[time-nuts] Handy iPhone app

iple providers during travel), say by using a background process to take a sample every few hours against NTP sources or against GPS if the phone has it (or both). Then any photos can be batch-corrected later if desired. Apple, give me control over the time on m

Re: [time-nuts] Handy iPhone app

g time, then put it back to the automatic setting, causing it to reacquire the time. Now my phone is within 3 seconds of NTP. Could there be some huge hysteresis/dead zone within which the iPhone doesn't bother to trim its clock to the cell tower? Sigh. Cheers,

Re: [time-nuts] NPR Story I heard this morning

Chris Albertson writes: > > But you are right, no two clocks will ever agree at that level because they > will experience different gravitational fields. At this level the reason > to have a clock is no longer to tell time. It is to measure the > gravitational field. I have a question about

Re: [time-nuts] NPR Story I heard this morning

Hi Tom, > Based on mass and radius, a clock here on Earth ticks about 6.969e-10 > slower than it would at infinity. The correction drops roughly as 1/R below > sea level and 1/R² above sea level. For practical and historical reasons we > define the SI second at sea level. > Yes, the change in c

Re: [time-nuts] GPS Signal Simulator for GnuRadio

And for the receiver: https://github.com/pmonta/GNSS-DSP-tools 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.

Re: [time-nuts] The Pendulum Paradigm by Martin Beech, 2014

> > Further, would you be able to see the phase of the moon and the tides? > This > is using the pendulum as a gravimeter. Would it be sensitive enough for > that? > Yes. There's a book called "My Own Right Time", by a skilled amateur clockmaker (Philip Woodward), that shows some periodograms

Re: [time-nuts] GPS down converter question

> > What should the IF pass band bandwidth be? > For GPS C/A with wide correlator, about 2 MHz; if you want Galileo BOC and (eventually) GPS L1C, or legacy C/A with narrow correlator, about 8 MHz; for GPS P code about 20 MHz. Books on GNSS software receivers will detail the many tradeoffs availab

Re: [time-nuts] GPS down converter question

Hi Attila, > > Galileo E1 and GPS L1C are not BOC(1,1). They both use a variant > of the MBOC(6,1), CBOC(6,1,3/11) for E1 and TMBOC(6,1,4/33) for L1C. > You can view those as a weighted combination of a BOC(1,1) signal with > a BOC(6,1). This gives an additional peak at 7MHz offset, compared to >

Re: [time-nuts] matlab, python, etc.

Let me put in a recommendation for python / scipy / numpy / matplotlib as a replacement for Matlab or octave. I used Matlab as a student and octave since, and they do their job well, but the python tools have the advantage of a better, more modular, less idiosyncratic language. The scipy project,

Re: [time-nuts] Photodiodes for high frequency OPLL

Hi Attila, > The goal is to make two lasers locked with about 7GHz of offset to > eachother. > > So far, i figured out that PIN photodiodes can go up to several 100MHz > transition frequency and avalanche photodiodes are available up to 2GHz. > If you need photodiode response only near 7 GHz, as

Re: [time-nuts] OT: Far-out space navigation from sideways satnav signals

Hi Magnus, > Would not an antenna with a deep zero focus on the earth center help to reduce earth-noise (ground temperature noise as well as man-made noise)? It might, although you'd need a large antenna to generate the angular resolution needed to reject Earth noise while listening to a GPS bird

Re: [time-nuts] OT: Far-out space navigation from sideways satnav signals

Hi Hal, > Why are X-Ray pulsars better than radio pulsars for navigation? > My impression is that it's easier to manage all-sky coverage at x-ray with a small spacecraft package (I think millisecond pulsars generally emit at both microwave and x-ray). Also there's some interstellar scintillat

[time-nuts] time transfer over USB

I wonder if the following scheme would work to improve measurement precision over USB for use with GPS devices or similar. Instead of USB interrupt transfers, which occur on 1 ms boundaries with some unknown epoch, use bulk transfers. In the good case, there are no other USB transactions in fligh

Re: [time-nuts] time transfer over USB

> > IMHO the transfer mode of choice for this purpose should > be the Isochronous Transfer (in USB 2.0 and 3.0) because > it happens periodically and thus can achieve a guaranteed > maximum latency (for high speed this means 125us). > If 1 ms or 125 us is good enough, then this would be fine; but

Re: [time-nuts] time transfer over USB

> > Bulk transfer might work well on a system where nothing else is going > on, > > so "best effort" translates to "now". > > Does it mean "now" or "next polling cycle"? > It means "now", or pretty close. No waiting for start-of-USB-frame or -microframe. Herbert mentions that all USB transfers

Re: [time-nuts] Homemade GPS Receiver

> How hard is the beam steering relative to everything else? > It's a weighted sum of the antenna signals (as with any phased array), so the cost is the extra arithmetic to do this (on a per-satellite basis). The weights can be computed open-loop from the positions of the satellites, provided you'

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

Re: [time-nuts] Why 9,192,631,770 ??

> Everyone should take ten seconds and look at this animated GIF: > http://leapsecond.com/pages/ut/ut-ani-v2.gif Very nice. I guess a comparable plot with ephemeris time would be a lot noisier and sparser, something like the graphs in the Markowitz 1988 paper. I wonder if there's some sort of IE

Re: [time-nuts] helibowl GPS antennas

> So, I've looked at several dozen helibowls and talked to makers of said > items.. Thanks for posting this; maybe a homemade helibowl is a good way to get a low-cost GPS antenna with full frequency coverage down to L5. In my search for survey-grade antennas at hobbyist prices, I ran across this,

[time-nuts] GPS / GNSS front-end board

ol, the bandwidth is limited and it seems geared toward high-spectral-efficiency signals with many (>=8) bits per sample. Cheers, Peter Monta ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman

Re: [time-nuts] GPS / GNSS front-end board

Hi Michael, > What is the function of the clock/PPS inputs? They could be used to compare a master station clock with the GPS signals. It seems like a good idea to put the clock and PPS through the same path as the satellite signals. The goal was to permit a good comparison between GPS and any

Re: [time-nuts] GPS / GNSS front-end board

Hi Attila, > * Connect all free pins of the FPGA to a 2.54mm header pin connector >  This would make extensions to the system a lot simpler. >  Up to the point of using a simple uC board for a full fledged >  GPSDO system. Additonally put onto this connecter an unused output >  of the LMK03806 and

Re: [time-nuts] GPS / GNSS front-end board

On Wed, Jun 6, 2012 at 9:33 AM, Eric Garner wrote: > On Tue, Jun 5, 2012 at 12:53 PM, Attila Kinali wrote: >> On Tue, 05 Jun 2012 15:40:48 -0400 >> Michael Tharp wrote: >> >>> On 06/05/2012 03:31 PM, Attila Kinali wrote: >>> > * The XC6SLX9 is<10USD more expensive than the SLX6. I think the adde

Re: [time-nuts] GPS / GNSS front-end board

Oops, sorry, hit the send button too soon. Another nice book on GPS signal processing is the one by James Tsui, _Fundamentals of Global Positioning Receivers: A Software Approach_. I learned a lot from it. Cheers, Peter ___ time-nuts mailing list -- ti

Re: [time-nuts] GPS / GNSS front-end board

Hi Attila, > Could you also add just the option of a power splitter at the input? I'm not really sure what the most appropriate RF interface is. I was planning to make another much simpler board with just a bias tee, a 3:1 splitter, and some hairpin microstrip filters. Then it would be three sh

Re: [time-nuts] GPS / GNSS front-end board

> [ Borre GPS book ] > > However, it does not appear that they let me download the > matlab code that comes on the CD that comes with the book. do you know > if it's available somewhere? I think it's here: http://kom.aau.dk/~borre/easy2/ The last entry, the zip file, looks to be the most recent.

Re: [time-nuts] GPS / GNSS front-end board

> http://kom.aau.dk/~borre/easy2/ Oops, sorry, that was for the previous book. For the software-receiver book, you want this page: http://kom.aau.dk/project/softgps/ I'm not sure the source code is in the demo CD image, though (the "GPS SDR demo" link). Cheers, Peter _

Re: [time-nuts] New wrist Watch

Jim Lux writes: > It won't be state of the art (I think tvb's cesium wrist watch does that.. > but it doesn't have the non-digital display you want) One would think wristwatches based on the Symmetricom CSAC would be on the market by now. Surely the prices some are willing to pay for high-end me

Re: [time-nuts] WWVB PM Receiver

> Have you actually tried it and gotten it working, except possibly in a > very strong signal area? This is precisely the issue. Squaring the WWVB signal results in a significant SNR penalty. At high SNR it doesn't matter that much; at low SNR you are in a world of hurt. I had suggested to John

Re: [time-nuts] WWVB PM Receiver

> I'm not sure about residual carrier aiding the tracking process. A Costas > loop recovers the carrier pretty well, and a symbol aided loop (where the I > channel has a hard limiter, for instance) does even better. Yes, these work (and a soft tanh() limiter improves on the hard limiter a little

Re: [time-nuts] WWVB Response

Hi John, Thank you for clarifying the openness of the transmission format. Could I ask whether there is any scenario under which aspects of the signal transmission design might be patented? If companies or individuals wish to patent aspects of receiver design, that's fine, but I'd be uncomfortabl

[time-nuts] WWVB PSK demodulation; simple carrier regeneration?

Here are a few demodulated frames of WWVB's new BPSK bits: 0011101101000 01101 0(0)001100111(0)011011011(0)1010110 00 0 000 00 0 0011101101000 00100 0(1)001100111(1)011011011(1)1010111 00 0 000 00 0 0011101101000 01000 0(0)001100111(0)011011011(0)1011000 00 0 000 00 0 The fields are d

Re: [time-nuts] Visiting Greenwich

Hi Dave, The Harrisons are indeed at the observatory; also look for a regulator pendulum clock in the octagon room. I'm not quite sure whether it was running when I was there some years back. Could it hurt to petition the observatory's powers-that-be for a little hut or something at the ITRF mer

Re: [time-nuts] Raw GPS signal samples

I've got a raw wideband GPS capture, dual frequency L1/L2, on this page about my GPS/GNSS front-end board project: http://pmonta.com/blog/2012/06/04/gnss-firehose/ I plan to do a new spin of this board with some minor improvements as soon as I have the time. (For those who want to build the curr

Re: [time-nuts] WWV/WWVH audio simulator?

Hi Jayson, You may already be aware of it, but there's a set of historical recordings of WWV and WWVH, covering 1955 to 2005: http://www.myke.me/atthetone/ As for the simulation, I'm sure it would be easy to do the tones and clicks, but the voice announcements would need a considerable amount of

Re: [time-nuts] nuts about position

Jim Lux writes: > But another poster did comment on "why not use the telescope" you could > precision point to a series of stars and calculate using celestial nav > where you are. Although, that might be painful to the 1 meter sort of > accuracy - the "tables" probably don't really account for

Re: [time-nuts] nuts about position

Hi Tom, > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an sur

Re: [time-nuts] Ashtech Z12 question.

> > Does the Z12 have an internal memory backup battery? Yes, there are two lithium thionyl chloride cells, Tadiran TL-5104. They are 3.6 V primary cells, cylinders roughly AA in size, with spot-welded axial leads. That part is obsolete, but Digikey has an equivalent, TL-5903/P, which worked fi

Re: [time-nuts] Ashtech Z12 question.

> Well, my Z12 stopped tracking sats yesterday. It passes all self-tests. > I then replaced the memory backup batteries... it fixed the bootup error > problem, but still won't track sats. > Rats. Is the antenna known to be good? Is the Z12 providing bias on the antenna cable? Did the Z12 sto

Re: [time-nuts] nuts about position (cheap receiver)

> > > Results from the Z12 in L1/L2 mode were... iffy... then the receiver died. > The teqc tool from UNAVCO can help with diagnosing iffy data. Can you put your RINEX somewhere? With the antenna in an unobstructed area my Z12 routinely gives 1 cm-ish horizonal, few-cm 3D, using OPUS-S or OPUS-

Re: [time-nuts] Thunderbolt code phase measurement

> ... One value is "code phase" (along with PRN, sample length, sig level, > dopple, and time-of-measurement). This is a single precision floating > point number in units of 1/16 of a chip. Does anybody know how to massage > this value into either a carrier phase (in cycles) or a pseudorange (

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

Time transfer over USB can be improved by timestamping on both ends, then using a robust estimator for the clock offset. For example, imagine the USB is a small microprocessor peripheral. It has a local timer, freely incrementing, based on its local clock. When it gets a USB interrupt from the h

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs.PPSdecoding cards

Hi Tom, > [ USB time transfer ] > > It seems to me that if the read path and the write path are different it breaks down. > > ... But turning that into precise time requires some kind of calibration of the actual code path delays. In other words, it sounds to me like your method is valid for frequ

Re: [time-nuts] GPS first LO need to be locked?

> I am curious if the first local oscillator on a GPS receiver must actually > be locked or coherent to the reference oscillator in the GPS receiver > typically running at some 10 MHz approximately. Or as long as the first LO > is quite stable it doesn't matter because the receiver can track the co

Re: [time-nuts] GPS first LO need to be locked?

> > BTW a lot of GPS receivers don't have a "first LO".. they are more like a >> Tuned RF receiver - an input BPF for L1, L2, or L5, then direct sampling at >> around 30-40 MHz - something that makes the GPS signals alias down >> somewhere convenient (and always have positive frequency offset from

Re: [time-nuts] Better GPS coming to phones

> > > Also the new iphones now support Galileo in addition to GPS and Glonass. > Any word on whether iOS will support raw observables, as Android has for a little while now? I gather the APIs need to support continuous tracking better so that phase observables are meaningful across epochs. Will

Re: [time-nuts] Compensating phase differnces in dual frequency GPS receviers?

Hi Attila, > [ L1 / L2 timing differences ] > How do dual frequency receivers deal with that? I've also been toying with the idea of an inexpensive dual- or tri-band GPS SDR, especially since there are now quite a few satellites emitting L2C, the civil L2 signal. (Though I'd still like to try my

Re: [time-nuts] Compensating phase differnces in dual frequency GPS receviers?

Speaking of GPS's L2C signal, it turns out there's a timing difference between L2C and L2, namely 90 degrees of phase (nominally). Apparently there was some controversy over whether to include this correction in the RINEX files. The RINEX 3.0 document has details. Even with all this complexity, i

Re: [time-nuts] Compensating phase differnces in dual frequency GPS receviers?

Hi Attila, > So, that'd mean there would be an automatic calibration system inside > the device, because i dont have any equipment with which i could > calibrate delays over a temperature range. I suppose they could do that---provide a weak broadband source (say a comb) combined with the antenna

Re: [time-nuts] Compensating phase differnces in dual frequency GPS receviers?

> What if the crystal driving the DSP changes frequency with temperature? I believe it would have no effect. The local clock should drop out of any navigation or timing solution, so long as the changes are slow enough to avoid loss of lock in carrier tracking. Let's take a GPS module with 1 PPS

Re: [time-nuts] GPS SDR (was: FE-.5680A trimming resolution)

> I think, a specialized GPS SDR can be build for less than 500 USD > in low (a dozen at max) volumes. The USRP works for GPS L1 (though P/Y is a little undersampled at 8 Ms/s complex), but I didn't find a way to acquire both L1 and L2 simultaneously at useful sample rates (maybe current USRP hard

Re: [time-nuts] nanoseconds in the news

> Time is money... I wonder if long-distance neutrino links might be attractive to the financial community. The SNRs are currently way too low, but with aggressive engineering, a link through the Earth would shave off many, many milliseconds (even at not greater than the speed of light :-) ). The

Re: [time-nuts] Low-long-term-drift clock for board level integration?

> ... but then they get taken indoors and plugged into the network, and > probably never get a clear view of a GPS or GLONASS satellite again. A high-sensitivity GPS receiver might still give useful results here, especially if it has a high-quality reference oscillator like an OCXO. Even 20 or 3

[time-nuts] WWVB phase modulation format?

Interesting that WWVB is running a phase-modulation test---thanks for the links. Is the signal format known? A quick search shows nothing specific, just "we're testing". Could someone record a few minutes of the broadband signal so that those of us without ready-to-hand LF receivers can have a l

Re: [time-nuts] WWVB phase modulation format?

> I believe what they were doing is applying a simple 180 deg phase shift to > the carrier (BPSK) during certain one second timecode intervals. I suppose this will help coherent receivers somewhat, but I was expecting something DCF77-like. A pity. Thanks for posting your data. You certainly ha

Re: [time-nuts] WWVB phase modulation format?

> ... or I suppose we could ask. I did ask, using the contact email on the NIST page (John Lowe). I'll forward any replies to the list. Perhaps we could encourage a more ambitious DCF77-like scheme, if that's really not in the current plans for WWVB. Especially given the recent demise of Loran-

Re: [time-nuts] WWVB BPSK Receiver Project?

> Many A/D converter systems use a sample and hold before the A/D converter. > If you do the same before your sound card (your A/D converter) and drive the > S&H with an audio output from your sound > card, say at 6.1 kHz you would get a 1 kHz signal into your sound card to > process. You can cal

Re: [time-nuts] WWVB BPSK Receiver Project?

>        I'm not clear how accurately one can resolve the phase transition > in the new scheme, but I suspect probably unambiguously to 1 cycle of > the 60 KHz... and from there is merely a function of how accurately one > can resolve the phase of the 60 KHz.    This potentially can supply a > much

Re: [time-nuts] WWVB BPSK Receiver Project?

> In thinking about it a bit further, one might be able to take the 60 kHz > received sine at some point in the receiver, full wave rectify and HP > filter it (which doubles the frequency) then divide by two in a Flip-Flop > and heavily filter the resultant. This is a hybrid solution... analog and

Re: [time-nuts] WWVB BPSK Receiver Project?

> Part of the processing gain comes directly from the BPSK modulation and that > amounts to a little over 10 dB improvement, but there's a further 18 dB gain > to be had by accumulating an hours worth of data and processing that. That part of the paper bothered me. There's nothing preventing a re

[time-nuts] WWVB phase plots

Attached are some more renderings of John Seamons' WWVB data. This is what one might expect from a receiver that knows when the phase reversals happen and takes them out noiselessly---re-reversing the out-of-phase bursts to recover an approximation of the usual WWVB signal. The first plot shows t

Re: [time-nuts] WWVB - Response to Question posed to John Lowe

> So I gather from this they are working on something, but no details were > given. One possibility for a workaround to keep the classical receivers happy is to leave some residual carrier. Instead of a 180-degree phase shift, make it 90 or 120, so that the signal can be regarded as the sum of a

Re: [time-nuts] WWVB phase plots

> The transitions (where the phase change!) are what you correlate, > the more, the better S/N you get. Yes---it's too bad that the proposed WWVB changes don't increase the number of transitions at all. Could they not do the low-modulation-index DCF77-like signal on top of the BPSK? That is, put

Re: [time-nuts] WWVB phase plots

> Okay. A little 3586B hacking was required, but here are some wide-band > results: Thanks very much. This data shows the full-bandwidth WWVB signal very well. Attached are some plots and an octave script. The first plot shows the demodulated WWVB w

Re: [time-nuts] Timing Distribution in Mountainous Terrain

hey pass muster in other respects. The mountaintop could also be passive if that helps: pairs of antennas connected by a transmission line and appropriately pointed. Cheers, Peter Monta ___ time-nuts mailing list -- time-nuts@febo.com To unsubscri

Re: [time-nuts] Timing Distribution in Mountainous Terrain

her is a problem. Cheers, Peter Monta ___ 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] Timing Distribution in Mountainous Terrain

> Satellite laser ranging using LAGEOS and friends? On second thought, this wouldn't work anyway (besides being too expensive)---stations would have to be very close together to have common view. Cheers, Peter Monta ___ time-nuts mailing list

Re: [time-nuts] Anybody experienced in using a prescaler as a wideband preamp?

Paul Swed writes: > I agree this does not make sense. There is a divider in the way so its not a > preamp. I'll bite: what does a small-signal model of a prescaler look like? As a guess, it might be a (flat? highpass?) attenuator (with a great deal of loss) up to some threshold amplitude, then a