Re: [time-nuts] A silly question ...
> Dave B. (G0WBX) > > PS: I do like the idea of setting up a camera to take a photo of the > 'scope every hour or so! Not practical for many I guess, but it > illustrates the point well. But the aliasing opportunity I think would > be perhaps too great, in essence being a sampled data system by then. > Also, one then needs an accurate 1 hour timer! And so it goes on ;-) For hourly photos consider using a webcam or smart phone & time-lapse photo app. Here's an example of measuring time drift in mains with a photo every 15 minutes. Watch how the red seconds hand drifts by up to 4 seconds during the day: http://leapsecond.com/pages/tec/mains-clock-ani.gif About the aliasing, yes, one must keep that in mind. If the drift between your 10 MHz signals is erratic or if you slip by more than half of 100 ns per hour there could be ambiguity in your interpretation of the photos. That aliasing must be avoided. There are two easy solutions: 1) Take a photo more often than once per hour. For example, once a minute improves the possibility of ambiguity by a factor of 60. 2) Divide the frequency from 10 MHz to 100 kHz. Now your cycles are 10 us instead of 100 ns, which reduces the chance of undetected cycle slip by a factor of 100. Taking this to an extreme, imagine taking a photo every second, and imagine dividing your 10 MHz down to 1 Hz. Now you've reduced the chances of aliasing by tens of billions. And ... now you know why almost all timing measurements are done with a TIC as the "camera" and 1PPS as the "cycle". This is also why, since 1972, UTC does time jumps (aka leap seconds) in steps of exactly 1 second instead of any smaller value -- it perfectly fools all the TIC's in the world. /tvb ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A silly question ...
Many thanks to all the respondents to my question. Nice to know I can still think some things through in a good way! ;-) Re the below.. Yes, I should have said "dual trace" not "dual beam". "My bad" as some say. I should know better, having spent some 3 1/2 years of my life as in-house service serf at Tek here in the UK (Harpenden and Maidenhead) towards the end of the transition between the venerable "steam driven" 500 series (Valved, or Tubed 'scopes) and the then new-fangled solid state equipment, I do indeed know how the 465 (and a lot of other Tek products of that era) work, and it's differences to the true "dual beam" instruments (such as the 556 and so on.) Also, as an RF guy, coax run's are always terminated where so needed at times like this, and trigger points set-up to be as close to the mid point of the sharpest edge of a clock signal as possible. (Taking note of the specification of whatever is producing it, so as not to get hit by any pulse width jitter that may be a "known feature" etc.) In this instance, two sinusiods, so I chose the rising edge, just because ... Though it is not "needed" to show two signals on screen at the time, it is a lot easier (on the eye) to compare one signal drifting past another (known frequency) signal, not relying on the otherwise excellent graticule for the purpose I need. In this instance, I'm more interested in the relative frequency between the two sources, so the mk1 eyeball and trigger set-up is good enough for my needs. When the project is eventually deployed, it will be referenced to the Thunderbolt and generate a sufficiently stable and accurate 20.45 (and divisions of) MHz clock for other equipment. But interesting reading none the lest. Thanks very much again to all respondents. Much appreciated. Dave B. (G0WBX) PS: I do like the idea of setting up a camera to take a photo of the 'scope every hour or so! Not practical for many I guess, but it illustrates the point well. But the aliasing opportunity I think would be perhaps too great, in essence being a sampled data system by then. Also, one then needs an accurate 1 hour timer! And so it goes on ;-) On 28/09/18 17:00, time-nuts-requ...@lists.febo.com wrote: > Subject: Re: [time-nuts] A silly question ... > Message-ID: > <1538136285.3807422.1523450984.2c16d...@webmail.messagingengine.com> > Content-Type: text/plain; charset="utf-8" > > On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote: >> Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having> the >> output of the OCXO on Ch2, the resulting display on Ch2 of course> drifts in >> relation to the static waveform on Ch1. (Both nice >> sinusoids.) > The Tek 465 analog cathode ray oscilloscope was/is a very flexible > instrument. But this flexibility allows you to set up the instrument in > ways which will not allow this commonly used oscillator comparison > technique to work correctly. Since you are interested in these > instruments, here are some details about setting up the instrument for > such comparisons. > (1) The Tek 465 is not a dual beam oscilloscope. Dual beam oscilloscopes > (such as the Tektronix 556 and 7844) use a special CRT which > incorporates two independent electron guns. Each electron gun -- Created on and sent from a Unix like PC running and using free and open source software. :: ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A silly question ...
In addition to nonlinear issues with output amplifiers, filters have poor performance when improperly terminated. This can lead to harmonic distortion and that can be a problem. You want the duty cycle to be exactly 50%. See:https://tf.boulder.nist.gov/general/pdf/1437.pdf -- Bill Byrom N5BB On Fri, Sep 28, 2018, at 10:30 AM, Dana Whitlow wrote: > Hi, > > There is one other issue that can bite you if you fail to properly > terminate the output of a source: > > Depending on the source's design, an essentially unloaded output > can have a substantially higher voltage swing than expected (by > 2X if the source impedance is actually 50 ohms), possibly leading > to the output stage's going into clipping, which can in turn distort > the timing, possibly even in an unstable manner. > So if you want to play the "unterminated game", at least take a > look at the waveform to be sure it's still a clean sinewave. I've > noticed such distortion on my PRS-10, for example, although I've > seen no evidence of unstable timing results. But in this arena, > it generally pays to be fussy. > > Dana Whitlow > > On Fri, Sep 28, 2018 at 7:06 AM Bill Byrom > wrote:> >> On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote: >>> Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and >>> having>>> the output of the OCXO on Ch2, the resulting display on Ch2 of >> course>>> drifts in relation to the static waveform on Ch1. (Both nice >>> sinusoids.) >> The Tek 465 analog cathode ray oscilloscope was/is a very flexible >> instrument. But this flexibility allows you to set up the >> instrument in>> ways which will not allow this commonly used oscillator >> comparison >> technique to work correctly. Since you are interested in these >> instruments, here are some details about setting up the >> instrument for>> such comparisons. >> (1) The Tek 465 is not a dual beam oscilloscope. Dual beam >> oscilloscopes>> (such as the Tektronix 556 and 7844) use a special CRT >> which >> incorporates two independent electron guns. Each electron gun >> assembly has a set of vertical and horizontal deflection plates. >> There are two vertical amplifiers (one for each electron gun) and >> two horizontal sweep systems (one for each electron gun). If >> you had>> a dual beam oscilloscope you could compare oscillator#1 to >> oscillator#2 while simultaneously comparing oscillator#3 with >> oscillator#4. It's like having two independent oscilloscopes >> sharing>> the same CRT display. >> (2) The Tek 465 single beam oscilloscope can display two traces on >> the>> display using one of two methods:(a) Chopped trace display: >> This mode>> works well at low sweep rates (such >> as 1 ms/div) but causes trouble at fast sweep rates (such as 1 >> us/div). The displayed trace is switched between Channel 1 and >> Channel 2 at a fixed rate of about 500 kHz.(b) Alternate trace >> display: This mode works well at high sweep rates >> but is hard to see at low sweep rates. The scope alternates between>> >> displaying one sweep of Channel 1 and one sweep of Channel 2. >> (3) The trigger source setting is crucial to using this technique to>> >> compare oscillators. The technique does not require you to display>> two >> channels. What is important is that you display one oscillator>> while >> triggering on the other oscillator. The trigger source can >> be set to:(a) CH 1: The Channel 2 display will drift if the two >> signals have a >> varying phase relationship.(b) CH 2: The Channel 1 display will >> drift>> if the two signals have a >> varying phase relationship.(c) NORM (normal): The trigger >> system gets>> input from the channel being >> displayed at that moment. So in chopped trace display mode the >> trigger is rapidly switched between CH1 and CH2, and in alternate >> trace display mode the trigger alternates between CH1 and CH2 on >> alternate sweeps. In all cases, you should not use NORM trigger >> source with both channels displayed when comparing oscillators!(d)>> EXT: >> You apply the trigger signal to the external trigger input >> connector. This works well well when comparing oscillators. If you>> use >> alternate trace display mode and an external trigger, you can >> compare oscillator#1 (on CH 1) to oscillator#0 (on the external >> trigger input) while you are also comparing oscillator#2 (on CH2) >> oscillator#0. So you could compare two oscillators (one on CH1 and>> the >> other on CH2) to a GPSDO (on the external trigger input). >> (4) When comparing oscillators, the fractional frequency difference >> (such as ppm Parts Per Million or ppb Parts Per Billion) you can >> measure depends on the oscilloscope sweep rate. What you are really>> >> measuring is the drift of the time delay between the edge (or zero>> >> crossing of a sine wave) of one signal relative to an edge or zero>> >> crossing of another signal. The relationship
Re: [time-nuts] A silly question ...
This is assuming that your oscilloscope is set at 100 nS/DIV. My Tek 2465A will sweep at 5 nS/DIV normally, and 500 pS/DIV when the sweep is set to X10. If I'm figuring correctly, this will allow 1e-12 in 432 seconds. I use a stop watch to time the zero crossings of the sine wave - something like: Assuming the wave moved 5 divisions in 185 seconds: (500 pS * 5 DIV)/185 seconds = 13.5e-12 ppm. (I think this is correct. tvb?) Since a 10 MHz sine wave tends to look like a flat line at 500 pS/DIV, I often set the vertical V/DIV to 2 mV/DIV. Tom From: Tom Van Baak To: Discussion of precise time and frequency measurement Sent: Thursday, September 27, 2018 11:19 AM Subject: Re: [time-nuts] A silly question ... > "I think", that if for example, it takes 1 second to drift one cycle, > that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it > takes 5 seconds, it's 0.02 ppm etc. Is that correct? Yes. At 10 MHz one full cycle is 100 ns. So if the cycles are drifting by 100 ns per second that's 100e-9 s / 1 s = 1e-7 = 0.1 ppm. At these levels of frequency accuracy, using a 'scope is plenty good enough. In fact, it's more educational and somehow more enjoyable to watch analog sinewaves drift past each other than it is to see the digital display of boring frequency counter. Where the 'scope method starts to break down is when the frequency error gets down to the ppb level. At 1e-9 it will take 100 s for the waveforms to drift by one cycle. And at 1e-12 you would have to wait an entire day (100 ns / 86400 s = 1.157e-12). On the other hand, with frequency offsets this low you don't have to sit there the whole time. One trick would be to take a photo of the 'scope once an hour, or, say, once every 1000 s. If you played that back at 1 fps you'd have a 1000x "time magnifier". /tvb ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A silly question ...
Hi, There is one other issue that can bite you if you fail to properly terminate the output of a source: Depending on the source's design, an essentially unloaded output can have a substantially higher voltage swing than expected (by 2X if the source impedance is actually 50 ohms), possibly leading to the output stage's going into clipping, which can in turn distort the timing, possibly even in an unstable manner. So if you want to play the "unterminated game", at least take a look at the waveform to be sure it's still a clean sinewave. I've noticed such distortion on my PRS-10, for example, although I've seen no evidence of unstable timing results. But in this arena, it generally pays to be fussy. Dana Whitlow On Fri, Sep 28, 2018 at 7:06 AM Bill Byrom wrote: > On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote: > > Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having> > the output of the OCXO on Ch2, the resulting display on Ch2 of course> > drifts in relation to the static waveform on Ch1. (Both nice > > sinusoids.) > The Tek 465 analog cathode ray oscilloscope was/is a very flexible > instrument. But this flexibility allows you to set up the instrument in > ways which will not allow this commonly used oscillator comparison > technique to work correctly. Since you are interested in these > instruments, here are some details about setting up the instrument for > such comparisons. > (1) The Tek 465 is not a dual beam oscilloscope. Dual beam oscilloscopes > (such as the Tektronix 556 and 7844) use a special CRT which > incorporates two independent electron guns. Each electron gun > assembly has a set of vertical and horizontal deflection plates. > There are two vertical amplifiers (one for each electron gun) and > two horizontal sweep systems (one for each electron gun). If you had > a dual beam oscilloscope you could compare oscillator#1 to > oscillator#2 while simultaneously comparing oscillator#3 with > oscillator#4. It's like having two independent oscilloscopes sharing > the same CRT display. > (2) The Tek 465 single beam oscilloscope can display two traces on the > display using one of two methods:(a) Chopped trace display: This mode > works well at low sweep rates (such > as 1 ms/div) but causes trouble at fast sweep rates (such as 1 > us/div). The displayed trace is switched between Channel 1 and > Channel 2 at a fixed rate of about 500 kHz.(b) Alternate trace > display: This mode works well at high sweep rates > but is hard to see at low sweep rates. The scope alternates between > displaying one sweep of Channel 1 and one sweep of Channel 2. > (3) The trigger source setting is crucial to using this technique to > compare oscillators. The technique does not require you to display > two channels. What is important is that you display one oscillator > while triggering on the other oscillator. The trigger source can > be set to:(a) CH 1: The Channel 2 display will drift if the two > signals have a > varying phase relationship.(b) CH 2: The Channel 1 display will drift > if the two signals have a > varying phase relationship.(c) NORM (normal): The trigger system gets > input from the channel being > displayed at that moment. So in chopped trace display mode the > trigger is rapidly switched between CH1 and CH2, and in alternate > trace display mode the trigger alternates between CH1 and CH2 on > alternate sweeps. In all cases, you should not use NORM trigger > source with both channels displayed when comparing oscillators!(d) > EXT: You apply the trigger signal to the external trigger input > connector. This works well well when comparing oscillators. If you > use alternate trace display mode and an external trigger, you can > compare oscillator#1 (on CH 1) to oscillator#0 (on the external > trigger input) while you are also comparing oscillator#2 (on CH2) > oscillator#0. So you could compare two oscillators (one on CH1 and > the other on CH2) to a GPSDO (on the external trigger input). > (4) When comparing oscillators, the fractional frequency difference > (such as ppm Parts Per Million or ppb Parts Per Billion) you can > measure depends on the oscilloscope sweep rate. What you are really > measuring is the drift of the time delay between the edge (or zero > crossing of a sine wave) of one signal relative to an edge or zero > crossing of another signal. The relationship is: > Fractional difference = (observed timing change) / (measurement > interval)Here are some examples: > Fractional difference in ppm = (time delay drift in us) per second of > observation timeFractional difference in ppb = (time delay drift in ns) > per second of > observation time > (5) As you can see in my previous section, you need a very fast sweep > rate (small time/div) to measure small fractional frequency > differences. This means
Re: [time-nuts] A silly question ...
On Thu, Sep 27, 2018, at 11:55 AM, Dave B via time-nuts wrote: > Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having> the > output of the OCXO on Ch2, the resulting display on Ch2 of course> drifts in > relation to the static waveform on Ch1. (Both nice > sinusoids.) The Tek 465 analog cathode ray oscilloscope was/is a very flexible instrument. But this flexibility allows you to set up the instrument in ways which will not allow this commonly used oscillator comparison technique to work correctly. Since you are interested in these instruments, here are some details about setting up the instrument for such comparisons. (1) The Tek 465 is not a dual beam oscilloscope. Dual beam oscilloscopes (such as the Tektronix 556 and 7844) use a special CRT which incorporates two independent electron guns. Each electron gun assembly has a set of vertical and horizontal deflection plates. There are two vertical amplifiers (one for each electron gun) and two horizontal sweep systems (one for each electron gun). If you had a dual beam oscilloscope you could compare oscillator#1 to oscillator#2 while simultaneously comparing oscillator#3 with oscillator#4. It's like having two independent oscilloscopes sharing the same CRT display. (2) The Tek 465 single beam oscilloscope can display two traces on the display using one of two methods:(a) Chopped trace display: This mode works well at low sweep rates (such as 1 ms/div) but causes trouble at fast sweep rates (such as 1 us/div). The displayed trace is switched between Channel 1 and Channel 2 at a fixed rate of about 500 kHz.(b) Alternate trace display: This mode works well at high sweep rates but is hard to see at low sweep rates. The scope alternates between displaying one sweep of Channel 1 and one sweep of Channel 2. (3) The trigger source setting is crucial to using this technique to compare oscillators. The technique does not require you to display two channels. What is important is that you display one oscillator while triggering on the other oscillator. The trigger source can be set to:(a) CH 1: The Channel 2 display will drift if the two signals have a varying phase relationship.(b) CH 2: The Channel 1 display will drift if the two signals have a varying phase relationship.(c) NORM (normal): The trigger system gets input from the channel being displayed at that moment. So in chopped trace display mode the trigger is rapidly switched between CH1 and CH2, and in alternate trace display mode the trigger alternates between CH1 and CH2 on alternate sweeps. In all cases, you should not use NORM trigger source with both channels displayed when comparing oscillators!(d) EXT: You apply the trigger signal to the external trigger input connector. This works well well when comparing oscillators. If you use alternate trace display mode and an external trigger, you can compare oscillator#1 (on CH 1) to oscillator#0 (on the external trigger input) while you are also comparing oscillator#2 (on CH2) oscillator#0. So you could compare two oscillators (one on CH1 and the other on CH2) to a GPSDO (on the external trigger input). (4) When comparing oscillators, the fractional frequency difference (such as ppm Parts Per Million or ppb Parts Per Billion) you can measure depends on the oscilloscope sweep rate. What you are really measuring is the drift of the time delay between the edge (or zero crossing of a sine wave) of one signal relative to an edge or zero crossing of another signal. The relationship is: Fractional difference = (observed timing change) / (measurement interval)Here are some examples: Fractional difference in ppm = (time delay drift in us) per second of observation timeFractional difference in ppb = (time delay drift in ns) per second of observation time (5) As you can see in my previous section, you need a very fast sweep rate (small time/div) to measure small fractional frequency differences. This means that for a small fractional frequency difference with a moderately low measured oscillator frequency (such as 1 MHz), you may not see any edges for a long time when you use a small time/div. The Tek 465 has a delayed timebase, and you can use this feature to move the signal edge (or zero crossing) onto the screen. You can then watch the signal for a few seconds to determine the timing drift rate. If the edge is drifting at 10 ns per 10 seconds, the fractional difference is 1 ppb (1 part in 10^9). If the displayed oscillator edge is drifting to the left (earlier in time), the displayed oscillator frequency is higher than the reference oscillator you are using for the trigger. If the displayed oscillator edge is drifting to the right (later in time), the displayed oscillator frequency is lower than the reference oscillator you are using
Re: [time-nuts] A silly question ...
This works for me: 1. 10 Mhz to be measured input to vertical channel 2. Standard input to ext trig. 3. Set scope for 10 ns per div. (1 cycle of 10 Mhz will fill up whole screen) 4 Time the time it takes for trace to move 1 div. (not the whole cycle - just one of its sides.) 5. Divide these seconds into 1x10-8 using your calculator. ( I set 1x10-8 into one of the memories) 6. The answer will give you your offset. 7. Example: If it takes 20 seconds for one of the sides of the cycle to move, your offset is 5x10-10. It does not take all day to get a reading, 73 Bill, WA2DVU Cape May -Original Message- From: time-nuts On Behalf Of Tom Van Baak Sent: Thursday, September 27, 2018 2:18 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] A silly question ... > "I think", that if for example, it takes 1 second to drift one cycle, > that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it > takes 5 seconds, it's 0.02 ppm etc. Is that correct? Yes. At 10 MHz one full cycle is 100 ns. So if the cycles are drifting by 100 ns per second that's 100e-9 s / 1 s = 1e-7 = 0.1 ppm. At these levels of frequency accuracy, using a 'scope is plenty good enough. In fact, it's more educational and somehow more enjoyable to watch analog sinewaves drift past each other than it is to see the digital display of boring frequency counter. Where the 'scope method starts to break down is when the frequency error gets down to the ppb level. At 1e-9 it will take 100 s for the waveforms to drift by one cycle. And at 1e-12 you would have to wait an entire day (100 ns / 86400 s = 1.157e-12). On the other hand, with frequency offsets this low you don't have to sit there the whole time. One trick would be to take a photo of the 'scope once an hour, or, say, once every 1000 s. If you played that back at 1 fps you'd have a 1000x "time magnifier". /tvb ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A silly question ...
> "I think", that if for example, it takes 1 second to drift one cycle, > that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it > takes 5 seconds, it's 0.02 ppm etc. Is that correct? Yes. At 10 MHz one full cycle is 100 ns. So if the cycles are drifting by 100 ns per second that's 100e-9 s / 1 s = 1e-7 = 0.1 ppm. At these levels of frequency accuracy, using a 'scope is plenty good enough. In fact, it's more educational and somehow more enjoyable to watch analog sinewaves drift past each other than it is to see the digital display of boring frequency counter. Where the 'scope method starts to break down is when the frequency error gets down to the ppb level. At 1e-9 it will take 100 s for the waveforms to drift by one cycle. And at 1e-12 you would have to wait an entire day (100 ns / 86400 s = 1.157e-12). On the other hand, with frequency offsets this low you don't have to sit there the whole time. One trick would be to take a photo of the 'scope once an hour, or, say, once every 1000 s. If you played that back at 1 fps you'd have a 1000x "time magnifier". /tvb ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A silly question ...
Even with a DSO, if you sync to the Thunderbolt output, you can watch the free running osc drift relative to the Thunderbolt. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A silly question ...
Correct. David N1HAC On 9/27/18 12:55 PM, Dave B via time-nuts wrote: > ... Because I'm sure I should be able to figure this out for myself! > > I have (as many of you do also) one of the venerable Trimble Thunderbolt > devices. No problem with that. All works fine, and is run 24/7, UPS > backup power and all... > > I also have (again, as many of you do...) a free running OCXO for 10MHz > used for "other" stuff etc. Also left running for long periods, but > only when I want to experiment with other stuff and don't want to > disturb what the TB is keeping sane.. > > Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having > the output of the OCXO on Ch2, the resulting display on Ch2 of course > drifts in relation to the static waveform on Ch1. (Both nice sinusoids.) > > If I time how long it takes for the OCXO to drift through one full cycle > (co-incidence to co-incidence) relative to the TB on Ch1, how exactly do > I turn that time, and knowing the base frequency of the TB at 10MHz, > into a ppm discrepancy? > > "I think", that if for example, it takes 1 second to drift one cycle, > that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it > takes 5 seconds, it's 0.02 ppm etc. Is that correct? > > If not, please feel free to educate me! > > As I said, a silly question that I'm sure I would have answered myself a > few decades ago, but age and medication etc... > > Interestingly, after "a lot" of googling, I see that anything like this > using "analogue" or "CRT" scopes, has fallen off the radar and the > interweb, and some of the practices using digital oscilloscopes seem to > rely on the instrument itself to make the measurement, rather than from > "observation" and common sense. (That I seem to lack at times too!) > > But I did get diverted into reading up on some of the early history of > CRO's. > > Regards to All. > > Dave B. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] A silly question ...
... Because I'm sure I should be able to figure this out for myself! I have (as many of you do also) one of the venerable Trimble Thunderbolt devices. No problem with that. All works fine, and is run 24/7, UPS backup power and all... I also have (again, as many of you do...) a free running OCXO for 10MHz used for "other" stuff etc. Also left running for long periods, but only when I want to experiment with other stuff and don't want to disturb what the TB is keeping sane.. Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having the output of the OCXO on Ch2, the resulting display on Ch2 of course drifts in relation to the static waveform on Ch1. (Both nice sinusoids.) If I time how long it takes for the OCXO to drift through one full cycle (co-incidence to co-incidence) relative to the TB on Ch1, how exactly do I turn that time, and knowing the base frequency of the TB at 10MHz, into a ppm discrepancy? "I think", that if for example, it takes 1 second to drift one cycle, that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it takes 5 seconds, it's 0.02 ppm etc. Is that correct? If not, please feel free to educate me! As I said, a silly question that I'm sure I would have answered myself a few decades ago, but age and medication etc... Interestingly, after "a lot" of googling, I see that anything like this using "analogue" or "CRT" scopes, has fallen off the radar and the interweb, and some of the practices using digital oscilloscopes seem to rely on the instrument itself to make the measurement, rather than from "observation" and common sense. (That I seem to lack at times too!) But I did get diverted into reading up on some of the early history of CRO's. Regards to All. Dave B. -- Created on and sent from a Unix like PC running and using free and open source software. :: ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
