Member postings for Joseph Noci 1

Not really noise analysis, although you can derive noise performance, phase performance, and other factors from the graphs.

Allan Variance is however a prime measure of stability, NOT accuracy. The frequency being 'measured' can be inaccurate, but if it is STABLE, the graph will show it - A good double oven OCXO - 10 minus 12, Maser, 10 minus 16 @ tau 10 days... or better..

Sheesh - I need to get a life..

What is the Super accurate picPet source of reference clock? I have not used picPet, but I assume it compare two signals for delta in edge time? And is a 'nominal 1 sec interval' a stable measure of time?...

Edited By Joseph Noci 1 on 20/02/2023 06:07:10

Why do we need an idea of planned use? Robin merely asked how THAT circuit works...

my enquiry is specifically about understanding this circuit.

One of the two transistors will conduct more on power on. Make that TR2. When it conducts fully ( base biased via R1 &2) its collector is low, pulling TR1 base low, so TR1 is off, collector hi.

So, TR2 base - 0.7v, as is the top of D2. TR1 base = 0v.

A negative pulse ( meaning, the pulse edge goes from HI to LOW) passes through the two capacitors connected to D1 and D2 - the pulse does naught via D1 since the top of D1 is LO, since TR1 Base is LO and OFF already

That negative pulse on the bottom of D2 causes D2 to conduct, since its top is HI ( TR2 base = HI, since TR2 is ON).

That neg pulse pulls TR2 base low, now turning it off. Its collector goes 'off' or open circuit and voltage appears on TR1 base via R3 and R4, turning TR1 ON. TR1 ON set its collector LO ( at gnd) pulling TR2 base LO via R2. Now TR2 is OFF and TR1 is ON.

A new pulse swaps the state again - the diodes 'steer' the pulse to turn off the base of the transistor whose base is HI

But you need a fast processor - catching microns - and its in a serial message - will that keep up - some sums to do..

You still need timing though - position won't integrate into rate or time...And time stamping the serial message data...

Edited By Joseph Noci 1 on 19/02/2023 17:37:30

Do you have a dual trace scope John? - A quicky is to set the GPS to 1MHz, trigger the scope on that, and feed the OCXO 10MHz into the other channel - adjust the OCXO so the trace stays put..

Sorry Dave - I have never needed to program the PPS output on the fly - always set it to a single value as per application needs. I have also for this only used GPS types with FLASH, so it was easier to just use Ucenter and program the flash so it remained fixed on power on.

Morning Michael - I see no need for you to apologise for anything! It's in the morphology of threads that so much useful info gets lost simply due to passage of posts. There have been many a beef about the 'poor' forum software/structure/way of working and I have never really agreed with these beefs - I do think it works well, EXCEPT for a search mechanism that works properly, not by devious routes, googling, standing on one leg, with binoculars in eye, etc...When I find a thread of interest I set aside time to read all posts to sieve out the gems, but sometimes its just to much - lots of guff inside good, long, threads is enough to rather set the thread aside.

Enough, lest I really take this thread down a dark road and are banned..

Soldier On Michael!

How does one consolidate the confusing cross pollination developing on these related posts?

In a related thread - Yet another Arduino Clock thread...I posted:

A very good ppt presentation by a master in the field:

**LINK**

A veritable bible on the subject: Handbook of Frequency Stability analysis.

**LINK**

Some measurement systems:

**LINK**

And Misc good stuff:

**LINK**

**LINK**

WJ Riley is a master in this field...

And since these related posts are rather active the info rolls down the page and is gone.. Some of the related threads are going down non-MEW paths, what with GPS, Allan Variance, etc, but for the Pendulum Chasers, and for me, hugely interesting.

Select the correct port, and baudrate ( usually 90600) ( 2nd line from top. left of screen).

The select VIEW, then CONFIGURATION VIEW, the scroll down on the left to TP or TP2 to set up the Frequency on the pps pin. Then lower left of that screen, make sure the yellow lock is unlocked, and click on SEND...

Noted...however, 6MHz will have a lot of jitter...But if you set up for 24MHz, then divide by two twice, you get a VERY clean signal, stable, and since the 24MHz is relatively jitter free, dividing by 4 will 1/4 the intrinsic remnant of jitter as well!

If you wish to use the GPS clock source to calibrate the OCXO better, divide the OCXO by 5 then 2 to give 1:1mark/space 1MHz, and set the GPS clock to 8MHz, and divide it by 2,2,2,2 to get 500KHz with very low Jitter.

Feed both into the TI TDC7200 chip and read the delta, or even easier, use a dual trace 'scope. chan-1 triggered on a 500KHz, edge, and the 1MHz GPS clock edge into chan-2. Adjust the OCXO so that the GPS clock edge stands still WRT the 500KHz edge, and you are on frequency...

And then breath a little loudly and start chasing the OCXO edge up and down the screen...

Edited By Joseph Noci 1 on 18/02/2023 20:37:39

You only need U-Centerand a serial or usb to serial to the GPS, is all. If your GPS is one with Flash, you can write the setup to it and it will be sticky and come up like that on power up.

You mentioned in your post in the precision pendulum thread WRT using the ublox pps output- you need 10MHz, etc....

10MHz comes with bad jitter - read my posts - you can only use 1,2,4,8,12,24Mhz. ALL other frequencies have moderate to very bad jitter. Change your reference timebase to suit, say , 12MHz, or change the pendulum to a 10/12 rate, ie, a 0.83333hz pendulum....after all , you are really only interested in stability detrmination, not 'actual' time ( are you?) - Call it the SOD-Second...

I think it was mentioned to feed the clock into a DDS chip and use that to generate the 10MHz - not really a good idea, - to get a low jitter 10MHz clock from the DDS the DDS input clock really needs to be 3 to 4x Nyquist, so 40MHz, which you can't get from the UBLOX. Some DDS chips have a PLL clock mulitiplier to generate 100MHz plus from low rate clocks ( 8MHz, etc), but the phase jitter from the PLL is high enough for it to reflect in the DDS output frequency as well, depending on the clock to output clock relationship.

The Si5351 is a better option for this - you can set the Ublox to 24MHZ, and feed that to the Si5351 clock input., and set it to generate 10MHz, which it does cleanly.  But that is another dark road, and deviating from your path...

If using the UBLOX to provide a 10MHz clock as measurement reference timebase you will reach the noise floor very quickly in Allan Variance.

And here I am opening my mouth again...

Edited By Joseph Noci 1 on 18/02/2023 19:24:30

Can see the oscillation rather nicely as the point sopen.

If they balance, the circuit is resonant...and they always will, at some frequency.

The cap and coil form a series resonant circuit and basic ignition coils ( not the 'hot' varieties, etc) had inductance values 'tween 0.5 and 1mH - around 300 to 500Hz at resonance with a 0.2uf cap. This would give a longer, decaying spark if 'tuned' , often done to give a better burn in the cylinder. Ignition coils with series ballast resistors messed that concept up a bit - if the value was 1 or 2 ohms, it still worked..The down side was quite a high , decaying AC voltage across the points with greater pitting..

Must exist, after all negative resistance exists..

Likewise:

Sorry Chaps, I will not add any more to the confusion I have already created!

Dave, do you have a frequency counter with variable timebase/gate - say to 10 sec maybe AND with an external ref clock input ( normally 10MHz)

Edited By Joseph Noci 1 on 16/02/2023 06:21:16

Like I suggested, perhaps better to move this stuff to another topic? John, the 7490 divide by 5 section is a BCD MOD-10 counter - no fancy adders, etc - it counts 4 and then resets on the 5th clock, so the output is not symmetrical but has a 4:1 ratio...

Dave - I beg to borrow your Forum Handle for the day please - I have been sprouting so much BS I am ashamed...

There is no TP2 pin on any of the GPS's - I have misread all data sheets and spoken C..p!

There is only 1 pin, called timepulse, and it can be set to 1PPS ( mostly the default on all GPS's) or to anything else by means of the UBX-CFG-TP5 message as you describe - ON SOME, not ALL GPS's - so you have to dig deeper in the data sheet to see if its possible..If is indicates that the default is 1pps, but to refer to the RX description for more info, it can do it.

All -7 and -8 series seems to be able to do it. Only the 6T seems able, so my neo-6 suggestion is useless.

The easy way to set the TP5 message is to use the U-center SW tool. If the chosen GPS has FLASH, you can program it in hard and from next power on it is always there...

Your wishfull thinking is correct, valid and true!

AND LASTLY:

Mixing terms with brain in neutral...

Disaster if 5MHz has jitter, but will it? 5MHz is 10MHz ÷2. It's the 1MHz signal I'd expect to jitter, due to ÷5.

In mitigation, John missed this as well... I meant the divide by 5 output, not the 5MHz output...The div by 5 will always have non-regular mark-space ratio, see above...

Going to sit in the corner looking at my navel with a mirror for the rest of the day