Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
For a lot of people the FFT seems to be the "one size fits all" solution to any frequency and phase related problem in DSP. It is NOT! For frequency/phase detection & comparisons from sets of sampled data the methods explained in http://ipnpr.jpl.nasa.gov/progress_report/42-121/121G.pdf are MUCH more appropiate. Best regards Ulrich Bangert > -Ursprungliche Nachricht- > Von: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] Im Auftrag von Hal Murray > Gesendet: Mittwoch, 3. Juni 2009 20:00 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] Sound Cards for locking to GPSDO 10 > MHz references > > > > > One of the main problems is that in working at milli-Hz > binwidths the > > FTT word length needs to be very long to cover even a few > tens of Hz > > range and we run into memory problems. > > I'm missing something. How much memory do you have on your laptop? > > I'm not a DSP wizard. If you have 10 Hz bandwidth and you > want milli-Hz > bins, that takes 2x10x1000 samples. Right? I'd expect that > to fit easily. > > That's 20K samples, at 8 bytes each, round up to 10, call it > 200K bytes. > > Jumping to micro-Hz might get interesting. That would be 200 > megabytes. > Lots of laptops have room for that. Maybe not an old one. > > Even with an old laptop without much memory, I'd expect you > could do several > factors of 2 better than milli-Hz bins. > > On the other hand, how much bandwidth do you really need? > Junk crystals are > 50-100 ppm. 100 ppm at 1 KHz is 1/10 Hz. So why do you need > more than 1 Hz > input bandwidth? You can probably get closer than that by > calibrating the > crystals in your particular gear. > > Connie's numbers were 250 micro-Hz drift with a 500 micro-Hz > offset. (That > was with reasonably stable temperature.) So a few milli-Hz > bandwidth looks > like enough. > > > > > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > > > > ___ > 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] Sound Cards for locking to GPSDO 10 MHz references
You know, I probably need to run the test again and do a better job of tracking room temp. My thermometer is high up on the wall in the shack. The computer sets under the bench in a corner. It does represent a typical afternoon in my shack however. 73, Connie K5CM -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Hal Murray Sent: Wednesday, June 03, 2009 12:24 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references connie.marsh...@suddenlink.net said: > www.k5cm.com/soundcard.htm Nice, thanks. >From there: > Sound card drift over this four hour period is about 250 micro Hertz. > The temp in the shack was going up during the measurement period. > Unfortunately I did not track the exact temp rise, but was about > around 4 to 6 degrees F. 250 micro Hz relative to 1000 Hz is 1/4 ppm. My memory is that junk PC crystals are ballpark of 1 ppm/degree. (That's probably per degree C rather than F, but that's only a factor of 2.) So 1/4 ppm for 4 degrees is better than I would have guessed. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] Sound Cards for locking to GPSDO 10 MHz references
> There is an overbeleif in what software is suitable for IMHO. [Fun discussion. Thanks.] Many years ago, somebody on the FPGA newsgroup pointed out that, in general, if you can do the problem in software that's probably the better way. One of the considerations is that it's easier to hire programmers rather than hardware designers. FPGAs are halfway between real hardware and software. You can try a simple change without any harsh time or cost penalty to make new masks and new chips. If that change is a bug fix, you might think of it as typical sloppy programmer behavior. On the other hand, that change may be a new idea you want to try... For many people in this group, fun is probably the most important consideration. Different things will appeal to different people. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] Sound Cards for locking to GPSDO 10 MHz references
> One of the main problems is that in working at milli-Hz binwidths the > FTT word length needs to be very long to cover even a few tens of Hz > range and we run into memory problems. I'm missing something. How much memory do you have on your laptop? I'm not a DSP wizard. If you have 10 Hz bandwidth and you want milli-Hz bins, that takes 2x10x1000 samples. Right? I'd expect that to fit easily. That's 20K samples, at 8 bytes each, round up to 10, call it 200K bytes. Jumping to micro-Hz might get interesting. That would be 200 megabytes. Lots of laptops have room for that. Maybe not an old one. Even with an old laptop without much memory, I'd expect you could do several factors of 2 better than milli-Hz bins. On the other hand, how much bandwidth do you really need? Junk crystals are 50-100 ppm. 100 ppm at 1 KHz is 1/10 Hz. So why do you need more than 1 Hz input bandwidth? You can probably get closer than that by calibrating the crystals in your particular gear. Connie's numbers were 250 micro-Hz drift with a 500 micro-Hz offset. (That was with reasonably stable temperature.) So a few milli-Hz bandwidth looks like enough. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] Sound Cards for locking to GPSDO 10 MHz references
connie.marsh...@suddenlink.net said: > www.k5cm.com/soundcard.htm Nice, thanks. >From there: > Sound card drift over this four hour period is about 250 micro Hertz. > The temp in the shack was going up during the measurement period. > Unfortunately I did not track the exact temp rise, but was about > around 4 to 6 degrees F. 250 micro Hz relative to 1000 Hz is 1/4 ppm. My memory is that junk PC crystals are ballpark of 1 ppm/degree. (That's probably per degree C rather than F, but that's only a factor of 2.) So 1/4 ppm for 4 degrees is better than I would have guessed. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Lux, James P skrev: -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur Sent: Tuesday, June 02, 2009 3:06 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references Hi all Thank you all for you advice and suggestions re my request. At this stage it does not look like there is a simple solution of a readily available USB sound card that can be locked to a 10 MHz GPSDO reference. The constraints of portable operation with a Laptop rule out a number of solutions. I have tried the software solution using Spectrum Lab but ran into problems and perhaps this just needs more work. One of the main problems is that in working at milli-Hz binwidths the FTT word length needs to be very long to cover even a few tens of Hz range and we run into memory problems. So there is little room to have a reference frequency spaced well away from the frequency range being used. The reference frequency can be right on top of your signal, as long as it's within the dynamic range. You can subtract it out before doing the FFT, after having determined where it is and how big it is. Considering the length of these traces, the local oscillator vs. the reference will shift around. What I would do is to ensure that the reference signal and input signal is either on very different frequencies or different channels. Then, I would in the sampling phase frequency convert the receive signal and reference signal using digital fixed NCO/quadrature oscillators (cos, sin) and do integrate and dump (synchronous dump for both receive and reference signals) processing for low pass filtering and reducing sample rate. Since the signal was fairly narrow banded, this digital receiver approach would significantly reduce the amounts of data while requiring a very reasonable amount of real-time processing. The remaining sample stream still contains the crutial information if sufficient bandwidth is maintained after the integrate and dump processing. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
Alberto di Bene skrev: Magnus Danielson wrote: Hmm, do you get a feeling that I am actually object very much to just toss it into the processor. I think you are right. :) I suppose you are familiar with the old American adage that says that to a man with a hammer every problem looks like a nail :-) Yes. :o) Each of us is more familiar with one or another technology (broadly speaking), and tend to see it as the best way to solve problems. I am not immune from this... This is why I try to find more tools and more approaches. Nothing wrong with software, but use it wisely. Build the test-benches as if you where doing a ASIC or full-custom design and thus also think about each compile costing you milions of dollars and a pipe-line depth of many months (6-9). Given the rate of compiles that sometimes I do especially when near to find the solution of a problem that bugged me for a long time, I would be bankrupted since long, should each compile cycle cost me thousands or millions of dollars, even if bogus dollars... :-) :-) I think you would learn important lessons in test-benching and overall design before the "compile". I guess I am becomming more conservative by the day. From my own and others mistakes and succsesses. This is a privilege of becoming older and wiser :-) Whiee... I got so much to learn then! :) Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
Hi Rex, Here is a plot of my sound card. Maybe I'm just lucky with this particular sound card/computer, but the drift was only about 250 micro Hertz over a four hour period. Also for critical measurements I try to run at 200 Hz center frequency rather than 1000 Hz. Cuts the error by five. Maybe that's not practical for you modulation schema. I did not bother to calibrate the sound card before I started the test so there is about 550 micro Hertz of static error when the test starts. www.k5cm.com/soundcard.htm 73, Connie K5CM ___ 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] Sound Cards for locking to GPSDO 10 MHz references
> -Original Message- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur > Sent: Tuesday, June 02, 2009 3:06 PM > To: 'Discussion of precise time and frequency measurement' > Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 > MHz references > > Hi all > > Thank you all for you advice and suggestions re my request. > At this stage it does not look like there is a simple > solution of a readily available USB sound card that can be > locked to a 10 MHz GPSDO reference. > > The constraints of portable operation with a Laptop rule out > a number of solutions. I have tried the software solution > using Spectrum Lab but ran into problems and perhaps this > just needs more work. One of the main problems is that in > working at milli-Hz binwidths the FTT word length needs to be > very long to cover even a few tens of Hz range and we run > into memory problems. So there is little room to have a > reference frequency spaced well away from the frequency range > being used. The reference frequency can be right on top of your signal, as long as it's within the dynamic range. You can subtract it out before doing the FFT, after having determined where it is and how big it is. > Some people asked for more details of the cloud scatter > experiments which area at http://reast.asn.au/optical.php > There is also a series of articles on our work in the last 3 > and next issue of DUBUS. > > ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Hi all Thank you all for you advice and suggestions re my request. At this stage it does not look like there is a simple solution of a readily available USB sound card that can be locked to a 10 MHz GPSDO reference. The constraints of portable operation with a Laptop rule out a number of solutions. I have tried the software solution using Spectrum Lab but ran into problems and perhaps this just needs more work. One of the main problems is that in working at milli-Hz binwidths the FTT word length needs to be very long to cover even a few tens of Hz range and we run into memory problems. So there is little room to have a reference frequency spaced well away from the frequency range being used. The SP DIF solution seems promising if I can generate the required input. This could perhaps be done with a product that already provides the SP DIF word output and locking that. But that could be just as hard as locking the sound-card in the first place. So at this time I think I will put some more effort into locking the sound card and let you know how I go, hi. Injection locking as suggested by some of you may be the answer. Some people asked for more details of the cloud scatter experiments which area at http://reast.asn.au/optical.php There is also a series of articles on our work in the last 3 and next issue of DUBUS. On the question of Doppler shift from clouds - this is much less than a mHz and not an issue due to the fact that we are using base band and the Doppler only applies to the audio frequency. In addition the very narrow beamwidths (around 2 degrees) mean that the possible paths are all very similar in length. Thanks again to everyone for their input. 73 Rex VK7MO ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Magnus Danielson wrote: Hmm, do you get a feeling that I am actually object very much to just toss it into the processor. I think you are right. :) I suppose you are familiar with the old American adage that says that to a man with a hammer every problem looks like a nail :-) Each of us is more familiar with one or another technology (broadly speaking), and tend to see it as the best way to solve problems. I am not immune from this... Nothing wrong with software, but use it wisely. Build the test-benches as if you where doing a ASIC or full-custom design and thus also think about each compile costing you milions of dollars and a pipe-line depth of many months (6-9). Given the rate of compiles that sometimes I do especially when near to find the solution of a problem that bugged me for a long time, I would be bankrupted since long, should each compile cycle cost me thousands or millions of dollars, even if bogus dollars... :-) :-) I guess I am becomming more conservative by the day. From my own and others mistakes and succsesses. This is a privilege of becoming older and wiser :-) Cheers, Alberto I2PHD ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Alberto di Bene skrev: Magnus Danielson wrote: No need to switch on the soldering iron... Never do in hardware what can be done in software :-) Respectfully I disagree. There are tasks which is better managed by software and tasks which is better managed by hardware. In the world of FPGAs, it is also worth mentioning that some tasks is best done there. The big trick is to find a balance between various methods, available resources, partitioning of the problem, doing it on time and achieving the needed performance. Of course you are right, the best solution must be decided case by case. But the biggest plus of the software is that it can be changed on the fly, without an expensive reworking station, and the manual ability to correctly use it. And a side effect is speed : you can test many variants of a solution in a time frame of a few minutes. Not so easily doable with hardware changes. This is why we do alot of things in FPGAs today, and in the FPGAs we often put dedicated DSPs of various complexity, often adapted to their task. Keeping quick turn-around is on our mind, but in general, the shorter turn-around, the poorer testing usually happends, and the sloopier design is often found, and the longer it takes to get the job done. In general, a CPU is suitable for doing non-common tasks. More dedicated designs like firmware and hardware is suitable to do things which is essentially the same but happends over and over and over and often at a high speed. Such monotonic tasks just waste energy, space and complexity when done in CPUs. The problem with a generic CPU is that it is generic, so it can do all kinds of tasks, which makes timing-critical bulk-processing tasks problematic to combine with sporadic and possibly high-dynamic processing. Splice the bulk off to some dedicated processing, which can be done in another CPU, and better performance is yielded. There are loads of designs where a few well thought 8-bit processors work together and shine over a more modern fancy design. One such example is found in the SR-620 which has a Zilog Z-8000 processor as main CPU and a Z-80 co-processor which only does the X-Y vector display. The Z-80 has so small program that it is loaded into SRAM from the Z-8000 as it boots. The HP 5334A has actually 3 different 3870 processor, one for overall control, one for measurements and one for GPIB. Hmm, do you get a feeling that I am actually object very much to just toss it into the processor. I think you are right. :) Nothing wrong with software, but use it wisely. Build the test-benches as if you where doing a ASIC or full-custom design and thus also think about each compile costing you milions of dollars and a pipe-line depth of many months (6-9). I guess I am becomming more conservative by the day. From my own and others mistakes and succsesses. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
Magnus Danielson wrote: No need to switch on the soldering iron... Never do in hardware what can be done in software :-) Respectfully I disagree. There are tasks which is better managed by software and tasks which is better managed by hardware. In the world of FPGAs, it is also worth mentioning that some tasks is best done there. The big trick is to find a balance between various methods, available resources, partitioning of the problem, doing it on time and achieving the needed performance. Of course you are right, the best solution must be decided case by case. But the biggest plus of the software is that it can be changed on the fly, without an expensive reworking station, and the manual ability to correctly use it. And a side effect is speed : you can test many variants of a solution in a time frame of a few minutes. Not so easily doable with hardware changes. 73 Alberto i2PHD ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Alberto di Bene skrev: J.D. Bakker wrote: You could always transform this from a hardware problem to a software problem. Take the output of your GPSDO, divide it down to somewhere inside the audio band, feed it to a spare input on your USB sound card and have software track this reference and correct the received signal. JDB. I am in complete agreement with this kind of solution. Sampling on the second channel a reference signal of known value allows the software to make a simple adjustment. Such a double-frequency conversion cancels fairly well the transfer oscillators frequency and jitter, as long as it is sufficienly low. No need to switch on the soldering iron... Never do in hardware what can be done in software :-) Respectfully I disagree. There are tasks which is better managed by software and tasks which is better managed by hardware. In the world of FPGAs, it is also worth mentioning that some tasks is best done there. The big trick is to find a balance between various methods, available resources, partitioning of the problem, doing it on time and achieving the needed performance. There is an overbeleif in what software is suitable for IMHO. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
Lux, James P skrev: -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson Sent: Tuesday, June 02, 2009 10:08 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references Some of the "pro" sound interfaces have a "word clock" input. There are a variety of things that take a external input and generate a S/PDIF that's properly timed, as well. Lots of boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 which was used by lots of Flex-Radio folk), so maybe that's something you could easily generate from your 10MHz. A chart at Cakewalk shows that MOTU has a USB interface (828MkII) which has a word clock sync. It's going to be a pricey beast though, with 8in/8out ($800?) Even if you have a word clock input, you're going to have to synthesize that from the 10 MHz. Maybe it's easier to just make a S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is something like 3 MHz) S/P-DIF [iec60958-3] has a baudrate which is 128 x sample rate and a bit rate which is 64 x sample rate, which is inherited properties from AES/EBU [aes3] [tech3250] [iec60958-4]. Locking up a S/P-DIF (128 x sample rate) is about the same job as locking up a superclock (256 x sample rate) or wordclock (1 x sample rate). However, if you're buying an off the shelf audio interface, you're stuck with whatever the mfr is providing for a sync input, and a (very) casual inspection of what's available these days (particularly at low cost) shows that S/PDIF seems to be the most common. Do they really lock up to the S/P-DIF input? I doubt it for the cheap boards. Rather, they decode the S/P-DIF signal and ship the samples into the DSP. The DSP tends to make very rought sample-rate conversions like dropping samples etc. A lockable board isn't that expensive. You can get them off ebay for instance. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
Hello The Net: For portable operations with a laptop, usually only one input channel is available and it is at mike (not line) level. The alternative to sum the analog reference and the analog signal of interest may be possible if the reference noise can be kept out of the signal of interest bandwidth. Maybe a external USB soundcard with at least 2 input channels is more appropriate. Stan, W1LEFN41sr Cape Cod Alberto di Bene wrote: J.D. Bakker wrote: You could always transform this from a hardware problem to a software problem. Take the output of your GPSDO, divide it down to somewhere inside the audio band, feed it to a spare input on your USB sound card and have software track this reference and correct the received signal. JDB. I am in complete agreement with this kind of solution. Sampling on the second channel a reference signal of known value allows the software to make a simple adjustment. No need to switch on the soldering iron... Never do in hardware what can be done in software :-) 73 Alberto I2PHD ___ 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] Sound Cards for locking to GPSDO 10 MHz references
J.D. Bakker wrote: You could always transform this from a hardware problem to a software problem. Take the output of your GPSDO, divide it down to somewhere inside the audio band, feed it to a spare input on your USB sound card and have software track this reference and correct the received signal. JDB. I am in complete agreement with this kind of solution. Sampling on the second channel a reference signal of known value allows the software to make a simple adjustment. No need to switch on the soldering iron... Never do in hardware what can be done in software :-) 73 Alberto I2PHD ___ 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] Sound Cards for locking to GPSDO 10 MHz references
> -Original Message- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson > Sent: Tuesday, June 02, 2009 10:08 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 > MHz references > > > > > > > Some of the "pro" sound interfaces have a "word clock" input. > > > > There are a variety of things that take a external input > and generate a S/PDIF that's properly timed, as well. Lots of > boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 > which was used by lots of Flex-Radio folk), so maybe that's > something you could easily generate from your 10MHz. > > > > A chart at Cakewalk shows that MOTU has a USB interface (828MkII) > > which has a word clock sync. It's going to be a pricey > beast though, > > with 8in/8out ($800?) > > > > Even if you have a word clock input, you're going to have to > > synthesize that from the 10 MHz. Maybe it's easier to just make a > > S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is > > something like 3 MHz) > > S/P-DIF [iec60958-3] has a baudrate which is 128 x sample > rate and a bit rate which is 64 x sample rate, which is > inherited properties from AES/EBU [aes3] [tech3250] [iec60958-4]. > > Locking up a S/P-DIF (128 x sample rate) is about the same > job as locking up a superclock (256 x sample rate) or > wordclock (1 x sample rate). However, if you're buying an off the shelf audio interface, you're stuck with whatever the mfr is providing for a sync input, and a (very) casual inspection of what's available these days (particularly at low cost) shows that S/PDIF seems to be the most common. ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Lux, James P skrev: -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur Sent: Monday, June 01, 2009 3:00 PM To: 'Discussion of precise time and frequency measurement' Subject: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references Hi all Does anyone have any experience of locking a USB external soundcard to a GPSDO 10 MHz reference. I am interested in advice on any good quality soundcards that can be readily locked to either 10 MHz or if necessary to some other frequency that we can derive from a GPSDO source. I have done some tests with the SignalLink soundcard that uses a Texas Instruments PCM2904 chip and requires a 12 MHz lock frequency. This requires some cutting of tracks to remove the internal oscillator feedback and insert the locking frequency. 12 MHz is readily derived from 10 MHz but I have not been able to get it to lock. The Texas instruments data sheet suggests that it is possible to use an external refernce but also says this is not recommended. With this expereicne I would rather find a sound card that is designed for external locking that does not require the cutting of tracks. For info the purpose of this request is that we are looking at using very narrow bandwidth modes at less than 1 mHz for light wave communcation. To date using LEDs and cloud reflection we have worked over 200 km with WSJT but we should be able to do 20 dB better if we can get down to milli-Hz bandwidths (at the expense of spending all night to complete a QSO). Our expereince to date is that standard sound cards are just not stable to better than 5 milli-Hz at 1000 Hz which should be readily solved by GPS locking let us get down to sub milli-Hz levels. Rex VK7MO Some of the "pro" sound interfaces have a "word clock" input. There are a variety of things that take a external input and generate a S/PDIF that's properly timed, as well. Lots of boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 which was used by lots of Flex-Radio folk), so maybe that's something you could easily generate from your 10MHz. A chart at Cakewalk shows that MOTU has a USB interface (828MkII) which has a word clock sync. It's going to be a pricey beast though, with 8in/8out ($800?) Even if you have a word clock input, you're going to have to synthesize that from the 10 MHz. Maybe it's easier to just make a S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is something like 3 MHz) S/P-DIF [iec60958-3] has a baudrate which is 128 x sample rate and a bit rate which is 64 x sample rate, which is inherited properties from AES/EBU [aes3] [tech3250] [iec60958-4]. Locking up a S/P-DIF (128 x sample rate) is about the same job as locking up a superclock (256 x sample rate) or wordclock (1 x sample rate). As long as the signal is samples with low jitter and A/D converted in a good fashion, delivery over S/P-DIF should not be too hard. An ADC is slammed onto a AES/EBU/S/P-DIF chip which is fairly trivial extra work. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
You could always transform this from a hardware problem to a software problem. Take the output of your GPSDO, divide it down to somewhere inside the audio band, feed it to a spare input on your USB sound card and have software track this reference and correct the received signal. JDB. -- LART. 250 MIPS under one Watt. Free hardware design files. http://www.lartmaker.nl/ ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Brian Kirby skrev: I use a Lynx One sound card, it has analog and digital I/O and MIDI I/O and clock I/O. Their manuals are available on line at www.lynxstudio.com. These are profession 24 bit cards, the analog I/O uses balanced interfaces. They handle AES/EBU and SP DIF digital audio formats. The sound card can take an internal clock, an external clock input on the MIDI port, there is a parallel clock header on the PC board, and a digital clock input on the digital audio lines. It can accept a 13.5 Mhz video dot clock, a 27 Mhz video dot clock, and a word clock and word clock/256. 13,5 MHz is ITU-R BT.601/BT.656 luminance sampling rate. 27 MHz is BT.601/BT.656 luminance/chroma-difference combined sampling rate (4:2:2). 27 MHz is the video reference rate of them all. Sad that they broke it when they did the North American HD stuff. Breaking numerology like that isn't very nice... it always cost extra now. I think you mean word-clock * 256 as this is Digidesign/ProTools clock distribution strategy, giving 12,288 MHz for 48 kHz sampling rate. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references
I use a Lynx One sound card, it has analog and digital I/O and MIDI I/O and clock I/O. Their manuals are available on line at www.lynxstudio.com. These are profession 24 bit cards, the analog I/O uses balanced interfaces. They handle AES/EBU and SP DIF digital audio formats. The sound card can take an internal clock, an external clock input on the MIDI port, there is a parallel clock header on the PC board, and a digital clock input on the digital audio lines. It can accept a 13.5 Mhz video dot clock, a 27 Mhz video dot clock, and a word clock and word clock/256. It can also take a single source frequency as a referenve clock. Its basicaly set up to sync and slave SMPTE timing systems Hope that helped.. Rex Moncur wrote: Hi all Does anyone have any experience of locking a USB external soundcard to a GPSDO 10 MHz reference. I am interested in advice on any good quality soundcards that can be readily locked to either 10 MHz or if necessary to some other frequency that we can derive from a GPSDO source. I have done some tests with the SignalLink soundcard that uses a Texas Instruments PCM2904 chip and requires a 12 MHz lock frequency. This requires some cutting of tracks to remove the internal oscillator feedback and insert the locking frequency. 12 MHz is readily derived from 10 MHz but I have not been able to get it to lock. The Texas instruments data sheet suggests that it is possible to use an external refernce but also says this is not recommended. With this expereicne I would rather find a sound card that is designed for external locking that does not require the cutting of tracks. For info the purpose of this request is that we are looking at using very narrow bandwidth modes at less than 1 mHz for light wave communcation. To date using LEDs and cloud reflection we have worked over 200 km with WSJT but we should be able to do 20 dB better if we can get down to milli-Hz bandwidths (at the expense of spending all night to complete a QSO). Our expereince to date is that standard sound cards are just not stable to better than 5 milli-Hz at 1000 Hz which should be readily solved by GPS locking let us get down to sub milli-Hz levels. Rex VK7MO ___ 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] Sound Cards for locking to GPSDO 10 MHz references
> -Original Message- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Rex Moncur > Sent: Monday, June 01, 2009 3:00 PM > To: 'Discussion of precise time and frequency measurement' > Subject: [time-nuts] Sound Cards for locking to GPSDO 10 MHz > references > > > Hi all > > Does anyone have any experience of locking a USB external > soundcard to a GPSDO 10 MHz reference. > > I am interested in advice on any good quality soundcards that > can be readily locked to either 10 MHz or if necessary to > some other frequency that we can derive from a GPSDO source. > I have done some tests with the SignalLink soundcard that > uses a Texas Instruments PCM2904 chip and requires a 12 MHz > lock frequency. This requires some cutting of tracks to > remove the internal oscillator feedback and insert the > locking frequency. 12 MHz is readily derived from 10 MHz but > I have not been able to get it to lock. The Texas > instruments data sheet suggests that it is possible to use an > external refernce but also says this is not recommended. > With this expereicne I would rather find a sound card that is > designed for external locking that does not require the > cutting of tracks. > > For info the purpose of this request is that we are looking > at using very narrow bandwidth modes at less than 1 mHz for > light wave communcation. To date using LEDs and cloud > reflection we have worked over 200 km with WSJT but we should > be able to do 20 dB better if we can get down to milli-Hz > bandwidths (at the expense of spending all night to complete > a QSO). Our expereince to date is that standard sound cards > are just not stable to better than 5 milli-Hz at 1000 Hz > which should be readily solved by GPS locking let us get down > to sub milli-Hz levels. > > Rex VK7MO Some of the "pro" sound interfaces have a "word clock" input. There are a variety of things that take a external input and generate a S/PDIF that's properly timed, as well. Lots of boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 which was used by lots of Flex-Radio folk), so maybe that's something you could easily generate from your 10MHz. A chart at Cakewalk shows that MOTU has a USB interface (828MkII) which has a word clock sync. It's going to be a pricey beast though, with 8in/8out ($800?) Even if you have a word clock input, you're going to have to synthesize that from the 10 MHz. Maybe it's easier to just make a S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is something like 3 MHz) The HPSDR folks also might have something... ___ 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] Sound Cards for locking to GPSDO 10 MHz references
The concern I'd have with modifying a USB sound card, or any of them for that matter, is that the glue logic between the ADC and the USB chip may be designed for a certain relationship between the ADC and USB clocks. Running the ADC asynchronously may or may not be robust depending on the assumptions baked into the gate array. It might be OK if your app can tolerate occasional misclocking or dropouts but I'd be reluctant to use a hacked sound card for anything timing-critical. I just (last week) got an AD7760 ADC eval board working with the Digilent Nexys2 FPGA platform, with the EVAL-AD7760 board running from its own 40 MHz clock. It will accept an external 40 MHz clock source that, in turn, wouldn't be hard to derive from 10 MHz. Way overkill for ultra low-bandwidth work, but if anyone is looking for a clean digitizer for audio rates in general, you could do a lot worse than this approach. Cost isn't too bad either, at $130 for the Nexys2 and $150 for the ADC7760 eval board. Of course the big drawback is the lack of any sort of standardized audio driver on the host side. If/when I spin a PCB for this project I'll definitely include a 10 MHz input. -- john, KE5FX > -Original Message- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on > Behalf Of Jeffrey Pawlan > Sent: Monday, June 01, 2009 3:08 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Sound Cards for locking to GPSDO 10 MHz > references > > > Soundcards for USB are poor at best. > > I have a set of PCI cards that were previously made by EMU and > they accept > external reference input. They no longer make the model I have > but perhaps > they have another PCI card with an external ref input. > > I am interested in your modulation technique which allows you to use WSJT. > Please let me know exactly what you are doing. I also do not know > how you are > using 5 milliHertz with WSJT since the group of discrete tones > occupy more > bandwidth. > ___ 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] Sound Cards for locking to GPSDO 10 MHz references
rmon...@bigpond.net.au said: > For info the purpose of this request is that we are looking at using > very narrow bandwidth modes at less than 1 mHz for light wave > communcation. To date using LEDs and cloud reflection we have worked > over 200 km with WSJT but we should be able to do 20 dB better if we > can get down to milli-Hz bandwidths (at the expense of spending all > night to complete a QSO). Our expereince to date is that standard > sound cards are just not stable to better than 5 milli-Hz at 1000 Hz > which should be readily solved by GPS locking let us get down to sub > milli-Hz levels. Sounds like a fun project. Do the clouds shift around enough to cause Doppler problems? You might find something in the way of a DSP or FPGA demo board. (I don't have any suggestions.) Or maybe a demo board for an audio chip. How stable is the osc on your current board? Do you need accuracy or stability? Can you feed a calibration signal in the other stereo channel and sort it out in software? Or tap off some signal in the board and feed that to a counter for calibration. -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] Sound Cards for locking to GPSDO 10 MHz references
Hi Jeff Thanks for your advice which I will follow up - the reason for going for a USB sound card is that the system must be operated portable with a Laptop - but perhaps there is a way to use a PCI sound card on a Laptop. While we use WSJT at present we have a new Mode under development for the mill-Hz bandwidth. In testing this new mode is acheiveing around 15 dB better than WSJT with 5 mHz binwidths and should get to 20 dB better with 1 mHz binwidths. It uses M-ary FSK like WSJT but does not need a reference tone for time or frequency locking on the basis that both soundcards are GPS locked. Timing errors are not an issue as the tone durations are 16 mins at 1 mHz binwidth. We use around 20,000 separate M-ary tones (cf 64 for WSJT), which is sufficient to send the first three characters of a call sign in Clark-Karn source encoded format - thus it requires only two tones to be sent to receve a full callsign. However at one mHz bandwidth this takes 16 minutes to send a single tone and thus an hour to send two callsigns. However, we have some shorter techniques for exchanging reports and RRR so a QSO can be comppleted in around 3 hours, hi. We can fit 20,000 tones spaced 1 mHz apart into just 20 Hz so there is not problem there. We have not yet added FEC which should allow a further improvement but we would like to resolve the sound card stablity issues first. 73 Rex VK7MO ___ 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] Sound Cards for locking to GPSDO 10 MHz references
I have seen it talked about (around the LF fraternity, but generally they are stable enough there and just need calibation) a lot but not accomplished yet. How about injection locking the on board oscmaybe gating the feedback with the referencenote I havent tried this? Another technique I have used to shift "logic-block" oscillators is to vary their supply voltage, they will oscillate from around 3v to well over 5.5v that might enable you to phase lock it using a variable regulator to vcxo to crystal?? Alan G3NYK - Original Message - From: "Rex Moncur" To: "'Discussion of precise time and frequency measurement'" Sent: Monday, June 01, 2009 10:59 PM Subject: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references > > Hi all > > Does anyone have any experience of locking a USB external soundcard to a > GPSDO 10 MHz reference. > > I am interested in advice on any good quality soundcards that can be readily > locked to either 10 MHz or if necessary to some other frequency that we can > derive from a GPSDO source. I have done some tests with the SignalLink > soundcard that uses a Texas Instruments PCM2904 chip and requires a 12 MHz > lock frequency. This requires some cutting of tracks to remove the internal > oscillator feedback and insert the locking frequency. 12 MHz is readily > derived from 10 MHz but I have not been able to get it to lock. The Texas > instruments data sheet suggests that it is possible to use an external > refernce but also says this is not recommended. With this expereicne I > would rather find a sound card that is designed for external locking that > does not require the cutting of tracks. > > For info the purpose of this request is that we are looking at using very > narrow bandwidth modes at less than 1 mHz for light wave communcation. To > date using LEDs and cloud reflection we have worked over 200 km with WSJT > but we should be able to do 20 dB better if we can get down to milli-Hz > bandwidths (at the expense of spending all night to complete a QSO). Our > expereince to date is that standard sound cards are just not stable to > better than 5 milli-Hz at 1000 Hz which should be readily solved by GPS > locking let us get down to sub milli-Hz levels. > > Rex VK7MO > > > ___ > 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] Sound Cards for locking to GPSDO 10 MHz references
Soundcards for USB are poor at best. I have a set of PCI cards that were previously made by EMU and they accept external reference input. They no longer make the model I have but perhaps they have another PCI card with an external ref input. I am interested in your modulation technique which allows you to use WSJT. Please let me know exactly what you are doing. I also do not know how you are using 5 milliHertz with WSJT since the group of discrete tones occupy more bandwidth. 73, Jeffrey Pawlan WA6KBL ___ 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.
