Re: [time-nuts] Phase Noise vs. AM noise
As long as the instrument is carefully adjusted so the that the measurement phase axis is correctly aligned with respect to the test signal an interferometer can be used to ensure that the measurement system PN noise floor is well below the thermal limit when measuring the residual noise of 2 port components such as amplifiers. In order to achieve sufficiently accurate alignment a pure AM modulator may be required. Bruce On Thursday, January 15, 2015 01:13:13 PM Mike Feher wrote: > Bob - > > I am maybe using the wrong word "discernible". By that I mean that you > cannot discern phase noise from AM noise at the real low levels. You can > certainly measure, or see the contribution of the total noise power, but do > not necessarily know if it is phase noise or AM noise or how much of each > is included. Regards - Mike > > Mike B. Feher, EOZ Inc. > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 office > 908-902-3831 cell > > > -Original Message- > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp > Sent: Thursday, January 15, 2015 7:48 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Current state of optical clocks and the definition > of the second > > Hi > > I guess the question becomes how low is low. > > If it’s a 50 ohm system > > If the power level is rational > > If you are at room temperature > > There are some limits on how low low can be. > > You have a -174 dbm / Hz thermal floor. AM or PM noise can only be 3db > better than the thermal floor. At a power level of 1 watt, that’s a -204 > dbc / Hz limit. You will spend some time correlating to that level. You > also may need to play a bit with the input circuits to handle the 1W > without damage. At a somewhat more common 100 mw, the limit is -194. People > have been measuring phase noise in the > -190 dbc / Hz range for at least > 20 years now. Correlation may take a week at some offsets. Time will be > longer or shorter at other offsets. As with anything else, the more money > (correlation channels) you throw at the problem, the quicker it will go. > Numbers in the -180 vicinity with normal gear, offsets, and FFT windows are > an overnight run sort of thing. > > > ___ > 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] New algorithm, better ADEV
Magnus Danielson writes: > > Which display is it? > Hi Mangus, I do not know the model name, but I found the same one on ebay (key word 2.2 TFT SPI). It's a SPI screen, so it shows things quite slow. However, 320x240 resolution is good to display a lot of slow changing stuffs. I use this because it's smaller than the LCD1602 module. ___ 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] New algorithm, better ADEV
Hi, On 01/14/2015 10:58 PM, John Miles wrote: Just now, I changed the way to calculate frequency and get a better ADEV chart. http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/0114.gif Looking good! Nice example of a white PM noise floor, just like a 'real' HP counter. Let it run for a few days and see how the environmental sensitivity looks. Indeed. Just recall that this is not all *real* white PM noise, it just behaves like it. BTW: I've put the counter into a box. http://www.qsl.net/b/bi7lnq/freqcntv4/pic/20150114_212857.jpg more pictures: http://www.qsl.net/b/bi7lnq/freqcntv4/pic/ Those small SPI LCDs are really neat, especially for the price. I just used one the other day to replace a 1" CRT in a receiver panadaptor. Sure looks good! Which display is it? 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] L1 and L2 frequencies
Magnus, >>> If civilian receivers where to implement L2C and L5 which now is >>> becoming common, they would gain quite a bit of precision in a similar >>> fashion. For car navigation, the GPS would know which lane you are in. >> >> There ARE civilian receivers doing this, and has been for quite some >> years. And its not from only a few vendors - all the big ones have it - >> Trimble, Novatel, Topcon, Javad, Leica, Septentrio and a few more. There >> are now receivers tracking "GPS L1/L2/L2C/L5, Galileo >> E1/E5A/E5B/AltBoc/E6, GLONASS L1/L2/L3, BeiDou B1/B2/B3, QZSS L1/L2/L5" >> >> The price exceeds my home hobby budget, but so does a replacement >> CS-tube >> a factory new OCXO based GPSDO and many other things you can sometime >> find >> at reasonable cost used/recycled. > > I naturally meant with a reasonable price-tag, sorry for being sloppy on > that detail, and I do know that there is vendors for those signals. > > If we had dual or triple frequency receivers below 500 USD things would > start to be interesting. If high-volume kits would be just twice as > expensive, it would be possible to consider for more luxury models. Receiver with 24 universal channels each of GPS L1/L2/L2C/L5 is cheaper than a entry level TCXO-based 19" GPSDO (M300GPS @ Dustin). And about the same price as a modern Loran receiver. What is a reasonable commercial price? But yes, multi frequency GNSS is much more expensive than the Oncore, Ublox traditionally used in a GPSDO. Is the performance gain worth the cost? Certainly not for all but a few. On the oscillator side, we consider everything from XO, TCXO, OCXO, DOCXO, to devar based designs - BVAs and others, and rubidiums, cesiums and Masers. What are reasonable price-tags for oscillators compared to various time transfer capable receiver? -- 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] L1 and L2 frequencies
> If we had dual or tripple frequency receivers below 500 USD things would > start to be interesting. If high-volume kits would be just twice as > expensive, it would be possible to consider for more luxury models. Hi Magnus, I am currently (but slowly) evaluating about a dozen near identical, surplus, dual-frequency, carrier-phase GPS receivers with the goal of making them available to a select handful of interested time nuts. This is at or below your price point (antenna not included). Priority given to those who are willing to actively work as a small group to share info and get the best use out of them, even it means some h/w or s/w hacking. Having a cesium LO is probably required. I am getting cm levels of accuracy; next step is to process the timing information. More info about all this a month from now. Contact me off-list. Thanks, /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] L1 and L2 frequencies
Björn, On 01/15/2015 07:55 PM, "Björn Gabrielsson" wrote: Brooke, The traditional GPS has C/A and P(Y) on L1 and P(Y) on L2. Most Civilian GPSes only uses C/A. Advanced receivers can also use P(Y) code, since the P-code is known, the hand-off to P code is known and the way that P-code is encrypted into Y-code is known (XOR with another code, called A-code or W-code in different sources). Modern receivers is able to do both code and carrier phase observations on the P(Y) code signals. Read up on semi-codeless tracking, I dont think (pure) codeless is used anymore. http://www.colorado.edu/ASEN/asen6090/ztracking.html https://books.google.se/books?id=-sPXPuOW7ggC&pg=PA240&lpg=PA240 This is a better reading: http://www.navcomtech.com/navcom_en_US/docs/download_center/white_papers/current/optimum_semi_codeless_carrier_phase_tracking_of_l2.pdf The Ashtech literature referred to 13 dB better efficiency of their Z12 Z-tracking compared to the cross-correlation technique of the then competitor Trimble 4000 receiver. The above paper indicate 14 dB difference between the methods. All semi-codeless receivers will experience "squaring loss", and it shifts with the C/N. This have made the original code-less squaring approach completely useless in comparison to the more modern approaches. The squaring method assumes that what-ever magic code there is, is encoded as multiplying the carrier by +1 or -1 and squaring it makes it go +1 and +1. Cross-correlation gains 3 dB, but real gain comes only when applying the known P-code. Since processing at these rates is relatively cheap these days, there is no point in wasting implementation on code-less. The military goal of this "break-in" is not lost, as those receivers still rely on the C/A code and that is easy to jam. Also, the "break-in" comes at a signal quality loss and the advancement of methods have reduced this loss. The benefit of dual frequency observation is that ionspheric shift can be almost completely taken out of the error budget, adjusting both code and carrier phase observations. Then working on the integer ambiguity you can get carrier phase observations with accurate pseudo-ranges. Carrier-phase observations has a much higher precision to them, so that gives a very high precision and using a good reference network corrections can be adjusted to give good absolute position. If civilian receivers where to implement L2C and L5 which now is becoming common, they would gain quite a bit of precision in a similar fashion. For car navigation, the GPS would know which lane you are in. There ARE civilian receivers doing this, and has been for quite some years. And its not from only a few vendors - all the big ones have it - Trimble, Novatel, Topcon, Javad, Leica, Septentrio and a few more. There are now receivers tracking "GPS L1/L2/L2C/L5, Galileo E1/E5A/E5B/AltBoc/E6, GLONASS L1/L2/L3, BeiDou B1/B2/B3, QZSS L1/L2/L5" The price exceeds my home hobby budget, but so does a replacement CS-tube a factory new OCXO based GPSDO and many other things you can sometime find at reasonable cost used/recycled. I naturally meant with a reasonable price-tag, sorry for being sloppy on that detail, and I do know that there is vendors for those signals. If we had dual or tripple frequency receivers below 500 USD things would start to be interesting. If high-volume kits would be just twice as expensive, it would be possible to consider for more luxury models. 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] L1 and L2 frequencies
> Brooke, > > The traditional GPS has C/A and P(Y) on L1 and P(Y) on L2. > Most Civilian GPSes only uses C/A. > Advanced receivers can also use P(Y) code, since the P-code is known, > the hand-off to P code is known and the way that P-code is encrypted > into Y-code is known (XOR with another code, called A-code or W-code in > different sources). Modern receivers is able to do both code and carrier > phase observations on the P(Y) code signals. Read up on semi-codeless tracking, I dont think (pure) codeless is used anymore. http://www.colorado.edu/ASEN/asen6090/ztracking.html https://books.google.se/books?id=-sPXPuOW7ggC&pg=PA240&lpg=PA240 > The military goal of this "break-in" is not lost, as those receivers > still rely on the C/A code and that is easy to jam. Also, the "break-in" > comes at a signal quality loss and the advancement of methods have > reduced this loss. > > The benefit of dual frequency observation is that ionspheric shift can > be almost completely taken out of the error budget, adjusting both code > and carrier phase observations. Then working on the integer ambiguity > you can get carrier phase observations with accurate pseudo-ranges. > Carrier-phase observations has a much higher precision to them, so that > gives a very high precision and using a good reference network > corrections can be adjusted to give good absolute position. > > If civilian receivers where to implement L2C and L5 which now is > becoming common, they would gain quite a bit of precision in a similar > fashion. For car navigation, the GPS would know which lane you are in. There ARE civilian receivers doing this, and has been for quite some years. And its not from only a few vendors - all the big ones have it - Trimble, Novatel, Topcon, Javad, Leica, Septentrio and a few more. There are now receivers tracking "GPS L1/L2/L2C/L5, Galileo E1/E5A/E5B/AltBoc/E6, GLONASS L1/L2/L3, BeiDou B1/B2/B3, QZSS L1/L2/L5" The price exceeds my home hobby budget, but so does a replacement CS-tube a factory new OCXO based GPSDO and many other things you can sometime find at reasonable cost used/recycled. -- 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] GPS 1PPS ultimate accuracy
Hi Andrea, Making measurements of quartz oscillator aging is much easier than you think and requires minimal equipment. In particular all you need is a GPS 1PPS and a simple counter. No need to worry about sawtooth. Any $20 GPS/1PPS receiver will work. Consider this rough example of measuring for one week a OCXO with 1e-10/day frequency drift rate. Say on day 1 it is 1e-10 low in frequency. It will lose 0.1 ns per second. That's a very small amount and expensive to measure. But who cares. You're not trying to measure phase noise, or short-term stability, or frequency; all you're trying to measure is frequency drift. So let it run all day. By the end of the day those 0.1 ns have added up to 8.6 us. One data point. 8 microseconds is a lot. You can measure this with a $1 PIC or a $10 Arduinio. Use either time interval or timestamping methods. See PIC examples at www.leapsecond.com/pic/ although you can turn just about any microcontroller into a microsecond, or sub-microsecond counter and results over serial or USB to a PC for logging. On day 2 it has drifted to be 2e-10 low in frequency, so it will lose an additional 17.2 us of time, etc. Another data point. By the end of the week, the slowly aging oscillator is 7e-10 low in frequency and will lose 60 us that day. This simple experiment would give you 7 data points which would nicely show your oscillator drift rate. You could collect data more than once a day if you wanted, like every hour or every minute. Differentiate the time error to get frequency error. Differentiate frequency to get frequency drift rate. Or just do a quadratic fit of the raw time error data. It requires so little hardware that you could easily let it run for a month, or year and collect wonderful data. The more the oscillator drifts the larger the time measurements are so the easier they are to measure with accuracy. This setup might even work for Rubidium. On the one hand Rubidium drift rates are 10x to 100x less than OCXO so your times will not grow nearly as rapidly, making precise measurements more difficult. On the other hand, Rubidium drift rates are so low that you would want to measure for months instead of weeks. In the end the two factors may balance themselves. So I don't think you need nanosecond counters or fancy sawtooth corrected GPS timing receivers or GPSDO or measurements every second. A slowly aging oscillator is very easy to measure, mostly because, in order to measure aging you need many days or weeks or months of data. The longer the measurement time, the less it matters what the resolution of the counter (or the GPS 1PPS) is or how quickly you collect data. /tvb - Original Message - From: "Andrea Baldoni" To: Sent: Monday, January 12, 2015 2:59 AM Subject: [time-nuts] GPS 1PPS ultimate accuracy > Hello all. > > I am planning to do some experiments to evaluate the aging of oscillators > (this one of the reasons I'm willing to buy the Milleren without EFC). > What I would like to do exactly is to sample the total of a counter (of > suitable number of bits, taking in account the fact that it will overflow) > whose clock is the DUT. > > The sampling interval could come from a (long time based on a) sawtooth > uncorrected PPS from a cheap GPS, a sawtooth corrected from a good one > (perhaps > the Lucent GPSDO), or a computer using NTP. > > Each of these sources should reach a goal stability (say, 1 part in 10^13) > after averaging them on a different (and very high I suppose) number of > seconds (averaging them for an infinity number of seconds should give the > stability of the underlying reference clock, but I'm willing to stop > sooner...). > I know there's no reason to go 1E-13 when the Milliren couldn't go that far, > but the DUT may be also something else like a FE-5680A). > > The sawtooth uncorrected GPS receiver may never yeld a good stability in the > short term, but in the long one it should as well because the internal clock > jitter would average results. > > If I'm using the correct teminology, after what tau the ADEV graph of the > different references intersect the 1E-13? > > By the way, the stability of the TAI is known or, because it's > the reference one, it has zero deviation for definition (so you can reach > its ultimate stability through GPS really only at the infinity...)? > > Best regards, > Andrea Baldoni > ___ > 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] Phase Noise vs. AM noise
Bob - I am maybe using the wrong word "discernible". By that I mean that you cannot discern phase noise from AM noise at the real low levels. You can certainly measure, or see the contribution of the total noise power, but do not necessarily know if it is phase noise or AM noise or how much of each is included. Regards - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Thursday, January 15, 2015 7:48 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Hi I guess the question becomes how low is low. If it’s a 50 ohm system If the power level is rational If you are at room temperature There are some limits on how low low can be. You have a -174 dbm / Hz thermal floor. AM or PM noise can only be 3db better than the thermal floor. At a power level of 1 watt, that’s a -204 dbc / Hz limit. You will spend some time correlating to that level. You also may need to play a bit with the input circuits to handle the 1W without damage. At a somewhat more common 100 mw, the limit is -194. People have been measuring phase noise in the > -190 dbc / Hz range for at least 20 years now. Correlation may take a week at some offsets. Time will be longer or shorter at other offsets. As with anything else, the more money (correlation channels) you throw at the problem, the quicker it will go. Numbers in the -180 vicinity with normal gear, offsets, and FFT windows are an overnight run sort of thing. ___ 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 1PPS ultimate accuracy
Hi > On Jan 15, 2015, at 4:56 AM, Andrea Baldoni wrote: > > On Mon, Jan 12, 2015 at 06:16:01PM -0500, Bob Camp wrote: > >> Actually it’s a bit worse than you might expect. >> The uncorrected sawtooth will give you about 20 ns of wander. At the one day >> level, GPS without some sort of ionosphere help (like a dual frequency >> receiver) will add another 10 ns or so to that. Net, your pps is spread over >> a 30 ns range. > > Hello Bob. > Thank you, now I have a better idea. > I understand that the NTP is completely ruled out and also between GPS there > is a strong difference. > >> With things like 5335’s running around for cheap prices, I would suggest >> doing this with a counter. You are going to spend a lot of days getting very >> much data. Your time’s got to be worth something …. > > Actually I own a Racal 1995 that should be better than the 5335 with its 1ns > single shot resolution. > However, I don't still own a GPSDO to reference the counter so how do you > suggest to use it? Divide both of the things you are testing down to 1 pps. Trigger the start on one and the stop on the other. Read out the difference to the 1 or 2 ns resolution of the counter. That’s going to be ~ 100 X better than measurement with the rolling counter. Bob > I should use total A over B with the DUT in A and the PPS in B? > > Best regards, > Andrea Baldoni > ___ > 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] Current state of optical clocks and the definition of the second
Bob - What I am saying is, even at the levels you mentioned, what is measured is I believe the combination of phase and AM. In other words, you are just measuring noise, but, are not certain if it is all phase, or phase plus some AM. At least that is my recollection when I was heavily involved in it some 30 years ago. Thanks - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Thursday, January 15, 2015 7:48 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Hi I guess the question becomes how low is low. If it’s a 50 ohm system If the power level is rational If you are at room temperature There are some limits on how low low can be. You have a -174 dbm / Hz thermal floor. AM or PM noise can only be 3db better than the thermal floor. At a power level of 1 watt, that’s a -204 dbc / Hz limit. You will spend some time correlating to that level. You also may need to play a bit with the input circuits to handle the 1W without damage. At a somewhat more common 100 mw, the limit is -194. People have been measuring phase noise in the > -190 dbc / Hz range for at least 20 years now. Correlation may take a week at some offsets. Time will be longer or shorter at other offsets. As with anything else, the more money (correlation channels) you throw at the problem, the quicker it will go. Numbers in the -180 vicinity with normal gear, offsets, and FFT windows are an overnight run sort of thing. Bob ___ 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] Current state of optical clocks and the definition of the second
Hi I guess the question becomes how low is low. If it’s a 50 ohm system If the power level is rational If you are at room temperature There are some limits on how low low can be. You have a -174 dbm / Hz thermal floor. AM or PM noise can only be 3db better than the thermal floor. At a power level of 1 watt, that’s a -204 dbc / Hz limit. You will spend some time correlating to that level. You also may need to play a bit with the input circuits to handle the 1W without damage. At a somewhat more common 100 mw, the limit is -194. People have been measuring phase noise in the > -190 dbc / Hz range for at least 20 years now. Correlation may take a week at some offsets. Time will be longer or shorter at other offsets. As with anything else, the more money (correlation channels) you throw at the problem, the quicker it will go. Numbers in the -180 vicinity with normal gear, offsets, and FFT windows are an overnight run sort of thing. Bob > On Jan 14, 2015, at 9:47 PM, Mike Feher wrote: > > Hi - > > I agree with what you stated, however, I am not sure that at real low levels > they are actually discernible. Regards - Mike > > Mike B. Feher, EOZ Inc. > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 office > 908-902-3831 cell > > -Original Message- > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp > Sent: Wednesday, January 14, 2015 6:14 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Current state of optical clocks and the definition > of the second > > Hi > > More or less by definition: > > AM noise has the sidebands in phase, PM noise has the sidebands out of phase. > PM adds to no envelope power, AM adds to the envelope power. If you have > purely random noise, half of the power is AM, half is PM by this approach. If > you have what is effectively a SDR (high speed ADC(s), decimators, cross > correlation …) doing your phase noise measurement, figuring out sidebands and > phase is part of the process. With an old style single mixer approach, you > switch your operating point on the mixer. > > Bob > > > ___ > 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] GPS 1PPS ultimate accuracy
On Mon, Jan 12, 2015 at 06:16:01PM -0500, Bob Camp wrote: > Actually it’s a bit worse than you might expect. > The uncorrected sawtooth will give you about 20 ns of wander. At the one day > level, GPS without some sort of ionosphere help (like a dual frequency > receiver) will add another 10 ns or so to that. Net, your pps is spread over > a 30 ns range. Hello Bob. Thank you, now I have a better idea. I understand that the NTP is completely ruled out and also between GPS there is a strong difference. > With things like 5335’s running around for cheap prices, I would suggest > doing this with a counter. You are going to spend a lot of days getting very > much data. Your time’s got to be worth something …. Actually I own a Racal 1995 that should be better than the 5335 with its 1ns single shot resolution. However, I don't still own a GPSDO to reference the counter so how do you suggest to use it? I should use total A over B with the DUT in A and the PPS in B? Best regards, Andrea Baldoni ___ 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 1PPS ultimate accuracy
On Mon, Jan 12, 2015 at 03:10:39PM +0100, Attila Kinali wrote: > The GNSS Timing AppNote for the LEA6-T receiver[1] will give you an idea > what jitter you get with GPS. Please be aware that these measurements > were done with an antenna located at a _good_ position (ontop of a 4 story > building with no other high buildings around). Unless you have a simlarly > good location you will have worse performance. Ciao Attila. By the way, I see there are LEA-6T from Hong Kong at 49 USD shipping included. If those are not a fake and I can extract the PPS from them, do you suggest this as the best GPS for the price actually available for timing? > It would average out if and only if the sawtooth correction would be > completely > independent of anything else. But it isn't. This results in effects where the > cycle to cycle jitter is quite low, but there is a large offset in the > sawtooth > correction. This is know as "hanging bridges" in the GNSS world. I can use the sawtooth correction with LEA-6T but if I am using it with a normal TIC I should obtain a way either to apply the correction in hardware, or to capture the numbers and postprocess them together with data from the TIC. Probably the simple solution is a GPSDO where everything is already done? Best regards, Andrea Baldoni ___ 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] Current state of optical clocks and the definition of the second
I have a page that illustrates how you can use a delay line and a mixer to separately obtain AM and PM http://www.ko4bb.com/Timing/Phase_Detector Didier KO4BB On January 14, 2015 1:19:11 PM CST, Mike Feher wrote: >At those low levels, how does one differentiate between phase or AM >noise? Thanks & Regards - Mike > >Mike B. Feher, EOZ Inc. >89 Arnold Blvd. >Howell, NJ, 07731 >732-886-5960 office >908-902-3831 cell > >-Original Message- >From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce >Griffiths >Sent: Wednesday, January 14, 2015 1:22 AM >To: Discussion of precise time and frequency measurement >Subject: Re: [time-nuts] Current state of optical clocks and the >definition of the second > >Although the phase noise when using optical combs to generate Rf >signals is low there is no mention of the am noise. > >Bruce > >___ >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. -- Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do other things. ___ 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] New algorithm, better ADEV
I have been following this thread quietly. But will comment. I noticed the construction methods. Lots of little holes. That is all to familiar to me. Good to see others do the same around the world. The project is really coming along nicely. Regards Paul WB8TSL On Wed, Jan 14, 2015 at 4:58 PM, John Miles wrote: > > Just now, I changed the way to calculate frequency and get a better > >ADEV chart. > >http://www.qsl.net/b/bi7lnq/freqcntv4/test/20150114/0114.gif > > Looking good! Nice example of a white PM noise floor, just like a 'real' > HP counter. Let it run for a few days and see how the environmental > sensitivity looks. > > > BTW: I've put the counter into a box. > > http://www.qsl.net/b/bi7lnq/freqcntv4/pic/20150114_212857.jpg > > more pictures: http://www.qsl.net/b/bi7lnq/freqcntv4/pic/ > > Those small SPI LCDs are really neat, especially for the price. I just > used one the other day to replace a 1" CRT in a receiver panadaptor. > > -- john, KE5FX > Miles Design LLC > > > ___ > 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] L1 and L2 frequencies
Brooke, The traditional GPS has C/A and P(Y) on L1 and P(Y) on L2. Most Civilian GPSes only uses C/A. Advanced receivers can also use P(Y) code, since the P-code is known, the hand-off to P code is known and the way that P-code is encrypted into Y-code is known (XOR with another code, called A-code or W-code in different sources). Modern receivers is able to do both code and carrier phase observations on the P(Y) code signals. The military goal of this "break-in" is not lost, as those receivers still rely on the C/A code and that is easy to jam. Also, the "break-in" comes at a signal quality loss and the advancement of methods have reduced this loss. The benefit of dual frequency observation is that ionspheric shift can be almost completely taken out of the error budget, adjusting both code and carrier phase observations. Then working on the integer ambiguity you can get carrier phase observations with accurate pseudo-ranges. Carrier-phase observations has a much higher precision to them, so that gives a very high precision and using a good reference network corrections can be adjusted to give good absolute position. If civilian receivers where to implement L2C and L5 which now is becoming common, they would gain quite a bit of precision in a similar fashion. For car navigation, the GPS would know which lane you are in. Cheers, Magnus On 01/14/2015 10:40 PM, Brooke Clarke wrote: Hi Martyn: On each frequency there are a couple or more different codes. The Civilian Acess (C/A) code on the L1 frequency is all public information and so is the most commonly used. But there are classified codes that have a much higher bit rate and allow for more accurate position, time and velocity measurements. Tom mentioned that there are civilian GPS receivers that make use of the L2 frequency, but they do that my using what's called carrier phase (that's to say they do not make use of the classified code). This is mainly used in surveying applications where, by recording a lot of data and post processing, you can get a very precise location. When two frequencies are used there's a possibility of removing an error related to the total electron count in the path of the signal. The new F5 frequency allows for doing that, but as far as I know none of the commercial GPS receivers make use of it yet. http://www.prc68.com/I/DAGR.shtml#GPSs Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Martyn Smith wrote: Hello, I have some questions on GPS and GNSS. Do all the civilian GPS receivers only operate on the L1 frequency? Are there any GPS frequency standards out there that use L1 and L2 and that can be purchased by non-military customers? I am playing with the new Lea-M8T receiver. How do I know what satellites are GPS, GLONASS, Galileo etc. >From my understanding GLONASS have different SV numbers but not 100% sure. Any help appreciated. Regards Martyn ___ 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] New algorithm, better ADEV
Tom Van Baak writes: > Just use: > ref_delta = ref_curr - ref_prev; > sig_delta = sig_curr - sig_prev; > > Not only is it much simpler but it also works in every case (your code would fail whenever curr equals prev). > > Here's a test program in case you don't believe me: http://leapsecond.com/tools/wrap1.c > > /tvb > Hi Tom, Yes, your way is simpler and reliable since the variables are all uint32_t type. Thanks for pointing out the mistake. ___ 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] L1 and L2 frequencies
On 1/14/15 1:40 PM, Brooke Clarke wrote: Hi Martyn: On each frequency there are a couple or more different codes. The Civilian Acess (C/A) code on the L1 frequency is all public information and so is the most commonly used. But there are classified codes that have a much higher bit rate and allow for more accurate position, time and velocity measurements. Tom mentioned that there are civilian GPS receivers that make use of the L2 frequency, but they do that my using what's called carrier phase (that's to say they do not make use of the classified code). This is mainly used in surveying applications where, by recording a lot of data and post processing, you can get a very precise location. Actually, there's L2c available for civil use now, on many satellites. And L5 is available for civilian use (on fewer satellites than L2c) L2 has an issue with "safety of life" applications: it's not an exclusive allocation, so there's an effort to move L1/L2 to L1/L5 When two frequencies are used there's a possibility of removing an error related to the total electron count in the path of the signal. The new F5 frequency allows for doing that, but as far as I know none of the commercial GPS receivers make use of it yet. There's only half a dozen or so L5 satellites so far.. http://www.prc68.com/I/DAGR.shtml#GPSs Mail_Attachment -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html http://www.prc68.com/I/DietNutrition.html Martyn Smith wrote: Hello, I have some questions on GPS and GNSS. Do all the civilian GPS receivers only operate on the L1 frequency? Are there any GPS frequency standards out there that use L1 and L2 and that can be purchased by non-military customers? I am playing with the new Lea-M8T receiver. How do I know what satellites are GPS, GLONASS, Galileo etc. >From my understanding GLONASS have different SV numbers but not 100% sure. Any help appreciated. Regards Martyn ___ 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] Current state of optical clocks and the definition of the second
Hi - I agree with what you stated, however, I am not sure that at real low levels they are actually discernible. Regards - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Wednesday, January 14, 2015 6:14 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Current state of optical clocks and the definition of the second Hi More or less by definition: AM noise has the sidebands in phase, PM noise has the sidebands out of phase. PM adds to no envelope power, AM adds to the envelope power. If you have purely random noise, half of the power is AM, half is PM by this approach. If you have what is effectively a SDR (high speed ADC(s), decimators, cross correlation …) doing your phase noise measurement, figuring out sidebands and phase is part of the process. With an old style single mixer approach, you switch your operating point on the mixer. Bob ___ 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.
