Re: [time-nuts] Phase measurement of my GPSDO

On Mittwoch, 12. August 2020 13:23:57 CEST Tobias Pluess wrote: > On the picture `gpsdo_180_210.png` one can see the last 30 hours of my > measured data. During this time, the DAC value need to change only by 9 > counts. I think the DAC value has a slight trend to go lower and lower, > this is perh

Re: [time-nuts] Phase measurement of my GPSDO

Dear Colleagues I have made some tests with my self-made GPSDO which we discussed on this very list. I was allowed to install it at my workplace and put the antenna on the roof, with almost 360° free sky view. (I will have to compare different oscillators anyways, so I could install mine as well.

Re: [time-nuts] Phase measurement of my GPSDO

An OP37 may not function well as a diode clamped limiter since the loop gain is <5 during limiting. A unity gain stable opamp would likely be better. Bruce > On 17 April 2020 at 09:26 Bob kb8tq wrote: > > > Hi > > The OP-37 is fine as long as the gain is over 5X. Under that gain level, you

Re: [time-nuts] Phase measurement of my GPSDO

Hi The OP-37 is fine as long as the gain is over 5X. Under that gain level, you need to run an OP-27. The OP-07 is pretty noisy. Limiter circuits have been covered in a lot of detail. One quick read is at: http://www.ko4bb.com/getsimple/index.php?id=bruces-zero-crossing-detectors

Re: [time-nuts] Phase measurement of my GPSDO

Hey Bob awesome, I actually have found some OP-07 and OP-37 in my junkbox! going to build an amplifier now for my mixers. Is it a wise idea to add diodes to prevent the amplifier from clipping? For example I would have done it similar to this https://www.allaboutcircuits.com/technical-articles/an

Re: [time-nuts] Phase measurement of my GPSDO

It's a feature not a bug. :-) I was going to address possible out-of-sequence output in this update, but after lots and lots of thinking and experiments, and discussions with a few bright folks on this list, I've come to the conclusion that there is no 100% reliable way to do sample ordering withi

Re: [time-nuts] Phase measurement of my GPSDO

Hi Have you tried it with the latest firmware update? I’ve never seen the problem here. Bob > On Apr 14, 2020, at 1:05 PM, Taka Kamiya via time-nuts > wrote: > > Bob, Tobias, et al > > TICC (TAPR) isn't problem free either. It has a tendency to get TimeLab > confused on data from port A a

Re: [time-nuts] Phase measurement of my GPSDO

Bob, Tobias, et al TICC (TAPR) isn't problem free either.  It has a tendency to get TimeLab confused on data from port A and port B.  The data stream has identifier on them but TimeLab discards it.  Then it expects A and B comes alternately.  I communicated with both developers but for time bei

Re: [time-nuts] Phase measurement of my GPSDO

Hi > On Apr 14, 2020, at 11:01 AM, Tobias Pluess wrote: > > Hi Bob > > yes I totally agree, you can save a lot of space by having those USB boxes > for almost every measurement. > However I am happy that we have at work the "old school stuff" (by which I > don't mean we have old equipment, actu

Re: [time-nuts] Phase measurement of my GPSDO

Hi Bob yes I totally agree, you can save a lot of space by having those USB boxes for almost every measurement. However I am happy that we have at work the "old school stuff" (by which I don't mean we have old equipment, actually it is pretty modern) because in my opinion the user experience is mu

Re: [time-nuts] Phase measurement of my GPSDO

Hi The whole “volume of clutter” on the desk / bench / around the lab / basement is one of the many drivers getting me to move over to some of the more modern USB based measurement gear. You can swap out 400 lb of cranky (but useful ) gear from the 1960’s for what would fit in a small backpack

Re: [time-nuts] Phase measurement of my GPSDO

Hi yes sure I agree that it is hard to beat. But from a commercial perspective, any hobby is more or less nonsense - the same is true for my own GPSDO. I just could have bought one and would be finished. But making my own is more interesting ;-) I'll see whether I buy a TAPR TICC. Maybe it would c

Re: [time-nuts] Phase measurement of my GPSDO

Hi Indeed all a time tagger does is spit out picoseconds since some arbitrary start point. Some run on and on forever ( counting up to pretty big numbers in the process). Others roll over at a pre-defined point. You then massage the data to take those out. I’d suggest that the “software/ firmw

Re: [time-nuts] Phase measurement of my GPSDO

Hi Bob yes sure I know. At least my homebrew GPSDO and the STAR4 GPSDO I have are always powered, but since they don't take much space on my desk that's okay. But for the signal generators (or SpecAn etc) it is a completely different story; I usually take them from the shelf when I need them and pu

Re: [time-nuts] Phase measurement of my GPSDO

G'day OK I see I must do it with time tagging :-) Is it correct that the time tagging just spits out the time (in ns, for example) when the rising edge on the A or B input occured? and then, you calculate the phase by subtracting the time tags for the A channel from the time tags for the B channel

Re: [time-nuts] Phase measurement of my GPSDO

Hi > On Apr 14, 2020, at 2:31 AM, Tobias Pluess wrote: > > Hi Taka > good to know you're working on the same stuff :-) > I also think that this is the goal, sort of. But apparently there are some > pitfalls. I hope the experts on this type of measurement (Bob) can give > more hints ;-) > > Btw

Re: [time-nuts] Phase measurement of my GPSDO

Hi If the phase slips are “well behaved” they can be handled. The problem with a dual channel setup is that they are often not well behaved. The period is 100 ns so a frequency drift of 1 ppb will put you in trouble in under 2 minutes. The only real answer is to do it properly and time tag th

Re: [time-nuts] Phase measurement of my GPSDO

Hi Taka good to know you're working on the same stuff :-) I also think that this is the goal, sort of. But apparently there are some pitfalls. I hope the experts on this type of measurement (Bob) can give more hints ;-) Btw good to know your 10811 took 2 months to settle. In that case I will try t

Re: [time-nuts] Phase measurement of my GPSDO

Hey Bob ok now I see your point! you talk about the phase spillovers. Timelab and also Stable32 can correct for them, so it shouldn't be a problem, right? But I agree, if you cannot correct for the spillovers it becomes even more difficult. Tobias On Tue., 14 Apr. 2020, 01:38 Bob kb8tq, wrote

Re: [time-nuts] Phase measurement of my GPSDO

Hi > On Apr 13, 2020, at 7:18 PM, Taka Kamiya via time-nuts > wrote: > > I am working on pretty much the same thing. My HP105B has an HP11801 inside. > There is no telling how long it has been off. Frequency wandered ALL OVER > THE PLACE. It took 2 months of continuous operation to settl

Re: [time-nuts] Phase measurement of my GPSDO

Hi The gotcha with using a conventional counter (as opposed to a time tagger) is that you never know when things are going to “slip” past each other. When they do you get a major burp in your data. Bill’s setup is running a time tagger …. ( = It runs an internal time count, each edge gets “label

Re: [time-nuts] Phase measurement of my GPSDO

I am working on pretty much the same thing.  My HP105B has an HP11801 inside.  There is no telling how long it has been off.  Frequency wandered ALL OVER THE PLACE.  It took 2 months of continuous operation to settle down and just do the normal aging/drifting.  I have a same question as you do

Re: [time-nuts] Phase measurement of my GPSDO

Hi Bob Riley suggests to use a single TIC http://wriley.com/A%20Small%20DMTD%20System.pdf when you look at the block diagram Fig. 4, you can see that one TIC allows to compare two oscillators. I don't know exactly how, though :-) OK and I see your point on the 8663. I will try to use another re

Re: [time-nuts] Phase measurement of my GPSDO

Hi If you don’t have a spare 10811, they run about $50 to $80 on eBay. With some intensive shopping, 5334 or 5335 counters are in the same vicinity. Shipping on the counters is a bit more than shipping on the 10811’s :) This guy: https://www.ebay.com/itm/HP-10811-60111-10-MHz-High-Stability-Cr

Re: [time-nuts] Phase measurement of my GPSDO

Hi > On Apr 13, 2020, at 5:06 PM, Tobias Pluess wrote: > > Hi Bob > awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-) > > Maybe I have some good OpAmps for this purpose in my box. I will try it! of You need something that is quiet (like the OP-37) and has a pretty good slew ra

Re: [time-nuts] Phase measurement of my GPSDO

If you have an extra 10811 use it as an offset all mine tune 20 Hz + and I have used it as offset at 5 MHz , 10 Hz at 10 MHz all will do. Bert Kehren In a message dated 4/13/2020 5:07:38 PM Eastern Standard Time, tplu...@ieee.org writes: Hi Bob awesome, thanks! of course it is 1e6, not 1e7, I go

Re: [time-nuts] Phase measurement of my GPSDO

Hi Bob awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-) Maybe I have some good OpAmps for this purpose in my box. I will try it! of course I saw that my setup was not ideal as there was a bit of noise on the signals which I guess does lead to some jitter in the trigger circuit an

Re: [time-nuts] Phase measurement of my GPSDO

Hi Ok, first the math: If your offset oscillator is 10 Hz high at 10 MHz, you have a: 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD You get to add a 6 to what Time Lab shows you. If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier gets you to 1x10^-10 So,

Re: [time-nuts] Phase measurement of my GPSDO

Hi again Bob I tried to do some measurements with a DMTD! In my junk box I found a little PCB from earlier experiments on that topic, with a power splitter and two SRA-3H mixers, it was even already wired for the DMTD configuration. So I gave it a try! As "transfer oscillator" I used my HP 8663A s

Re: [time-nuts] Phase measurement of my GPSDO

Hi Tobias -- Several years ago, with a bunch of help from Bruce and John Miles, I did a very high isolation, very low phase noise buffer amp design that TAPR sold for a limited run. It's built with surface mount parts but they are user-friendly sized. Details and schematic are at https://www.feb

Re: [time-nuts] Phase measurement of my GPSDO

Tobias The diode connected BJT (2N) mixer is compared with various commercial mixers and phase detectors in a NIST paper that has a graph showing the PN of various mixers as a function of offset frequency. The RPD series phase detectors have a higher output and lower PN than most mixers. T

Re: [time-nuts] Phase measurement of my GPSDO

Hi A single mixer compares two devices. Provided you can offset the frequency of one of your devices, it does exactly what you need to do. Bob > On Apr 3, 2020, at 7:56 PM, Tobias Pluess wrote: > > Hey Bob > > hmm how would a *single mixer* design look like? in the end I need to > compare *tw

Re: [time-nuts] Phase measurement of my GPSDO

Hi Bruce the NIST design you mentioned - do you mean that publication where they used 2N's for a diode ring mixer? if so I can perhaps build this as well because I think I even have some 2Ns in my home lab :-) Concerning the RPD vs. TUF mixers - what is the actual property which makes the

Re: [time-nuts] Phase measurement of my GPSDO

Tobias That would certainly work for a start and have a better performance that a counter front end. The performance can be estimated using the tools at the link Bob provided. Lower noise opamps will improve the performance somewhat. A wider bandwidth opamp with a higher slew rate may be useful f

Re: [time-nuts] Phase measurement of my GPSDO

Hey Bob hmm how would a *single mixer* design look like? in the end I need to compare *two* clock signals, so a single mixer won't be of much use, would it? Tobias On Sat., 4 Apr. 2020, 01:51 Bob kb8tq, wrote: > Hi > > A *single mixer* setup is something that can be done quickly and easily. >

Re: [time-nuts] Phase measurement of my GPSDO

Hi A *single mixer* setup is something that can be done quickly and easily. The *dual mixer* setup brings in a bunch of issues that are far more easily handled on a good PCB layout. Either way, it is going to work far better with the right sort of low noise ( = single digit nanovolt per root hz

Re: [time-nuts] Phase measurement of my GPSDO

Hi Gerhard ah yes I didn't know that only old OpAmps have the phase reversal problem. At least in the data sheets for some newer types it is sometimes explicitly mentioned - "no phase reversal" - but for others it is not, and so far I never was enough interested in this problem to find out that it

Re: [time-nuts] Phase measurement of my GPSDO

Hi Bruce I have some TUF-1 mixers in my junk box as well as some JFET OpAmps AD8626. So, if I connect the OpAmps appropriately with some diode limiters as you suggest, would you say this would give an acceptable DMTD system? If so it sounds like something that can easily be built on a breadbord or

Re: [time-nuts] Phase measurement of my GPSDO

Gerhard wrote: Has anybody here ever tried the OPA698 / OPA699 limiting op amps? A lower 1/f corner would be appreciated, and slightly less noise. I haven't used the TI parts, but I have used the similar AD parts (AD8036/8037) quite a bit, with excellent results. The input noise is lower t

Re: [time-nuts] Phase measurement of my GPSDO

Am 03.04.20 um 23:08 schrieb Bruce Griffiths: One can merely add diodes to the opamp feedback network form a feedback limiter and maintain the opamp outputs within the range for which the opamp is well behaved whilst maintaining the increase in slew rate for the output. Has anybody here  eve

Re: [time-nuts] Phase measurement of my GPSDO

One can merely add diodes to the opamp feedback network form a feedback limiter and maintain the opamp outputs within the range for which the opamp is well behaved whilst maintaining the increase in slew rate for the output. Bruce > On 04 April 2020 at 04:26 Tobias Pluess wrote: > > > Jup, so

Re: [time-nuts] Phase measurement of my GPSDO

Your counter can measure 1e-9 *at 1 Hz* but you are feeding it with 10 MHz's worth of noise, so divide the reading by the factor of the down mixing (1e7) so the result is 1e-16 -- you are multiplying the effective noise. Though as Bob says, you don't get close to 7 digits of improvement without p

Re: [time-nuts] Phase measurement of my GPSDO

I had trouble understanding this as well. Your PPS is derived from 10MHz internally by variety of method but usually by dividing of some kind.  So the error rate of 10MHz and PPS is usually the same of similar.  Please note, I said RATE.  If one moves by 1%, the other moves 1%. DMTD is mixing.  T

Re: [time-nuts] Phase measurement of my GPSDO

Hi Your 5335 resolves 1 ns, that is what limits it’s performance. If you have a gate time of 1 second, you will get 9 digits in a second, regardless of frequency. That’s the advantage of a “computing counter”. If you had a 10 Hz signal with fast enough edges, you could read it out to 9 digits.

Re: [time-nuts] Phase measurement of my GPSDO

Hi John Yes, I totally agree with you and I also understand the difference. But what I still don't understand is the following: Obviously, my 5335A is not accurate/precise enough to measure below 1e-9 for short tau. Currently I am comparing the 1PPS signals, but when I change that and use the DMTD

Re: [time-nuts] Phase measurement of my GPSDO

Hi Without a local reference that is *better* than your expected performance, there is no simple way to know what’s going on. Ideally you would like any measurement to be based on a reference that is 5X better than the expected result (tolerance wise). If you are looking for 1x10^-12, the ideal r

Re: [time-nuts] Phase measurement of my GPSDO

Hi When you generate a 1 pps signal, you divide the DUT 10 MHz by 10,000,000 to get the 1 pps. If the 10 MHz moves by X%, the 1 pps moves by X% as well. If you *subtract* the DUT from the offset OCXO, you get the *difference* of the two frequencies. So with division: 10 MHz to 10 MHz + 1 Hz 1

Re: [time-nuts] Phase measurement of my GPSDO

I think the difference is between *mixing* or *dividing* down to a low frequency. When you divide, you divide the noise along with the carrier frequency. When you mix, you "translate" the noise. If the signal bounces around 0.1 Hz at 10 MHz (awful, I know), when you divide to 1 PPS the noise is

Re: [time-nuts] Phase measurement of my GPSDO

Jup, some of them even have phase reversal when they are overloaded, so it is perhaps not a good idea in general, but I think there are opamps which are specified for this. Tobias On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow wrote: > Caution: opamps make terrible limiters- their overload behavi

Re: [time-nuts] Phase measurement of my GPSDO

Hi again Bob, yes you describe a simple DMTD measurement. But could you tell me what the difference is between that and comparing the 1PPS pulses? I mean, I could set the 10811 high in frequency by just 1Hz, and then it would result in two 1Hz signals which are then compared. Which is essentially

Re: [time-nuts] Phase measurement of my GPSDO

Hi Bob knowing that my counter's noise floor is terrible (even though I still don't understand why) I tried to measure the ADEV and MDEV of my GPSDO against another GPSDO. >From the graphs, everything below tau=10s is, I would say, rubbish. But I tend to mistrust these complete results, as I have

Re: [time-nuts] Phase measurement of my GPSDO

Hi If you are doing a limiter for a 5 Hz sine wave, a “normal” comparator is very much not what you want to use. The slew rates involved are simply way to far below what it is targeted to do. Effectively, it’s what’s in the counter input circuit that has already failed miserably trying to do t

Re: [time-nuts] Phase measurement of my GPSDO

Caution: opamps make terrible limiters- their overload behavior is generally ugly and unpredictable. It's much better to use a genuine level comparator, and wire it up so that it has a modest amount of hysteresis. Dana On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq wrote: > Hi > > The quick way to

Re: [time-nuts] Phase measurement of my GPSDO

Hi The quick way to do this is with a single mixer. Take something like an old 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz. Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone. That tone is the *difference* between the 10811 and your device under

Re: [time-nuts] Phase measurement of my GPSDO

hi John yes I know the DMTD method, and indeed I am planing to build my own DMTD system, something similar to the "Small DMTD system" published by Riley ( https://www.wriley.com/A Small DMTD System.pdf). However I am unsure whether that will help much in this case, because all what the DMTD does i

Re: [time-nuts] Phase measurement of my GPSDO

> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution does > my counter need? If the above was true, I would expect that a 1ps > resolution (and an even better stability!) was required to measure ADEV of > 1e-12, The fact that the (as far as I know) world's most recent, > rocket-s

Re: [time-nuts] Phase measurement of my GPSDO

Hi What you have measured *is* the noise floor of a 5335 when trying to use it to measure ADEV. Anything past the numbers on your plot will be “past” what the 5335 can “see”. Indeed, even when you get close to those numbers, things may get a bit weird due to the fact that you are measuring counte

Re: [time-nuts] Phase measurement of my GPSDO

Hello all in the meantime I figured out most of my problems and my GPSDO is working now with some very ugly prototype code. Today, I wanted to do some ADEV measurements. My plan was to compare the 1PPS generated from my GPSDO to the 1PPS of my Oscilloquartz STAR4; unfortunately I have nothing else

[time-nuts] Phase measurement of my GPSDO

I have seen differences between both UCT and Oscilloquartz 8663 ocxo’s. The attached plot shows an example. Both boxes use Ublox LEA-6T receiver, surveyed in, AD5680 DAC 18 bit DAC, same level shift circuit and same control circuit. The reference is an LPRO-101. The Oscilloquartz ocxo was purcha

Re: [time-nuts] Phase measurement of my GPSDO

On Thu, 19 Mar 2020 20:32:30 +0100 Tobias Pluess wrote: > The GPS phase detection happens on page 3. I use the TDC7200 as > interpolator. > Inside the STM32 microcontroller, I let a timer run with the 10MHz clock. > The timer overflows to 0 when it reaches the value 999. > Further, the 1PPS p

Re: [time-nuts] Phase measurement of my GPSDO

On Donnerstag, 19. März 2020 22:17:22 CET Matthias Welwarsky wrote: > You cannot expect to see the OCXO for small tau if your reference is the > GPS. The GPS 1PPS jitter and the quantization errors will dominate the ADEV > graph for small tau. Once you correct the quantization error (you need to >

Re: [time-nuts] Phase measurement of my GPSDO

On Donnerstag, 19. März 2020 20:32:30 CET Tobias Pluess wrote: > My recorded data is here: > > https://hb9fsx.ch/files/gpsdo/phase.txt > > Now I made two plots (here: https://hb9fsx.ch/files/gpsdo/phase.png). The > upper is the raw phase data, and I also fitted a linear function to it > (i.e. if

Re: [time-nuts] Phase measurement of my GPSDO

Hi > On Mar 19, 2020, at 3:32 PM, Tobias Pluess wrote: > > Dear colleagues, > as you may remember I am still working on my own GPSDO project. > So far I have populated all the components on the PCBs I made, and I have > written some very basic software to test everything. Currently, I am > runn

[time-nuts] Phase measurement of my GPSDO

Dear colleagues, as you may remember I am still working on my own GPSDO project. So far I have populated all the components on the PCBs I made, and I have written some very basic software to test everything. Currently, I am running following simple test: I set my DAC to a constant value (5 Volts at