Re: [time-nuts] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I guess it depends on signal to noise ratio. With reciprocal counters, you only need one period to measure as acurately as you need, but to have good acuracy, you need very good S/N, as there is no filtering possible. For example, the HP 5370 can measure a single period of a signal with a resolution of 20pS (excluding noise and trigger imperfections), so excluding these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal with 7 x10-5 precision (if I have not goofed the calculations) More periods improve the resolution proportionately to the quare root. Accuracy is another matter. Didier KO4BB The jitter on a single period is likely very, very high, especially if it comes over the air. That's why one usually measures over a duration of thousands or even millions of periods (effectively called the gate time). The HP 53132A makes something like 200,000 measurements per second. As a result, for a certain range of frequencies, it claims 12 digits/sec of resolution (vs. HP 5370 ~11 digits/sec). /tvb ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Did mounting it on a block of foam help? That is a rather bad solution. You want much softer material to react to quicker things, such as silicon rubber. Also, that would only be a 12 dB/Oct solution. You would really like a few more poles there. The trick is to add weight to the calculation. So you want a very soft material, holding a thick block (lead) and from this base suspend the oscillator through a soft material again. Now you have a 24 dB/Oct solution. The trouble you now will have is that the wires will be another shock/vibration transport mechanism. They would need to be connected to the middle-frame such that outer forces hit the middle weigth and not directly on the sensitive part. They would need to be soft and arranged is such a way that they do not push or pull the inner end, but is allowed to flex alot. Yes, but inserting a chunk of foam is a lot easier than finding a block of lead. It's likely to be good enough. (Make that good enough for most application. This is time-nuts. Nothing is good-enough that somebody won't suggest something better/nuttier. :) Packing bubbles might work too. I'm thinking of the sheets of bubble wrap that are fun to snap rather than the foam peanuts that get all over the place and are really nasty if you have a slight static charge. Does anybody have any data on the sensitivity of a crystal oscillator vs frequency of mechanical shock/vibration? Does it scale with amplitude or acceleration or ??? -- 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY From: Tom Van Baak [EMAIL PROTECTED] Subject: Re: [time-nuts] FMT on October 13 Date: Tue, 25 Sep 2007 23:45:12 -0700 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I guess it depends on signal to noise ratio. With reciprocal counters, you only need one period to measure as acurately as you need, but to have good acuracy, you need very good S/N, as there is no filtering possible. For example, the HP 5370 can measure a single period of a signal with a resolution of 20pS (excluding noise and trigger imperfections), so excluding these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal with 7 x10-5 precision (if I have not goofed the calculations) More periods improve the resolution proportionately to the quare root. Accuracy is another matter. Didier KO4BB The jitter on a single period is likely very, very high, especially if it comes over the air. That's why one usually measures over a duration of thousands or even millions of periods (effectively called the gate time). The HP 53132A makes something like 200,000 measurements per second. As a result, for a certain range of frequencies, it claims 12 digits/sec of resolution (vs. HP 5370 ~11 digits/sec). As was discussed recently, didn't they do averaging such that they updated value every second but the raw singel-shot resolution doess not give you the 12 digits/sec. There was a nice explanation in an article on how this was not improving say ADEV measurements in the end. 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I just wanted to point out that with reciprocal counters, you can get resolution much better than the 1Hz/s you would get with conventional frequency counters, even though the actual accuracy of the measurement may be way off. The original question seemed to imply that with a short transmission time, you could not guarantee a frequency accuracy of 1e-6 Hz, which you probably can't anyhow, but the limit is not the resolution of the instrument or the measurement method. I do not know how far off calibration my HP 5370s are, but the 20pS resolution is at best only usable under some circumstances that I have not isolated yet, due to jitter. When measuring a 3.5 MHz signal (@1dBm) from my HP 8657B through 1 meter of good coax cable (with counter and generator phase locked to the Thunderbolt GPSDO) in Frequency mode with a 1s gate time, the resolution is 1e-5Hz, with about 1e-3Hz p-p variation. When measuring over 1 period with 10,000 periods sample size, the resolution is only 1e-1Hz with a standard deviation of ~400 Hz (or about 0.1%). Of course, over the air, it will be much worse due to noise, let alone propagation, fading and multipath. Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak Sent: Wednesday, September 26, 2007 1:45 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] FMT on October 13 I guess it depends on signal to noise ratio. With reciprocal counters, you only need one period to measure as acurately as you need, but to have good acuracy, you need very good S/N, as there is no filtering possible. For example, the HP 5370 can measure a single period of a signal with a resolution of 20pS (excluding noise and trigger imperfections), so excluding these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal with 7 x10-5 precision (if I have not goofed the calculations) More periods improve the resolution proportionately to the quare root. Accuracy is another matter. Didier KO4BB The jitter on a single period is likely very, very high, especially if it comes over the air. That's why one usually measures over a duration of thousands or even millions of periods (effectively called the gate time). The HP 53132A makes something like 200,000 measurements per second. As a result, for a certain range of frequencies, it claims 12 digits/sec of resolution (vs. HP 5370 ~11 digits/sec). /tvb ___ 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] FMT on October 13
From: Didier Juges [EMAIL PROTECTED] Subject: Re: [time-nuts] FMT on October 13 Date: Wed, 26 Sep 2007 05:57:14 -0500 Message-ID: [EMAIL PROTECTED] Didier, I just wanted to point out that with reciprocal counters, you can get resolution much better than the 1Hz/s you would get with conventional frequency counters, even though the actual accuracy of the measurement may be way off. These days conventional counteras are reciprocal counters. It is only the old-school counters which is not reciprocal. Nothing wrong with old-school, but a conventional counter of the shelf today is probably a reciprocal jobbie. The original question seemed to imply that with a short transmission time, you could not guarantee a frequency accuracy of 1e-6 Hz, which you probably can't anyhow, but the limit is not the resolution of the instrument or the measurement method. I do not know how far off calibration my HP 5370s are, but the 20pS resolution is at best only usable under some circumstances that I have not isolated yet, due to jitter. When measuring a 3.5 MHz signal (@1dBm) from my HP 8657B through 1 meter of good coax cable (with counter and generator phase locked to the Thunderbolt GPSDO) in Frequency mode with a 1s gate time, the resolution is 1e-5Hz, with about 1e-3Hz p-p variation. When measuring over 1 period with 10,000 periods sample size, the resolution is only 1e-1Hz with a standard deviation of ~400 Hz (or about 0.1%). Of course, over the air, it will be much worse due to noise, let alone propagation, fading and multipath. When measuring over a longer period you see a different spot on the ADEV/MDEV curve. Chances are that you are more unstable there for an OCXO. Both linear and noise products will make things harder. It can be a challenge to separate the drift rate due to signal path shifts and that of the OCXO. 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Tom Van Baak said the following on 09/24/2007 08:57 PM: I would think this is especially true for non-local frequencies, such as one received over the air. I'll leave it to you FMT guys to comment on the magnitude of degradation due to transmission and reception noise. Absolutely. Probably the best real-world performance you can get with a skywave signal is on the order of 0.01 Hz. Propagation effects play havoc, but the longer the averaging period, the more short-term effects will average away. One of the reasons for the fairly long transmission periods is to both allow longer averaging, but also provide the opportunity to observe the atmospheric conditions at work. While were at it, in the case mentioned above I'm a curious about their FMT frequency standard -- if it's really accurate to parts in 10^12, as they imply, over 10 minutes. I could believe this if it were an Rb or Cs-based GPSDO. We're using an Austron 1250A OXCO that's been measured as better than 9x10e-13 for averaging times of 1 second out to 1000 seconds; over a broader range, it's better than 3x10e-12 from 0.1 seconds to 40,000 seconds. Now, an important point -- we're not trying to trim the Austron to be precisely on frequency. We're going to let it run at whatever offset it happens to be. That will help make sure that the signal doesn't have lots of zero's at the end, even though the resolution of the synthesizers driving the transmitters is limited to 0.1 Hz. We'll be comparing the Austron against a Z3801a (via my TSC-5120A analyzer) and logging the frequency difference for at least several hours prior to the test until several hours following. The TSC gives 16 digits over 1000 seconds; depending on how much jitter we see, we'll probably throw away the last two or three. Even though the Z3801A may be wandering around a bit, with successive 1000 second measurements we should have confidence in the actual frequency over 1000 second periods to at least parts in the 12s, ultimately limited by the Austron's stability. But since that's known to be in the 13s over the averaging period of interest, we think we're safe in claiming accuracy and stability of parts in the 12s. Tom, if I'm missing something in this analysis, I'm seriously open to education... By the way -- the synthesizers used to drive the transmitter amplifiers will be PTS 250 SX-51 low noise units, so hopefully the transmitted signals will have a better-than-the-average-ham-rig phase noise. The synthesizers will directly feed the driver and final amplifier stages of some vintage Kenwood TS-520 ham transceivers with no other mixing -- it'll purely be the synthesizer and a transistor buffer amp driving two vacuum tube stages to get up to about 75 watts (the rigs can run 100 watts, but we're derating -- and adding fans -- to support the long key-down times). John ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Didier Juges said the following on 09/24/2007 09:40 PM: ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I guess it depends on signal to noise ratio. With reciprocal counters, you only need one period to measure as acurately as you need, but to have good acuracy, you need very good S/N, as there is no filtering possible. For example, the HP 5370 can measure a single period of a signal with a resolution of 20pS (excluding noise and trigger imperfections), so excluding these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal with 7 x10-5 precision (if I have not goofed the calculations) More periods improve the resolution proportionately to the quare root. Accuracy is another matter. I did some measurements on the frequency counter capability of my 5370B some time ago, and found that the performance wasn't as good as in time interval mode. But it's still not bad -- the internal noise floor was 4x10e-11 for 1 second (using the 1 second gate time). See http://www.febo.com/time-freq/hardware/5370B/index.html John ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY While were at it, in the case mentioned above I'm a curious about their FMT frequency standard -- if it's really accurate to parts in 10^12, as they imply, over 10 minutes. I could believe this if it were an Rb or Cs-based GPSDO. We're using an Austron 1250A OXCO that's been measured as better than 9x10e-13 for averaging times of 1 second out to 1000 seconds; over a broader range, it's better than 3x10e-12 from 0.1 seconds to 40,000 seconds. Ah, if they is you, then I have no more worries. Yes, using that free-running 1250A is the perfect solution; much better than using the output of a GPSDO. Now, an important point -- we're not trying to trim the Austron to be precisely on frequency. We're going to let it run at whatever offset it happens to be. That will help make sure that the signal doesn't have lots of zero's at the end, even though the resolution of the synthesizers driving the transmitters is limited to 0.1 Hz. Clever. We'll be comparing the Austron against a Z3801a (via my TSC-5120A analyzer) and logging the frequency difference for at least several hours prior to the test until several hours following. The TSC gives 16 digits over 1000 seconds; depending on how much jitter we see, we'll probably throw away the last two or three. Even though the Z3801A may be wandering around a bit, with successive 1000 second measurements we should have confidence in the actual frequency over 1000 second periods to at least parts in the 12s, ultimately limited by the Austron's stability. But since that's known to be in the 13s over the averaging period of interest, we think we're safe in claiming accuracy and stability of parts in the 12s. Yes, running the measurement for hours before and after is the right thing to do. All sounds good. Make sure not to get near any of the equipment. Free-running oscillators are sensitive to vibration or shock. You've probably heard the story of my best Sulzer oscillator making small phase or jumps which I eventually correlated to when the kids flushed the toilet down the hall. Tom, if I'm missing something in this analysis, I'm seriously open to education... Nothing missing; you nailed it. /tvb ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Make sure not to get near any of the equipment. Free-running oscillators are sensitive to vibration or shock. You've probably heard the story of my best Sulzer oscillator making small phase or jumps which I eventually correlated to when the kids flushed the toilet down the hall. Did mounting it on a block of foam help? -- 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY The Midwest VHF/UHF Society (located in Southwest Ohio) is pleased to announce that the first annual MVUS Frequency Measuring Test will be held on Saturday, October 13, 2007. There will be two transmission periods: the first at 14:30 EDT (1830 UTC), and the second at 21:30 EDT (0130 UTC Sunday). Transmissions will be on the 80M, 40M, and 30M amateur bands from Dayton, Ohio under the callsign W8KSE. Frequencies will be approximately: 3555 kHz, 7055 kHz, and 10115 kHz, but be prepared to tune as we will adjust to minimize QRM. The transmitters will be running about 75 watts output into wire antennas for each band. All the transmitters will be driven from a common frequency standard. We will transmit on all three bands simultaneously. Plans are to transmit two 10 minute test periods, and a third if the transmitters aren't melting by that point. The frequency will be changed by a small amount (less than 200 Hz) between transmission periods. So, a complete submission will include two or three separate measurements for each band. Our goal is to transmit a signal known in frequency to parts in 10e-12 (i.e., less than 0.0001 Hz error at 10 MHz) and stable to a similar level during the course of the transmission. Frequencies will be measured at the transmitter site with a system capable of microHertz resolution referenced to a GPS disciplined oscillator, and will also be monitored by another station in groundwave range that can measure the frequencies with similar accuracy. The MVUS Frequency Measuring Test is intended to supplement, not replace, the ARRL FMT. Further information, including approximate transmission frequencies, will be posted at http://www.febo.com/time-freq/FMT. You can also send email with questions or comments (or, after the test, your results!) to [EMAIL PROTECTED]. For discussion about off-air frequency measurement, we suggest you check out the FMT-nuts mailing list, sponsored by Connie Marshall, K5CM. For details, go to http://tech.groups.yahoo.com/group/FMT-nuts/. ___ 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] FMT on October 13
Plans are to transmit two 10 minute test periods, and a third if the transmitters aren't melting by that point. Our goal is to transmit a signal known in frequency to parts in 10e-12 (i.e., less than 0.0001 Hz error at 10 MHz) and stable to a similar level during the course of the transmission. Frequencies will be measured at the transmitter site with a system capable of microHertz resolution referenced to a GPS disciplined oscillator, and will also be monitored by another station in groundwave range that can measure the frequencies with similar accuracy. Suppose I have a pile of good lab gear, and it gets N seconds of signal. How accurately can it measure the frequency? -- 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] FMT on October 13
Plans are to transmit two 10 minute test periods, and a third if the transmitters aren't melting by that point. Our goal is to transmit a signal known in frequency to parts in 10e-12 (i.e., less than 0.0001 Hz error at 10 MHz) and stable to a similar level during the course of the transmission. Frequencies will be measured at the transmitter site with a system capable of microHertz resolution referenced to a GPS disciplined oscillator, and will also be monitored by another station in groundwave range that can measure the frequencies with similar accuracy. Suppose I have a pile of good lab gear, and it gets N seconds of signal. How accurately can it measure the frequency? Hi Hal, If you have a low noise CW signal, a cheap, legacy 1 ns resolution counter will give you 9 digits of resolution per second. So to measure to parts in 10^12 requires gate times on the order of a thousand seconds. A fancier, modern counter like a HP 53132A is almost ten times better than that so 100 s gate times are all you need for 12 digits. Further, if it's an oddball frequency (i.e., not a nice multiple or fraction of 10 MHz) even 10 second gate times are sufficient with this counter (it does clever CW oversampling inside). For extreme counters like HP 5370 or SR 620 with resolution well under 50 ps you can measure any frequency to 12 digits in a matter of tens of seconds. The main problems at this level are often that neither your frequency reference nor the frequency you are measuring are stable to parts in 10^12th. So the measurements you get will contain the sum of noise in both sources and the counter itself. And this noise is often well above parts in 10^12th. It takes time, statistics, or other tests to determine the noise contribution of each. I would think this is especially true for non-local frequencies, such as one received over the air. I'll leave it to you FMT guys to comment on the magnitude of degradation due to transmission and reception noise. While were at it, in the case mentioned above I'm a curious about their FMT frequency standard -- if it's really accurate to parts in 10^12, as they imply, over 10 minutes. I could believe this if it were an Rb or Cs-based GPSDO. Usually the accuracy of GPS disciplined oscillators are spec'd for averaging times over a day. And at one day, parts in 10^12 is very easy (many are down in the low 13's or 14's). But over a short span like 10 minutes most quartz-based GPSDO wander in frequency by many parts in 10^11. See, for example, these two nice quartz GPSDO over 10 minutes and note the scale is 1e-11 per *division*; which is almost 1e-10 full-scale. http://www.leapsecond.com/pages/fury/#6 /tvb ___ 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] FMT on October 13
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I guess it depends on signal to noise ratio. With reciprocal counters, you only need one period to measure as acurately as you need, but to have good acuracy, you need very good S/N, as there is no filtering possible. For example, the HP 5370 can measure a single period of a signal with a resolution of 20pS (excluding noise and trigger imperfections), so excluding these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal with 7 x10-5 precision (if I have not goofed the calculations) More periods improve the resolution proportionately to the quare root. Accuracy is another matter. Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Hal Murray Sent: Monday, September 24, 2007 5:26 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] FMT on October 13 Plans are to transmit two 10 minute test periods, and a third if the transmitters aren't melting by that point. Our goal is to transmit a signal known in frequency to parts in 10e-12 (i.e., less than 0.0001 Hz error at 10 MHz) and stable to a similar level during the course of the transmission. Frequencies will be measured at the transmitter site with a system capable of microHertz resolution referenced to a GPS disciplined oscillator, and will also be monitored by another station in groundwave range that can measure the frequencies with similar accuracy. Suppose I have a pile of good lab gear, and it gets N seconds of signal. How accurately can it measure the frequency? -- 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] FMT on October 13
Didier Juges wrote: I guess it depends on signal to noise ratio. With reciprocal counters, you only need one period to measure as acurately as you need, but to have good acuracy, you need very good S/N, as there is no filtering possible. For example, the HP 5370 can measure a single period of a signal with a resolution of 20pS (excluding noise and trigger imperfections), so excluding these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal with 7 x10-5 precision (if I have not goofed the calculations) More periods improve the resolution proportionately to the quare root. Accuracy is another matter. Didier KO4BB Didier With band limited gaussian noise and an SNR of 40dB the rms error in measuring the period of a single cycle is about 0.3% Bruce ___ 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.
