Hi Magnus, See answers below Erik. On 10-3-2025 16:03, Magnus Danielson wrote: > Hi Eric, > > So, what is apparent for counter C is that there is a systematic noise > in there, which causes the ripple in the ADEV. Through selection of a > tau at the end of that, your tau filters out this systematic and you > access the underlying random noise precision. > > The ADEV for counter A have the tell-tale of having systematic noise > as it does not follow the expected slope. In comparison the B counter > has some systematics, but not much to fully dominate. > > If you can, rather than sweeping frequency, just offset the 10 MHz > frequency with +/- 2 mHz to sweep all phase-relationships in 500 ns. > The RMS of that is a good judge of which is the best linearity counter. Here is a almost 4000 s run at a 0.001 Hz offset of only counters A and C. I guess this is still not long enough but you can see pulling for counter C in the phase view. The frequency view: http://athome.kaashoek.com/time-nuts/+0.001%20Hz.png The phase view: http://athome.kaashoek.com/time-nuts/+0.001%20Hz%20Phase.png ADEV view: http://athome.kaashoek.com/time-nuts/+0.001%20Hz%20ADEV.png Is it correct to conclude the phase view confirms counter C does a phase measurement as the phase has no random walk? > > Questions: > > Can you disclose the single-shot resolution of these four solutions? Counters A,B and C do have a published single shot resolution of 40 ps Counter D can not do single shot as it is of the direct sampling type with a dual mixer in front. Here is the single shot ADEV measurement of a 1 Hz source at 0.02 Hz offset from 10 MHz: http://athome.kaashoek.com/time-nuts/Single%20shot%20ADEV.png And here the phase view of the single shot measurements: http://athome.kaashoek.com/time-nuts/Single%20shot%20Phase.png Counter A does not have a time stamping option so the single shot measurement was done by using input 1 for the 1 Hz input and input 2 for the 10 MHz reference and measure the interval between inputs 1 and 2. To get the phase wrapping for this type of measurement correct you must specify 10 MHz input frequency in Timelab even when it is a 1 Hz input frequency. I assume this doubles the single shot RMS error leading to the ADEV at tau=1 s of 80 ps? > Can you disclose the datasheet "spec" for the counters? Counter A: - 12 digits / s - Reciprocal counter - 40 ps single shot resolution, 120 ps RMS resolution - Uses resolution enhancement using sub measurements. Counters B and C: - Reciprocal counter - 40 ps single shot resolution - Uses resolution enhancement using sub measurements. > Can I assume that you used none frequency estimation improvement > processing on any of these counters? No post processing is done, just the numbers these counter report. I can not disable the resolution enhancement in counter A. > > Cheers, > Magnus > > On 3/10/25 15:07, Erik Kaashoek wrote: >> Many thanks for the excellent replies >> >> Back to basic measurements. Of course I may do stupid things so >> feedback is most welcome. >> >> 4 counters where used A,B,C and D >> I removed the counter details to ensure a focus on what the >> measurements tell us. >> Counters A,B and C are general purpose counters using zero crossing >> detection, 1 s gate time, reciprocal counting and possible resolution >> enhancement. >> Counter D works as Attila mentioned at the end of his reply. An >> offset signal is used to down mix both inputs (test signal and >> reference) after which both down mixed signals are sampled and in the >> digital domain converted to an I/Q signal to calculate the phase >> using all available samples thus greatly reducing the noise. >> >> First test is done with 500 s period 10 Hz sweep around 10 MHz to see >> if anything is happening that makes further experiments relevant. >> The sweep is done using a Digital Signal Generator that can not do a >> true sweep but uses about 1000 steps (or 1024?) for its 500 s sweep. >> Of course this step wise sweeping could cause all kind of unwanted >> effects so the impact of the steps has to be investigated >> http://athome.kaashoek.com/time-nuts/Sweep%2010%20Hz.png >> A lot is happening for counter A and also to some extent with counter >> B when close to 10 MHz >> Counter D was not used in this sweep but it has been used to confirm >> the exact nature of the stepping of the generator >> >> Next step is to zoom in using a reduced span of 1 Hz >> http://athome.kaashoek.com/time-nuts/Sweep%201%20Hz.png >> Still a lot is happening with counter A and the "increased noise >> around 10 MHz" for counter B is better visible >> Reduced frequency/step has changed the spiky pattern for counter A >> and its now clearly visible that whatever weird is happening it is >> reduced when close to 10 MHz. As the size of the peaks is comparable >> to when sweeping with 10 Hz the steps of the signal generator may not >> be the primary driver for the peaks. >> Counter D runs at 0.1 s gate time to catch the generator steps and is >> just able to see these steps >> >> Next step is to zoom in even further to a span of 0.1 Hz >> http://athome.kaashoek.com/time-nuts/Sweep%200.1%20Hz.png >> Counter A still shows some weird peaks that could be phase pulling >> Counter B shows many more but slightly smaller peaks. >> To show the measurement variations a HDEV (not ADEV because of the >> frequency drift) was created >> http://athome.kaashoek.com/time-nuts/Sweep%200.1%20Hz%20HDEV.png >> Counter A and B perform similar in the HDEV. counter C is roughly a >> factor 10 better and as expected counter D is much better. >> >> To test if there is phase pulling a signal with 0.01 Hz offset from >> 10 MHz was created and the frequency was measured during 500 s to >> check if any pattern repeats every 100 s >> http://athome.kaashoek.com/time-nuts/+0.01%20Hz.png >> Counter A is stable except for a rather large deviation every 100 s >> Counter B is noisy >> Counter C is better and D as expected much better >> This is clearly visible in the ADEV >> http://athome.kaashoek.com/time-nuts/+0.01%20Hz%20ADEV.png >> From the ADEV you can also see that that counters B,C and D are >> actually measuring phase which is converted to frequency in Timelab >> if needed. >> Counters B, C and to some extent D do have a dip in the ADEV at 100 s >> so there must be some kind of repeating pattern with 100 s period for >> these counters >> >> Please let me know if what I am doing makes sense and if you have >> suggestions for what next to do. >> Erik. >> >> >> >> >> >> >> >>