Re: [time-nuts] nuts about position
In message , Mark Sims writes: >The effects of things like antenna position changing a couple of cm due to >expansion and humidity effects are swamped by the receiver accuracy and noise. Short term: Yes. Long term: No. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
The typical receiver default self-surveys of 30 minutes to 2 hours are not ideal. They will not include a lot of satellites or the effects of multi-path over time. A survey of at least 12 hours is needed to include all the sats. 24-48 hours is even better. The effects of things like antenna position changing a couple of cm due to expansion and humidity effects are swamped by the receiver accuracy and noise. - > That said, there are certainly a lot of issues with how the self-survey position should be calculated *and* maintained, because it really needs to change over time for optimal performance. ___ 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] nuts about position
In message , Mark Sims writes: >The next thing I want to try is a receiver self-survey vs the post processed >results... I fell into that trap many years ago as well :-) The post processed result eliminates and compensates for a lot of effects which are invisible to the receiver, that is the entire point of post processing. But if your goal is to get good 1PPS out of your receiver, forcing it to hold a "perfect" position, means asking it to deal with effects it cannot measure, and as a result you get *worse* 1PPS performance than if you use the "wrong" self-survey position. That said, there are certainly a lot of issues with how the self-survey position should be calculated *and* maintained, because it really needs to change over time for optimal performance. Almost any suboptimal antenna-position means that you should vary the position-hold coordinates over the orbital period (but see below), but over longer periods also environmental factors come into play. For instance if you put the antenna on a wood-construction, be it a pole or a house, it coordinates will vary at the cm level over the seasons as the wood expands and contracts. The good news is that the receiver gives you the input data to work and model these biases, the bad news you don't get a lot of data. I did some experiments when ten Oncore M12+T's passed through my lab many years ago: I plotted the reported "residuals" vs. satellite position, and I tried to update the held position on a daily basis using the trend, and the results were measurable at the several ns level: http://phk.freebsd.dk/raga/sneak/ I didn't persue this further, because my latitude is particular unfavourable to the simple (N/S+E/W) approach (no birds north of me) and with only a single receiver the amount of input data is too low for such a crude algorithm. A more complex geometrical model could probably get more mileage out of the sparse data, as would tracking more birds than the 12 the M12 could track. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
The tripod is a survey grade tripod on a limestone terrace (in a horrible location for an antenna). Heather's precision survey uses the receiver's reported position data. It does not take advantage of carrier phase/pseduorange/doppler data and post-processing. Unlike the simple averaging self-surveys that most receivers do it processes the average of medians over 1 minute/1 hour/24 hour intervals. It typically produces results 1-2m better than the simple self-surveys. The next thing I want to try is a receiver self-survey vs the post processed results... I may be able to kludge up a test that does a self-survey / precision survey / post processed survey and compare the results of the methods on the same data set. ___ 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] nuts about position
Hi Hmmm …… that’s a very big difference between the RINEX and the “precision survey”. How do each compare to other receivers on the same antenna ( and super duper stable mount) ? Even with a tripod on the grass, meter level variations likely are not the tripod’s fault. :) Bob > On Jun 5, 2018, at 1:39 PM, Mark Sims wrote: > > I did Lady Heather's 48-hour precision survey on an NVS-08 receiver and > collected RINEX data at the same time. The NVS was tracking GPS and SBAS > satellites. > > The RINEX result had lat/lon/alt error estimates of .175/.153/.396 meters. > > The difference between Heather's precision survey results and the RINEX > position were: > lat/lon/alt: -.638m/1.190m/1.526m > ___ > 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] nuts about position
I did Lady Heather's 48-hour precision survey on an NVS-08 receiver and collected RINEX data at the same time. The NVS was tracking GPS and SBAS satellites. The RINEX result had lat/lon/alt error estimates of .175/.153/.396 meters. The difference between Heather's precision survey results and the RINEX position were: lat/lon/alt: -.638m/1.190m/1.526m ___ 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] Raw phase data of super-5065
Attila, I will send you some raw data. Attached is a combined plot of a recent successful filter installation. Only 20 to 25% of units will be improved with the filter mod. Two things to look for. 1- The short term stability at 1 Sec (Allan Deviation) should drop from the 2X10-12th range down to the mid -13ths. 2- The Allan Deviation plot should drop into the -14ths between 32 and 64 Seconds. #1 is easily tested but not many have a reference to test #2 against. Also as Bob indicated longer term plots need to be in a benign environmental setting. Cheers, Corby___ 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] Possible new run of TNS-BUF High Isolation, Low Noise Buffer Amp boards
Good news -- we had enough orders to justify doing a small production run of the TNS-BUF isolation amplifiers. We'll be placing the order with our contract manufacturer this week, and expect delivery in six to eight weeks. There will be a few extra boards available, so if you haven't ordered yet, there's still time. John On 05/08/2018 03:09 PM, John Ackermann N8UR wrote: Back in October, 2016, TAPR did a build-to-order offering of the TNS-BUF low noise, high isolation buffer amplifier. The original 2016 post is attached below. All of those units sold out, and recently I've had a few questions about whether more will be available. TAPR will do another one-off production run if we can get orders for at least 25 boards (the minimum to make manufacturing viable) by *June 1*. You can place an order by going to http://tapr.org/kits_tns-buf. The price will be the same as the previous production -- $119 plus shipping. If we receive orders for at least 25 boards by June 1, we will charge credit cards and place the production order with our contract manufacturer. If we don't get 25 orders, we'll cancel the project and your card will not be charged. We expect to ship finished TNS-BUF boards about 60 days after placing the production order. Best regards, John Forwarded Message Subject: [time-nuts] TNS-BUF High Isolation, Low Noise Buffer Amp Available Date: Wed, 5 Oct 2016 10:15:46 -0400 From: John Ackermann N8UR I've previously mentioned a high performance buffer amplifier called the "TNS-BUF" that I built based on a design by Dr. Bruce Griffiths with further input from John Miles. Key numbers are: * Phase noise -140dBc/Hz at 1 Hertz offset, noise floor -175dBc/Hz. (PN plot attached) * Reverse isolation greater than 100dB; low enough that I can't make a trustworthy measurement. * Gain from -10 to +7 dB from 1 to 30 MHz; maximum output >18dBm. * Nominal 18VDC operation, but works down to 12V with lowered maximum output level. There's information, including performance data and schematic, at http://www.febo.com/pages/TNS-BUF There seems to be some interest in an amplifier like this, so TAPR has decided to do a limited production run. The amp is built with surface mount parts, so we thought an assembled and tested board was better than a kit. The price will be $119 each. But we have no idea how much interest there is, and we need to build a minimum of 25 units to make production feasible. So, here's the deal: you can order your TNS-BUF at http://tapr.org/kits_tns-buf through *October 20*. If we receive orders for at least 25 boards by then, we will charge credit cards and place the production order with our contract manufacturer. If we don't get 25 orders, we'll cancel the project and credit cards will not be charged. There's no guarantee that boards will be available for later order. We expect about 60 days between placing the manufacturing order and receipt of the boards at TAPR. We'll ship to customers ASAP after receipt. So that means you can expect to receive your order shortly after January 1. So, go to http://tapr.org/kits_tns-buf now to place your order before the deadline! John ___ 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] Raw phase data of super-5065
Hi It is pretty well known that without “help” ( beyond the filter stuff on the super) the 5065 has fairly poor temperature stability and somewhat variable response to pressure and humidity. Taking two samples right off the production line likely would have given you different long term data as a result. If you are going to the trouble of watching these devices for a long time, monitor temperature, pressure and humidity. I suspect you will find correlations …. Bob > On Jun 5, 2018, at 5:44 AM, tim...@timeok.it wrote: > > > Hi Attila, > I am doing the long therm stability test on a couple of HP5065, one > original A type, the second B or "super" compared with my best long therm > stability, a GPSDO HPz3816A. > This test will be 30 days long. It is a second test, with a second couple > of HP5065A/B, to verify the long therm stability of both the version. > > Up to now the data available for version B or "super" only concerned the > improvement of phase noise. > > From the first results it seems that the HP5065A is more stable within > 30days than the modified version with the filter. > It must be considered that the short-term stability of 5065 is better than > the GPSDO / TICC up to 10-80k sec then, in this test configuration the valid > data will be beyond these values. > The results will be ready within 28 days and I will be happy to share them > in order to have everyone's opinion. > Regards, > Luciano > > > Da "time-nuts" time-nuts-boun...@febo.com > A "Discussion of precise time and frequency measurement" time-nuts@febo.com > Cc > Data Mon, 4 Jun 2018 10:11:50 +0200 > Oggetto [time-nuts] Raw phase data of super-5065 > Hoi zäme! > > Would one (preferably multiple) of the owners of a super-5065 be so kind > and share the raw phase data of an super-5065 against a stable reference > with me? The longer the data trace, the better. > > Thanks in advance! > > Attila Kinali > > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neil Stephenson > ___ > 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] Raw phase data of super-5065
Hi Attila, I am doing the long therm stability test on a couple of HP5065, one original A type, the second B or "super" compared with my best long therm stability, a GPSDO HPz3816A. This test will be 30 days long. It is a second test, with a second couple of HP5065A/B, to verify the long therm stability of both the version. Up to now the data available for version B or "super" only concerned the improvement of phase noise. From the first results it seems that the HP5065A is more stable within 30days than the modified version with the filter. It must be considered that the short-term stability of 5065 is better than the GPSDO / TICC up to 10-80k sec then, in this test configuration the valid data will be beyond these values. The results will be ready within 28 days and I will be happy to share them in order to have everyone's opinion. Regards, Luciano Da "time-nuts" time-nuts-boun...@febo.com A "Discussion of precise time and frequency measurement" time-nuts@febo.com Cc Data Mon, 4 Jun 2018 10:11:50 +0200 Oggetto [time-nuts] Raw phase data of super-5065 Hoi zäme! Would one (preferably multiple) of the owners of a super-5065 be so kind and share the raw phase data of an super-5065 against a stable reference with me? The longer the data trace, the better. Thanks in advance! Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
On Mon, 4 Jun 2018 21:31:56 +0800 mimitech mimitech wrote: > I'm planning to build a CPT (coherent-population-trapping) rubidium clock > as my next hobby project. The main purpose is to learn the principles > behind CPT rubidium clock, and hopefully got similar or better performance > than commercial miniature rubidium clock such as FE-5680A. Building a CPT clock is slightly more involved than you might think at first. The laser diode is only one part of it. You will most likely be able to improve on the short-term stability of the FE-5680 (which is rather poor). But I doubt you will be able to improve much on the long term stability, which is where things actually become interesting, if you use a naive approach. Nevertheless, I have not seen many 794/795nm diodes around. The only one that I have the datasheet of is the one from Vixar. You might want want to consider going for the D2 line instead of the D1 line, as 780nm diodes are more commonly available than 795nm. You will also need to buy several of those and select the ones that come closest to the wavelength at the desired opearating conditions (usuall spread is +/-1nm to +/-10nm). Do not assume you can tune more than 0.1nm with temperature and current (rule of thumb is that you get about 10GHz per °C and mA). If you need more tuning range, you will need to add an external cavity (can give you up to 5nm range), which then needs to be tuned to the 3.45GHz (ie it's length needs to be approximately 8-9cm). Alternatively, you can get two S1-0780-XXX from Sacher Laser (cost IIRC 2500€ each) and keep them 6.9GHz apart (using an optical PLL). If you have enough money to spend, I'd go for two Cateye diode laser CEL's from Moglabs (cost AFAIK 5000€ each) No matter what you choose, you will need some wavelength stabilization scheme. You can either do that with the vapor cell itself or use an additional cell and do a DVALL or a saturated absorption locking. Note that this addtional cell will need to be without buffer gas. An external cell will offer better stability and thus lower noise, which directly translates into higher stability. As polarisation scheme, I suggest using σ+/σ- as it seems to be more robust than the lin/lin schemes. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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.
