Re: [time-nuts] Question about precise frequency / phase measurement
On 04/20/2012 03:49 PM, ewkeh...@aol.com wrote: It is a circuit that they for instance use in the 2110 where they take the reference input in case of 10 MHz divide by 2 and also divide the 5 MHz down to 500 Hz use an exor and out comes 5.000500 MHz filtered and divided by 5. A similar approach is being used in many rubidiums to generate the 5,3125 MHz signal, taking the 5 MHz, divide it by 16 and then XOR them together and then toss it through a LC tank to pick out the right frequency component. The rubidium is then tweaked using the C-field such that the locked 5 MHz lines up with SI second. That's just one aspect of why rubidiums have been relatively cheap from the start. The isotopic match of D lines allowing fairly easy filtering and selective pumping is another. The result is 1.000100 MHz which is mixed with the unknown divided to 1 MHz. The result is 100 Hz counted with a 100 MHz period counter and you have 1 E 12 in a second. My counter which is part of the system and thanks to Richard MCC is a PIC, has 0.1, 1, 10 and 100 seconds gate time. The 100 or 200 MHz are generated from the reference channel. All logic is in a MAX3000A G/A. The output is RS 232 and can also be stored on a USB memory stick, no PC needed. Austron uses a Xtal as a filter and I use 2 because I do not have access to their Xtal but it works. A nicer solution would be to use an AD 9833 DDS but it would require an additional PIC to do the math since the DDS can not produce an exact 1.000100 MHz. If some one is willing to do that chip please contact me off list. If you do quadrature signal multiplication, you can avoid the mirror frequency without high-Q filters. Look up the Tayloe detector for some inspiration. In this case you can generate an I and Q signal by adding a DFF. By producing a 2 kHz and 500 Hz, you let the 500 Hz be the I signal and then let the additional DFF have that as D input and clocked by the 2 KHz it will produce the 90 degree shifted Q signal on the Q output. By quadrature separation of the 5 MHz you can then use the 5 MHz I and Q, mix and then analogue sum prior some mild filtering such as a LC-tank. 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] Question about precise frequency / phase measurement
Moin On Thu, 19 Apr 2012 18:18:24 -0400 (EDT) ewkeh...@aol.com wrote: I have quite a collection of equipment and have build Dual Mixer, PICTIC and what I think is best for you a circuit I call the Austron circuit. What is this Austron Circuit? And how does it look like? :-) Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Question about precise frequency / phase measurement
On Thu, 19 Apr 2012 23:39:32 +0200 skywatcher skywatc...@web.de wrote: BTW i'm using the Parallax 'Propeller' controller which has 8 cores running at 80 MHz each, and can measure time intervals with 12.5 ns resolution. [...] Looks like an interesting thing. But also very specialized. If you have already experience with it, ok. But if you start from scratch i would recomend to use one of the Cortex-M3 or Cortex-M4 processors. There is a lot more knowledge available for these and you get a lot of tools just for free. I think the DDMTD could be a good solution. The question is, if 74HCxx parts would be good enough to get 1 mHz resolution for a 10 MHz frequency with an update rate of 1 sec. That's a simple calculation. 1mHz of 10MHz is a precision of 10^-10. Sampling at a second you need a time resolution of 1s*10^-10 = 0.1ns. Modern CMOS (ie not HC/HCT) have a jitter in the region of 1-5ns. (ECL are in the region of a couple 100ps) Ie, if you build a DDMTD with just HC/HCT, your jitter will be dominated by the logic circuit and you have to average several samples to get below the 10^-10 you want. ECL would be definilty better. Also keep in mind, that in this region of precision, you have to model your digial circuit partially as analog. Especially taking into account that you have a a finite rise time, input and output jitter, power supply noise, signal noise etc pp. All these will limit the precision you will achieve for single measurements. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Question about precise frequency / phase measurement
Attila Kinali wrote: On Thu, 19 Apr 2012 23:39:32 +0200 skywatcherskywatc...@web.de wrote: BTW i'm using the Parallax 'Propeller' controller which has 8 cores running at 80 MHz each, and can measure time intervals with 12.5 ns resolution. [...] Looks like an interesting thing. But also very specialized. If you have already experience with it, ok. But if you start from scratch i would recomend to use one of the Cortex-M3 or Cortex-M4 processors. There is a lot more knowledge available for these and you get a lot of tools just for free. I think the DDMTD could be a good solution. The question is, if 74HCxx parts would be good enough to get 1 mHz resolution for a 10 MHz frequency with an update rate of 1 sec. That's a simple calculation. 1mHz of 10MHz is a precision of 10^-10. Sampling at a second you need a time resolution of 1s*10^-10 = 0.1ns. Modern CMOS (ie not HC/HCT) have a jitter in the region of 1-5ns. (ECL are in the region of a couple 100ps) Not in this application, where DDJ and other pattern dependent jitter is absent. 4ps per inverter of flipflop is more typical for HCMOS. Ie, if you build a DDMTD with just HC/HCT, your jitter will be dominated by the logic circuit and you have to average several samples to get below the 10^-10 you want. ECL would be definilty better. Try it and you'll be pleasantly surprised. CERN do much better than you speculate (White Rabbit project) Also keep in mind, that in this region of precision, you have to model your digial circuit partially as analog. Especially taking into account that you have a a finite rise time, input and output jitter, power supply noise, signal noise etc pp. All these will limit the precision you will achieve for single measurements. Yes, but in practice is easy to achieve hitter about 2-3 orders of magnitude lower than your speculation in a DDMTD. Attila Kinali 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.
Re: [time-nuts] Question about precise frequency / phase measurement
It is a circuit that they for instance use in the 2110 where they take the reference input in case of 10 MHz divide by 2 and also divide the 5 MHz down to 500 Hz use an exor and out comes 5.000500 MHz filtered and divided by 5. The result is 1.000100 MHz which is mixed with the unknown divided to 1 MHz. The result is 100 Hz counted with a 100 MHz period counter and you have 1 E 12 in a second. My counter which is part of the system and thanks to Richard MCC is a PIC, has 0.1, 1, 10 and 100 seconds gate time. The 100 or 200 MHz are generated from the reference channel. All logic is in a MAX3000A G/A. The output is RS 232 and can also be stored on a USB memory stick, no PC needed. Austron uses a Xtal as a filter and I use 2 because I do not have access to their Xtal but it works. A nicer solution would be to use an AD 9833 DDS but it would require an additional PIC to do the math since the DDS can not produce an exact 1.000100 MHz. If some one is willing to do that chip please contact me off list. Bert Kehren In a message dated 4/20/2012 6:56:14 A.M. Eastern Daylight Time, att...@kinali.ch writes: Moin On Thu, 19 Apr 2012 18:18:24 -0400 (EDT) ewkeh...@aol.com wrote: I have quite a collection of equipment and have build Dual Mixer, PICTIC and what I think is best for you a circuit I call the Austron circuit. What is this Austron Circuit? And how does it look like? :-) Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Question about precise frequency / phase measurement
You may want to look at how that was done many years ago with frequency difference multiplication as in the old Tracor meters - I think the 528 was the main one. They synthesized a 9 MHz reference from one input, and then subtracted it from the other to get a 1 MHz result, which was used as a reference for another 10 MHz PL oscillator. The 9 MHz was subtracted from this, and so on to a next identical stage. The net result is that each stage of this process multiplies the frequency difference by ten times. These can be cascaded until you reach the limit of the noise performance of the stage designs - they managed around 10,000 times fairly readily. This method can be duplicated fairly easily with modern logic parts. With a setup like this you can produce a 1 or 10 MHz carrier that can be counted to very high resolution at one second gating - you just ignore the carrier digits and look at the multiplied difference frequency digits. Or, you can subtract the carrier and get just the multiplied difference - but you have to keep track of the phase info to know if it's plus or minus. It's of course possible to use whatever frequencies and stage multiplication factors you want, but the tradeoffs are in making the numbers come out rationally (especially if you want a number of decade multiplier ranges), and the precision and quality of the intermediate frequency filtering and processing. About ten to one hundred times per stage is within reason. For example, I have an experimental (way unfinished) setup started with three stages of 1 GHz PLOs for multiplication, and a 990 MHz reference. This will give 100X per stage, reaching 10E6 difference frequency multiplication at one second gating, presuming I can manage the phase noise sufficiently. A quick two-stage setup indicated no problem reaching 10E4, but that last 100X will be tricky - I have to build it up for real first, with extremely clean power supplies, shielded signal processing modules, and solid signal routing, just to see if it's possible. I would not recommend this approach - I'm only doing it because I happened to have all the main parts on hand. It would be better to keep everything down to 100 MHz or less for processing in ECL or ACMOS, and using crystal VCOs and filters. Ed ___ 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] Question about precise frequency / phase measurement
I have and use a Tracor 527E how ever the Austron circuit including counter is a PCB board 2.2 X 2.5 inches and I have not seen a Tracor for $ 50. I think I paid $ 800 fifteen years ago. Bert Kehren In a message dated 4/20/2012 11:37:16 A.M. Eastern Daylight Time, e...@telight.com writes: You may want to look at how that was done many years ago with frequency difference multiplication as in the old Tracor meters - I think the 528 was the main one. They synthesized a 9 MHz reference from one input, and then subtracted it from the other to get a 1 MHz result, which was used as a reference for another 10 MHz PL oscillator. The 9 MHz was subtracted from this, and so on to a next identical stage. The net result is that each stage of this process multiplies the frequency difference by ten times. These can be cascaded until you reach the limit of the noise performance of the stage designs - they managed around 10,000 times fairly readily. This method can be duplicated fairly easily with modern logic parts. With a setup like this you can produce a 1 or 10 MHz carrier that can be counted to very high resolution at one second gating - you just ignore the carrier digits and look at the multiplied difference frequency digits. Or, you can subtract the carrier and get just the multiplied difference - but you have to keep track of the phase info to know if it's plus or minus. It's of course possible to use whatever frequencies and stage multiplication factors you want, but the tradeoffs are in making the numbers come out rationally (especially if you want a number of decade multiplier ranges), and the precision and quality of the intermediate frequency filtering and processing. About ten to one hundred times per stage is within reason. For example, I have an experimental (way unfinished) setup started with three stages of 1 GHz PLOs for multiplication, and a 990 MHz reference. This will give 100X per stage, reaching 10E6 difference frequency multiplication at one second gating, presuming I can manage the phase noise sufficiently. A quick two-stage setup indicated no problem reaching 10E4, but that last 100X will be tricky - I have to build it up for real first, with extremely clean power supplies, shielded signal processing modules, and solid signal routing, just to see if it's possible. I would not recommend this approach - I'm only doing it because I happened to have all the main parts on hand. It would be better to keep everything down to 100 MHz or less for processing in ECL or ACMOS, and using crystal VCOs and filters. Ed ___ 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] Question about precise frequency / phase measurement
Ed at one time I used two 9 GHz multiplier chains out of FTS 4000's mixed them, if you are interested contact me off list I may still have them. Have thrown out many things because I am downsizing in preparation for a move. Bert In a message dated 4/20/2012 11:37:16 A.M. Eastern Daylight Time, e...@telight.com writes: You may want to look at how that was done many years ago with frequency difference multiplication as in the old Tracor meters - I think the 528 was the main one. They synthesized a 9 MHz reference from one input, and then subtracted it from the other to get a 1 MHz result, which was used as a reference for another 10 MHz PL oscillator. The 9 MHz was subtracted from this, and so on to a next identical stage. The net result is that each stage of this process multiplies the frequency difference by ten times. These can be cascaded until you reach the limit of the noise performance of the stage designs - they managed around 10,000 times fairly readily. This method can be duplicated fairly easily with modern logic parts. With a setup like this you can produce a 1 or 10 MHz carrier that can be counted to very high resolution at one second gating - you just ignore the carrier digits and look at the multiplied difference frequency digits. Or, you can subtract the carrier and get just the multiplied difference - but you have to keep track of the phase info to know if it's plus or minus. It's of course possible to use whatever frequencies and stage multiplication factors you want, but the tradeoffs are in making the numbers come out rationally (especially if you want a number of decade multiplier ranges), and the precision and quality of the intermediate frequency filtering and processing. About ten to one hundred times per stage is within reason. For example, I have an experimental (way unfinished) setup started with three stages of 1 GHz PLOs for multiplication, and a 990 MHz reference. This will give 100X per stage, reaching 10E6 difference frequency multiplication at one second gating, presuming I can manage the phase noise sufficiently. A quick two-stage setup indicated no problem reaching 10E4, but that last 100X will be tricky - I have to build it up for real first, with extremely clean power supplies, shielded signal processing modules, and solid signal routing, just to see if it's possible. I would not recommend this approach - I'm only doing it because I happened to have all the main parts on hand. It would be better to keep everything down to 100 MHz or less for processing in ECL or ACMOS, and using crystal VCOs and filters. Ed ___ 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] Question about precise frequency / phase measurement
Wolfgang asked Does anybody know a possibility to get a resolution 1 mHz ? (in 1 second) The goal is look for frequency deviations caused by external influences ... A silly question to ask time nuts. :) How good do you really want it to be? 1 mHz out of 10 MHz in one second is only 1 part in 1e-10 and needs a resolution of 0.1 ns For a high end example showing external influences causing small freq variation, see the swinging OSC test at http://www.thegleam.com/ke5fx/tpll/swing.gif This has a resolution of ~0.01 mHz (1e-12) at ~100 Hz update rate, which is about 10K better than what you have asked for. Many of the high end suggestions you are getting is how to do it 100 plus times better than what you've asked for. Yes, plain old HC parts and some care can get you resolution and repeatability below 0.1 ns when averaging for one second. For something pretty simple, see Bruce's XOR Linear Phase detector page at, http://www.ko4bb.com/~bruce/LinearPhaseComparators.html I made a version of that using 74AHCxx parts that gives ~1 mHz freq difference resolution at 100 Hz update rate. For really high end, simple, low cost, with no digital parts, there is a 2.0 version of the TPLL with resolution of 1e-14/sec. That is capable of near 1mHz resolution with an update rate of 10K/sec. Information on TPLL version 1 is at http://www.ke5fx.com/tpll.htm ws snip I want to monitor the frequency deviation continuously (that means: i don't want to look at a scope ;) and log the data several times per second. The goal is not to make a 'quality test' of the oscillator, but to look for frequency deviations which are caused by external influences of various kind. The question is, if 74HCxx parts would be good enough to get 1 mHz resolution for a 10 MHz frequency with an update rate of 1 sec. Regards, Wolfgang Hello @all, my name is Wolfgang and i'm new to the list. :) I browsed through the list archive, but i didn't find the infos i need, so i decided to join the list and to ask the experts directly. :) I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Best regards, Wolfgang ___ 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] Question about precise frequency / phase measurement
On 2012/04/20 13:44, time-nuts-requ...@febo.com wrote: For a high end example showing external influences causing small freq variation, see the swinging OSC test at http://www.thegleam.com/ke5fx/tpll/swing.gif Neat! Is there a page explaining a bit more about it? I was summarizing the Hafele-Keating experiment to my brother the other day -- just bullshitting, really, 'cause I barely know what's going on here myself -- so it occurs to me to wonder. Acceleration is probably the cause, but a mechanical effect in the oscillator, something tightened in cockpit? Surely not a relativistic effect. Not at 18 inches. (This is where we figure out that I grasp the concepts, but can't actually do the problems.) ___ 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] Question about precise frequency / phase measurement
No page. The effect is nothing very special. No relativity. Mostly just the effect of the oscillator's G sensitivity caused by tilting and acceleration as it swings. What is generally measured with a 2 G static turn over test. The thing about the test is that it gives a signal that is very hard to measure and a wave form shape that is easy to verify. This shows how good the TPLL is at detecting small frequency changes very quickly. The TPLL2.0 gives the best results for that test that I've seen from any instrument. ws On 2012/04/20 13:44, time-nuts-request at febo.com wrote: For a high end example showing external influences causing small freq variation, see the swinging OSC test at http://www.thegleam.com/ke5fx/tpll/swing.gif Neat! Is there a page explaining a bit more about it? I was summarizing the Hafele-Keating experiment to my brother the other day -- just bullshitting, really, 'cause I barely know what's going on here myself -- so it occurs to me to wonder. Acceleration is probably the cause, but a mechanical effect in the oscillator, something tightened in cockpit? Surely not a relativistic effect. Not at 18 inches. (This is where we figure out that I grasp the concepts, but can't actually do the problems.) ___ 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] Question about precise frequency / phase measurement
Hello @all, my name is Wolfgang and i'm new to the list. :) I browsed through the list archive, but i didn't find the infos i need, so i decided to join the list and to ask the experts directly. :) I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Best regards, Wolfgang ___ 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] Question about precise frequency / phase measurement
Just a speculation on my part, but if you got some non-saturating logic like ECL, the jitter would be less. I haven't done any ECL in years, but the traces I got from ECL circuits are amazingly clean. I was evaluating a competitions ECL DAC. -Original Message- From: skywatcher skywatc...@web.de Sender: time-nuts-boun...@febo.com Date: Thu, 19 Apr 2012 21:10:03 To: time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] Question about precise frequency / phase measurement Hello @all, my name is Wolfgang and i'm new to the list. :) I browsed through the list archive, but i didn't find the infos i need, so i decided to join the list and to ask the experts directly. :) I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Best regards, Wolfgang ___ 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] Question about precise frequency / phase measurement
Welcome, Hello @all, my name is Wolfgang and i'm new to the list. :) I browsed through the list archive, but i didn't find the infos i need, so i decided to join the list and to ask the experts directly. :) I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. You would only see a sine wave if the difference frequency was stable an such that the LPF cut off all but the fundamental. If you want sine wave output, use an analog mixer on sine waves, and don't overdrive it. -John === Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Best regards, Wolfgang ___ 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] Question about precise frequency / phase measurement
Hi Wolfgang, On 19/04/12 21:10, skywatcher wrote: Hello @all, my name is Wolfgang and i'm new to the list. :) Welcome! I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Have you looked at the PICTIC II project? It's not too bad. There is several other possible projects to consider, but the PICTIC II may be a good start. Also look at a divide down system such as the TADD 2 divider or the just released TADD 2 Mini. There is a challenge in doing fairly high precission for low budget here on the list. Besides measuring frequency, we pride ourselves in measuring the frequency stability, Allan Deviation (ADEV), as good as possible. 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] Question about precise frequency / phase measurement
And, if you are measuring, by analog mixing, two very slightly different frequencies, what do you expect to obtain if not a signal that is slow, very slow. How can you measure milliHertz or microHertz without waiting? On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi Wolfgang, On 19/04/12 21:10, skywatcher wrote: Hello @all, my name is Wolfgang and i'm new to the list. :) Welcome! I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Have you looked at the PICTIC II project? It's not too bad. There is several other possible projects to consider, but the PICTIC II may be a good start. Also look at a divide down system such as the TADD 2 divider or the just released TADD 2 Mini. There is a challenge in doing fairly high precission for low budget here on the list. Besides measuring frequency, we pride ourselves in measuring the frequency stability, Allan Deviation (ADEV), as good as possible. 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] Question about precise frequency / phase measurement
Hi Wolfgang, one of the easiest and very accurate ways to do this is simply to measure the drift of the two 10MHz signals on an oscilloscope. Adjust the OCXO so that this drift between the two traces is as slow as you can get it. Then simply measure it over time. Use one signal for trigger, the other to display if you only have a one channel scope. If you get say 10ns drift over 1 hour (which you can easily measure even with the cheapest scopes), that is a resolution of 10ns/3600s = 2.78E012. Or in other words 27.7uHz! This has been discussed before and documented in the time nuts archives some time ago. bye, Said In a message dated 4/19/2012 12:10:53 Pacific Daylight Time, skywatc...@web.de writes: My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Best regards, Wolfgang ___ 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] Question about precise frequency / phase measurement
Using a dual mixer time difference system (either the digital dual mixer time difference (DDMTD) or the analog variant (DMTD)) can easily achieve the required resolution. The DDMTD is relatively cheap to implement however it requires an offset oscillator to beat against the 2 signals being compared. However a DDMTD can use a 5MHz offset oscillator can be used with 5MHz, 10MHz, 15MHz ... input signals whereas a DMTD requires a 10MHz offset oscillator to be used with 10Mhz input signals. The DDMTD uses a pair of shift registers clocked by the offset source where each of the 2 signals being compared is connected to the data inputs of its shift register. The time difference between beat outputs of the 2 shift registers is then measured with relatively low resolution. Some digital filtering of the shift register output transitions is usually required. A pair of 74HC164's will typically have a equivalent input jitter of around 10ps or so, a 74AC164 will be about 4x quieter. With a 5.55MHz offset oscillator and 10MHz inputs the shift register output beat frequency will be 110Hz. It is usually advantageous to use an FPGA to implement the digital filtering, timestamping and even the shift registers (although external shift registers will have less crosstalk). Bruce skywatcher wrote: Hello @all, my name is Wolfgang and i'm new to the list. :) I browsed through the list archive, but i didn't find the infos i need, so i decided to join the list and to ask the experts directly. :) I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Best regards, Wolfgang ___ 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] Question about precise frequency / phase measurement
Yes, and, as you can see, you have to wait 1 hour. On Thu, Apr 19, 2012 at 9:49 PM, saidj...@aol.com wrote: Hi Wolfgang, one of the easiest and very accurate ways to do this is simply to measure the drift of the two 10MHz signals on an oscilloscope. Adjust the OCXO so that this drift between the two traces is as slow as you can get it. Then simply measure it over time. Use one signal for trigger, the other to display if you only have a one channel scope. If you get say 10ns drift over 1 hour (which you can easily measure even with the cheapest scopes), that is a resolution of 10ns/3600s = 2.78E012. Or in other words 27.7uHz! This has been discussed before and documented in the time nuts archives some time ago. bye, Said In a message dated 4/19/2012 12:10:53 Pacific Daylight Time, skywatc...@web.de writes: My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Best regards, Wolfgang ___ 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] Question about precise frequency / phase measurement
Use a dual mixer system with an offset LO. Bruce Azelio Boriani wrote: And, if you are measuring, by analog mixing, two very slightly different frequencies, what do you expect to obtain if not a signal that is slow, very slow. How can you measure milliHertz or microHertz without waiting? On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi Wolfgang, On 19/04/12 21:10, skywatcher wrote: Hello @all, my name is Wolfgang and i'm new to the list. :) Welcome! I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Have you looked at the PICTIC II project? It's not too bad. There is several other possible projects to consider, but the PICTIC II may be a good start. Also look at a divide down system such as the TADD 2 divider or the just released TADD 2 Mini. There is a challenge in doing fairly high precission for low budget here on the list. Besides measuring frequency, we pride ourselves in measuring the frequency stability, Allan Deviation (ADEV), as good as possible. 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. ___ 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] Question about precise frequency / phase measurement
Of course, there are PICTIC II, DMTD, DDMTD, SR620, HP5370B, Wavecrest, PM6681, HP53132. The simplest is using a scope and... wait. On Thu, Apr 19, 2012 at 9:53 PM, Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: Use a dual mixer system with an offset LO. Bruce Azelio Boriani wrote: And, if you are measuring, by analog mixing, two very slightly different frequencies, what do you expect to obtain if not a signal that is slow, very slow. How can you measure milliHertz or microHertz without waiting? On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi Wolfgang, On 19/04/12 21:10, skywatcher wrote: Hello @all, my name is Wolfgang and i'm new to the list. :) Welcome! I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Have you looked at the PICTIC II project? It's not too bad. There is several other possible projects to consider, but the PICTIC II may be a good start. Also look at a divide down system such as the TADD 2 divider or the just released TADD 2 Mini. There is a challenge in doing fairly high precission for low budget here on the list. Besides measuring frequency, we pride ourselves in measuring the frequency stability, Allan Deviation (ADEV), as good as possible. 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. ___ 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] Question about precise frequency / phase measurement
Hi Bruce, this sounds very good, and seems to fit my requirements quite well. :) I will have a closer look to this concept. I also had the idea to take the reference frequency, divide it, and mix the division result again with the reference to get an offset to the reference frequency which would give a higher beat frequency which allows a reasonable measurement rate. But it didn't turn out as i expected, because there was a lot of 'garbage' in the signals. Best regards, Wolfgang Am 19.04.2012 21:51, schrieb Bruce Griffiths: Using a dual mixer time difference system (either the digital dual mixer time difference (DDMTD) or the analog variant (DMTD)) can easily achieve the required resolution. The DDMTD is relatively cheap to implement however it requires an offset oscillator to beat against the 2 signals being compared. However a DDMTD can use a 5MHz offset oscillator can be used with 5MHz, 10MHz, 15MHz ... input signals whereas a DMTD requires a 10MHz offset oscillator to be used with 10Mhz input signals. The DDMTD uses a pair of shift registers clocked by the offset source where each of the 2 signals being compared is connected to the data inputs of its shift register. The time difference between beat outputs of the 2 shift registers is then measured with relatively low resolution. Some digital filtering of the shift register output transitions is usually required. A pair of 74HC164's will typically have a equivalent input jitter of around 10ps or so, a 74AC164 will be about 4x quieter. With a 5.55MHz offset oscillator and 10MHz inputs the shift register output beat frequency will be 110Hz. It is usually advantageous to use an FPGA to implement the digital filtering, timestamping and even the shift registers (although external shift registers will have less crosstalk). 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.
Re: [time-nuts] Question about precise frequency / phase measurement
Depends on the scope.. if your scope has 100ps A-to-B measurement resolution, then waiting 5 minutes in this scenario would give 0.83ns drift, with 100ps uncertainty IF your oscillators were synced to ~3ppt which is very tough to do with a free-running OCXO (It would be unrealistic to get that stability from the two sources if they are free running). A more realistic scenario would give say 100ns drift in 5 minutes, then a 0.1ns resolution on the scope would give a very accurate reading in just 5 minutes (100ns +/-0.1ns = +/-0.1% error). The result would be 3.33E-010, +/-3.33E-013. Who needs more resolution than that as the OCXO will likely wander much more than that in 5 minutes.. bye, Said In a message dated 4/19/2012 12:52:07 Pacific Daylight Time, azelio.bori...@screen.it writes: Yes, and, as you can see, you have to wait 1 hour. On Thu, Apr 19, 2012 at 9:49 PM, saidj...@aol.com wrote: Hi Wolfgang, one of the easiest and very accurate ways to do this is simply to measure the drift of the two 10MHz signals on an oscilloscope. Adjust the OCXO so that this drift between the two traces is as slow as you can get it. Then simply measure it over time. Use one signal for trigger, the other to display if you only have a one channel scope. If you get say 10ns drift over 1 hour (which you can easily measure even with the cheapest scopes), that is a resolution of 10ns/3600s = 2.78E012. Or in other words 27.7uHz! This has been discussed before and documented in the time nuts archives some time ago. bye, Said ___ 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] Question about precise frequency / phase measurement
Wolfgang It would help if you would let us know what equipment other than a scope you have. Also what resolution you would want to achieve. One time set up or want to use repeatedly. Bert Kehren In a message dated 4/19/2012 4:53:40 P.M. Eastern Daylight Time, saidj...@aol.com writes: Depends on the scope.. if your scope has 100ps A-to-B measurement resolution, then waiting 5 minutes in this scenario would give 0.83ns drift, with 100ps uncertainty IF your oscillators were synced to ~3ppt which is very tough to do with a free-running OCXO (It would be unrealistic to get that stability from the two sources if they are free running). A more realistic scenario would give say 100ns drift in 5 minutes, then a 0.1ns resolution on the scope would give a very accurate reading in just 5 minutes (100ns +/-0.1ns = +/-0.1% error). The result would be 3.33E-010, +/-3.33E-013. Who needs more resolution than that as the OCXO will likely wander much more than that in 5 minutes.. bye, Said In a message dated 4/19/2012 12:52:07 Pacific Daylight Time, azelio.bori...@screen.it writes: Yes, and, as you can see, you have to wait 1 hour. On Thu, Apr 19, 2012 at 9:49 PM, saidj...@aol.com wrote: Hi Wolfgang, one of the easiest and very accurate ways to do this is simply to measure the drift of the two 10MHz signals on an oscilloscope. Adjust the OCXO so that this drift between the two traces is as slow as you can get it. Then simply measure it over time. Use one signal for trigger, the other to display if you only have a one channel scope. If you get say 10ns drift over 1 hour (which you can easily measure even with the cheapest scopes), that is a resolution of 10ns/3600s = 2.78E012. Or in other words 27.7uHz! This has been discussed before and documented in the time nuts archives some time ago. bye, Said ___ 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] Question about precise frequency / phase measurement
Hi Bert I want to monitor the frequency deviation continuously (that means: i don't want to look at a scope ;) and log the data several times per second. The goal is not to make a 'quality test' of the oscillator, but to look for frequency deviations which are caused by external influences of various kind. I have a digital 500 MS scope, so i can use this for circuit development, but i don't want to use it for the actual measurements. Time measurements with microsecond accuracy can be done with a microcontroller, that's not a problem. BTW i'm using the Parallax 'Propeller' controller which has 8 cores running at 80 MHz each, and can measure time intervals with 12.5 ns resolution. It has also some very interesting timing circuitry, and can even generate VGA video signals with user-defined timing without any external special components. May be of interest for one or the other here on the list. :) For those who are interested: http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/Propeller-P8X32A-Datasheet-v1.4.0.pdf I think the DDMTD could be a good solution. The question is, if 74HCxx parts would be good enough to get 1 mHz resolution for a 10 MHz frequency with an update rate of 1 sec. Can i use a 74HCT4046 PLL for the 'helper PLL' or is this one not good enough ? Maybe i will do some tests next weekend to see what i can achieve with these 74HC parts, before looking for better ones... Regards, Wolfgang Am 19.04.2012 23:14, schrieb ewkeh...@aol.com: Wolfgang It would help if you would let us know what equipment other than a scope you have. Also what resolution you would want to achieve. One time set up or want to use repeatedly. Bert Kehren ___ 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] Question about precise frequency / phase measurement
The traditional approach was to use a double-balanced mixer configured as a phase detector, pass the phase detector output through a low-pass filter (with 1 Hz bandwidth), and plot the result using a chart recorder. The chart recorder would also have marks from some kind of accurate clock. After a few days of recording, the beat frequency is easily determined, as is variations over the day. The present-day equivalent replaces the chart recorder with a recording digital voltmeter of some kind. Joe Gwinn From: Azelio Boriani azelio.bori...@screen.it To: Discussion of precise time and frequency measurement time-nuts@febo.com Date: 04/19/2012 03:38 PM Subject:Re: [time-nuts] Question about precise frequency / phase measurement Sent by:time-nuts-boun...@febo.com And, if you are measuring, by analog mixing, two very slightly different frequencies, what do you expect to obtain if not a signal that is slow, very slow. How can you measure milliHertz or microHertz without waiting? On Thu, Apr 19, 2012 at 9:31 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi Wolfgang, On 19/04/12 21:10, skywatcher wrote: Hello @all, my name is Wolfgang and i'm new to the list. :) Welcome! I want to measure the frequency difference between a 10 MHz OCXO and a 10 MHz Rubidium. I think that's what many people here have done many times... but i don't want to use expensive equipment like time interval counters with picosecond resolution etc. I would prefer a cheap and easy solution. I also would like to have an update rate of more than 1 measurement per second, or even more. My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution 1 mHz ? Have you looked at the PICTIC II project? It's not too bad. There is several other possible projects to consider, but the PICTIC II may be a good start. Also look at a divide down system such as the TADD 2 divider or the just released TADD 2 Mini. There is a challenge in doing fairly high precission for low budget here on the list. Besides measuring frequency, we pride ourselves in measuring the frequency stability, Allan Deviation (ADEV), as good as possible. 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. inline: graycol.gif___ 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] Question about precise frequency / phase measurement
Wolfgang I have quite a collection of equipment and have build Dual Mixer, PICTIC and what I think is best for you a circuit I call the Austron circuit. For less than $ 50 you can have a standalone system that gives you a RS 232 output with 1 E 12 resolution in 1 second, the PIC has 0.1, 1, 10 and 100 second gate time. At 100 seconds you get 1 E 14. The circuit does use a two stage Xtal filter which is the most difficult part of the circuit. How ever a DDS could be used, but the DDS does not give you 1.000100 MHz with 14 digit accuracy so post processing would be needed. If you have uProcessor expertise that would be perfect way to eliminate the filter part, making it even lower cost and much simpler. Never did a DDMTD so I do not know how it compares. If you are interested contact me off list and I send you all information. Bert Kehren In a message dated 4/19/2012 5:41:08 P.M. Eastern Daylight Time, skywatc...@web.de writes: Hi Bert I want to monitor the frequency deviation continuously (that means: i don't want to look at a scope ;) and log the data several times per second. The goal is not to make a 'quality test' of the oscillator, but to look for frequency deviations which are caused by external influences of various kind. I have a digital 500 MS scope, so i can use this for circuit development, but i don't want to use it for the actual measurements. Time measurements with microsecond accuracy can be done with a microcontroller, that's not a problem. BTW i'm using the Parallax 'Propeller' controller which has 8 cores running at 80 MHz each, and can measure time intervals with 12.5 ns resolution. It has also some very interesting timing circuitry, and can even generate VGA video signals with user-defined timing without any external special components. May be of interest for one or the other here on the list. :) For those who are interested: http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/Propeller-P8X32A- Datasheet-v1.4.0.pdf I think the DDMTD could be a good solution. The question is, if 74HCxx parts would be good enough to get 1 mHz resolution for a 10 MHz frequency with an update rate of 1 sec. Can i use a 74HCT4046 PLL for the 'helper PLL' or is this one not good enough ? Maybe i will do some tests next weekend to see what i can achieve with these 74HC parts, before looking for better ones... Regards, Wolfgang Am 19.04.2012 23:14, schrieb ewkeh...@aol.com: Wolfgang It would help if you would let us know what equipment other than a scope you have. Also what resolution you would want to achieve. One time set up or want to use repeatedly. Bert Kehren ___ 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.