[time-nuts] Re: First PN measurement results at 1 Hz to 20 kHz from carrier
Hi, On 2022-06-27 18:06, Bob kb8tq via time-nuts wrote: Hi On Jun 27, 2022, at 1:43 AM, Erik Kaashoek via time-nuts wrote: Magnus, Bob, When the mixer is operating in the linear region for the DUT input (0dBm or lower), would it be possible to use a calibrated noise sources to do an extra verification of the noise level measurement? Of course with a noise source you get 3dB as both sidebands fold. The “normal” approach is to put the mixer into saturation. This gives you the best noise floor. It also does a bit better at separating AM noise from PM noise (since you are trying to measure phase noise …..). It could be worth mentioning that there are both linear and non-linear AM->PM conversion as well as PM->AM conversion. They *should* be perfectly separate, but real life circuits is unable to maintain perfect symmetry. Now, the AM noise tends to be stronger than the PM noise, so leakage tends to be more severe in that direction, in that it causes more harm. Running the signal into clipping is a non-linear way to cut away most of the AM and maintain the PM, and such limiter detectors turns out to be very good for FM reception (FM is just a variant of PM). Modern high-speed ADC receivers with arctan CORDIC processing has supperiour AM and PM separation and avoids much of those problems. Just for reference, does not help here. A linear filter provides AM->PM conversion when the upper side-band and the lower side-band does not have the same gain for the same offset frequency. This asymmetry converts AM (even) to PM (odd) as well as PM (odd to AM (even), while AM to AM and PM to PM reduces amplitude. Even a simple low-pass filter will do this, and to minimize it's effect the cut-off frequency should be higher than the carrier frequency so it is essentially flat and equal for both LSB and USB. Similarly should a resonator be tuned to be on the carrier frequency, or the upper and lower slopes will not match well. Anyway, wanted to take the opportunity to explain a little more. Verification steps: Verify the DUT output level is correctly brought to 0dB (using attenuators) using a calibrated spectrum analyzer Connect the DUT to the phase measurement setup and set the reference to a 500Hz offset to get a beat note and verify the beat note is registered at 0dB, change the DUT level some dB up and down to confirm its in a linear region. Measure the per Hz output power of a noise source using a calibrated spectrum analyzer and a noise marker set to 10MHz. Connect the noise source to the phase measurement setup and check if the noise level is measured at level measured by the spectrum analyzer + 3dB This should work if the RBW of the phase measurement is indeed set to 1Hz. If you do it this way, you still need to do conversion for the “one radian” reference level that is used with phase modulation ( = the reference is *not* one cycle ). Yes that’s a bit weird / obscure. But then again, it's exactly what the standard says. We even rewrote that section to clarify it. Another verification option may be to use the phase modulation of a signal generator. This can not check the effective noise bandwidth of the FFT but it can check linearity over the whole range. The output of the mixer is terminated with 50ohm so a factor of 10 in voltage should give a 20dB power step. Audio termination at 50 ohms does not do much for isolation. (again a bit of an obscure point). By terminating in 10X the nominal impedance ( so 500 ohms in this case) you get another 6 db of gain in the system. Since this is ahead of the preamp, it might improve your noise floor. You may however want to have 50 Ohm termination for RF frequencies (sum-frequency as well as leakage of carrier frequency). The NIST T&F archive has illustrations of different mixer loading networks such that it is high impedance at LF but low impedance at RF. Loading down the LF which is detected signal makes no sense, as we amplify the voltage and not the power received. We do want to terminate the RF so that it is not reflected back into the mixerin a termal unstable fashion. If the RF termination can be close enough to the mixer, other impedance than 50 Ohm can be considered for even more optimal result, but unless one knows what one does, I'd say stick with 50 Ohms for that is what the mixer is mast likely designed for. Cheers, Magnus Bob When operation in the linear range the phase noise measurement setup should measure 20dB less with every factor 10 reduction in phase modulation depth where 90 degrees is equal to 100% modulation depth so equal to the signal you get when measuring a beat note. When measuring with modulation depth of 90,9,0.9,0.09 and 0.009 degrees the measured level should step from 0,-20,-40, -60 to -80dB Any feedback? Erik. On 26-6-2022 20:52, Magnus Danielson via time-nuts wrote: Hi Erik! Great progress! Sure interesting to look at them phase-noise plots, right? It's a
[time-nuts] Re: Noise down-converter project
It looks identical to my Agilent U1732B, thjough I think the Agilent's spec is poorer. It was replaced by a U1732C which may be closer thjough both are going back a way now. Presumably Agilent badged it and it has continued to improve. I don't know whether there's a corresponding Keysight version. On Mon, Jun 27, 2022 at 11:55 PM Mike Monett via time-nuts < time-nuts@lists.febo.com> wrote: > The Tonghui has arrived. It is ideal for measuring small RF components. It > has a resolution of 100 microohms, 1 nanohenry and 0.001 picofarad. > > There is no need to buy Kelvin clips. It comes with a complete set, > including SMD and ordinary multimeter clips. > > TH2822 series are equipped with the following > contents: > • TH2822/TH2822A/TH2822C handheld LCR meter > • Instruction manual (in Chinese) > • Mini USB Interface Cable > • Short-circuit plate > • *9V Alkaline battery or 8.4 rechargeable battery > • *AC adapter (240V, 4mm) > • *TH26027A Kelvin clip test leads > • *TH26009C SMD test tweezers > • Red / Black Banana plugs—Crocodile clip Test Leads > > It also has a USB interface for data transfer. This requires a special > driver available from www.tonghui.com.cn. > > The only problem is the charger is 240V to 12V with a 4mm connector. This > is a problem for North America customers, but the needed chargers appear to > be available at Amazon. For example, see > > > https://www.amazon.ca/SHNITPWR-Universal-Switching-Adjustable-Transformer/dp/B08N46GMM8/ > > The manual is available all over the place, for example at > > http://file.yzimgs.com/327099/2011101217170714.pdf > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Noise down-converter project
The Tonghui has arrived. It is ideal for measuring small RF components. It has a resolution of 100 microohms, 1 nanohenry and 0.001 picofarad. There is no need to buy Kelvin clips. It comes with a complete set, including SMD and ordinary multimeter clips. TH2822 series are equipped with the following contents: TH2822/TH2822A/TH2822C handheld LCR meter Instruction manual (in Chinese) Mini USB Interface Cable Short-circuit plate *9V Alkaline battery or 8.4 rechargeable battery *AC adapter (240V, 4mm) *TH26027A Kelvin clip test leads *TH26009C SMD test tweezers Red / Black Banana plugsCrocodile clip Test Leads It also has a USB interface for data transfer. This requires a special driver available from www.tonghui.com.cn. The only problem is the charger is 240V to 12V with a 4mm connector. This is a problem for North America customers, but the needed chargers appear to be available at Amazon. For example, see https://www.amazon.ca/SHNITPWR-Universal-Switching-Adjustable-Transformer/dp/B08N46GMM8/ The manual is available all over the place, for example at http://file.yzimgs.com/327099/2011101217170714.pdf ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Noise down-converter project
On Tue, 24 May 2022, I posted the following: Ed, You spoke of difficulty measuring inductors. There are quite a few LCR meters on the market that offer the performance needed in your project. Here are three: 1. TH2822C Handheld LCR Meter counts/Accuracy 0.25%/100Hz,120Hz,1kHz,10kHz,100kHz CAD$293.91 https://www.aliexpress.com/item/32429957886.html - Watch out for counterfeits on asian sites TH2822C Handheld LCR Meter USD$339.00 https://www.amazon.com/TH2822C-Handheld-Meter-Frequency-100kHz/dp/B07H68D1DP TH2822C PORTABLE handheld Pro LCR USD$371.48 eBay item number:281423062278 I elected to buy one from the actual Shenzhen Measuring Instruments Store to avoid counterfeits. When I ordered it, the price was C$433.02. As I was checking for the delivery date, I noticed the price had dropped to C$170.10, a drop of -61%. Shipping is C$40.94 plus duty via DHL. Be advised you will need a cellphone to deal with DHL. This is one of the most powerful handheld LCR bridges on the market with an accuracy of 0.25% and covers the range of 100Hz, 120Hz, 1kHz, 10kHz, and 100kHz. This is one of the largest ranges for this class of instrument and allows you to measure the largest and smallest components available. You can find it at: https://www.aliexpress.com/item/32429957886.html The Kelvin Clips are C$46.22 with free shipping: https://www.aliexpress.com/item/4001038783823.html You need the Kelvin Clips to take advantage of the 0.25% accuracy. A big advantage of the TH2822C is the ability to average the readings, which allows you to take full advantage of the Kelvin Clips. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: First PN measurement results at 1 Hz to 20 kHz from carrier
Hi Erik, On 2022-06-27 11:43, Erik Kaashoek via time-nuts wrote: Magnus, Bob, When the mixer is operating in the linear region for the DUT input (0dBm or lower), would it be possible to use a calibrated noise sources to do an extra verification of the noise level measurement? Yes. NIST build such calibrators for exactly that purpose. Of course with a noise source you get 3dB as both sidebands fold. Naturally. Verification steps: Verify the DUT output level is correctly brought to 0dB (using attenuators) using a calibrated spectrum analyzer Connect the DUT to the phase measurement setup and set the reference to a 500Hz offset to get a beat note and verify the beat note is registered at 0dB, change the DUT level some dB up and down to confirm its in a linear region. Measure the per Hz output power of a noise source using a calibrated spectrum analyzer and a noise marker set to 10MHz. Connect the noise source to the phase measurement setup and check if the noise level is measured at level measured by the spectrum analyzer + 3dB This should work if the RBW of the phase measurement is indeed set to 1Hz. 500 Hz is kind of arbitrary number you chose there. At the very least it should be verified, but I would assume there is an underlying goal which made you choose 500 Hz and that should be specified. The RBW is not the noise BW. You need to correct the bin-bandwidth with the specific noise bandwidth correction for the window-filter you use. There is a neat article [1] on it which I also contributed into IEEE 1139. Another verification option may be to use the phase modulation of a signal generator. This can not check the effective noise bandwidth of the FFT but it can check linearity over the whole range. The output of the mixer is terminated with 50ohm so a factor of 10 in voltage should give a 20dB power step. When operation in the linear range the phase noise measurement setup should measure 20dB less with every factor 10 reduction in phase modulation depth where 90 degrees is equal to 100% modulation depth so equal to the signal you get when measuring a beat note. When measuring with modulation depth of 90,9,0.9,0.09 and 0.009 degrees the measured level should step from 0,-20,-40, -60 to -80dB For higher modulation depth it's very hard to do linear modulation well. There is a different variant you can use, to inject a signal to form a side-band signal next to the carrier. By creating a specific amplitude compared to the carrier, and for a particular offset, it's trivial exercise to know the AM and PM noise level. A single sideband sine will divide equally to AM and PM, thus reducing 3 dB. Thus, setting a side-band at 27 dB bellow the carrier, makes a -30 dBc phase modulation. [1] https://pure.mpg.de/pubman/faces/ViewItemOverviewPage.jsp?itemId=item_152164 Cheers, Magnus Any feedback? Erik. On 26-6-2022 20:52, Magnus Danielson via time-nuts wrote: Hi Erik! Great progress! Sure interesting to look at them phase-noise plots, right? It's a really good tool in addition to the stability of ADEV and friends. As I recall it, the ADE-1 is not documented to be isolated, but it is very obvious when you look down the backside of it. However, it has capacitive coupling and one should consider both common mode rejection and common mode loading it down for these to work well. Word of caution when it comes to levels, as the windowing filter used causes shifts in noise-levels, so estimation of noise-levels becomes a little bit tricky as you try to get the nitty gritty right, but getting the overall shape view you already gained a lot with the things you achieved. A technique used to push further down into lower noise-levels is the cross-correlation technique, where you split the signal into two channels, each being exactly what you have now, and then rather than squaring the output of the FFT from each channel, you multiply one with the completment of the other, then average on those. This allows you to supress the noise of each reference oscillator. You do not have to go there from start, as you already make very useful measurements, but I'm just suggesting what may lie up ahead. Compared to some of the other sources, the Rigol SG does fairly well, but then again, things can be even more quiet. For the XO you can see the 15 dB/Oct slope as expected for flicker frequency. Try to locate the source of the peaks you see and see if you can clean it up. The XO seems to be a fairly good DUT for doing that. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: First PN measurement results at 1 Hz to 20 kHz from carrier
Hi > On Jun 27, 2022, at 1:43 AM, Erik Kaashoek via time-nuts > wrote: > > Magnus, Bob, > When the mixer is operating in the linear region for the DUT input (0dBm or > lower), would it be possible to use a calibrated noise sources to do an > extra verification of the noise level measurement? > Of course with a noise source you get 3dB as both sidebands fold. The “normal” approach is to put the mixer into saturation. This gives you the best noise floor. It also does a bit better at separating AM noise from PM noise (since you are trying to measure phase noise …..). > Verification steps: > Verify the DUT output level is correctly brought to 0dB (using attenuators) > using a calibrated spectrum analyzer > Connect the DUT to the phase measurement setup and set the reference to a > 500Hz offset to get a beat note and verify the beat note is registered at > 0dB, change the DUT level some dB up and down to confirm its in a linear > region. > Measure the per Hz output power of a noise source using a calibrated spectrum > analyzer and a noise marker set to 10MHz. > Connect the noise source to the phase measurement setup and check if the > noise level is measured at level measured by the spectrum analyzer + 3dB > This should work if the RBW of the phase measurement is indeed set to 1Hz. If you do it this way, you still need to do conversion for the “one radian” reference level that is used with phase modulation ( = the reference is *not* one cycle ). Yes that’s a bit weird / obscure. > > Another verification option may be to use the phase modulation of a signal > generator. This can not check the effective noise bandwidth of the FFT but it > can check linearity over the whole range. > The output of the mixer is terminated with 50ohm so a factor of 10 in voltage > should give a 20dB power step. Audio termination at 50 ohms does not do much for isolation. (again a bit of an obscure point). By terminating in 10X the nominal impedance ( so 500 ohms in this case) you get another 6 db of gain in the system. Since this is ahead of the preamp, it might improve your noise floor. Bob > When operation in the linear range the phase noise measurement setup should > measure 20dB less with every factor 10 reduction in phase modulation depth > where 90 degrees is equal to 100% modulation depth so equal to the signal you > get when measuring a beat note. > When measuring with modulation depth of 90,9,0.9,0.09 and 0.009 degrees the > measured level should step from 0,-20,-40, -60 to -80dB > > Any feedback? > Erik. > > On 26-6-2022 20:52, Magnus Danielson via time-nuts wrote: >> Hi Erik! >> >> Great progress! Sure interesting to look at them phase-noise plots, right? >> It's a really good tool in addition to the stability of ADEV and friends. >> >> As I recall it, the ADE-1 is not documented to be isolated, but it is very >> obvious when you look down the backside of it. However, it has capacitive >> coupling and one should consider both common mode rejection and common mode >> loading it down for these to work well. >> >> Word of caution when it comes to levels, as the windowing filter used causes >> shifts in noise-levels, so estimation of noise-levels becomes a little bit >> tricky as you try to get the nitty gritty right, but getting the overall >> shape view you already gained a lot with the things you achieved. >> >> A technique used to push further down into lower noise-levels is the >> cross-correlation technique, where you split the signal into two channels, >> each being exactly what you have now, and then rather than squaring the >> output of the FFT from each channel, you multiply one with the completment >> of the other, then average on those. This allows you to supress the noise of >> each reference oscillator. You do not have to go there from start, as you >> already make very useful measurements, but I'm just suggesting what may lie >> up ahead. >> >> Compared to some of the other sources, the Rigol SG does fairly well, but >> then again, things can be even more quiet. For the XO you can see the 15 >> dB/Oct slope as expected for flicker frequency. Try to locate the source of >> the peaks you see and see if you can clean it up. The XO seems to be a >> fairly good DUT for doing that. >> >> Cheers, >> Magnus > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: TimeProvider 2700 PTP UTC offset issue.
Hi Markus, I've pasted output from some pmc GET commands below, along with show clock on the GM. Seems like the grandmaster is getting 37 from GPS, while announcing 35? Also not sure why TIME_PROPERTIES_DATA_SET has currentUtcOffsetValid and timeTraceable both set to true, but GRANDMASTER_SETTINGS_NP has these set to false. Best, Andrew // andrew@bbb:~$ sudo pmc -u -b 0 'get TIME_PROPERTIES_DATA_SET' sending: GET TIME_PROPERTIES_DATA_SET 94e36d.fffe.d2695e-0 seq 0 RESPONSE MANAGEMENT TIME_PROPERTIES_DATA_SET currentUtcOffset 35 leap61 0 leap59 0 currentUtcOffsetValid 1 ptpTimescale 1 timeTraceable 1 frequencyTraceable 1 timeSource 0x20 andrew@bbb:~$ sudo pmc -u -b 0 'get PARENT_DATA_SET' sending: GET PARENT_DATA_SET 94e36d.fffe.d2695e-0 seq 0 RESPONSE MANAGEMENT PARENT_DATA_SET parentPortIdentity 00b0ae.fffe.0357ef-2 parentStats 0 observedParentOffsetScaledLogVariance 0x observedParentClockPhaseChangeRate 0x7fff grandmasterPriority1 128 gm.ClockClass 6 gm.ClockAccuracy 0x21 gm.OffsetScaledLogVariance 0x6400 grandmasterPriority2 128 grandmasterIdentity 00b0ae.fffe.0357ef andrew@bbb:~$ sudo pmc -u -b 0 'GET GRANDMASTER_SETTINGS_NP' sending: GET GRANDMASTER_SETTINGS_NP 94e36d.fffe.d2695e-0 seq 0 RESPONSE MANAGEMENT GRANDMASTER_SETTINGS_NP clockClass 255 clockAccuracy 0xfe offsetScaledLogVariance 0x currentUtcOffset 35 leap61 0 leap59 0 currentUtcOffsetValid 0 ptpTimescale 1 timeTraceable 0 frequencyTraceable 0 timeSource 0xa0 tp2700> show clock System time : 2022-06-27 12:43:58 Leap Seconds : 37 Leap pending : +0 On 27/06/2022 12:22, Markus Kleinhenz via time-nuts wrote: > Hi Andrew, > > have you checked the PTP-Messages themselves? There is a field > currentUtcOffset in the PTP announce message used to transfer leapsecond > info. If thats 35, then it seems like a firmware issue. > > Regards > Markus > > Am 25.06.2022 um 10:30 schrieb Andrew Back via time-nuts: >> Hoping that someone may be able to shed some light on a PTP issue I'm >> experiencing, which could well be a simple configuration issue or, as I >> suspect, somehow related to the grandmaster firmware. >> >> I have a Symmetricom TimeProvider 2700, with firmware which I think dates >> from ~2014, connected to a BeagleBoneBlack running Debian and Linux PTP. A >> direct Ethernet connection with no switches in between. The TP2700 has the >> 1588 Annex J Default profile active, with all default configuration. Linux >> PTP client is configured for utc_offset 37. The GM is referenced to GPS and >> "show clock" returns "Leap Seconds : 37". However, when ptp4l is started on >> the client I get the running in a temporal vortex message and "updating UTC >> offset to 35", despite not seeing an offset of 35 configured anywhere. >> >> I did also run "pmc -u -b 0 'get TIME_PROPERTIES_DATA_SET'" on the client, >> which similarly confirmed a UTC offset of 35. >> >> I don't seem to be able to manually configure UTC offset on the TP2700 and >> when I try, it complains that this is not possible with the current mode, >> since it's referenced to GPS I guess. >> >> Other than this perhaps being a grandmaster firmware issue, I'm out of ideas. >> >> Andrew >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-le...@lists.febo.com >> > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: TimeProvider 2700 PTP UTC offset issue.
Hi Andrew, have you checked the PTP-Messages themselves? There is a field currentUtcOffset in the PTP announce message used to transfer leapsecond info. If thats 35, then it seems like a firmware issue. Regards Markus Am 25.06.2022 um 10:30 schrieb Andrew Back via time-nuts: > Hoping that someone may be able to shed some light on a PTP issue I'm > experiencing, which could well be a simple configuration issue or, as I > suspect, somehow related to the grandmaster firmware. > > I have a Symmetricom TimeProvider 2700, with firmware which I think dates > from ~2014, connected to a BeagleBoneBlack running Debian and Linux PTP. A > direct Ethernet connection with no switches in between. The TP2700 has the > 1588 Annex J Default profile active, with all default configuration. Linux > PTP client is configured for utc_offset 37. The GM is referenced to GPS and > "show clock" returns "Leap Seconds : 37". However, when ptp4l is started on > the client I get the running in a temporal vortex message and "updating UTC > offset to 35", despite not seeing an offset of 35 configured anywhere. > > I did also run "pmc -u -b 0 'get TIME_PROPERTIES_DATA_SET'" on the client, > which similarly confirmed a UTC offset of 35. > > I don't seem to be able to manually configure UTC offset on the TP2700 and > when I try, it complains that this is not possible with the current mode, > since it's referenced to GPS I guess. > > Other than this perhaps being a grandmaster firmware issue, I'm out of ideas. > > Andrew > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: First PN measurement results at 1 Hz to 20 kHz from carrier
Magnus, Bob, When the mixer is operating in the linear region for the DUT input (0dBm or lower), would it be possible to use a calibrated noise sources to do an extra verification of the noise level measurement? Of course with a noise source you get 3dB as both sidebands fold. Verification steps: Verify the DUT output level is correctly brought to 0dB (using attenuators) using a calibrated spectrum analyzer Connect the DUT to the phase measurement setup and set the reference to a 500Hz offset to get a beat note and verify the beat note is registered at 0dB, change the DUT level some dB up and down to confirm its in a linear region. Measure the per Hz output power of a noise source using a calibrated spectrum analyzer and a noise marker set to 10MHz. Connect the noise source to the phase measurement setup and check if the noise level is measured at level measured by the spectrum analyzer + 3dB This should work if the RBW of the phase measurement is indeed set to 1Hz. Another verification option may be to use the phase modulation of a signal generator. This can not check the effective noise bandwidth of the FFT but it can check linearity over the whole range. The output of the mixer is terminated with 50ohm so a factor of 10 in voltage should give a 20dB power step. When operation in the linear range the phase noise measurement setup should measure 20dB less with every factor 10 reduction in phase modulation depth where 90 degrees is equal to 100% modulation depth so equal to the signal you get when measuring a beat note. When measuring with modulation depth of 90,9,0.9,0.09 and 0.009 degrees the measured level should step from 0,-20,-40, -60 to -80dB Any feedback? Erik. On 26-6-2022 20:52, Magnus Danielson via time-nuts wrote: Hi Erik! Great progress! Sure interesting to look at them phase-noise plots, right? It's a really good tool in addition to the stability of ADEV and friends. As I recall it, the ADE-1 is not documented to be isolated, but it is very obvious when you look down the backside of it. However, it has capacitive coupling and one should consider both common mode rejection and common mode loading it down for these to work well. Word of caution when it comes to levels, as the windowing filter used causes shifts in noise-levels, so estimation of noise-levels becomes a little bit tricky as you try to get the nitty gritty right, but getting the overall shape view you already gained a lot with the things you achieved. A technique used to push further down into lower noise-levels is the cross-correlation technique, where you split the signal into two channels, each being exactly what you have now, and then rather than squaring the output of the FFT from each channel, you multiply one with the completment of the other, then average on those. This allows you to supress the noise of each reference oscillator. You do not have to go there from start, as you already make very useful measurements, but I'm just suggesting what may lie up ahead. Compared to some of the other sources, the Rigol SG does fairly well, but then again, things can be even more quiet. For the XO you can see the 15 dB/Oct slope as expected for flicker frequency. Try to locate the source of the peaks you see and see if you can clean it up. The XO seems to be a fairly good DUT for doing that. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Repeatability of stability measurements
Hi Hans-Georg, Maybe it is better to refer to this as the inverse of 20,48 GHz, since that is the virtual clock rate of the interpolated coarse-clock. Considering that it is 2048 * 10 MHz, it is not hard to imagine that a coarse clock of say 80 MHz is then interpolated by 256 to achieve that, which is entierly reasonable. 160 MHz and 128 is another example. A look down the manual should indicate which one it is. Cheers, Magnus On 2022-06-25 21:10, Hans-Georg Lehnard via time-nuts wrote: Sorry, this was completely nonsense .. i correct the resolution factor and forgot the "e" so i get 4.88281248-11 as factor and scaled the timelab plots with it. My interpretation is just as stupid. The correct Factor is 4.88281248e-11. Am 2022-06-25 17:15, schrieb Hans-Georg Lehnard via time-nuts: First of all the resolution factor from my first post is a copy error the correct value is 4.88281248-11 (less decimal places). In the attached diagrams the correct factor was used. I generated testfiles with 2046,2047,2048,2049,2050 intervals, loaded into timelab and scaled them with 4.8828124998-11. MDEV shows more noise as real measurements . Another testfile with 2000 intervals and scaled with 5e-11 shows similar results. In the Frequenc difference plot you can see the difference grows stepwise with time. The zoom shows where the 2048 intervals are already in the next time step and the 2000 intervals are not yet. By zooming in you can also see this between the 2046 and 2050 intervals. Possibly an overflow or rounding error ? I think the overlap of this effect with the white noise of the real measurements creates my measured jumps. More noise attenuates this step-like progression. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
