Re: [time-nuts] time-nuts Digest, Vol 130, Issue 27
I would buy that (Google Maps being off) except that I'm less than 2 miles from the SF bay and -5M would have me underwater. That may well happen but not for a few years at least. Also the Arbiter does match Google maps pretty closely. It doesn't really matter a lot, just a curiosity. Demian Date: Mon, 18 May 2015 18:12:58 -0400 From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt Height Error Message-ID: 1ae37b6b-35fd-4c5f-95d6-01316d6c4...@n1k.org Content-Type: text/plain; charset=us-ascii Hi The simple answer is that Google maps may or may not be correct. There are a lot of examples of them being off by 10M or more. That said, my *guess* would be that the Thunderbolt is closer to the truth. Bob On May 18, 2015, at 2:34 AM, Demian Martin demianm@gmail.com wrote: I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old but it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has the 1995 firmware issue, and I could get new firmware for it ($$) but I'm not using it as a clock, just a frequency source. I just moved and have re-setup both. They share an antenna. I got both to do a self survey. The Arbiter was really close to what Google maps indicate is my location. The Thunderbolt was about the same except it has me underground. The arbiter has the height as +30M. The Thunderbolt as -6M. What setting do I have wrong in the Thunderbolt? Would it affect the operation as a frequency standard in any way? Demian Martin San Leandro, CA 94577 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Thunderbolt Height Error
I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old but it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has the 1995 firmware issue, and I could get new firmware for it ($$) but I'm not using it as a clock, just a frequency source. I just moved and have re-setup both. They share an antenna. I got both to do a self survey. The Arbiter was really close to what Google maps indicate is my location. The Thunderbolt was about the same except it has me underground. The arbiter has the height as +30M. The Thunderbolt as -6M. What setting do I have wrong in the Thunderbolt? Would it affect the operation as a frequency standard in any way? Demian Martin San Leandro, CA 94577 ___ 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] OCXO Voltage Input?
I have used an FM tuner pretty successfully to look at modulation and phase noise in oscillators. For a 10 MHz oscillator you will be looking at the 10th harmonic so modulation and phase noise is multiplied and much easier to see. You do need a square wave output to get a lot of harmonics. Sinewave outputs will be pretty low at the 10th harmonic if the oscillator is working well. This does work and I have tried it both on 10 MHz and 5 MHz oscillators with some success. It's not a replacement for a real phase noise analyzer but its way cheaper and adequate to spot real problems. The math to transform the output of a tuner into quantifiable phase noise was more than I had patience for. The low frequency limit is in the 5-10 Hz range. The AFC of a good tuner will eliminate most everything below that frequency. More details here http://www.diyaudio.com/forums/blogs/1audio/983-fm-tuner-jitter-analysis.html Subject: Re: [time-nuts] OCXO Voltage Input? (Bob Camp) Message-ID: ccc8bc9e-c7af-4965-88c5-d3d21b41d...@n1k.org Content-Type: text/plain; charset=windows-1252 Hi Yes indeed, as you go below 1 Hz (or 1 radian/sec) all the things that “help” you roll off wise now hurt you. If you are worried about sidebands inside 1 Hz, you need to change a sign here and there. The only thing that saves you is that the noise floor is now coming up pretty fast. If you modulate a crystal oscillator, the loaded frequency of the crystal is changed to accomplish the modulation. When your FM swings 100 Hz high, your crystal is tuned 100 Hz high. When your modulation swings 100 Hz low, your crystal is tuned 100 Hz low. The Q has no impact in this case. No I did not believe it worked that way until I did it …. Since then I’ve built a *lot* of VCXO’s with modulation bandwidths than their crystal Q bandwidths. The biggest problem comes from crystal spurs rather than crystal Q. Bob On Sep 6, 2014, at 6:09 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Bob, On 09/06/2014 03:00 AM, Bob Camp wrote: Hi Oddly enough (and yes it is odd) you can modulate an oscillator well outside the crystal’s bandwidth. The bigger issue is that the EFC does not pull the crystal very far on a normal OCXO. The FM modulation index drops to very small numbers pretty fast as you go up in modulation frequency. You typically only worry about modulation sidebands that are above the phase noise floor. Since phase modulation sidebands go down as 1/Fmod on an FM modulator (for small modulation index) they get pretty low pretty fast. If your OCXO has an EFC range of 0.1 ppm at 10 MHz, it will swing 1 Hz p-p (+/- 0.5 Hz) for the full EFC voltage. At 5 Hz, you have a modulation index of 0.1. Of course if you are multiplying to 10 GHz, the index could be quite large. This gets back to the “this all depends on what you are doing”. If your EFC is 5V, a reasonably quiet signal would have noise below 0.5 mV. That’s already 80 db down. A very quiet supply should be in the 5 nV / sqrt(Hz) range. That would put the noise down 180 db. It’s unlikely that your OCXO has a phase noise spec of -180 dbc / Hz at 10 Hz. We may already be done … To bring all the numbers together: At 1 Hz the modulation will do a sideband X db down at your desired frequency. You will drop 20 db by the time you get to 10 Hz simply due to the 1/F FM-PM. Since the oscillator integrate frequency into phase, you have a 1/(2*pi*f) factor. The typical LaPlace model for an oscillator is Ko/s, where Ko is the input sensitivity of the oscillator. A more complete model needs to include the Q of the crystal, naturally, unless you are in-band of that Q where it has less drastic properties. Bottom line - it’s not all that hard to get a quiet enough EFC voltage. Agreed. I've found that thinking about systematic noises of low frequency (i.e. comparator frequency and overtones) as well as loop dynamics is what one should think about. Lack of DAC resolution hurts. 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. ___ 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] 5370 processor boards available
Most routers use a similar model and can save important settings but still recover from a crash with no problem. There are several router distros that are good examples on how to do it. I would suggest looking at Voyage Linux http://linux.voyage.hk/ for an example. They have a specific versing for the BeagleBone Black. You can run user space apps on it just fine and it can save changes as necessary. I'm sure there are other examples as well. I'm just looking to making the box more reliable and stable. Running apps on it seems more complex than I'm up for. However a web page to control and read back seems like a nice trick. Demian On Thu, Feb 27, 2014 at 2:21 PM, Poul-Henning Kamp p...@phk.freebsd.dkwrote: In message ca+9gzujtzon9+uxg1r1brxx8zyv4wnjq22qpsbityako20w...@mail.gmail.com , cheater00 . writes: Oh, of course it's not about keeping the computer on at all times, it's about having a contingency for the 0.1% case when your computer does not shut down in the assumed time. You're missing the point: If all the permanent filesystems are mounted read-only, and only ram-disks are mounted read-write, you don't even need to shut down, you can just yank the power. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] 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? Demian Martin PDS ___ 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] have 10MHz need 19.5Mhz
From: kevin-use...@horizon.com To: albertson.ch...@gmail.com Cc: time-nuts@febo.com, kevin-use...@horizon.com Subject: Re: [time-nuts] have 10MHz need 19.5Mhz Message-ID: 20130606162408.10277.qm...@science.horizon.com Any 2-pin crystal connection to an IC is a simple Pierce oscillator. There's an on-chip inverter, with a high-impedance feedback resistor to keep the duty cycle balanced. You want to disconnect the output pin XTALN, and feed the input XTALP with an AC-coupled waveform of about 1 V p-p. So use a capacative divider between the PLL output and ground to get the voltage right. If the crystal is close to the desired frequency I have had good success capacitively coupling an external clock to the xtal in pin on a gate oscillator leaving the crystal in place. I have used 100 pF or less to get this to work. If the external oscillator is missing the circuit still runs but if its present at some level the circuit locks to the external source. If there is a possibility the external source is not present (GPS system is down) the rest of the system still runs with reduced accuracy. Demian ___ 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] Best phase detector / mixer for 100MHz?
I asked Wenzel about mixers for phase noise measurement and they directed me to Marki Microwave as what they use: http://www.markimicrowave.com/2770/Mixers.aspx I have not obtained or tested any myself but it's a pretty solid recommendation I think. I got this guy to add cross correlation to his FFT software suite: http://www.hpw-works.com/ however I have not built hardware to try it. He has a 30 day trial and its not expensive for what it is, $300. I would use it with an ESI Juli@ card http://www.esi-audio.com/products/julia/ ($150 or less on eBay or elsewhere) since you can be pretty sure it won't do something to mess with the measurement and it runs at 192 KHz sample rate quite well. Around $450 for a cross correlation analyzer. Or you can go shopping for an old FFT with the capability and potential service nightmare. Thanks a lot guys for all the input! The nist articles was a very interesting read. I have ordered the minicircuits ZRPD-1 and will try to build the 2NA mixer to to see how far that will take it. I probably also will build a low noise jfet preamp to see if that will reduce the noise. But I probably have to go to build myself a crosscorrelation system to be able to -180dBc with confidence. Is there any cheap way into cross correlation measurement, using high quality soundcard for example? Or do I have to buy one of these big old expensive dual FFT analyzers? /Anders ** ___ 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] 5MHz ocxo- Opening Solder sealed cans
Bob: Perhaps you can describe how to do this. I can't see a way that would not make a huge mess (big torch) or not ever get there (big soldering iron). I would really like to be able to get inside of some of these without making them all into trash. Demian _ Date: Wed, 25 Jul 2012 18:10:55 -0400 From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] 5MHz ocxo Message-ID: a99eee8d-e120-48cf-84d6-d3434b754...@rtty.us Content-Type: text/plain; charset=windows-1252 Hi That's just a basic solder sealed package. It should be pretty easy to pop open. You'll use up a bit of solder wick doing it? Bob ___ 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] disciplining sound card
We need a better idea what the goal is. If it's to sample and digitize data at a specific time you may need to roll your own but if it's to figure out the time of an event or to look at spectral info a mid price premium soundcard like the Juli@ should be more than adequate. Knowing when in a sample cycle the actual sample was taken may not have a lot of meaning since the incoming info is bandlimited. The standard sample rates, 44.1, 48, 88.2, 96, 176.4 and 192 KHz have roots in the video world and are not nice numbers per 10 MHz references. Audio cards use either a single 24.576 MHz crystal and PLL to generate the other frequencies or both a 24.576 MHz and a 22.5792 MHz crystal. The ones with separate crystals do have less jitter. Word clock can only be used with difficulty if the card was not designed for it. You cannot force word clock and have the rest of the I2C buss work right. You can lock to an external SPDIF or AES signal (they are virtually the same except for some info bits and the signal levels. AES is 4V P-P differential into 110 Ohms. SPDIF is 1V P-P into 75 Ohms (an AES variant is the same). The same receivers are used for both. If absolute timing is important you can easily use an external capture device (TI, ADI and AKM all have very good demo boards) that you can clock. Clocking at 10 MHz will work in some systems on the external spdif input but many will reject it since it's too far from an accepted frequency. The high end cards that might will resample everything messing with your carefully captured data. If you do get the data in the existing software will give you confusing results. There may be a simple way to add a SMPTE time code to the data as its captured. It's done in the video industry. If you don't want a delta sigma ADC you can substitute a different kind but there will be tradeouts. Usually bit depth vs sample rate vs. accuracy. A simple way to discipline a 22.5792 and a 24.576 VCXO to a 10 MHz reference would be very interesting. A good way to verify the performance and any issues with a capture system would be to make a count down from the 10 MHz to an audio frequency and capture it. Do a really deep fft and look for stuff that should not be there (anything but the countdown). Demian Martin ___ 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?
There are a number of sound cards (and have been for 10 years now) that can capture up to 95 KHz with extraordinary fidelity. They sample at 192 KHz and usually have 24 bit converters good tor 20+ bits. These can capture the complete FM MPX output pretty easily. Some of the newer ADC's have less that .001% THD at 192 KHz sampling. The AK5394a for example has -105 dB THD at 1 KHz. Can be had as a chip for about $22 ea if you want to build your own. Some current motherboards have an SPDIF input that can handle the 192 KHz sample rate. The next challenge is getting the OS to handle it, not difficult. Demian ___ 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] broadband MPX signal stereo
I have tested a number of soundcards and while the EMU 2020 has issues (serious jitter and noise from the USB interface) I can recommend the ESI Juli@ as having flat response and good SNR up to 90 KHz. It's a PCI card, no USB. I have measured the performance of FM MPX adapters and tested FM Transmitter performance with one. You get 24 bit at 192 X 2 continuously as long as you want. With some simple pre-filtering and gain you should be able to get some 60 KHz signal at very low levels. With a deep FFT I get to -130 dBFS easily. With the demo board for the AKM AK5345a I am getting better than -160dBFS. That has SPDIF out. Depending on the filter selection, most chips have a flat option, there is no significant phase shift up to frequencies close to the cutoff. I have tried and dumped a number of other sound cards that were dead ends. The ESI Juli@ is usually around $120. Demian __ Chris Albertson writes: Some audio interfaces have a low pass filter to cut off at about 20KHz but many don't have the filter. The user manual should list the bandwidth of the interface. Mine claims to be flat out to 40KHz. But it varies. For example the EMU 2020 user manual reads Frequency Response (min gain, 20Hz-20kHz): +0.0/-0.07dB But what happens after 20KHz? The specs don't say. You have to test it yourself and see. ___ 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] Lightsquared's latest PR
Lightsquared wants GPS users to pay to fix their own problems! They are trying to get part of the phone industry behind them with the prospect of making more $$$ and to push the small group of precision GPS users to pay for their own fixes. The GPS industry has long relied on equipment that relies on spectrum which bleeds into the spectrum that LightSquared plans to use for its network. While the industry had been warned of its potential use, the GPS companies opted not to change the design of their devices or shield them against potential interference. Boulben said that the GPS industry's stance has steadily changed over the past few months, from outright denial of LightSquared's right to exist to refusing to pay for the new components. He added he believes that the GPS companies will eventually change their minds and come to an agreement. Read more: http://reviews.cnet.com/8301-12261_7-20119551-10356022/lightsquareds-gps-fi x-could-cost-industry-$400m/#ixzz1ah3RygUW http://reviews.cnet.com/8301-12261_7-20119551-10356022/lightsquareds-gps-fix -could-cost-industry-$400m/#ixzz1ah3RygUW I feel setup by this positioning and I'm sure most others on this list will also feel that way. How do we organize enough to exert some political pressure? Notwithstanding the impact of obsolescing the GPS in my car (not replacable) so they can make some money. Demian Martin Product Design Services 784 Cary Drive San Leandro, CA 94577 demian...@yahoo.com 209 613 6990 ___ 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] Could someone please recommend GPIB card?
Paul The quick and cheap migration to a desktop PC if you have the PCMCIA GPIB card is to get a PCI to PCMCIA adapter. They are cheap and plentiful for as little at $6.50. e.g. http://www.ebay.com/itm/PCI-PCMCIA-CARD-ADAPTER-/130584195663?pt=LH_DefaultD omain_0hash=item1e676cb24f#ht_500wt_1413 They do work well with the NI card, having used the combo with the 5370 successfully. Demian Date: Sun, 9 Oct 2011 18:36:52 -0400 From: Paul A. Cianciolo pa...@snet.net To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Subject: [time-nuts] Could someone please recommend GPIB card Message-ID: 003501cc86d3$fdd79fd0$f986df70$@snet.net Content-Type: text/plain; charset=us-ascii Hello, I am looking for a PCI-GPIB card to use in a machine running windows XP. After looking on Ebay there are many different options at many different prices. I am not sure which would be compatible with my set up. Currently I have a ACER Laptop, with a NI PCMCIA GPIB card and I was able to locate the drivers to make it run with the TimeLab, the HP 5730B, I have a Dell dimension 2400 desktop, which runs other Ham radio software, like weak signal DSP, some Seismograph, Dataq data logging and others. This computer has a spare PCI slot and I would like to move the HPIB capabilities into this machine, so I only need to run 1 computer. Maybe someone is looking for a trade for the PCMCIA GPIB Card and cable? Thank you for the help Paul A. Cianciolo W1VLF ___ 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] Plot phase noise spectrum from DMTD
I would like to see more in one place about implementing these ideas. The bits are scattered in different places and I'm not sure where to find them all. One resource for getting the signals sampled at SOTA performance for a reasonable price is this demo board from TI: PCM4222EVM http://focus.ti.com/lit/ug/sbau124/sbau124.pdf $149 from TI https://estore.ti.com/Search.aspx?k=pcm4222evm It supports differential input at 192 KHz sampling with spdif/aes outputs. It has on board crystal oscillators from Pletronics. You can also run it from an external oscillator. I'm not sure how far from the standard frequencies you can go and still have the system get good data. You would need a sound card that has an SPDIF input that runs at 192 KHz. Some motherboards may be able to do this. The board is a very good implementation of their best audio frequency ADC. I don't think you could build it anywhere near the price of the demo board. You would need a sound card that has a native ASIO driver to keep Windows from mucking around with the signals ideally. I would not recommend a USB audio interface at this time. They are linked to the PC through some ugly mechanisms if accuracy is important (adaptive sample??). Better solutions are happening for USB but they are few and expensive for now. You can get PCI cards from ESI, M-audio, EMU that would do the job pretty well with drivers that work. For Linux I would suggest the ESI Juli@ since I know it works well in Linux. It may be possible to create a plug in for Audacity that will do the math and conversion to get the phase noise plots etc from the system. Audacity will do the job of collecting the data. http://audacity.sourceforge.net/ --Demian Date: Fri, 11 Mar 2011 14:21:55 -0800 From: John Miles jmi...@pop.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Plot phase noise spectrum from DMTD measurement? Message-ID: hmebkhfeacmnlmhiafdnoeaeaeah.jmi...@pop.net Content-Type: text/plain; charset=us-ascii Ok some cool advice - this thread is an interesting thought exercise. I'm going to think about it a some more, but it seems, in comparison at least, the loose phase-lock technique remains the simplest. Provided you have a low-frequency spectrum analyser handy. It would be a better idea from the standpoint of VCO modulation bandwidth as well. If you measure PN by looking at the tuning voltage in the tight-PLL configuration, you'll probably be limited to offsets of a few kHz before the response rolls off. The sound card idea is clever as well - however, I'd assume one needs to measure the ADCs clocking oscillator offset, since that will be apparent when plotting the beat frequency phase (what I mean is that sampling will then look like another mixing process). What I usually due is to clock the sampling system off a clock that's correlated to the clock under test. This resolves that issue. Sound cards will usually end up running within 1 Hz of the desired sampling rate, but it's important to pick a sampling rate that's native to the hardware, or the driver will resample the data. On Windows, many drivers for popular sound cards rely on some imprecise resampling code that apparently was distributed by Microsoft in the DDK. Stick with 44100 or 48000 Hz, or you'll be lucky to land within a few dozen Hz in some cases. Warren's been getting some really nice ADEV plots from a tight PLL sampled with a USB sound card, running a quick and dirty command-line utility I put together to acquire the data and downsample it. I'll post the next build on my web page if anyone else is interested in playing with it. However, I'd like to experiment with the cross-correlation idea, since I've got a setup that will lend itself perfect to that. Maybe I could save myself some time, with clever post-processing. Can anyone recommend a fundamental text on the cross-correlation technique? The easy way out is to look for a dual-channel FFT analyzer or one of its successors. The HP 3562A and 3563A models are pretty affordable these days, and they've been used in a number of papers on cross-correlation measurements of various types of noise. SRS also sells some nice multichannel analyzers. If you're looking to write your own processing code, you should search for information on 'cross spectrum' as well as 'cross correlation' techniques, because the former is the correct term for the scenario where the sampled data from both channels is already time-aligned. For its part, the cross spectrum is just a $5 mathematical buzzword for the vector length between the corresponding output bins of two FFTs, obtained by multiplying one array by the complex conjugate of the other. When averaged over time, the real component of the cross spectrum will converge to the common signal at the ADC inputs. Unlike the DUT signal, the ADCs' noise contribution is randomly distributed in phase space. It will
[time-nuts] Changing frequency of an HP 10811 oscillator
Having seen the note on alternate crystals for the HP10811 oscillator I was wondering if its realistically possible to re-crystal one to frequencies in the 20 MHz range? Some other components may need to be changed of course but is this worthwhile exploring? Who would be a good vendor for a few custom SC crystals that would work in an HP10811? I have been quoted prices in the $500+ range for finished products and want to explore a more cost effective option before I spend a lot of money. Demian Martin Product Design Services San Leandro, CA 94577 209 613 6990 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] A different timenuts interest
Another perspective on time: http://www.longnow.org/clock/ And some fascinating mechanical stuff. -Demian Message: 4 Date: Fri, 23 Jul 2010 02:11:04 +0200 From: Magnus Danielson mag...@rubidium.dyndns.org Subject: Re: [time-nuts] A different timenuts interest To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 4c48de18.7040...@rubidium.dyndns.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 07/23/2010 01:54 AM, Oz-in-DFW wrote: Hmmm. I thought time-nuts were nuts about time, with branch interests in accuracy, resolution, history... History is nanoseconds ago. Recent history is picoseconds ago. Just now is femtoseconds ago. Fraction of mind ago is attoseconds ago. Acient history is microseconds ago. Ages is microseconds ago Major epochs in time i seconds ago. Geological short period is minutes ago. Geological epoch period is hours ago. No? 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.
[time-nuts] Wavecrest vs. HP 5370 vs. SR620 Jitter measurements
At some point I'll re-run tempco and jitter measurements of the dividers and 1PPS distribution amps I have here. Last time I used a 5370B and a SR620. This time I'd like to try a Wavecrest. If someone on the list has done this already can you let me know? Thanks, /tvb I have read through the data sheets on all of these and am very interested in the differences in reality. The Wavecrest claims 2 pS Jitter measurement. The HP has a single shot resolution of 20 pS, The SR620 is 25 pS and the Wavecrest specs say 20 pS. How does the Wavecrest get .1X minimum Jitter measurement of the others with the same resolution? Can that trick be applied to the others? Demian ___ 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] 5370A vs 5370B
I got an almost perfect 5370A some years ago for less than $100. It had one dead input. I discovered that those input devices were essentially unobtanium so I went shopping for a substitute. I found a Maxim chip that seems to work as well as the original comparator, possibly slightly better. I also found that the input was not very easy to work with. However the time interval probes HP 5363a or b (pretty easily available) address the input flexibility issues very well and seem to talk to the inputs better than I can directly. Its output seems to be an ecl signal. Is there anything a 5370B can do that the A version can't? It seems the major upgrade is the processor, the timer circuits seem essentially the same. In fact this suggests some enterprising time nut could design a new processor taking advantage of much faster and cheaper new processor chips to improve the throughput considerably and could sell the upgrade to all of us with 5370's. I would not be surprised if a PIC could do the task. . . Demian Date: Tue, 9 Mar 2010 16:56:41 -0500 From: Bob Camp li...@rtty.us Subject: Re: [time-nuts] 5370A vs 5370B To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Message-ID: 565d26fda92d48a89cebe425506e1...@vectron.com Content-Type: text/plain; charset=us-ascii Hi Assuming there's enough of the pot left, (as in the pot still works) that's very likely what I'll do. Bob ___ 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] 5370A vs 5370B
Being naïve I didn't know the HP custom chip would be difficult to substitute. Since it was blown and not available I went searching and found a Maxim chip (MAX9691 I think) that would work on paper. It is surface mount and I managed to find a header that fit the HP socket and some careful wiring from the legs of the chip to the pins on the header got it up and running. I'm not sure my eyes are still up to this task. It seems it would be a simple task to create the header with chip. I don't know if the 5370B would be as easy to substitute. -Demian Date: Wed, 10 Mar 2010 00:03:04 + From: Mark Sims hol...@hotmail.com Subject: [time-nuts] 5370A vs 5370B To: time-nuts@febo.com Message-ID: blu125-w25460fafb6ba00b5258f2ce...@phx.gbl Content-Type: text/plain; charset=iso-8859-1 I've had the pleasure of fixing way too many 5370A and 5370B front panels. It's been a while so these musings may be clouded... also beware of the two or three different front panel designs. Also there are hybrid 5370A's out there with 5370B front ends. --- The biggest bugaboo in buying a 5370 is the state of the HP custom input amplifier chips. They can be damaged by overloading the input. Blow one and you are screwed. Buy a 5370 with a blown input amp and you are screwed. The 5370A and 5370B used different chips. The 5345A counter is a source of input amp chips. It would be VERY nice if some clever person built drop in replacement chips built of modern SMD parts on a DIP header. Those input amp chips are socketed. They are little more than a comparator. Quick check of the 5370A inputs is to set the unit to SEParate inputs and connect the back panel 10 MHz ref signal to each of the inputs. The signal level LED should flash. A steady LED means that input is toast (or the input PCB slide switches are full of navel lint and need cleaning). ___ 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 Card Spectrum Analyzer
While I have little experience looking at phase noise I have a lot with using commercial sound cards in acoustic analysis. I use a system from this guy : http://libinst.com/ called Praxis. The designer had to resolve the same issues re: calibration of the chain. He uses an external box that generates a square wave of known amplitude and frequency. The spectrum is known so it's easy to check the system calibration. I would think its possible to inject the square wave into the freq trim pin of the reference oscillator for cal purposes. If the varactor diode isn't filtered you could get response to 100 KHz. To deal with the dynamic range issue you can equalize the preamp. If you know the eq you can correct for it in the fft. The same problem exists in a magnetic phono cartridge (remember those?) and the preamp has a 40 dB difference in gain between 20 Hz and 20 KHz. This measurement is a little different since the compensation is different, less gain at low frequencies and more at high frequencies. Some of the semi-pro soundcards sample at 192 KHz. You need to check the response, since to get better s/n numbers some mfr's roll of the top early and are way down at 90 KHz. Low frequency response is a different issue. The mfr's don't publish schematics. Look suggests that DC response is possible. The absolute DC accuracy won't be good since it's not an issue for soundcards. I have a lot of experience working with this card: http://www.esi-audio.com/products/julia/ and can furnish measurements of it. I also have resources for modifying the analog section to some degree. It also has single ended and differential inputs to help reduce common mode noise. Its well supported under Linux, important, since both the Windows and the Mac sound system will muck around with your bits. -Demian ___ 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] Cheap Rubidium
MuMetal us great when you need a shield that is thin and pretty light. It needs to be hydrogen annealed after you form it etc. and its expensive. However for shielding what you need is a magnetic shunt. If weight isn't a problem (probably isn't if it's a stationary application) the cheap way to get good shielding is cast iron sewer pipe. The thickness is enough that even if its hard magnetically very little flux will get past it. Plus, once it's at temperature it will take a long time to change. It's very heavy but that helps reduce the internal vibration. The styling may be an issue, you might want to make an external housing. Here are some general details: http://www.acipco.com/adip/pipe/flanged/specs.cfm Date: Thu, 24 Dec 2009 15:55:23 -0500 From: Bob Camp li...@cq.nu Subject: Re: [time-nuts] Cheap Rubidium To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 8f61b9af-818d-4d1c-b7a9-ac005d688...@cq.nu Content-Type: text/plain; charset=us-ascii Hi Every time I've tried the coli thing, field uniformity has become an issue. I'm also not real sure just how stable multi axis mag sensors are. If I had a bunch of mu metal sitting in the basement I'd certainly use it in the setup. Last time I checked the stuff was not cheap Bob Demian Martin Product Design Services * ___ 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] Splitting GPS antenna output
I have two GPSDO's, a Tbolt and an Arbiter. When I got them (simultaneously) I wanted to get them up and I only had one antenna. However I confirmed that a consumer TV splitter works very well with the GPS antennas. There are some splitters that claim 2 GHz bandwidth. It's not useful for the intended application (CATV rarely goes above 850 MHz) but they are fine for this. And they will have a power pass output port that is the one that powers the antenna. In my case the Arbiter had a more precise supply for the antenna for what its worth. The Arbiter has a Motorola receiver and a Wenzel Oscillator. Demian Martin Product Design Services ___ 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] Using cheap sound cards for measurements
Here is a backgrounder on the 44.1 KHz sample frequency. I dimly remembered that it was related to video. http://www.cs.columbia.edu/~hgs/audio/44.1.html USB audio is often outside the AES spec for frequency since the USB clock isn't easily related to 44.1 or 48. Some external DAC's won't lock to USB spdif sources since they are so far out. The clock is derived from the PC's internal clocks. USB audio output is usually locked and syncronous to the PC's USB interface so a local clock would require buffering and some way to manage the data. There is an asyncronous audio for USB standard but not used except by a few devices. A lot of the pro market uses Firewire for this reason and others. The spec for a good digital audio chip is here: http://envy24.svobodno.com/datasheets/via/vt1724.pdf and a lot more here: http://envy24.svobodno.com/datasheets/ Demian Martin PDS From: Hal Murray hmur...@megapathdsl.net Subject: Re: [time-nuts] Using cheap sound cards for measurements james.p@jpl.nasa.gov said: [External clock at strange frequency.] That's an interesting idea. I would imagine that the clock going into the chip is probably some multiple of the sample rate (e.g. 48kHz*16*2 = 1.536 MHz), so you could pick the closest 1/N from 10 MHz and pump that in. However, what about the USB interface? These are inexpensive devices, and I'll bet all the rates are carefully chosen so that everything shares one clock. I guess somebody will have to take the lid off and look inside. Most USB gizmos that I've looked at have something like a 24 MHz crystal. I assume that is a sweet spot for cost. At the root hub, that turns into the clock/bit rate. At the device end, I think it's PLLed to the upstream clock. My guess is that any claimed-to-be-good audio gear would have it's own audio clock just to avoid the wander as the PLL follows its view of the upstream clock. I don't understand the audio numbers. Is there a crystal frequency that works well with all normal sampling frequencies? I don't see one if you want both 44.1 and 48 KHz. (There could easily be some sneaky scheme I don't know about.) tract...@ihug.co.nz said: Are USB data transfer delay times an issue? IIRC they can vary quite a lot, depending on processor loading etc. DaveB, NZ USB gets a lot of bad press because it's polled. In reality, that polling is implemented in hardware so there is another layer of buffering to separate things from the interrupt latency. One big question for communication systems is how much buffering do you need? Buffers are expensive (or were in the old days) so hardware guys try to avoid them. On the other hand, they let software guys be sloppy so software guys always want more buffering. USB has two modes sharing the same controller and tree of wires. Devices like audio gear can reserve bandwidth. All the rest of the bandwidth is shared by the other devices like disks. So something like an audio device would get allocated X bytes per polling interval and hence needs enough buffering for that much data. X is just the data rate times the polling interval. (rounding up a bit) I think the USB 1.1 polling interval is 1 ms. I think the USB 2.0 polling interval has stuff to get lower than 1 ms while still working with the old 1.1 stuff. I'd have to do some work to understand the details. The bottom line is that USB was designed with things like audio in mind so it should do a good job. That's assuming reasonable driver support and OS support and good applications and probably several other factors too. Modern OSes have support for real-time work. You should be able to write code that reads from USB, crunches the data, and writes a summary to disk, and does that while the system is also doing other work. That's assuming that you only need reasonable amounts of CPU, memory, disk, whatever... Mostly, this allocates some CPU to that work, giving the rest of the CPU to the non real-time work. (Roughly like USB bandwidth is allocated.) -- 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] Using cheap sound cards for measurements
Be careful of the Emu/Creative stuff. They have always has resampling in their products in the past. This new generation doesn't but it still has an inline DSP to muck around with the bits. Also the Windows (and MAC) sound systems are notorious for resampling internally. This can be very hard to get around. You can use ASIO drivers to go around the internal engine if you write your app for that. The EMU 0202 isn't supported fully in Linux yet. Demian Martin PDS Ok, I have looked at a few USB cards and reviews. For SD radios, and as far as I can tell for time use, the Creative E-MU 0202 will do nicely, at a reasonable cost of $99.00. According to the company info, the E-MU 0404 might be synchronizable; it costs about $150. The plug-in card (takes two slots) equivalent to the 0404 is apparently the E-MU 1212. It might be possible to modify the 0202 to provide an external clocking signal, at least to provide a more stable oscillator, I don't know. The 100 ps jitter if true is satisfactory? Oh, the 1212 input amplifiers are DC coupled (!). I suggest, of course, that interested parties have a look at the website: http://us.creative.com/products/welcome.asp?category=237 I'll probably be ordering an 0202 in the near future. Don Latham ___ 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] Using cheap sound cards for measurements
A decent home studio soundcard would have easily 60+ dB of separation across it range and probably much higher. For the outrageous sum of around $150 you can get the ESI Juli@ from eBay (and real dealers) with better than 60 dB of separation, below 5 Hz to 100 KHz response, differential inputs and good Windows, Mac and Linux support. It seems any other approach would probably value time at below minimum wage or less for the effort. Here is a review showing 100+ dB separation http://ixbtlabs.com/articles2/esi-julia/ The card uses local crystals for its oscillators so it has lower jitter than the cheap solutions. If it helped the measurement you could drive the crystal input with an external oscillator etc. For more extended low frequency response you could bypass the input caps but the dc offsets would need attention. Demian Martin Product Design Services Date: Fri, 21 Aug 2009 22:51:40 +0200 From: Christian Vogel vogel...@vogel.cx Subject: Re: [time-nuts] Using cheap sound cards for measurements To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 4a8f08dc.6010...@vogel.cx Content-Type: text/plain; charset=ISO-8859-1; format=flowed Hi Lux, Syncing inexpensive cards is a real chore (and the only reason to be thinking about using this in the first place is to keep the cost to a minimum, otherwise, you might as well build a special purpose little box with counters A/Ds, and an interface) I've had too many problems with cheap (onboard) soundcards in the past, even when using them for their intended purpose, so I would not advice to use them for anything quantitative. But if you *really* want to syncronize inexpensive soundcards, it's rather trivial, see for example http://quicktoots.linuxaudio.org/toots/el-cheapo/ . Just buy a few dozens for a EUR/$ each and hunt down the ones with identical oscillator frequencies ;-). But don't expect miracles, you end up with a few synchronized cards that only happen to not skip samples with respect to each other. Compared to decent signal input they are still cheap cards, and hog the CPU for their individual servicing. Chris ___ 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] Using cheap sound cards for measurements
Modern soundcards using stereo DACs have very little shift between the channels. Usually much less than a sample period, probably less than m-clock period (64 to 256 X the sample period). And a high res card at 24 bits (probably 20 usable) will give you a lot of data to chew on. Demian Martin Product Design Services Date: Fri, 21 Aug 2009 22:06:28 + From: Mark Sims hol...@hotmail.com Subject: [time-nuts] Using cheap sound cards for measurements To: time-nuts@febo.com Message-ID: blu125-w21d283c0dfe19fdb6641a7ce...@phx.gbl Content-Type: text/plain; charset=iso-8859-1 Just because the cards have the same ADC clock does not mean that they will be sampling at the same time. There will be differences in the startup characteristics, register programming, etc. that can affect just when the input is sampled. They may be sampling at the same rate, but the cards could be an indeterminate number of cycles off from each other. ___ 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] Using cheap sound cards for measurements
USB sound sample rates above 48 KHz are problematic. There are efforts to overcome the limits but they end up with special drivers etc. The bulk of the USB audio interfaces are based on Burr Broun chips which do virtually all you need. There are some pro models for around $150 - $200 that have high sample rates etc, but they use special drivers to work. Emu has several high performance boxes to consider. Linux support is problematic. . . Demian Martin PDS From: Don Latham d...@montana.com Subject: Re: [time-nuts] Using cheap sound cards for measurements To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 2f5e8fceb09e1b00c72c1c16ed514570.squir...@webmail.montana.com Content-Type: text/plain;charset=iso-8859-1 On this track, what's the group opinion as to the best USB sound card? I'm looking for one for time as well as sd radio use. Should have the best separation, best s/n, highest digitization rate, 24 bit, etc. Any recommendations? Thanks Don ___ 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] EFRATOM MFTD-AC4 FREQUENCY REFERENCE DISTRIBUTION AMP - update
I received the unit. The shipping and packing was very good- no peanuts! The one I got was different from what I expected. It's a 5 MHz unit with 20 outputs. More than I could conceivably need. I looked inside. The supply is actually 25V. The input module has an FPGA for some reason, probably to communicate fault back to a host. The signal is distributed as a low level square wave on the backplane and amplified through a high gain tuned amp before going to the output amps. The outputs are all monitored. I need to figure out the tuned circuit so I can retune it. Would the performance be better if I bypass the input module and drive the output modules with a sine wave? I'm using it as a reference for some not-too-sophisticated counters and generators so the phase noise will be much better than those could benefit from regardless. Demian Martin PDS -- Message: 2 Date: Mon, 20 Jul 2009 22:46:44 -0700 From: Demian Martin demian...@yahoo.com Subject: [time-nuts] EFRATOM MFTD-AC4 FREQUENCY REFERENCE DISTRIBUTION AMP To: time-nuts@febo.com Message-ID: 9a1668b965254471953484d102b6a...@pdsdesktop Content-Type: text/plain; charset=us-ascii EFRATOM MFTD-AC4 FREQUENCY REFERENCE DISTRIBUTION AMP I just bought this off eBay. I was about to look into building one but for $50 + $25 shipping I could not justify the effort. They have 6 more. Item number 290330439821. Probably a deal for the box alone. Is there anything I should know about it? I'm planning to mount a Thunderbolt inside it. There is a decent datasheet on the family of products here: http://www.freewebs.com/beststuff2u/MFS-207.pdf Demian Martin ___ 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] EFRATOM MFTD-AC4 FREQUENCY REFERENCE DISTRIBUTION AMP
EFRATOM MFTD-AC4 FREQUENCY REFERENCE DISTRIBUTION AMP I just bought this off eBay. I was about to look into building one but for $50 + $25 shipping I could not justify the effort. They have 6 more. Item number 290330439821. Probably a deal for the box alone. Is there anything I should know about it? I'm planning to mount a Thunderbolt inside it. There is a decent datasheet on the family of products here: http://www.freewebs.com/beststuff2u/MFS-207.pdf Demian Martin ___ 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] Prologix GPIB-USB vs. GPIB-LAN
I looked at the Prologix stuff long and hard BUT it is something of a dead end. I didn't want to write new software and I have some existing apps that I use. I found an NI gpib-enet ( http://digital.ni.com/public.nsf/allkb/D2E1B6D23CD75B0686256D4E006E980D http://digital.ni.com/public.nsf/allkb/D2E1B6D23CD75B0686256D4E006E980D ) on ebay that has worked fine for me. The first gen is a little bit of a problem to use since it predated DHCP and setting its IP address is involved. Ones its up all of the NI GPIB stuff work with it as does other GPIB stuff. I would get the gpib-enet 100 for a business application since it supports DHCP and NI supports it in the latest releases. Demian Martin Product Design Service ___ 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
Magnus Danielson wrote: The digital link in question is S/PDIF; with the current popularity of Home Theater systems cheap cards with digital I/O have become quite prevalent. As an added bonus, S/PDIF can be run over both coaxial and optical media, the latter being attractive in further isolating PC noise from any measurement setup. And of course, a manufacturer's evaluation board is much better documented and more suited to measurement-specific mods than a random sound card. The optical link commonly being used for S/P-DIF is TosLink and it seems like it can be the cause of many problems. It seems like some care in doing the optical link setup is needed. I have never digged into why the optical links have that problem. I can only guess, but bad optical coupling seems reasonable. The multimode fiber seems to be leaving one or two things to ask for. Cheers, Magnus Without getting too audiophile there are several considerations. Toslink is bandwidth limited- the LED's are not really fast enough for 96K and really not for 192K sampling. The effect is high jitter on the link or a lost connection. The high jitter may not matter if the sampling is done with the external capture system (most of which are much more expensive). SPDIF or AES/EBU don't have the bandwidth limitation but can have other issues. The cheap ones don't have transformer isolation, however the transformers can increase the jitter on the link. You can use external USB capture, I'm playing with an EMU Tracker pre gadget that seems to do 192K at 24 bits pretty well and for $125. But I get better results from the ESI Juli@ pci card for around the same price, very low distortion and noise, and good Alsa support in Linux. It may be all that's needed. -Demian ___ 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.
