Re: [time-nuts] Acam TDC's
I looked into one of the high end units for a project. From what I recall, the resolution was high. The problem for me was the continuous throughput was not there. I was looking at making around 30 to 40 million measurements per second. As I recall, it it could burst at that, but not sustain it. At which resolution do you wish to get 40Msps? Tell me the single-shot jitter figure. So far we had only several ksps of throughput in our TDC circuit, but the bottleneck lies within a computer interface. Anyway, it is not an easy task to get some 200MB/s into the computer in a sustained fashion. (And to process such amounts of data in real time is hard, too.) Best regards, Marek ___ 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] fast edge, rise time.
The target is 4ns, while ideas seemed to be clear at some point, now I'm having doubts if better to use a MOSFET or a bipolar transistor as the switch element. Experiments with MOSFETs presented me some difficulties charging the gate capacitance having some trouble to achieve something in the 4ns region. Well 4ns seems hard whatever device anyway. I have seen recently two kinds of devices for similar task: MOSFETs and avalanche breakdown transistors. Try the second ones, might be a good fit if the pulsing is not very frequent (say, kHz range). Regards, Marek ___ 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] exponential+linear fit
Hello, Jim, On Fri, 4 Oct 2013, Jim Lux wrote: I'm trying to find a good way to do a combination exponential/linear fit (for baseline removal). It's modeling phase for a moving source plus a thermal transient, so the underlying physics is the linear term (the phase varies linearly with time, since the velocity is constant) plus the temperature effect. the general equation is y(t) = k1 + k2*t + k3*exp(k4*t) Working in matlab/octave, but that's just the tool, I'm looking for some numerical analysis insight. (...etc) The control estimation practice is to model such a disturbance as a response of LTI system to, in your particular case, (almost) deterministic excitation. Specifically, the exp() term is a response of 1st-order lowpass (1/(1+s*T). The k1+k2*t is a response of double cascaded integrator (1/s^2). If you need to fit the model to data, the inputs to the subsystems should be found (inverse filtration for simple systems, spectral factorization and inverse filtration for the more complicated ones). If you don't know the T, a greybox identification should be done in addition. What is interesting: the model and often also the fit methods are the same either for the deterministic signal (such as your y(t)), as well as for the stochastic signals, like colored noise. Following statements from optimal estimation theory, both white noise as well as Dirac (delta) function share some common properties w.r.t. to LTI system description, and it is enoiugh to describe (and fit, estimate, etc.) then with the same tools. (Of course, this is limited to the linear system domain, L2 criterions etc.) Similar matter of clock drifts have been briefly discussed in our recent paper, dealing with two-clock ensembling: Clock Composition by Wiener Filtering Illustrated on Two Atomic Clocks (M.Peca, V.Michalek, M.Vacek) http://rtime.felk.cvut.cz/~pecam1/eftf/ In case of interest, feel free to contact me directly. Best regards, Marek ___ 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] exponential+linear fit
Dear Jim, I'm removing a slowly varying bias term from fairly noisy data. Maybe several 10s of thousands of data points, And I want to do it quickly on a slow processor. I think the LTI framework should work very well for that; easy fixpoint implementation etc. Since I am a space fan, I'd be happy to try my tools. Would you like to send me the data? I've done that and it works.. but I'm looking for a more basic sort of approach, given that I actually know something about the underlying model. One example of such an estimator (working real-time), which I did in 2008: http://www.youtube.com/watch?v=Di4yG6ZRV3k Only the exp() term is missing here, the rest is same -- and besides the position and heading, it contains also 2nd order clock estimation -- similar way as in the GNSS. Best regards, Marek ___ 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] SITime oscillators
SITime just got some press for their temperature insensitive mems oscillators. I went to the web site and saw some interesting parts with pretty ambitious claims. Specifically better than Quartz. http://www.sitime.com/index.php http://www.sitime.com/products/datasheets/sit8208/SiT8208-datasheet.pdf They look too good to be true. However the phase noise plot stops at 1 KHz. There is another that stops at 100 Hz elsewhere on the site. Does anyone have real experience with the technology? Not yet. I hope we will be able to buy few of them soon, if the price will be reasonable. However, there was a good introductory presentation of SiTime founder Aaron Partridge two weeks ago at IFCS-EFTF conference, describing lots of their MEMS' internals. Basically, the fine frequency tuning and temperature independence is all done using frac-N PLL, implemented completely within ordinary non-MEMS CMOS chip. So, the MEMS osc output is not directly led out. The MEMS is there, as far as I got it, to maintain long-term stability. Regards, Marek ___ 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] 1. Clock ensembling; 2. Delay controller-synthesizer -- preprints of this year's UFFC IFCS-EFTF contributions
Dear time-nuts In case of interest, you may check our fresh conference preprints from IEEE--UFFC International Frequency Control Symposium -- European Frequency and Time Forum 2013, just finished: 1. Clock Composition by Wiener Filtering Illustrated on Two Atomic Clocks - about clock ensembling using estimator - advantages over PLLFLL (+ case study) - much simpler in LTI case over currently used Kalman filters 2. Programmable Delay Controller Allowing Frequency Synthesis and Arbitrary Binary Waveform Generation - controllable delay line within FPGA fabric - likely novel enhancement, possibly allowing to replace DDSes etc. - still unsure, if it may actually improve frequency control circuits and become widespread, or remain a curiosity only... You can read papers and view poster/presentation at: http://rtime.felk.cvut.cz/~pecam1/eftf/ Best regards, Marek P.s After proceedings will be published, I'll replace by IEEE marked versions, in accordance with Copyright agreement. ___ 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 measurement with a scope
Hello, given that digital scopes have a multichannel ADC for acquisition, which is similar to what a cross-correlating phase noise measurement instrument has, it occurred to me that phase noise measurement might also be possible with a standard digital scope and some post-processing software. The scope usually will have only 8 bits of resolution, but it will have a rather high sampling rate. With oversampling math, one may be able to trade one for the other, at least if the scope's analog frontend is not too bad. Has anyone investigated or tried this? Is it a silly idea to start with? yes, did it last week. I think it may have a sense with 1Gsps scope with good quality guts (should check with LC584AL at work). I have tried it with a very cheap one, Rigol 2-channel, originally 50MHz, reflashed to 100MHz. 2 signals, refmeasured, into Ch1, Ch2. Waveforms (2x500Msps) acquired, sinc() interpolated. Results: short-term single-shot jitter around 100ps RMS. Long-term was of no interest for my purpose now, so no observations here. Therefore, it is almost of no use at all for higher precision needs. Regards, Marek ___ 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 measurement with a scope
(..) I have tried it with a very cheap one, Rigol 2-channel, originally 50MHz, reflashed to 100MHz. 2 signals, refmeasured, into Ch1, Ch2. Waveforms (2x500Msps) acquired, sinc() interpolated. Results: short-term single-shot jitter around 100ps RMS. Long-term was of no interest for my purpose now, so no observations here. Therefore, it is almost of no use at all for higher precision needs. I was thinking about using a 4-channel scope with cross-spectrum averaging. Look at the Timepod by John Miles for an example of the method. I'm trying to guesstimate if the RS RTO scope, perhaps with the aid of the I/Q option, is capable of doing such measurements, and with what kind of performance. My point was, that DSO is basically an ADC. Therefore, there is some amount of noise, nonlinearity and drift, limiting the jitter measurement. Do you think any method can dig more information from given data than sinc() interpolation and zero-crossing computation? Regards, Marek ___ 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 measurement with a scope
My point was, that DSO is basically an ADC. Therefore, there is some amount of noise, nonlinearity and drift, limiting the jitter measurement. Do you think any method can dig more information from given data than sinc() interpolation and zero-crossing computation? The cross-spectrum averaging does indeed do just that, relying on two ADCs to produce uncorrelated noise, which can be averaged out. Or am I misunderstanding your point? Nothing against that. It depends on what noise level after averaging you require. I only posted my experience with a very low-quality DSO, which has 100psRMS single-shot. Using sinc() interpolation, but my point was, that I suppose there is no way to obtain better single-shot performance than this. To average out 100psRMS to, say, 1psRMS, it would require 10^4 edges (under the assumption, that the 100psRMS is well behaved noise). What performance it could yield with a better scope? I hope I'll try LC584AL some day, I guess it might give sth like 10psRMS single-shot... Regards, Marek ___ 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] Very challenging phase noise measurement, does anyone have an idea??
running mode and lock the other one to the first one using an XOR gate and then use the output of the XOR gate as an output signal. However, we are wondering if any of you know a better idea. Maybe there is an off-the-shelf piece Nearly any idea is better than the XOR gate you proposed. A simple double balanced diode mixer followed by an LT1028 preamp would easily meet your needs. What about simply mixing two signals in a resistor network, sampling by ADC, and mixing purely in DSP domain on a non-linearity (e.g. f(x)=x^2)? Regards, Marek ___ 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] Very challenging phase noise measurement, does anyone have an idea??
This last idea is interesting... could be simulated by Matlab or similar. It is known to work in ordinary non-linear transistor-based mixers. It will produce more messy spectrum than double-balanced mixer, however, for this purpose and completely within digital domain, it makes absolutely no harm, in my oppinion. On the other hand, simplicity of two resistors ADC may help. If in doubt, let the original poster try this and send us the data for analysis. (Mailing-list or personal e-mail(s).) Regards, Marek ___ 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] Confused about Rubidium oscillators
Hello, There are no ?wear-out? or ?use-up? mechanisms in a Datum Efratom Rubidium oscillator. (..) But also: Unlike a quartz crystal oscillator which has no clearly-defined wear out period and, if well-designed, can actually improve as time goes on, a Rubidium reference has a definite lifetime associated with its lamp: (..) so maybe both points of view are correct? (..) Yes, both of the points bear some meaning. The Rb does not age substantially by means of long-term frequency variation, unlike typical quartz. However, the Rb lamp is maintained hot (~100Celsius in LPRO-101) and contains aggresive light metal, therefore one day the glass will wear out and the lamp does not shine enough or shine at all. The Rb synthesis circuit will be able to detect such a situation and you are at least informed, that thigs went wrong. Of course, there are other minor circuit elements inside of the Rb clock, which may vary in long term -- eg. magnetic field bias regulator, output buffer. But these do not age systematically with predictable sign and magnitude. Regards, Marek___ 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] Multiple Time Interval Counters to measure Transients?
Hello, just few quick comments: Unfortunately, I don't have a more precise technical spec. I'm just trying to find a viable solution to characterize a chip manufacturing process with regard to Single-Event Transients. As this is supposed to only be a side task for my PhD, I would prefer to use something that already exists. On the other hand, until now I have no own budget, so if I have to ask for money to buy stuff, it would better be something that can be used for oher purposes as well. Agreed. Fortunately, TDCs are usually made to be flexible enough, unless they are tailored to a specific need of your application. What seemed to me at the beginning of your requests. What I had in mind here was the tradeoff between the flexibility of an FPGA and the performance of a dedicated ASIC. Of course, this very much depends on which optimizations were done and which technology is targeted. (..) In general, it's true. However, last year we have got results quite comparable to ACAM's ASIC within relatively slow FPGA. We need to perform more temperature-stability and aging tests to confirm the results. Depends on what you refer to by testing. I'll be definitely the wrong guy to ask for elaborated jitter measurements, especially in the single-digit picosecond range. But if testing means giving your stuff a shot to see if it fits my needs, I'm all in. The second option. I will let you know after assembling our eval boards. They are 2-channel only. Regards, Marek ___ 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] Multiple Time Interval Counters to measure Transients?
Hello, On Sat, 8 Sep 2012, Florian Teply wrote: (..) But then I'll have to throw a few hundred Time Interval Counters at the problem in order to get the information on the duration of the transients. So in general, amplitude information comes from the comparator trigger levels, time information from the TICs. What I expect from the DUTs is transients in the range between 1 and maybe 50 nanoseconds duration, but on some circuits they may be a lot quicker as the bipolars are wicked fast (about 3-5 ps gate delay in ECL inverters). What do you guys think, would a truckload of TICs do the job? Maybe not on the Bipolars, but at the plain CMOS this should do. It depends on how much precise you need the TICs (TDCs) to be. If it may be around +-100ps..1ns, the solution is simple enough and some hundreds of channels are feasible. If you need units of ps, the challenge is big, IMHO. Currently, we are testing our Time-to-Digit Converter within single FPGA, out last design exhibited 7ps RMS of accuracy. In case you were interested, I expect finishing of demo board during October. It would be more FPGA-resources consuming, though. Best regards, Marek ___ 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] Multiple Time Interval Counters to measure Transients?
Hello, Well, for the CMOS stuff 100ps should do just fine. Of course, less is better, but there's only so much one can reasonably do for so many channels... Even a PICTIC should be able to do better than 500 ps for a single channel. From what I've read, a few hundred units of HP5370 should solve the problem as well, but then there's only so much space... Indeed, with such a precision, several dozens of TDCs could easily fit into one FPGA chip. The task is to design clever data processing to handle all the events. We may be able to deliver such a custom product, but you have mentioned your need to save as much money as possible -- it should have be made more precise by means of technical specification to say more about time/price. I'd be very much interested. 7ps to me seems to be even more than I'd need for the CMOS stuff. Just out of curiosity: Does this work already from 0ps on or is the minimum count higher than that? And what's the limiting factor to accuracy you experience with your current design? Is it actually the FPGA and its properties or something else? Of course, the 7ps _RMS_ is the jitter of the TDC. The measurement is continuous w.r.t. reference clock, i.e. 0ps is of course possible. There is (almost) no other component than the FPGA. So, the limit is indeed the FPGA itself, you may include its power-supplies and comparators, as well. However, you have been probably asking, how far from the limits imposed bhy single FPGA cell's inherent jitter are we -- this is what I exactly can not answer with certainty, but according to our indirect measurements, best cells of the given FPGA exhibited estimated jitter about 1..3ps, whereas our last complete design has overall 7ps RMS, under the assumption of asynchronous measured signal. Under deterministic worst case, the precision will drop to 21ps abs max. (Note: this last number may be a too pesimistic value; stay tuned for newer revision after soldering recent pcbs). Feel free to ask more, if you were interested in testing our device. Best regards, Marek ___ 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] GLONASS receiver
Hello, Miguel, [sorry for replying to 2nd e-mail, accidentally deleted the original msg] Everything is fine but I am a bit worried about the GPS reliability because GPS is ruled by the USA. Me too, this is why I welcome upcoming expensive Galileo. Would a GPS disciplined oscillator solve any potential problems? A receiver for GLONASS, even though I did not find any at a reasonable price, would be better? What do you mean by reasonable price -- there are already Android smartphones supporting GPS GLONASS fusion. Attachment of external antenna would be a challenge, indeed. Also, they may probably have no 1pps signal inside (but who knows). On the other hand, you may run your NTP time provider on the Android phone itself. If you are worried about Java (Dalvik) VM jitter, let's run in under ARM based Linux native code. Regards, Marek ___ 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] EFTF 2012 -- anyone to meet there?
Dear Time-Nuts, is there anybody coming to 2012 EUROPEAN FREQUENCY AND TIME FORUM, http://www.eftf2012.org/ (next week, Sweden)? It would be nice to meet there live. Greetings, Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
My choice would be a center tapped, shielded, air core loop, running into a low noise instrumentation amp. Center tap of loop to twinax shield, grounded at preamp. The instrumentation amp has fixed gain, and very high CMRR and PSRR. It also does the differential to single ended conversion properly and has a low output impedance. I have used an instrumentation amp in my breadboard, however, without center tapping and shielding. But it seemed to me to be a very good component for such low frequencies. Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Hello, gary, I lost track of who wrote this, but why is it assume a ferrite rod has non-linear phase. [Group delay error I presume). Now I assume this presumes the rod is used in a LC circuit, but if the Q is not high, the phase linearity won't necessarily be bad. Basically I'd like to hear more from whomever wrote this. It was me, a time-nuts newbie. My previous related posts were: http://www.febo.com/pipermail/time-nuts/2012-March/065049.html http://www.febo.com/pipermail/time-nuts/2012-March/065003.html http://www.febo.com/pipermail/time-nuts/2012-March/065009.html etc. and http://www.febo.com/pipermail/time-nuts/2012-March/065135.html The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like standards with PRBS is about 1.5kHz. Of course the ferrite rod as an input filter *will* have a non-linear phase, but it still seems to me it is the simplest and most common receiptor for LF time signals. Let me clarify the unclear statement. I was reacting to Poul-Henning Kamp's (true) statement, that: The reason I use 1MSPS is that it allows me to use a very sloppy low-pass filter filter which just cuts off somewhere around 150-200 kHz, and do everything else in software. This means that I have no phase/group-delay distortion in the analog part that I need to compensate in software. In my design, I have used a ferrite rod LC circuit as and antenna and also the only element of selectivity in front of sampling. So, there was a 2nd order only filter. The useful signal of DCF77 (afaik yout WWVB is very similar now with BPSK) spans over ~1kHz. In my design, in contrast to P.-H. K.'s approach, I use only ~40ksps, so the 2nd order ferrite rod circuit should pass 1kHz, but it should attenuate somewhere around +-10..20kHz. I.e., the result will be always a compromise. Unfortunately, I don't have a measurement of my worked circuit's Q, but let us assume Q=20..100 can be realistic value for ferrite rods. Then, the filter's BW will be somewhere 0.8..4kHz, what means, that its phase over the interesting 1kHz band will _not_ be straight line, but somewhat curved. This is the only thing about ferrite rod and phase I meant. To conclude, I would like to repeat, that in my oppinion the ferrite rod is easy and common antenna for LF signals, so that in such a case the phase will be curved anyway. Of course you can feed the P.-H. K.'s 1Msps input by more wide-band antenna, not the ferrite rod, to get more linear phase without SW compensation. Greeting from Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Dear Poul-Henning, My only argument against your versatile and well-performing solution is that it is a little bit overkill. As if running a handfull precision oscillators just for fun isn't overkill also ? :-) I don't know -- are there any limits for the fun in a time-nut sense? :-) I hope not. The point is, with which kind of toy we would like to play. In other words, it would be certainly better to buy USRP N210, Actually that would be a very idea, because you cannot get rid of the down-sampler in the USRP and that would make Loran-C reception very tricky to implement. Are you sure there are such a limitations? I must reveal, that I have not even once played with USRP N210, but I hope it does not have any BW limitations up to the Gig-Eth speed. Anyway, it would be an expensive and heavy receiver for LF-only signals. My point is to do something with relevant performance wrt. 10kHz wide LF signals. The crucial question is if your are doing timenuttery or radionuttery. If you are doing timenuttery, you want you ADC synchronized to your OCXO/Rb/Cs or whatever you have, Yes, I would like to have an option of external frequency standard. However, I would like to lock ordinary onboard quartz too, since many people without Rb (though they are pretty cheap these days) may use it as a disciplined frequency source, too. I mean no time-nuts, but ordinary hobbyists, going to tune their filters etc. Or people, wanting some time signal in place of poor GNSS reception without good NTP access (I know such a set i almost empty :-)). and you don't want to have to deal with getting your IF frequency locked too. Soundcards use inconvenient frequencies and are seldom built to take an external clock signal. So this is why I would like to supply a little bit tweaked sound card, tailored to receive LF-HF band signals up to say 10..20kHz of width. The useful bandwidth of LF to HF radio is about 9kHz, You need more than 25kHz for good Loran-C OK, thank you for this notice. I have not yet thinked about Loran, so I must look in more detail on it. Best regards, Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
I've designed filters for datacom chips. I know filtering. My point is the original author is making some assumptions in the design which are not stated. Yes, my fault, I didn't write it properly, so by a ferrite rod in context of DCF/WWVB reception, I meand a ferrite antenna in an LC tuned circuit. Apologies for all who have been confused. What I don't have a lot of hands on experience is with open circuit magnetics. (I do with closed circuit magnetics.) But I claim if the ferrite rod antenna is not capacitively loaded to resonate at the comm frequency, then there isn't significant group delay error. Yes, see above. I meant an LC circuit, containing the ferrite rod antenna as the L. The antenna will have a natural resonant frequency comprised of the inductance and parasitic capacitance. But this represents an upper frequency limit. So simply operate below resonance and the group delay error is minimized. Filtering can be done following the preamp that connects to the antenna, and thus will not interact with it. Thank you for your understanding. Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Any filter's group delay can be equalized by all pass filters. Delay builds up at the filter corner. Since everything in the real world is causal, you add delay outside that corner frequency but in the passband to equalize it. This is to say, you can't remove delay, but just add it to flatten out the group delay. Yes, the compensation can be made and it has been also pointed out in the first comment by Poul-Henning. The only remaining question is, how stable are the analogue filter parameters over time, to be compensated by fixed digital filter. It seems to me, that some very small phase errors produced by such a filter-filter mismatch may be acceptable. At least for low-cost device which I would like to rebuild and offer for WWVB audience (which is not present in our land). Best regards, Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Which basically matched my assumption. If the inductor is loaded, you have a narrowband filter. So again, this does not imply that a ferrite rod antenna per se has phase distortion. It is the LC filter than effects the group delay. Yes, exactly. Excuse my loose speech before not explicitly mentioning LC tuned circuit. Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Yes, in order to equalize group delay, you need to know what to equalize. But with an educated guess as to the system response, he could get close. All this said, in 2012, I would rather the amplifier be simple gain, the inductor not loaded with capacitance and the filtering done past the amplifier. We aren't living in the era of 3 transistor circuits. When delta-sigma converters came on the scene. I wisely found new design skills. [They replaced much analog filtering.] So better just to do the filtering in DSP IF there is no critical power budget. This may not be true, if you have some strong interference at the ferrite rod input. Of course, if it would be strong and near the signal frequency, it will not be attenuated much even by the 2nd order LC circuit, indeed. However, for f0=77.5kHz and B=1kHz, the LC circuit with Q=40 gives phase error over specified bandwidth about +-0.5deg p-p. Does such a phase non-linearity bother you? Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
I think the tempco of the ferrite is more significant than drift in the analog filter. Perhaps I was unclear in this as well. I do not use nor plan to use any other filter than the (ferrite-L)-C resonant circuit itself. So, yes, the tempco of the ferrite makes its coefficients variation. The question is, whether phase errors 1deg p-p over 1kHz band are significant. Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
That would be 36ns group delay variation if I did the math correctly. OK And in article P. Hetzel: Time dissemination via the LF transmitter DCF77 using a pseudo-random phase-shift keying of the carrier, 2nd EFTF Neuchatel, 1988., they conclude with timing results of about 2..10e-6 s RMS over ~1000km distance. However, I do not know what is the reality and whether such a performance is limited by atmosphere/ground conditions, or whether it could be better within LF band. However, what material are you using for the ferrite? The material can have a significant tempco. In my project, I have used noname rod taken from within DCF77 alarm clock. If I will recreate it, I will look for something defined at the store. Regards, Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Dear Henry, I don't know where you are in CZ. I'm on the boarder in DE near PL and CZ. my former measurement (the one at YouTube, fairly good reception, winter) has been done under Erzgebirge, Teplice, CZ. Now I moved near Sumava (Boehmischer Wald), so tests may follow, if I will return to the topic. The distance to DCF77 is about 450km and if I check the amplitude across 24h I see considerable very deep fading effects! I think it is useless as a phase-coupled time receiver. At least in specific positions. It will loose phase at least for twice the day for approx. 2h ! That was the report for a ferrite rod. Thank you. The other way would be a high-impedance FET-preamp vertical-wire antenna. I think this will resist much more fading effects. But it is unchecked at the moment. You're welcome to do it. The benefit of a resonated ferrite rod is the good bandpass filtering for local interferers like TV. The FET vertical wire will need heavily filtering thereafter. All in the whole dynamice range, of course. This was almost the only reason for ferrite rod -- simplicity and attenuation of TVs, some LCDs, 50Hz etc. Ferrites can be temperature controlled. They have big spreads in parameters anyway! The production procedure is explained in the classical book about Ferrites: Snelling Soft Ferrites. Thank you for your pointer. Your idea of ferrite ovenization is cool. Best regards, Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Hello, thank you for your oppinion. On Thu, 15 Mar 2012, Poul-Henning Kamp wrote: In message Pine.LNX.4.64.1203152001370.3542@tesla, Marek Peca writes: Yes, it should work on any USB audio capable OS, ie. Linux, Windows, MacOS etc. I would like to recommend against this approach for a number of reasons. First, yes, while you can do undersampling and such, it puts very high requirements on your analog filters. The reason I use 1MSPS is that it allows me to use a very sloppy low-pass filter filter which just cuts off somewhere around 150-200 kHz, and do everything else in software. This means that I have no phase/group-delay distortion in the analog part that I need to compensate in software. It also means that I don't have to change hardware to play with different signals, they're all there, all the time, for instance the stuff under http://phk.freebsd.dk/Leap/ is pulled out that way. (..) You are right. I admit, that using comfortable oversampling, the converter is more versatile and analogue-side filters are absolutely non-critical ones. Nothing against that, moreover, I confess that I often use this approach, oversampling simple anti-aliasing, rather than converse. Now, I am still unsure whether to deploy the relatively cheap lower performance board with sampling in order of 40..80ksps. You are right, that 1Msps solves the task better or at least with the same performance. But, you pay few $ more (not so important), some few watts more and take more data before decimation (may be done in FPGA, of course). I know that USB2.0 handles 30MB/s on majority of HWOSes and you still need only about 2MB/s. My only argument against your versatile and well-performing solution is that it is a little bit overkill. In other words, it would be certainly better to buy USRP N210, then you may sample directly 0..250MHz @100Msps, and 1Gbps Ethernet is quite common these days, too. You have everything coded inside and its software support is also very good, including virtual soundcard connection etc. My point is to do something with relevant performance wrt. 10kHz wide LF signals. Well, I still think that 40..100ksps (1-2 inputs) module acting like a SAR sound-card may be usable as well as 1Msps for LF time-nuttery with a bare ferrite rod, and together with a mixer for DRM and Synchronous AM fans. The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like standards with PRBS is about 1.5kHz. Of course the ferrite rod as an input filter *will* have a non-linear phase, but it still seems to me it is the simplest and most common receiptor for LF time signals. Well, I will wait for more reactions, till now I have 2 positive and 1 yours, discouraging from 40ksps approach. Thank you and please note my respect to your approach and achievements. Best regards, Marek ___ 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] WWVB BPSK Receiver Project?
I know I am not one of the good-ole-boys here but I'd say go 100% SDR with your PC without an external A/D converter. Ok, how would you do this? You use under sampling. 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 SH 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 call it under sampling aliasing or whatever. Unfortunately, this works only with a few types of sound cards. Last several years, most of PC audio cards use sigma-delta ADCs and there is no way to get quality undersampling. Tried it. I can not tell there was no signal -- there were really some carriers mirrors, but on odd frequencies and largely attenuated. Greetings, Marek ___ 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] WWVB BPSK Receiver Project?
Dear american colleagues, as I read last few posts about WWVB, I am very tempted to return to LF time signal fun. As I wrote you, there vere very good results using cheap 2 IC circuitry and a PC with our local DCF77 signal. Under influence of this maillist, I am thinking about recreating of the receiver using recent MCU, ferrite rod on one side, optional 10MHz input, USB device acting as a standard USB audio class soundcard output. Everything working with GNUradio, MATLAB, HAM waterfalls etc. out of the box. Could be used as an audio frequency front-end for HAM radio, too. Would you be interested in such a kit? It should be $100 all inclusive, if there will be more people involved (let say 5-10) to cover PCBs. Best regards, Marek ___ 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] WWVB BPSK Receiver Project? (fwd)
Forgot to Cc: the maillist, sorry. So, FYI: -- Forwarded message -- Date: Thu, 15 Mar 2012 16:31:14 +0100 (CET) From: Marek Peca ma...@duch.cz To: David J Taylor david-tay...@blueyonder.co.uk Subject: Re: [time-nuts] WWVB BPSK Receiver Project? Hello, I would perhaps be interested in something which would pick up our local 60 KHz transmissions, and having a USB interface would be OK. However, all my systems are Windows, so whatever software was produced would have to work on Windows. Of course I mean it should pick your 60kHz, as well as other systems known to me: Japanese 40kHz, 60kHz, Swiss 75kHz, British 60kHz and possibly others. Highly unsure about Russian 25kHz, even do not know, whether it is still on air. Yes, it should work on any USB audio capable OS, ie. Linux, Windows, MacOS etc. I take it that you are thinking of all the detection and processing in the PC? I would prefer as much processing as possible to be in the device, and that it perhaps output serial data over the USB port, looking like a GPS. Is that too much to ask? Well, I will tell you, what I would like to do in larger picture: 1. first, deliver simple USB audio sampling unit with 77.5kHz-proven ferrite rod preamplifier, ready to work with 40..80kHz signals at least; every processing within PC / Gnuradio framework; BUT 2. be ready to upgrade a firmware of the board to do all the PRBS BPSK tracking etc. within the board's MCU and deliver at least 1pps output, preferably also sinewave LF-locked output (range 100kHz..1MHz) for further processing. So, I mean, the board will work in PC-based SDR mode in first iteration, and after all the processing will be proven by multiple users, we can then switch to better firmware, which will do basic tasks even without the PC. I think I can provide basic firmware by myself, for more elaborate things it seems to me the best solution is to start our common open-source project. However, the board's MCU will accept anyone's firmware, anyway. Please, tell me your oppinion. I would like to know, whether to put some time into development, so if there are really some people, who would appreciate such a LF-SDR-USB kit. Best regards, Marek ___ 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] WWVB BPSK Receiver Project?
Dear Time-Nuts, (new at this list, but reading for long time excellent timekeeping oscillator articles) I sure would like a WWVB BPSK receiver for the new modulation. (..) I'm sure in time there will be plenty of low cost ICs designed to receive the new signal, but my guess is that many Time Nuts would like to be in on the ground floor. Also NIST probably would like to get reports on the new signal when they do test transmissions. How to move forward? I have no experience with WWVB, since I live in central Europe, but some time ago I received quite well German DCF77 (77.5kHz) using absolutely simplistic circuit with no tuned parts except very tolerant ferrite rod antenna. The point was direct sampling into an ADC and doing all the business in a SDR fashion. I wanted to do PRBS PSK tracking and also PLL-less clock disciplining this way, but there were another priorities, though. However, if anybody would be interested in, I would be happy to return to these nice LF circuits. Greetings from Marek P.s A very little bit from DCF77, but only the pre-SDR stage: http://www.youtube.com/watch?v=Fx9bas49Uow ___ 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] WWVB BPSK Receiver Project?
I will share my few bits of worked experience. But it may seem obvious. I'd say to go 100% SDR. In other words a simple front and that pushes as much of the functionality into software as possible. The carrier is only 60K. That is low enough that one can directly digitize the RF using an ADC that samples at only 192K/sec. Not necesarilly. I received 77.5kHz very well in first sampling mirror, sampling using ADS7813 16bit ADC @44ksps, yielding carrier at 10.5kHz in discrete-time domain. 192K/Sec is a common sample rte for high-end audio and you can buy a 24-bit dual channel interface for under $200. Beware, there are lots of sigma-delta ADCs for this purpose and I am in doubt whether they could perform better than less-bits SAR ADC. So I'd use an antenna (the best would be a shielded loop with many turns of wire but ferrite loop stick could work) Follow that be an RF amp and very narrow filter and then the above 24-bit 192K ADC. I must object a little bit against RF and very narrow -- I have used very slw amplifiers (they were in a shack, original purpose DC measurement up to some 100s of kHz) and nothing narrow (or even tuned) -- except the ferrite rod itself. The rest were 2 ICs (amp ADC) and simple RC network. Worked very well, including few centimeters from laptop's CCFL inverter. Best regards, Marek ___ 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.
