MSL and if I apply that to my Z3801A reported height it make the difference with my TBolt even greater. I had read elsewhere , though I can't find the reference, that the difference at my latitude is more like 30m which would make more sense. Can someone with a Z3801A check the result for their location? If you live in the USA you can now download for free the USGS topographic maps. I'm pretty sure thy have full coverage of all of the US. THese will have 20 foot contour intervals and you can interpolate to at least half that. So for most normal purposes you can find your elevation without a GPS. Just look on the topo map. Most of these maps where made with stereo camera pairs. They get relative elevation optically by matching the two images and then they sent survey teams to ground check some points. And updated the elevation data with radar measurements from SRTM, as well. ___ 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] Clocks for Audio gear
On Thu, 10 May 2012 19:25:33 +0200 Heinzmann, Stefan (ALC NetworX GmbH) stefan.heinzm...@alcnetworx.de wrote: Benjamin and Gannon, the first reference in Ashihara's paper, come to lower figures for sinusoidal jitter with carefully selected frequencies relative to the main signal, which is also sinusoidal. Their results reach down to the single figure nanosecond range, and that can be regarded as the real limit of audibility. Of course, that still leaves those who claim to hear jitter in the picoseconds range out in fairy-tale land. I'm not so sure there. Having been active in the video coding scene for quite a while i know that a trained ear/eye can be easily a factor 10 better than the average. Eg, after a couple of months of hunting for bugs in the A/V sync code, i got sensitive to A/V desync down to 3-5ms. Yes, i know this is below the frame rate. But i cannot otherwise explain it as something started to feel odd, when the desync got over that limit. From somewhere between 5 and 10ms i could usually tell in which direction the desync was. Yes.. still below the frame rate. And i know that there are eyes and ears out there that are much better trained than mine ever could be. So i wouldnt imediatly dismiss it, if someone would tell me he could detect a A/V desync of 1ms (given proper frame rate). So, if someone proves that 1ns jitter is audiable for an average person, i would definitly not decline the possibility that a trained ear can hear 100ps jitter. But that is still a jitter level you can get with an crystall quite easily. You need to take care of a few things to not introduce any jitter from power supply or bad shielding, but nothing too difficult. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Clocks for Audio gear
On Thu, 10 May 2012 11:36:40 -0700 Hal Murray hmur...@megapathdsl.net wrote: Heartbeats may be more interesting than breathing. Does anybody know of spectrum domain data? It should be possible to collect position info while also monitoring heartbeat and chest diameter and then crunch some numbers do see how much of the position correlates with heartbeat vs breathing and then plot each part in the frequency domain. Please do not forget that there is a quite sofisticated error correction system attached to the hear, which we usually refere to as the brain. Breathing and heart beat are filtered out and corrected for by the brain, otherwise we would have difficulties to hear a lot of things. For more infos, please have a look at perceptual psychology. A not too bad introduction to that field is Sensation and Perception by E. B. Goldstein. But please do not expect mathematical rigor in that field. It's still a subfield of psychology. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Clocks for Audio gear
This audio thread had some interesting information; thank you. Now I welcome you to get back to the focus of the group; please. Thanks, /tvb p.s. If we need to start another mailing list that includes audio let me know; contact me off-line. ___ 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] Trimble Resolution SMT - good/bad/indifferent?
The first problem is, I didn't even know that was the command set the unit had, the @@Cf looked familiar though. I wasted an hour trying to get the Trimble application to work, until I tried WinOncore12 and the unit responded. Can't use TeraTerm to send commands, and the user manual doesn't document which Motorola commands are supported, some I found are not, and it doesn't send PVT sentences by default, it requires the user to initialize the GPS every time the power is cycled. I never got that, why would Motorola assume the receiver should be muted until enabled via software command? That doesn't make any sense to me. By default, send some useful PVT messages (Ha, Hn, for example) and allow the user to set up the unit to be mute when so desired. I wonder how many folks have pulled out their hair trying to get their Motorola units talking at the right baud rate etc etc. Maybe using it in products makes sense when one has time to learn and program for the binary messages, but debugging and development are a hassle.. Lastly, can't use the host of NMEA compatible applications that are out there, the Motorola-aware apps are pretty limited. Again uBlox has it right in my opinion: support for a huge host of binary commands if so desired, and standard NMEA output by default without any user interaction required. bye, Said In a message dated 5/10/2012 14:07:55 Pacific Daylight Time, azelio.bori...@screen.it writes: What's bad with the Motorola binary protocol? In my opinion it is superior to the NMEA one... On Thu, May 10, 2012 at 9:55 PM, saidj...@aol.com wrote: Ok, ___ 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] Trimble Resolution SMT - good/bad/indifferent?
There is the problem: I used the Trimble GPS Studio application that was posted here yesterday, that does not support the TEP protocol.. Will try with GPS Monitor.. Is the TrimbleMon available somewhere safe on the web? Can't seem to find it with Google. I got it working with Oncore12, and I am capturing 1PPS raw data already. Already noticed that while the signal strengths look good, there are way less Sats being seen than on the 50 channel receivers, and none of the WAAS ones are being decoded. thanks, Said In a message dated 5/10/2012 14:07:38 Pacific Daylight Time, hol...@hotmail.com writes: The receivers from fluke.l are the TEP version that emulates Motorola protocols by default. I used Trimble GPS Monitor V1.05 to set it for TSIP. Select the Initialize Menu, Detect Receiver, click TEP protocol button. It then found the receiver and offered to enable it for TSIP. Then clicked SAVE CONFIG (so some such). I set it up for 9600,8,N,1 to make it easier to use with Lady Heather (default is 9600,8,Odd,1) using the Recever Configuration menu. ___ 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] Trimble Resolution SMT - good/bad/indifferent?
Why in the hell would anybody build a 50 channel receiver? At most you MIGHT see 12 usable GPS sats... I don't think that I've seen over 10. WAAS should be fairly useless for a timing receiver. Supposedly the Nortel NTGS50AA docs and support info (including GPSMONITOR were uploaded to the KO4BB site). ___ 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] Trimble Resolution SMT - good/bad/indifferent?
Why in the hell would anybody build a 50 channel receiver? At most you MIGHT see 12 usable GPS sats... I don't think that I've seen over 10. WAAS should be fairly useless for a timing receiver. Or 216 channels (GPS L1/L2/L2C/L5; GLONASS L1/L2; Galileo E1/E5A): http://www.javad.com/jgnss/products/triumph.html /tvb ___ 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] Trimble Resolution SMT - good/bad/indifferent?
Think Galileo, Waas, Glonass, and gps could give you more than 38 sats, over determination will give better results and much faster cold starts without almanac and assist. Waas helps a lot when you run on a Uav chasing bad guys, think timing under motion without position hold mode, so there are four parameters to find every second and waas does improve timing in that scenario. And why would one not want to have 0.7m horizontal accuracy while moving at 100s of knots? Why not offer 50 Sats? Silicon doesn't cost anything anymore. Companies in china pay less than $8 for these parts in large quantity. I think the quality of the results speak for themselves.. CNS verified the ublox timing is almost as good as the M12+ but with everything else vastly improved. Trimble soarly seems lacking so far. We would love to use a US made or at least US designed GPS but alas there are none so far. Waiting to be proved wrong.. Sent From iPhone On May 10, 2012, at 21:02, Mark Sims hol...@hotmail.com wrote: Why in the hell would anybody build a 50 channel receiver? At most you MIGHT see 12 usable GPS sats... I don't think that I've seen over 10. WAAS should be fairly useless for a timing receiver. Supposedly the Nortel NTGS50AA docs and support info (including GPSMONITOR were uploaded to the KO4BB site). ___ 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] Why 9,192,631,770 ??
Are there better estimates of the ET second nowadays (relative to the SI second)? It would be interesting to know what the cesium frequency should have been if much better estimates of the ephemeris-time second were available at the time. One would think that with all the solar-system data JPL and others have had at their disposal since the 1970s, a very good ET-second number could be cooked up; better than 1950s Moon cameras at any rate. For that matter, what are the inherent long-term limits on ET as a timescale? I gather the observation noise is very high on short timescales, but what is the situation for, say, tau1year? It's not as if the Earth's orbit is randomly perturbed very much, I'm guessing, and any deterministic perturbations or relativistic corrections would be compensated for; it's the noiselike processes that would be interesting. (Solar wind?) Cheers, Peter ___ 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.
