Bruce, At 3:54 AM +0000 12/19/08, time-nuts-request@febo.com wrote: > >Message: 6 >Date: Fri, 19 Dec 2008 16:54:12 +1300 >From: Bruce Griffiths <bruce.griffiths@xtra.co.nz> >Subject: Re: [time-nuts] Sub Pico Second Phase logger >To: Discussion of precise time and frequency measurement > <time-nuts@febo.com> > >Joe >Joe Gwinn wrote: >> This is from home. I'll not be at work until next year. >> >> At 11:48 PM +0000 12/18/08, time-nuts-request@febo.com wrote: >> >>> Message: 4 >>> Date: Fri, 19 Dec 2008 12:17:33 +1300 >>> From: Bruce Griffiths <bruce.griffiths@xtra.co.nz> >>> Subject: Re: [time-nuts] Sub Pico Second Phase logger >>> To: Discussion of precise time and frequency measurement > >> <time-nuts@febo.com> > >> >>> Joe >>> >>> >>> >>> > >> >[snip] > >> >> Sources: >>> >>>>> 1) Wien bridge or equivalent (eg state variable oscillator with soft >>>>> clamping) relatively low distortion oscillator. >>>>> >>>>> 2) Buffered low pass filtered output of binary divider driven by a >>>>> crystal oscillator >>>>> >>>>> >>> > RC oscillator sounds far simpler and more flexible. >>> >>> A Wien bridge using a lamp is perhaps the simplest. >>> I'll create a circuit schematics for this using an OPA2134 (dual lowish >>> noise JFET opamp). >>> One opamp for the oscillator one to drive the sound card (attenuation of >>> the oscillator output will be required for some sound cards and it is >>> desirable to have a low output impedance driver). >>> >> >> Jim Williams of Linear Technology had a very good low-distortion AGC >> controlled Wein Bridge oscillator. If I recall, he used a photo-FET >> or the like as the servoed resistor in the bridge. There may be an >> application note on the LT website, but I saw it in a chapter of a >> book on analog circuitry, the chapter author being Jim W. >> >> >> >I have the application note. LT App Note 43 is what JW mentions. Figure 47 is the key. (He also mentions App Note 5.) These cites are from the refs of "Max Wien, Mr. Hewlett, and a Rainy Sunday Afternoon", Jim Williams, Chapter 7 in "Analog Circuit Design -- Art, Science, and Personalities, edited by Jim Williams, Butterworth-Heinemann 1991. The relevant section of App Note 43 seems to be shared with this chapter. It wasn't a photo-FET he used, it was a Vactec model VTL5C10 optically (LED) driven CdS photocell. Most of it is here (what's missing is some history and the refs): <http://books.google.com/books?id=Il4xxTTyhbEC&pg=PA43&lpg=PA43&dq=Max+Wien,+Mr.+Hewlett,+and+a+Rainy+Sunday+Afternoon&source=bl&ots=jnHNItJrOF&sig=ZL_CB_yIdT0ZbsD7Ieu_CjVYJHk&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA53,M1>. > >> For an AP192 the directly (without sample rate interpolation) available >>> output sample rates are: >>> >>> 192, 96, 64, 48, 32, 8 KSPS. >>> >> >> OK. I would start with 8 ksps. We will end up decimating below that >> anyway, except for 1 KHz test signals. >> >> >> Joe >> >> >I'll breadboard an oscillator over the holidays and take some samples. A rainy-day activity for sure. In the Boston area, the issue is snow - a noreaster is just now starting, with a foot of snow expected. Joe

<time-nuts@febo.com>

Joe Joe Gwinn wrote: > Bruce, > > At 3:54 AM +0000 12/19/08, time-nuts-request@febo.com wrote: > >> Message: 6 >> Date: Fri, 19 Dec 2008 16:54:12 +1300 >> From: Bruce Griffiths <bruce.griffiths@xtra.co.nz> >> Subject: Re: [time-nuts] Sub Pico Second Phase logger >> To: Discussion of precise time and frequency measurement >> <time-nuts@febo.com> >> >> Joe >> Joe Gwinn wrote: >> >>> This is from home. I'll not be at work until next year. >>> >>> At 11:48 PM +0000 12/18/08, time-nuts-request@febo.com wrote: >>> >>> >>>> Message: 4 >>>> Date: Fri, 19 Dec 2008 12:17:33 +1300 >>>> From: Bruce Griffiths <bruce.griffiths@xtra.co.nz> >>>> Subject: Re: [time-nuts] Sub Pico Second Phase logger >>>> To: Discussion of precise time and frequency measurement >>>> >> >> <time-nuts@febo.com> >> >> >> >>>> Joe >>>> >>>> >>>> >>> >>>> >> >> >> [snip] >> >> >> Sources: >> >>>> >>>> >>>>>> 1) Wien bridge or equivalent (eg state variable oscillator with soft >>>>>> clamping) relatively low distortion oscillator. >>>>>> >>>>>> 2) Buffered low pass filtered output of binary divider driven by a >>>>>> crystal oscillator >>>>>> >>>>>> >>>>>> >>>> > RC oscillator sounds far simpler and more flexible. >>>> >>>> A Wien bridge using a lamp is perhaps the simplest. >>>> I'll create a circuit schematics for this using an OPA2134 (dual lowish >>>> noise JFET opamp). >>>> One opamp for the oscillator one to drive the sound card (attenuation of >>>> the oscillator output will be required for some sound cards and it is >>>> desirable to have a low output impedance driver). >>>> >>>> >>> Jim Williams of Linear Technology had a very good low-distortion AGC >>> controlled Wein Bridge oscillator. If I recall, he used a photo-FET >>> or the like as the servoed resistor in the bridge. There may be an >>> application note on the LT website, but I saw it in a chapter of a >>> book on analog circuitry, the chapter author being Jim W. >>> >>> >>> >>> >> I have the application note. >> > > LT App Note 43 is what JW mentions. Figure 47 is the key. (He also > mentions App Note 5.) > > These cites are from the refs of "Max Wien, Mr. Hewlett, and a Rainy > Sunday Afternoon", Jim Williams, Chapter 7 in "Analog Circuit Design > -- Art, Science, and Personalities, edited by Jim Williams, > Butterworth-Heinemann 1991. The relevant section of App Note 43 > seems to be shared with this chapter. > > It wasn't a photo-FET he used, it was a Vactec model VTL5C10 > optically (LED) driven CdS photocell. > > Note for those (in Australia, NZ and Europe) who may want to replicate that oscillator: The VTL5C10 device is obtainable locally from RS Components. > Most of it is here (what's missing is some history and the refs): > <http://books.google.com/books?id=Il4xxTTyhbEC&pg=PA43&lpg=PA43&dq=Max+Wien,+Mr.+Hewlett,+and+a+Rainy+Sunday+Afternoon&source=bl&ots=jnHNItJrOF&sig=ZL_CB_yIdT0ZbsD7Ieu_CjVYJHk&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA53,M1>. > > > >> >> For an AP192 the directly (without sample rate interpolation) available >> >>>> output sample rates are: >>>> >>>> 192, 96, 64, 48, 32, 8 KSPS. >>>> >>>> >>> OK. I would start with 8 ksps. We will end up decimating below that >>> anyway, except for 1 KHz test signals. >>> >>> >>> Joe >>> >>> >>> >> I'll breadboard an oscillator over the holidays and take some samples. >> > > A rainy-day activity for sure. In the Boston area, the issue is > snow - a noreaster is just now starting, with a foot of snow expected. > > Joe > > AFAIK it has never snowed here. It does snow on the central NI Plateau but not usually in December. I'll start with a diode limited (soft clamps - resistance in series with diodes) oscillator and move to a lower distortion one if necessary. Bruce

Joe, I have been following this thread from the start & learned a lot from it. Thanks to you and Bruce for the insights. I thought I would take a look at a simple, passive approach, just to see what happens. I also limited my attention to stable 5 or 10 MHz sources & observation windows of <100s. I used a Mini-circuits SYPD-1 PD with a PSCQ-2-10.5 90 deg hybrid plus an ATM P1506 phase shifter (delta=0.32ns). There are lots of other items which will work just as well, this stuff happens to be on hand. The SYPD-1 also needs a diplexer to terminate the high order products & low pass filter the desired output; this is a cobble together item from the parts box. I used a PC logging program with my HP 3478A to take DC readings from the diplexer output. Thus armed, I first checked the DVM logging with no RF in to see if it was stable enough to yield a useable noise floor. This first result was good enough. Reading 720 points over 100 seconds; the data was limited to -1, 0 or +1 uV. Then I applied 10MHz @ to the 90 deg hybrid & connected one hybrid output to the SYPD-1 LO & the other hybrid output to the ATM P1506. The ATM output then drives the SYPD-1 RF port. I measured both SYPD-1 inputs to be +6.4dBm. Now I was able to set the ATM phase to zero the SYPD-1 output & verify it was stable over the 100s time I was interested in. The 3478A readings ranged from -1 to +2uV during this time with STDDEV of 0.6uV -again, good enough for me. Finally, I used a HP 105B to get a quiet 5MHz source & a 1MHz ext. reference for my HP3336C sythesizer. All this to give me 2 "nearly" identical. phase locked sources to measure the calibration factor of the SYPD-1/Diplexer output. The 3336C was set to 5,000,000.005Hz & +6.4dBm driving the SYPD-1 LO port. The 105B 5MHz output was attenuated to +6.4dBm driving the RF port. The resulting 5mHz data was logged & analyzed at the zero crossings (max gain). The result is a phase sensitivity of 1.22uRad/uV. The + & - zero crossings were identical and the 1.22uRad/uV factor is linear (+/- 2 %) up to +/- 20 % of FS. FS = 1.023V If my math is about right, @10MHz, 1uRad = 16fs; so a noise floor of +/- 2uV (+/-2.5uRad) equals +/-40fs. I expect that, if 2 sources are near zero phase, then it should only require <10s to estimate the actual phase error within 1ps, or less. Anyone agree? I await & hope for constructive comments and/or corrections. Pete Rawson

Pete Pete wrote: > Joe, > > I have been following this thread from the start & learned a lot from it. > > Thanks to you and Bruce for the insights. > > I thought I would take a look at a simple, passive approach, just to > see what happens. I also limited my attention to stable 5 or 10 MHz > sources & observation windows of <100s. I used a Mini-circuits > SYPD-1 PD with a PSCQ-2-10.5 90 deg hybrid plus an ATM > P1506 phase shifter (delta=0.32ns). There are lots of other items > which will work just as well, this stuff happens to be on hand. > > The SYPD-1 also needs a diplexer to terminate the high order > products & low pass filter the desired output; this is a cobble > together item from the parts box. I used a PC logging program > with my HP 3478A to take DC readings from the diplexer output. > > The use of a diplexer perpetuates a common fallacy. You get significantly lower noise with a capacitive IF port termination. This is true even in the microwave region when reflecting the sum frequency back into the mixer reduces the noise. At low frequencies this has little effect on the Rf and LO port VSWR. The capacitive termination limits the IF port bandwidth to a few tens of kHz and a 50 ohm termination is more useful if an IF bandwidth of several MHz is desired. > Thus armed, I first checked the DVM logging with no RF in to see > if it was stable enough to yield a useable noise floor. This first result > was good enough. Reading 720 points over 100 seconds; the data > was limited to -1, 0 or +1 uV. > > Then I applied 10MHz @ to the 90 deg hybrid & connected one > hybrid output to the SYPD-1 LO & the other hybrid output to the > ATM P1506. The ATM output then drives the SYPD-1 RF port. > I measured both SYPD-1 inputs to be +6.4dBm. Now I was able > to set the ATM phase to zero the SYPD-1 output & verify it was > stable over the 100s time I was interested in. The 3478A readings > ranged from -1 to +2uV during this time with STDDEV of 0.6uV > -again, good enough for me. > Can you produce ADEV and MDEV plots for tau up to 1000sec or more? This would then give us some idea of the noise floor of your setup. SDEV by itself can be very misleading as for some noise processes it diverges. The RPD and MPD series are better, in that they allow low frequency isolation of the RF, LO and IF port grounds. This can be critical for low offset frequency measurements. > Finally, I used a HP 105B to get a quiet 5MHz source & a 1MHz > ext. reference for my HP3336C sythesizer. All this to give me 2 > "nearly" identical. phase locked sources to measure the calibration > factor of the SYPD-1/Diplexer output. The 3336C was set to > 5,000,000.005Hz & +6.4dBm driving the SYPD-1 LO port. The > 105B 5MHz output was attenuated to +6.4dBm driving the RF > port. The resulting 5mHz data was logged & analyzed at the zero > crossings (max gain). The result is a phase sensitivity of 1.22uRad/uV. > The + & - zero crossings were identical and the 1.22uRad/uV factor > is linear (+/- 2 %) up to +/- 20 % of FS. FS = 1.023V > > If my math is about right, @10MHz, 1uRad = 16fs; so a noise floor > of +/- 2uV (+/-2.5uRad) equals +/-40fs. I expect that, if 2 sources > are near zero phase, then it should only require <10s to estimate > the actual phase error within 1ps, or less. Anyone agree? > > I await & hope for constructive comments and/or corrections. > > Pete Rawson > > At 10MHz 1 radian = 16ns 1 millirad = 16 ps. 1urad = 16fs. It would be more useful if you logged the DVM readings for an hour or more so that ADEV, MDEV plots can be produced. Eyeballing the data doesnt always deliver the full story. If one compares a couple of oscillators one has to be very careful to ensure that inadvertent injection locking isn't occuring. This can happen with almost imperceptible coupling if the oscillators are very close in frequency. You need to use very high reverse isolation ( ideally 150dB or more) buffer amplifiers to ensure this doesnt occur. The first test you made only indicates the system noise floor. When the mixer/phase detector is driven by 2 different oscillators the noise level will be much higher that the noise level of the mixer system itself. In fact practically all OCXOs will/should be much noisier. If the noise is too low this is an indication of injection locking. One thing to watch out for is the measurement system noise bandwidth. You need to know this as ADEV, MDEV etc depend on the actual noise bandwidth. When you use a DVM it usually has built in low pass filtering as well as its inherent sinc response due to the integration process. It can be useful to use external passive components to accurately define the noise response. Bruce

Pete Another very useful thing to do is to measure the output noise spectrum at the of mixer port both with capacitive termination and with a diplexer. You can do this with your PC sound card system (even the motherboard one) and a low noise preamp. If you want a simple low noise preamp circuit I can supply several. The gain required depends on the sound card depends on the sound cards internal noise level. One way is to drive the RF and LO ports with quadrature phase signals and measure the IF spectrum. Another is to just drive the LO port and look at the IF port spectrum. Try both with the Rf port open circuit and terminated in 50 ohms. Once you've obtained spectra posting them would be useful and informative. Bruce Bruce Griffiths wrote: > Pete > > Pete wrote: > >> Joe, >> >> I have been following this thread from the start & learned a lot from it. >> >> Thanks to you and Bruce for the insights. >> >> I thought I would take a look at a simple, passive approach, just to >> see what happens. I also limited my attention to stable 5 or 10 MHz >> sources & observation windows of <100s. I used a Mini-circuits >> SYPD-1 PD with a PSCQ-2-10.5 90 deg hybrid plus an ATM >> P1506 phase shifter (delta=0.32ns). There are lots of other items >> which will work just as well, this stuff happens to be on hand. >> >> The SYPD-1 also needs a diplexer to terminate the high order >> products & low pass filter the desired output; this is a cobble >> together item from the parts box. I used a PC logging program >> with my HP 3478A to take DC readings from the diplexer output. >> >> >> > The use of a diplexer perpetuates a common fallacy. > You get significantly lower noise with a capacitive IF port termination. > This is true even in the microwave region when reflecting the sum > frequency back into the mixer reduces the noise. > At low frequencies this has little effect on the Rf and LO port VSWR. > The capacitive termination limits the IF port bandwidth to a few tens of > kHz and a 50 ohm termination is more useful if an IF bandwidth of > several MHz is desired. > >> Thus armed, I first checked the DVM logging with no RF in to see >> if it was stable enough to yield a useable noise floor. This first result >> was good enough. Reading 720 points over 100 seconds; the data >> was limited to -1, 0 or +1 uV. >> >> Then I applied 10MHz @ to the 90 deg hybrid & connected one >> hybrid output to the SYPD-1 LO & the other hybrid output to the >> ATM P1506. The ATM output then drives the SYPD-1 RF port. >> I measured both SYPD-1 inputs to be +6.4dBm. Now I was able >> to set the ATM phase to zero the SYPD-1 output & verify it was >> stable over the 100s time I was interested in. The 3478A readings >> ranged from -1 to +2uV during this time with STDDEV of 0.6uV >> -again, good enough for me. >> >> > Can you produce ADEV and MDEV plots for tau up to 1000sec or more? > This would then give us some idea of the noise floor of your setup. > SDEV by itself can be very misleading as for some noise processes it > diverges. > The RPD and MPD series are better, in that they allow low frequency > isolation of the RF, LO and IF port grounds. > This can be critical for low offset frequency measurements. > > >> Finally, I used a HP 105B to get a quiet 5MHz source & a 1MHz >> ext. reference for my HP3336C sythesizer. All this to give me 2 >> "nearly" identical. phase locked sources to measure the calibration >> factor of the SYPD-1/Diplexer output. The 3336C was set to >> 5,000,000.005Hz & +6.4dBm driving the SYPD-1 LO port. The >> 105B 5MHz output was attenuated to +6.4dBm driving the RF >> port. The resulting 5mHz data was logged & analyzed at the zero >> crossings (max gain). The result is a phase sensitivity of 1.22uRad/uV. >> The + & - zero crossings were identical and the 1.22uRad/uV factor >> is linear (+/- 2 %) up to +/- 20 % of FS. FS = 1.023V >> >> If my math is about right, @10MHz, 1uRad = 16fs; so a noise floor >> of +/- 2uV (+/-2.5uRad) equals +/-40fs. I expect that, if 2 sources >> are near zero phase, then it should only require <10s to estimate >> the actual phase error within 1ps, or less. Anyone agree? >> >> I await & hope for constructive comments and/or corrections. >> >> Pete Rawson >> >> >> > At 10MHz 1 radian = 16ns > 1 millirad = 16 ps. > 1urad = 16fs. > > It would be more useful if you logged the DVM readings for an hour or > more so that ADEV, MDEV plots can be produced. > Eyeballing the data doesnt always deliver the full story. > > If one compares a couple of oscillators one has to be very careful to > ensure that inadvertent injection locking isn't occuring. > This can happen with almost imperceptible coupling if the oscillators > are very close in frequency. > You need to use very high reverse isolation ( ideally 150dB or more) > buffer amplifiers to ensure this doesnt occur. > > The first test you made only indicates the system noise floor. > When the mixer/phase detector is driven by 2 different oscillators the > noise level will be much higher that the noise level of the mixer system > itself. > In fact practically all OCXOs will/should be much noisier. > If the noise is too low this is an indication of injection locking. > > One thing to watch out for is the measurement system noise bandwidth. > You need to know this as ADEV, MDEV etc depend on the actual noise > bandwidth. > When you use a DVM it usually has built in low pass filtering as well as > its inherent sinc response due to the integration process. > It can be useful to use external passive components to accurately define > the noise response. > > 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. > >