Hi My point isn’t so much that it can’t be done. The point is that you are unlikely to find a “stock” setup that does what you are after. You probably can’t just download this project from that GitHub and you have it all going. As mentioned in other posts, PHK did this all with a home brew SDR setup “way back when”. It certainly can be done with enough effort put into the project. What would you likely want to do? That’s obviously going to have a number of answers depending on this or that. Bob > On Sep 25, 2023, at 5:30 AM, Jürgen Appel via time-nuts <time-nuts@lists.febo.com> wrote: > > Hej Bob, > > On Sunday, 24 September 2023 18:38:34 CEST Bob Camp via time-nuts wrote: > >> Hi >> >> The issue with doing this with a low cost SDR board is not so much receiving >> / demodulating the signal. It’s a pretty good bet somebody out there has >> been there / done that. The issue is pulling an accurate “time pulse” out >> of your typical SDR setup. This is a somewhat unusual thing to want to >> do. Finding a “stock” setup on a low cost board that does this will be a >> bit of a challenge. >> Bob > > Not that I have any experience in (E)Loran, but what about generating a time > signal yourself and adding it to the RF input (in the most basic realization > by simply pulsing off or AM modulating the RF input with an RF-switch, or > slightly more sophisticated by adding a micro-controller generated PRN-time- > code)? Then you you could recover the time-stamp from your recorded, de- > modulated data. > > Cheers, > Jürgen > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

John I don't see the code for the teensy?? It is quite a good description of the LORAN signal and the new bit encoding. I might see something like plumbing the teensy into a austron 2100. Simply sniffing the RF out of the unit. Plenty of filtering and gain. Regards Paul On Mon, Sep 25, 2023 at 10:27 AM john.haine--- via time-nuts < time-nuts@lists.febo.com> wrote: > > https://forum.pjrc.com/threads/45693-A-second-T31-Precision-Frequency-Standa > rd > > On the second page of the thread he posts his Teensy code. > > John. > -----Original Message----- > From: David Taylor via time-nuts <time-nuts@lists.febo.com> > Sent: Sunday, September 24, 2023 2:15 PM > To: time-nuts@lists.febo.com > Cc: David Taylor <david-taylor@blueyonder.co.uk> > Subject: [time-nuts] Re: Eloran long test from now to August or September. > > On 15/09/2023 14:43, john.haine--- via time-nuts wrote: > > This discussion reminds me, there is one eLoran station operating in > > the UK, co-located with the MSF transmitter at Anthorn, for research > > purposes. There is also some discussion about licensing some new > > operators mainly for timing purposes. Does anyone have any information > > on the coverage available from Anthorn please? John. > > Yes, I can confirm reception in Edinburgh using a Youloop antenna in an > attached garage. > > So, is there any sort of software decoder for the signal? I don't have a > specialised hardware receiver, just the usual SDR boxes including an Airspy > HF+ Discovery. > > Thanks, > David > -- > SatSignal Software - Quality software for you > Web: https://www.satsignal.eu > Email: david-taylor@blueyonder.co.uk > Twitter: @gm8arv > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an > email to time-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com >

My bad it is on the second page of some 38. Quite a good topic and detail and the code is there to attempt to decode eurofix data one of two possible data transmissions. Very nice work. Regards Paul On Mon, Sep 25, 2023 at 10:49 AM paul swed <paulswedb@gmail.com> wrote: > John I don't see the code for the teensy?? It is quite a good description > of the LORAN signal and the new bit encoding. > I might see something like plumbing the teensy into a austron 2100. Simply > sniffing the RF out of the unit. Plenty of filtering and gain. > Regards > Paul > > On Mon, Sep 25, 2023 at 10:27 AM john.haine--- via time-nuts < > time-nuts@lists.febo.com> wrote: > >> >> https://forum.pjrc.com/threads/45693-A-second-T31-Precision-Frequency-Standa >> rd >> >> On the second page of the thread he posts his Teensy code. >> >> John. >> -----Original Message----- >> From: David Taylor via time-nuts <time-nuts@lists.febo.com> >> Sent: Sunday, September 24, 2023 2:15 PM >> To: time-nuts@lists.febo.com >> Cc: David Taylor <david-taylor@blueyonder.co.uk> >> Subject: [time-nuts] Re: Eloran long test from now to August or September. >> >> On 15/09/2023 14:43, john.haine--- via time-nuts wrote: >> > This discussion reminds me, there is one eLoran station operating in >> > the UK, co-located with the MSF transmitter at Anthorn, for research >> > purposes. There is also some discussion about licensing some new >> > operators mainly for timing purposes. Does anyone have any information >> > on the coverage available from Anthorn please? John. >> >> Yes, I can confirm reception in Edinburgh using a Youloop antenna in an >> attached garage. >> >> So, is there any sort of software decoder for the signal? I don't have a >> specialised hardware receiver, just the usual SDR boxes including an >> Airspy >> HF+ Discovery. >> >> Thanks, >> David >> -- >> SatSignal Software - Quality software for you >> Web: https://www.satsignal.eu >> Email: david-taylor@blueyonder.co.uk >> Twitter: @gm8arv >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an >> email to time-nuts-leave@lists.febo.com >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-leave@lists.febo.com >> >

The challenge is that most inexpensive SDR modules do not provide the time stamping of the ADC. They’re more a RF to stream of samples device. Some of the devices could be programmed (in their FPGA logic) to do such a thing, but in the “out of the box” configuration, they don’t.  In your cited work you had to do this: “ the counter and control logic driving the 1-PPS generation have been added next to the existing dataflow handling logic as described at https://github.com/ oscimp/gnss-sdr-1pps.”  As you discovered, this whole getting the phase of the 1pps “on the mark” is tricky - There’s all kinds of assumptions built into the default gnuradio (or other platform) that occasionally drop or add samples, so even if you have good time stamps, you spend a fair amount of time making sure that the time stamp remains aligned with the appropriate sample (particularly if there’s any resembling in the processing chain). This is no reflection on your work, which is quite nice - it’s more that for a lot of SDR work, there wasn’t any thought to the need for precision timing - as long as you got RF in and the right bits out, the job is considered done.  This is especially so because the platform is inherently asynchronous (Ethernet and USB both have non-deterministic delays) and everyone uses some form of buffering to adapt to the uneven processing rates. And this is especially so at the bottom of the price range - the RTL-SDR, the Red Pitaya, the Pluto.  - the “out of the box” configuration of software/FPGA is inappropriate for timing. On Sun, 24 Sep 2023 19:59:12 +0000, "jeanmichel.friedt--- via time-nuts" <time-nuts@lists.febo.com> wrote: > I agree. Most inexpensive SDRs, and more particularly, the gnuradio or other software, tends not > to be designed for deterministic timing. It is true that you can run some tests and empirically > determine the delay through the software, but then, you have to worry about the non-deterministic > behavior of the host OS. If I may disagree, the only part that matters when generating a timing information from a SDR is the knowledge that not a single sample is lost in the periodic acquisition by the ADC, and the time information encoded in the received message. Since both information propagate through the asynchronous processing chain at the same rate, they end up being decoded simultaneously and can be compared with each other to adjust e.g. the clock of the ADC which also acts as the source of the 1-PPS generator. This is at least what we did in http://jmfriedt.free.fr/ifcs2021.pdf: our initial error in this investigation was indeed to try and steer the GP-CPU clock and use it to generate the timing information, when the only deterministic part of the processing is in the FPGA clocking the ADC. Best, Jean-Michel > > Typically, what you’d need is to simultaneously grab a counter running off the sample clock AND the > ADC samples (presumably decimated in the hardware), and then you can deal with the uncertainty, and > generate a count that can be compared against that same counter to generate an output pulse. Most > of the SDR hardware out there uses one of the multitude of chips that implements some form of pre > filtering and decimation and post filtering - but those are typically deterministic in delay. It’s > everything after the interface to the host processor that’s non deterministic. > > Now, if you’re implementing the SDR on a dedicated processor, with no OS, and careful use of > interrupts, you can do it. But that’s what commercial timing receivers do. > > On Sun, 24 Sep 2023 12:38:34 -0400, Bob Camp via time-nuts wrote: > > Hi > > The issue with doing this with a low cost SDR board is not so much receiving / demodulating the > signal. It’s a pretty good bet somebody out there has been there / done that. The issue is pulling > an accurate “time pulse” out of your typical SDR setup. This is a somewhat unusual thing to want > to do. Finding a “stock” setup on a low cost board that does this will be a bit of a challenge. > > Bob > >> On Sep 24, 2023, at 11:47 AM, paul swed via time-nuts wrote: >> >> David >> There have been various things posted in the past that have required A/Ds >> and such. Poul here on Time-nuts did a semi software version. (I think) But >> the fact is the old LORAN C receivers for frequency are a great way to go. >> The only difference between LORAN C and eLORAN is the 9th pulse used as a >> data channel. There was no 9th pulse in the old LORAN C. I have not seen >> anything that describes the coding. It may be out there but I haven't been >> interested in that. For many of us its an alternate very accurate Cesium >> referenced source. >> How it all develops if the governments supports it will be pretty >> interesting. Certainly the old positioning is possible. The data channel >> can provide propagation behaviors to allow for very accurate time and >> positioning. The new generation receivers will all be SDR based. >> I have actually seen an operational prototype numbers of years ago. >> Regards >> Paul >> WB8TSL >> >> On Sun, Sep 24, 2023 at 11:04 AM David Taylor via time-nuts < >> time-nuts@lists.febo.com> wrote: >> >>> On 15/09/2023 14:43, john.haine--- via time-nuts wrote: >> >> This discussion reminds me, there is one eLoran station operating in the >>> UK, >> >> co-located with the MSF transmitter at Anthorn, for research purposes. >>> There is >> >> also some discussion about licensing some new operators mainly for >>> timing >> >> purposes. Does anyone have any information on the coverage available >>> from >> >> Anthorn please? John. >>> Yes, I can confirm reception in Edinburgh using a Youloop antenna in an >>> attached garage. >>> >>> So, is there any sort of software decoder for the signal? I don't have a >>> specialised hardware receiver, just the usual SDR boxes including an >>> Airspy HF+ >>> Discovery. >>> >>> Thanks, >>> David >>> -- >>> SatSignal Software - Quality software for you >>> Web: https://www.satsignal.eu >>> Email: david-taylor@blueyonder.co.uk >>> Twitter: @gm8arv >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe send an email to time-nuts-leave@lists.febo.com >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-leave@lists.febo.com > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com  

This may out of scope for most users of the RTL-SDR but if you have a local GPSDO time / frequency source, you might consider a coupled injection of a local modulated signal that can be used to time stamp the output bit steam to the required precision, and then sample time derived from the marker detection, assuming the sample clock is stable enough until the next injected (out of band) local. The injected calibration signal could be as simple as a A1 carrier transition, on up to a time synced spread spectrum underneath the noise gloor. Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1) lester@veenstras.com 452 Stable Ln Keyser WV 26726 USA GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 Jamaica cell: +1-876-456-8898 -----Original Message----- From: Jim Lux via time-nuts [mailto:time-nuts@lists.febo.com] Sent: Monday, September 25, 2023 11:10 AM To: time-nuts@lists.febo.com Cc: Jim Lux Subject: [time-nuts] Re: Eloran long test from now to August or September. The challenge is that most inexpensive SDR modules do not provide the time stamping of the ADC. They’re more a RF to stream of samples device. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

I’ve experimented with just this idea - injecting a pilot tone, with modulation.  I was contemplating building an interferometer with surplus Ku-band dishes/LNBs, so there’s no easy way to phase lock the front end. I did it with 4 RTL-SDRs, and I’ll scrounge up the measurements.    My first attempt was just to couple the 1pps from a GPS module into the inputs - that’s not easily detectable (I was hoping that the fast edges would be sufficiently broadband to be detectable in the sampled data stream - nope..) Next was an in-band tone from a 10 MHz oscillator.  It’s easy to recover the narrow band tone, and if the level is appropriate, it’s easy to adaptively subtract it from the sampled data.   My next strategy was to put a BPSK modulated tone (at a low rate), and I never got that one to work right - whether because my lash up modulator wasn’t right, or because of software problems.  It should be easy to recover, to recover the chip and carrier phase, etc.  If one ran the PN generator at an exact divisor of the tone, that would probably help.  On Tue, 26 Sep 2023 10:18:43 -0400, "Lester Veenstra" <m0ycm@veenstras.com> wrote: This may out of scope for most users of the RTL-SDR but if you have a local GPSDO time / frequency source, you might consider a coupled injection of a local modulated signal that can be used to time stamp the output bit steam to the required precision, and then sample time derived from the marker detection, assuming the sample clock is stable enough until the next injected (out of band) local. The injected calibration signal could be as simple as a A1 carrier transition, on up to a time synced spread spectrum underneath the noise gloor. Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1) lester@veenstras.com 452 Stable Ln Keyser WV 26726 USA GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 Jamaica cell: +1-876-456-8898 -----Original Message----- From: Jim Lux via time-nuts [mailto:time-nuts@lists.febo.com] Sent: Monday, September 25, 2023 11:10 AM To: time-nuts@lists.febo.com Cc: Jim Lux Subject: [time-nuts] Re: Eloran long test from now to August or September. The challenge is that most inexpensive SDR modules do not provide the time stamping of the ADC. They’re more a RF to stream of samples device. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com  

> I did it with 4 RTL-SDRs, and I’ll scrounge up the measurements. My first attempt was just to > couple the 1pps from a GPS module into the inputs - that’s not easily detectable (I was hoping that > the fast edges would be sufficiently broadband to be detectable in the sampled data stream - > nope..) See attached: I capacitively inject the 1-PPS on the RTL2832 input (either I or Q), not the R820(T2) radiofrequency frontend. This allows for timestamping on the rising edge of GPS 1-PPS the datastream fetched by the ADCs of the RTL-SDR. Best, JM

Exactly.. That does work, although it requires opening up your RTL-SDR (and on V3, in HF receiver mode, the RF input is directly coupled to the Q input, without going through the front end downconverter.). It didn’t work well. And ultimately, I was trying to figure out something that would work at Ku band, so I could “calibrate out” the delay through the LNB, the coax, and the RTL-SDR.   The basic technique has been around since the 1960s.  Bracewell used it at Stanford, and a similar scheme was used for the Jansky VLA in New Mexico. On Tue, 26 Sep 2023 19:24:21 +0000, jeanmichel.friedt@femto-st.fr wrote: > I did it with 4 RTL-SDRs, and I’ll scrounge up the measurements. My first attempt was just to > couple the 1pps from a GPS module into the inputs - that’s not easily detectable (I was hoping that > the fast edges would be sufficiently broadband to be detectable in the sampled data stream - > nope..) See attached: I capacitively inject the 1-PPS on the RTL2832 input (either I or Q), not the R820(T2) radiofrequency frontend. This allows for timestamping on the rising edge of GPS 1-PPS the datastream fetched by the ADCs of the RTL-SDR. Best, JM

Agree very old and multi used idea. For the clever ones in DSP, penetrate a time coherent spread spectrum that can be inband but under the noise floor of the collection bandwidth. Correlate on receive in the same sample environment as you are doing science. Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1) lester@veenstras.com 452 Stable Ln Keyser WV 26726 USA GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 Jamaica cell: +1-876-456-8898 -----Original Message----- From: Jim Lux via time-nuts [mailto:time-nuts@lists.febo.com] Sent: Tuesday, September 26, 2023 3:33 PM To: jeanmichel.friedt@femto-st.fr; time-nuts@lists.febo.com Cc: Jim Lux Subject: [time-nuts] Re: Eloran long test from now to August or September. Exactly.. That does work, although it requires opening up your RTL-SDR (and on V3, in HF receiver mode, the RF input is directly coupled to the Q input, without going through the front end downconverter.). It didn’t work well. And ultimately, I was trying to figure out something that would work at Ku band, so I could “calibrate out” the delay through the LNB, the coax, and the RTL-SDR. The basic technique has been around since the 1960s. Bracewell used it at Stanford, and a similar scheme was used for the Jansky VLA in New Mexico. On Tue, 26 Sep 2023 19:24:21 +0000, jeanmichel.friedt@femto-st.fr wrote: > I did it with 4 RTL-SDRs, and I’ll scrounge up the measurements. My first attempt was just to > couple the 1pps from a GPS module into the inputs - that’s not easily detectable (I was hoping that > the fast edges would be sufficiently broadband to be detectable in the sampled data stream - > nope..) See attached: I capacitively inject the 1-PPS on the RTL2832 input (either I or Q), not the R820(T2) radiofrequency frontend. This allows for timestamping on the rising edge of GPS 1-PPS the datastream fetched by the ADCs of the RTL-SDR. Best, JM _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

This is indeed the approach I promoted in https://www.youtube.com/watch?v=rqa8VqSj7m8&t=9246s but on a dedicated channel since the timing accuracy improvement over the sampling period is determined by the signal to noise ratio during the peak fitting. Thank you for the insight indeed. -- JM Friedt, FEMTO-ST Time & Frequency, 26 rue de l'Epitaphe, 25000 Besancon, France September 27, 2023 5:16 PM, "Lester Veenstra" <m0ycm@veenstras.com> wrote: > Agree very old and multi used idea. > For the clever ones in DSP, penetrate a time coherent spread spectrum that can be inband but under > the noise floor of the collection bandwidth. Correlate on receive in the same sample environment as > you are doing science. > > Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1) > lester@veenstras.com > > 452 Stable Ln > Keyser WV 26726 USA > > GPS: 39.336826 N 78.982287 W (Google) > GPS: 39.33682 N 78.9823741 W (GPSDO) > > Telephones: > Home: +1-304-289-6057 > US cell +1-304-790-9192 > Jamaica cell: +1-876-456-8898 > > -----Original Message----- > From: Jim Lux via time-nuts [time-nuts@lists.febo.com] > Sent: Tuesday, September 26, 2023 3:33 PM > To: jeanmichel.friedt@femto-st.fr; time-nuts@lists.febo.com > Cc: Jim Lux > Subject: [time-nuts] Re: Eloran long test from now to August or September. > > Exactly.. That does work, although it requires opening up your RTL-SDR (and on V3, in HF receiver > mode, the RF input is directly coupled to the Q input, without going through the front end > downconverter.). It didn’t work well. > And ultimately, I was trying to figure out something that would work at Ku band, so I could > “calibrate out” the delay through the LNB, the coax, and the RTL-SDR. > The basic technique has been around since the 1960s. Bracewell used it at Stanford, and a similar > scheme was used for the Jansky VLA in New Mexico. > > On Tue, 26 Sep 2023 19:24:21 +0000, jeanmichel.friedt@femto-st.fr wrote: > >> I did it with 4 RTL-SDRs, and I’ll scrounge up the measurements. My first attempt was just to >> couple the 1pps from a GPS module into the inputs - that’s not easily detectable (I was hoping that >> the fast edges would be sufficiently broadband to be detectable in the sampled data stream - >> nope..) > > See attached: I capacitively inject the 1-PPS on the RTL2832 input (either I or Q), not > the R820(T2) radiofrequency frontend. This allows for timestamping on the rising edge > of GPS 1-PPS the datastream fetched by the ADCs of the RTL-SDR. > > Best, JM > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com