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The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator
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Old 24th September 2020, 11:13 AM   #2741
andrea_mori is offline andrea_mori  Italy
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Quote:
Originally Posted by Joseph K View Post
Now this is only brainfarting, but
We have seen that the noise floor halves at each division by 2 of the carrier frequency.
From 11MHz to 176kHz there is an 62.5 division factor.
Let's round it to 64..
If the system would keep the physics all right, then it should show 2^6, that is -36dB difference in the floor, instead of 8dB.. and changing shape..
So there is something which is not perfect.
I expected exactly this reply, now please comment on this plots (I know the reply, but just to confirm ...)
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Old 24th September 2020, 11:38 AM   #2742
andrea_mori is offline andrea_mori  Italy
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Quote:
Originally Posted by Joseph K View Post
Just so as to annoy You, the applied Wilkinson splitter does have a certified lower bandwith at 1MHz.. and already there it's not totally the same as at higher frequencies.
I can understand that it continues to work somehow, but care should be taken.
We have to take the maximum care, since one time there is something which is not perfect (blue line) while another time it works as expected (pink line).

Maybe on odd days there is something wrong ....
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File Type: png 176 KHz square wave vs Rigol 200kHz square wave.png (133.5 KB, 392 views)
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Old 24th September 2020, 11:42 AM   #2743
Joseph K is offline Joseph K  Hungary
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I have already told my conclusion that the Fifopi seemingly does add a certain floor.
It does not have anything to do with your previous graphs and what I have told for those. I feel it's a bit of shifting the target
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Old 24th September 2020, 11:46 AM   #2744
Joseph K is offline Joseph K  Hungary
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At this point I feel to quit. It's Your game, and you change the parameters /environment as You wish..
(at this point it comes to mind: what we had been looking at in those first graphs..)
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Old 24th September 2020, 12:23 PM   #2745
andrea_mori is offline andrea_mori  Italy
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Quote:
Originally Posted by Joseph K View Post
I have already told my conclusion that the Fifopi seemingly does add a certain floor.
It does not have anything to do with your previous graphs and what I have told for those. I feel it's a bit of shifting the target
Very strange, I don't remember you told that.
Can you quantify how much noise floor is seemingly added?

Anyway I have not changed any parameters /environment, all the last plots have been already published (as an example the last plot was published in post #2433 The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator).

No game here, simply measurements (and sometimes unheard suggestions).
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Old 25th September 2020, 10:17 PM   #2746
andrea_mori is offline andrea_mori  Italy
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Default Just to clarify once and for all

This is the last time we waste time demonstrating what was obvious from the beginning: the Timepod measures correctly the phase noise of square wave clocks, the harmonics of the signal (unlike what someone claims) absolutely don't affect the phase noise analysis as shown below.

We have measured the phase noise of a 5 MHz CMOS output CTS oscillator with and without a low pass filter at 7.5 MHz before the input of the Timepod to suppress the undesired harmonics above its fundamental.

The first picture shows the spectrum analysis of the square wave at 5 MHz without the input filter (green curve) vs the same square wave with the filter at 7.5 MHz (blue line).
As you can see the spectrum of the signal without filter is charged with lot of harmonics, while inserting the low pass filter the harmonics practically disappear.

The second picture shows the AC characteristic of the filter we have used.

Finally the third picture shows the phase noise plot comparison between the 5 MHz square wave with (pink line) and without (blues line) the low pass input filter.
As you see the two plots are exactly superimposed, the harmonics of the square wave don't affect the phase noise measurement in the least.
And this was obvious for us since we are measuring the phase noise and not the amplitude noise.

Measuring a 5 MHz square wave its harmonics fall into the passband of the input filter used in the Timepod but the phase noise result is not affected, that demonstrates the reliability of the gear even with square wave clock.
I hope this helps to understand.
Attached Images
File Type: jpg FREQ COMPARISON.jpg (117.2 KB, 289 views)
File Type: jpg 7.5M FILT FR.jpg (94.0 KB, 286 views)
File Type: png 5MHz CMOS osc vs 5MHz CMOS osc + filter.png (142.2 KB, 285 views)
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Old 25th September 2020, 11:18 PM   #2747
andrea_mori is offline andrea_mori  Italy
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Before and after the filter.
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File Type: jpg Before and after.jpg (223.2 KB, 112 views)
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Old 26th September 2020, 12:41 AM   #2748
Terry Demol is offline Terry Demol  Australia
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Andrea,

What LPF did you use, or is this an integral option included in the Timepod?

TCD
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Old 26th September 2020, 08:15 AM   #2749
andrea_mori is offline andrea_mori  Italy
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Timepod has no filter option, it’s an external 5th Chebishev low pass filter with cut off at 7.5 MHz.
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Old 26th September 2020, 08:26 AM   #2750
HpW is offline HpW
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Quote:
Originally Posted by andrea_mori View Post
This is the last time we waste time demonstrating what was obvious from the beginning: the Timepod measures correctly the phase noise of square wave clocks, the harmonics of the signal (unlike what someone claims) absolutely don't affect the phase noise analysis as shown below.
OK, what I have to ask you, while you wrote, low freq. (of master clock) variations is hear able...

Can you post more details about those low freq. variations:

. link or source about

. and may, when or when not it will be hear able as in mHz & Levels

while this relates to the now presented product(s) and measurements...

Hp
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