What do you want from a GPSDO?

[Johnny B Good]

but looking at the Lady Heather screen I see that the DAC currently shows 11.03% and it has been dropping steadily 0.1% every day for two weeks. So in less than 4 months it will be dead and now it does not seem to be the bargain I was hoping for. Unless there is some way to retune the oscillator range.

There is no documentation on what the UCCM DAC range is, but a lot of receivers use -100% to +100% with 0% being the center of the DAC range.

 That's an interesting conundrum. Hopefully, you're right about JBeale's situation but, even so, it does look an alarmingly high drift rate notwithstanding that it will have reached the halfway point rather than the end in about 4 months time. The ageing effect slows down with, well, age so hopefully it won't have reached the end of its tether in a mere 44 months time. I guess JBeale is going to find out whether it's got another 40 months or longer when it hits the zero percent mark in four months time. Fingers crossed that it starts showing negative values as it crosses that point.

 I find this interesting simply because one virtue of a used VCOCXO module is the fact of its pre-ageing having already slowed the pace down somewhat. However, this does assume it has been handled with TLC during the recovery process and subsequent shipping to you the end user and still has a useful ageing margin left to give many more years of service.

 Being the cheapskate that I am, this is an important question to me. Do I 'cheap out' on a used module or do I blow a wad of serious (to me) cash on a brand new pristine item that's had lavish TLC in both its manufacture and subsequent delivery into my hands. Choices, choices, choices. I think you can guess which option I'll be going for, after all the clue is in the above statement.

 Still, any advice on this subject will be most welcome. 

JBG

[texaspyro]

If your GPSDO has not been run in a while, it can take a couple of months to settle down.   A few months ago I fired up a NTBW that came off the boat from China a few years ago.   The DAC was falling at over 5-10 mV per day for three months, then it settled in at +/- 1 mV/day.

If your GPSDO EFC had been stable for a long time before, then just starting dropping rapidly... you might have a problem.

[FransW]

These are probably the cheapest on ebay at the moment: http://www.ebay.com/itm/163064988493

And, come with all the cables and additional ewaste goodness :-)

Anyone with info about this LMU300 or documentation?
I could not find anything.

Thanks in advance,  Frans

[Towger]

Anyone with info about this LMU300 or documentation?

It contains the newer version of the 'Trueposition GPSDO', the rest of the unit probably cannot be used for much except parts.  There are multiple threads about it here and other sites.

Beware the Packrat PDF document, it is useful but contains multiple mistakes.  e.g.:
  The GPSDO is 3.3v RS232, but they connect it directly to a 5v Arduino. 
  They state the old version of the GPSDO needs 13.5 to 15v, while it is actually 12v.  They probably needed the extra voltage to get it working with the 5V Arduino  
  The pin out for the new version says 'Pins 5,6 TX', but 7 and 8 are TX.

[FransW]

Hi Towger,

Thanks. I am aware of Packratt and the True Position GPSDO. No problems there.
However, the question was about the LMU300 19" module.
The only info was in the Time-Nuts archeve which I could not directly get.

So, the question remains, what does the unit contain and what exactly is the functionality of the various units on the board?

Frans

This the person that was offering info: Paul - K9MR
However, I do not know how to contact him.
Anyone?

[JBeale]

Sorry about further hijacking this thread, but there is some TruePosition LMU300 info here: https://www.mail-archive.com/time-nuts@febo.com/msg86139.html

A couple of observations on the LMU300:
- the console port is the AEP port, a 6 pin RJ-11 - and you need a 6 pin connector
- the USB port is non-functional
- pin 1 (furthest left looking into the jack) is ground, pin 1 (furthest right) is LMU300 txd, pin 3 is LMU300 rxd
- 115200,N,8,1 speed and format
- the unit *will not boot completely* on it’s own due to missing T1/E1 signaling from the SMLC
- the unit *will not boot completely* without GPS initialization
- both of the above conditions can be bypassed
- in spite of the above, both of my units are still unhappy and eventually reboot with watchdog timeouts or other errors

Sounds like significant work is required for it to be of much use, I guess that's why it's relatively cheap.

In other news, after reading the replies here about my Trimble UCCM GPSDO (which I've only had 2 weeks so far) I plotted the DAC % values from the log, and yes it's not quite a straight line, there is a hint of levelling off or at least a slight improvement over the past week in the downward drift, so maybe it won't crater after 4 months after all. I'll keep my fingers crossed.

[Johnny B Good]

Thanks for all the feedback so far - I will try to make all this into one device 

Datasheets for parts chosen so far:

LEA-M8F u-blox M8 time & frequency reference GNSS module: https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf
DAC8571: http://www.ti.com/lit/ds/symlink/dac8571.pdf
Bliley TCVCXO: http://www.farnell.com/datasheets/2674668.pdf?_ga=2.168041506.2031284271.1552628280-648269207.1446653940&_gac=1.15460994.1552288765.EAIaIQobChMI6cXx7MX54AIVTZPtCh1MbgSdEAAYASAAEgL4pvD_BwE

Please let me know where I have gone wrong already! 

 That tiny 3.2 by 2.5 mm smd TCVCXO chip for starters! Did you not realise just how tiny this thing was? 

 For a home hobbyist project, the smd XO chip does seem rather out of place imo. Are you trying to limit the appeal of this project to just those with regular access to high grade SMD reflow workstations?

 I'd suggest using a VCOCXO in a metal canned DIP package since not only is it easier to work with, it's also more readily handled both as something rather more tangible for the 50 to 100 dollars' worth of investment than an itsy bitsy smd component that could disappear down a crack in the floor should you sneeze it off the bench plus the fact that it's a lot easier to retrieve from the circuit board should you have a rethink of the board design in favour of a completely new PCB layout. A tiny smd part designed for a mobile phone would be my last choice for a GPSDO project like this.

 BTW, apropos of OCVCXOs, I'm currently looking at Digikey UK's offerings right now and seriously thinking of blowing some 40 to 60 quid's worth of my hard earned[1]. However, I'm a little dismayed at the seemingly low stability performance of even these ovenised VCXOs (5 to 50ppb figures). I'm hoping this is the basic 'stand alone' at a fixed Vfc setting with no external assistance to hold them to within 50ppt and that such, seemingly unimpressive ppb figures are normal for OCVCXO modules typically used in a GPSDO. Really, I'm just after some clarification and assurance on this point before I splash the cash. 

 I've finally come to realise just why a VCOCXO (or at the very least, a VCTCXO) is an absolute requirement to make a GPSDO based low phase noise 10MHz frequency reference suitable to feed the external 10MHz reference input sockets on the back of communications and high end test and measurement kit, hence my new found interest in VCOCXO modules (I have a u-Blox NEO M8N based module as the basis of my very first GPSDO project). 

 An interesting fact about this u-blox module is that, whilst it can output 18MHz clock signals (and even 19.2MHz - checked it just now) on its PPS line, the 16MHz option produces a rather curious toggling on each phase correction event between a 33 and 67 percent duty cycle as a consequence of this division by 3 ratio of its 48MHz TCXO.

 Trying to avoid the clock jitter effect such as typically observed on the 10MHz frequency setting by choosing only integer based division ratios for output frequencies such as 1, 2, 3, 4, 6, 8 and 12MHz will be doomed to failure if the integer is devoid of any even number factors such as that factor of 3 on its own in the example above. Configuring a frequency of 9.6 and 6.857143 MHz ( factors of 5 and 7) for example, produces the same toggling effect as witnessed in the 16MHz case (Oh! The new found joys of 'scope ownership!  ). I've no doubt this will also apply to other stand alone odd division ratios such as 9, 11, 13 etc. but ICBA to do any more tests.

[1] I tried tracking down used VCOCXO modules on Ebay but there are pitifully few to be found and of those, the Chinese sellers don't seem to understand the concept of providing meaningful technical data on what appears to be obsolete kit that the manufacturer no longer offers any data sheets for. Unlike Victor Kyam, I was so unimpressed by these sellers, I didn't buy the product, hence my trawling sites like Farnell and Digikey with a preparedness to spend some real (by my standards) money.

JBG

[jpb]

 An interesting fact about this u-blox module is that, whilst it can output 18MHz clock signals (and even 19.2MHz - checked it just now) on its PPS line, the 16MHz option produces a rather curious toggling on each phase correction event between a 33 and 67 percent duty cycle as a consequence of this division by 3 ratio of its 48MHz TCXO.

 Trying to avoid the clock jitter effect such as typically observed on the 10MHz frequency setting by choosing only integer based division ratios for output frequencies such as 1, 2, 3, 4, 6, 8 and 12MHz will be doomed to failure if the integer is devoid of any even number factors such as that factor of 3 on its own in the example above. Configuring a frequency of 9.6 and 6.857143 MHz ( factors of 5 and 7) for example, produces the same toggling effect as witnessed in the 16MHz case (Oh! The new found joys of 'scope ownership!  ). I've no doubt this will also apply to other stand alone odd division ratios such as 9, 11, 13 etc. but ICBA to do any more tests.

[1] I tried tracking down used VCOCXO modules on Ebay but there are pitifully few to be found and of those, the Chinese sellers don't seem to understand the concept of providing meaningful technical data on what appears to be obsolete kit that the manufacturer no longer offers any data sheets for. Unlike Victor Kyam, I was so unimpressed by these sellers, I didn't buy the product, hence my trawling sites like Farnell and Digikey with a preparedness to spend some real (by my standards) money.

JBG

The Ublox timing application note discusses it a bit but their example is 8MHz so the extra divide by 2 probably evens things out.
https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_%28GPS.G6-X-11007%29.pdf

A couple of sources of VCOCXOs on ebay that are worth looking at are :
(The first I haven't bought from but they look interesting and have data)
https://www.ebay.com/itm/1-x-CTS-OCXO-Crystal-Oscillator-Model-1190027-3-3V-20MHz/273776000063?hash=item3fbe523c3f:g:saMAAOSwMDhcZtYH&autorefresh=true

and
https://www.ebay.com/itm/UCT-OSA-MY-108663-01-10MHz-12V-Double-Oven-OCXO-Crystal-Oscillator/264230742882?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
I've bought three of the 108663 which are equivalent of the Oscilloquartz 8663 I think. I'm currently measuring them at the moment.
They are new old stock and are taking a little while to settle down.

[rfspezi]

By the way... the NEO-M8N maximum clock output is 24 MHz.

[Johnny B Good]

By the way... the NEO-M8N maximum clock output is 24 MHz.

 I've just tested that. Any frequency selection in 1Hz steps, from 1Hz, all the way up to 24000000Hz, will produce a valid result. The jitter will vary depending on the programmed frequency but the averaged frequency output will match the programmed output with a precision that improves with ever longer integration times. Trying to set a frequency of 24000001Hz or higher via the u-centre application will be rejected as invalid.

 The jitter free output frequency options include this 24MHz maximum which will now exhibit corrective phase jumps of 180 deg. The next lower set of jitterless frequencies in descending order, all derived from even numbered division ratios of the 48MHz TCXO, are:- 12, 8, 6, 4, 3, 2, 1.5, and 1 MHz before dropping into the KHz range with corrective phase jumps corresponding to:- 90, 60, 45, 30, 22.5, 15, 11.25 and 7.5 degrees, getting ever smaller with each reduction in frequency below the 1MHz mark. By the time you get down to 15625Hz, these corrective phase jumps (correctionally applied jitter) will have shrunk to a mere 117.1875 millidegrees.

 If we take the idea of using an even integer value of divisor to the limiting value of 48000000 to generate a 1Hz output, these corrective phase jumps will be reduced to just 7.5 microdegrees. Since the rate at which these corrective phase jumps seems to vary from around 5 per second down to one every 5 to 10 seconds (and possibly much longer, given the right conditions) with the particular example of M8N module I've been testing, it would seem the key thing in phase locking a VCXO (OC or TC type) to the GPS reference is that of using a PLL with relatively long time constants in the range of tens of seconds or longer, regardless of which frequency has been chosen to lock the PLL onto.

 If you're going to forego the microcontroller with 16 bit DAC option to drive the Vfc line and just use a PLL directly, the best you can do for the 'hold over' function is to have a separate manually calibrated 'hold over' voltage reference for the lock/unlock detection circuit to switch the VCXO module to, requiring that you regularly adjust this 'hold over' voltage source on a routine basis to match the control voltage output being generated by the PLL in the locked state. This might mean daily calibration/adjustments during the initial weeks of the commissioning period until the VCXO has settled down to the point where once a week calibration checks/adjustments will suffice.

 For hobby use, this will probably be a satisfactory solution in a home built GPSDO, especially when the microcontroller with DAC option can be added as a later upgrade to complete the GPSDO project, otherwise, the alternative would be to allow the 48MHz TCXO of the module to provide a degraded reference during any such loss of lock events as a "Better than nothing" choice to maintain the supply of 10MHz pulses, hopefully for only seconds to minutes per once in a blue moon event that may never happen barring having the GPS antenna knocked out of commission by  storm damage or sabotage, whether by neglect or malicious intent.

 For a home built GPSDO, you can be as pragmatic as you like when it comes to projects like this. There'll be ample opportunity to upgrade it later on after you've learn't a few valuable lessons in the art of designing and building your very own GPSDO. 

JBG

[Johnny B Good]

 An interesting fact about this u-blox module is that, whilst it can output 18MHz clock signals (and even 19.2MHz - checked it just now) on its PPS line, the 16MHz option produces a rather curious toggling on each phase correction event between a 33 and 67 percent duty cycle as a consequence of this division by 3 ratio of its 48MHz TCXO.

 Trying to avoid the clock jitter effect such as typically observed on the 10MHz frequency setting by choosing only integer based division ratios for output frequencies such as 1, 2, 3, 4, 6, 8 and 12MHz will be doomed to failure if the integer is devoid of any even number factors such as that factor of 3 on its own in the example above. Configuring a frequency of 9.6 and 6.857143 MHz ( factors of 5 and 7) for example, produces the same toggling effect as witnessed in the 16MHz case (Oh! The new found joys of 'scope ownership!  ). I've no doubt this will also apply to other stand alone odd division ratios such as 9, 11, 13 etc. but ICBA to do any more tests.

[1] I tried tracking down used VCOCXO modules on Ebay but there are pitifully few to be found and of those, the Chinese sellers don't seem to understand the concept of providing meaningful technical data on what appears to be obsolete kit that the manufacturer no longer offers any data sheets for. Unlike Victor Kyam, I was so unimpressed by these sellers, I didn't buy the product, hence my trawling sites like Farnell and Digikey with a preparedness to spend some real (by my standards) money.

JBG

The Ublox timing application note discusses it a bit but their example is 8MHz so the extra divide by 2 probably evens things out.
https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_%28GPS.G6-X-11007%29.pdf

A couple of sources of VCOCXOs on ebay that are worth looking at are :
(The first I haven't bought from but they look interesting and have data)
https://www.ebay.com/itm/1-x-CTS-OCXO-Crystal-Oscillator-Model-1190027-3-3V-20MHz/273776000063?hash=item3fbe523c3f:g:saMAAOSwMDhcZtYH&autorefresh=true

and
https://www.ebay.com/itm/UCT-OSA-MY-108663-01-10MHz-12V-Double-Oven-OCXO-Crystal-Oscillator/264230742882?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
I've bought three of the 108663 which are equivalent of the Oscilloquartz 8663 I think. I'm currently measuring them at the moment.
They are new old stock and are taking a little while to settle down.

 I had a read of that u-blox app note. I noticed it didn't fully explain the issues but it said enough to confirm that my own conclusions on how the M8N module keeps the PPS synchronised to GPS (or UTC) time had been right on the money.

 That extra divide by two to generate the 8MHz doesn't probably even things out, it simply does even out the 16MHz waveform irregularity created by dividing the 48MHz TCXO by 3 which the drop/add corrections so nicely displays as an alternation of the resulting 2:1 mark/space ratio on a 'scope trace. Probability doesn't come into it. 

 I took a look at those oscillator modules you linked to but neither were of the VC type, both being simply OCXOs with, presumably some sort of trimmer to calibrate them manually. Both had been described as OCXOs and neither mentioned tuning voltage rates in their descriptions.

 OCXOs just aren't suited for use as a disciplined oscillator, there's simply no means by which a GPS referenced PLL can electrically fine tune the frequency of such modules. I wasted a fair bit of time looking at such Ebay traders' OCXO offerings before finally coming to the conclusion that there were only two or three far eastern traders offering VCOCXOs, typically used units, hence my turning to Digikey in desperation.

 As yet, I haven't placed any orders with Digikey, I'm still mulling over my options.

JBG

[texaspyro]

The 8663 has an EFC input.   All mine are on freq with am EFC in the 4 .. 5V range.   The 8663 also has a very stable Vref ouput around 7V.

[rfspezi]

Does anybody know, what best case ppb-range can be expected from a PLL based implementation?

What i need from a GPSDO would be an "absolutely" clean, or at least cleaner than my best measurement equipments internal 10MHz clock.
Otherwise i would only use the GPSDO to calibrate one instrument from time to time and use the output of that particulare one to sync all my other measurement equipment.
For me it does not make sense to have a 10 Mhz reference with 1 ppt accuracy, but poisoned with phase noise etc. that ruins my spectrum analyzer measurements.

I also wonder why the designs i saw so far don't care about apprupt changes in DAC value instead of smoothly adapting the EFC voltage to the new level.

[SoundTech-LG]

I have not seen an OCXO without an EFC input. (that is how you control the freq. externally, such as GPS) Can anyone show one? Seems no EFC would be a waste of an OCXO.

The NOS MY 108663 on ebay seem quite full of phase noise. I have been burning one in for months.
Maybe years of burn-in required? Can't touch the old used 8663-XS.

[jpb]

I took a look at those oscillator modules you linked to but neither were of the VC type, both being simply OCXOs with, presumably some sort of trimmer to calibrate them manually. Both had been described as OCXOs and neither mentioned tuning voltage rates in their descriptions.

They are both of the VC type. I know the 108663 are because I have three of them - they come with a Vref output that can be used to set the control voltage via a pot but you don't have to use it - you can just apply voltage.

On the CTS ones, if you look at the Frequency Control section you can see that they are tunable over +/- 0.8ppm with a control voltage range of 0 to 3.3V. They even state that there is sufficient range to tune back to nominal for up to 10 years.

[jpb]

I have not seen an OCXO without an EFC input. (that is how you control the freq. externally, such as GPS) Can anyone show one? Seems no EFC would be a waste of an OCXO.


The NOS MY 108663 on ebay seem quite full of phase noise. I have been burning one in for months.
Maybe years of burn-in required? Can't touch the old used 8663-XS.

Quite a few OCXOs are non-tunable, you have to be a little careful when buying say from Digikey as often the same type have a V variant (tunable) and an F variant which isn't. I've also found quite a few on ebay are non-tunable or just physically tuned.
Here is one example :
https://abracon.com/Precisiontiming/AOCJYR-10.000MHz-M5625LF.pdf

Interesting what you say on the phase noise. I'm measuring short-term stability and they are definitely worse than the old 8663-XS in my GPSDO but they have been getting better over the few weeks that I've been measuring them.

Perhaps they take a long time to settle. Or perhaps these were all ones that were deemed failures which is why they are now being sold cheap.

What power supply are you using? I found this made a huge difference on my measurements. I got very wavy results when using my Hameg supply and much better (smoother results) when using a Keithley supply or a purely linear TTi supply.

[kj7e]

I'm currently testing 2 of the NOS UCT 108663's and two older 8663's.  The 8663's short term stability drifted rapidly over the first few days, then leveled off quickly.  The 108663's are slowly settling down, the drift is slowing more everyday.  I've been taking EFC voltage readings twice a day for the last month.  I suspect it will take months for the 108663's to really settle down.  I don't have a way to measure the phase noise unfortunately.

[texaspyro]

Here is some drift testing I did on a UTC8663 that I put into a 53132A counter:

UTC 8663 mounted on Sweeny DOCXO card in a HP 53132A counter.  The 8663 had
not been powered up for over 10 years.  Below is the frequency drift per day
as the 8663 aged in.  THe 8663 is spec'd at 1E-10 (1 mHz) per day aging. From
past experience, they are capable of much better than that (1E-11 to 1E-12 per
day).  They seem to be limited in this application by the EFC DAC / VREF
performance.

The 8663 was mounted on the Gerry Sweeny aftermarket OCXO board for the 531xx
counters.  For the first 30 days, the board was configured for the 0 .. 10V
EFC DAC range.  The Sweeny board powers the DAC with +/- 12V which is a bit
out of the spec'd minimum +/- 13.5V required for optimum performance on
the 0 .. 10V range.

The Sweeny OCXO board is based upon the HP design with a couple of nice mods.
First it has footprints for several common OCXO modules.  Second, it allows
the DAC range to be configured for 0 .. 5V,  0 .. 10V, and +/- 5V. 

The circuit feeds the OCXO output through a differential line driver.  The line
driver sends the OCXO to the HP counter mother board through a ribbon cable.
The motherboard makes the OCXO output available on a BNC on the counter
back panel.  Checking the ADEVs of the raw OCXO outout and the counter output
shows that the 53132A degrades the DOCXO output by around 1.5E-12 (raw DOCXO
value around 5.1E-12 at 200 seconds,  counter 10 MHz output BNC around
6.5E-12)

For the first 30 days the EFC DAC reading was recorded and the HP53132A was
then auto-cal'd and the new EFC DAC output was recorded.  (The DAC readings
for the first 10 days were lost when a momentary power failue occured and the
system was not shut down cleanly).

The initial 30 day run was done with the Sweeny board DAC configured
for the 0 .. 10V range.  Given the DOCXO EFC sensitivity (around 0.75 V / Hz)
and the 12-bit DAC, the minimum auto-cal resolution is 0.002 Hz.  Several
auto-cal cycles were performed each morning until one was within 0.001 Hz.

DAC readings were made by a Tektronix DMM914 4.5 digit DMM, not the best tool
for the task, but it was available. 


        drift (Hz/day)    DAC (after cal -> 24 hrs later)
day 1:    .298000 Hz       
day 2:    .057000 Hz       
day 3:    .033000 Hz       
day 4:    .022000 Hz       
day 5:    .017000 Hz       
day 6:    .011800 Hz       
day 7:    .009640 Hz      4.471V
day 8:    .008400 Hz      4.458V
day 9:    .006380 Hz      4.451V
day 10:   .003880 Hz      4.443V
day 11:   .002840 Hz      4.446V -> 4.438V  // power glitch caused reset
day 12:   .003470 Hz      4.437V -> 4.437V
day 13:   .002100 Hz      4.432V -> 4.433V
day 14:   .001590 Hz      4.430V -> 4.430V
day 15:   .001380 Hz      4.426V -> 4.428V
day 16:   .001660 Hz      4.424V -> 4.426V
day 17:   .000526 Hz      4.422V -> 4.423V
day 19:   .000284 Hz      4.421V -> 4.423V
day 20:   .000038 Hz      4.423V -> 4.424V
day 21:   .001019 Hz      4.420V -> 4.420V
day 22:   .001350 Hz      4.417V -> 4.418V
day 23:   .000402 Hz      4.417V -> 4.417V
day 24:   .000953 Hz      4.418V -> 4.419V
day 25:   .000304 Hz      4.417V -> 4.416V
day 26:  -.000441 Hz      4.417V -> 4.418V
day 27:   .000214 Hz      4.415V -> 4.415V
day 28:   .000517 Hz      4.415V -> 4.416V
day 29:  -.000998 Hz      4.415V -> 4.415V
day 30:   .001300 Hz      4.415V -> 4.414V
day 31:   .000423 Hz


Powered down, replaced 53132A fan, changed DAC range to 0 .. 5V, and
the 53132A was put back into case (hence no more DAC readings).  The 0 .. 5V
DAC range reduced the auto-cal minimum step size to 0.001 Hz.   Hopefully
it should also improve the DAC stability.

Warmup frequency error after power up:
   1 Hz     - 3m     
   0.1 Hz   - 3m 25s
   0.01 Hz  - 5m 45s
   0.001 Hz - 6m 15s

After 24 hours the unit was auto-cal'd once and left alone.  The frequency
error for the next week:

day 32:   .000152 Hz  (0.00009 Hz/day for last 18 hours)
day 33:  -.000825 Hz
day 34:  -.000730 Hz
day 35:  -.000287 Hz
day 36:  -.000144 Hz
day 37:  -.000086 Hz
day 38:  -.000083 Hz

[Johnny B Good]

I took a look at those oscillator modules you linked to but neither were of the VC type, both being simply OCXOs with, presumably some sort of trimmer to calibrate them manually. Both had been described as OCXOs and neither mentioned tuning voltage rates in their descriptions.

They are both of the VC type. I know the 108663 are because I have three of them - they come with a Vref output that can be used to set the control voltage via a pot but you don't have to use it - you can just apply voltage.

On the CTS ones, if you look at the Frequency Control section you can see that they are tunable over +/- 0.8ppm with a control voltage range of 0 to 3.3V. They even state that there is sufficient range to tune back to nominal for up to 10 years.

 When you're dealing with Chinese traders on Ebay, the possible lack of an electrical tuning pin is something to watch out for when you consider the cost of return postage involved in returning such items for a full refund. Although the electrically tunable OCXOs are the more common type, it's not something one should ASS-U-ME, hence my concern over the use of "OCXO" as a shorthand for "VCOCXO".

 Anyway, I stumbled across a 13MHz CQE OCXO at last Sunday's NARSA rally which I snapped up for a mere 4 quid. There was a disturbing lack of traders selling OCXOs, ICs and other electronic components at an event where I'd have expected the traders to be falling over themselves to maximise such a golden opportunity to sell their wares to a discerning market demographic.

 One trader said he had OCXOs in stock but didn't think there was going to be sufficient demand to warrant bringing them to this major rally event ( ). Worse still, he wasn't the only trader with a similar excuse for not bothering with selling the many ICs he had in stock, using the excuse that it wasn't worth the effort to sort the many hundreds of types that he had into organised packaging (again  ). Talk about a self fulfilling prophecy! 

 Regardless of imposing such a self fulfilling prophesy over the past decade or so since I was last disappointed by this attitude amongst traders, if the market demographic has actually shifted so far to the consumerist extreme as to suggest that no one in the amateur radio and hobby electronics camp today now even so much as sully their hands with soldering irons and side cutters et al is actually true, then I am truly dismayed by this state of affairs. 

 All that aside, it seems my punt on that OXCO has paid off. After searching for any info on my acquisition, I eventually discovered an image of a single A4 page alongside of the image for a very similar looking 13MHz Vectron OCXO on an Ebay trader's page which implied the use of 12 volts supply along with the accurate pin out and dimensions details.

 Knowing that there was a real possibility that my unit could be a 5 volt part which would be instantly fried by a connection to a 12 volt supply, I tried it initially with 5 volts which, surprisingly, after a 7 or 8 minute warm up at 280mA, suddenly started to output a clean 13MHz 3Vpp square wave (after outputing what I suspect may have been a 4.3333MHz signal during the warm up phase - the use of 3rd overtone SC cut crystals being fairly common in OCXOs). This transition was accompanied by a relatively swift plummet in heater current down to 200mA (20 seconds or so period) where it remained more or less the same.

 The Vref pin voltage was just over 3 volts which isn't enough to allow it to be used as a stabilised tuning voltage (trimming the Vfc pin voltage to get it within +/- 0.5ppb of frequency results in a reading of 3.31v on my 3 1/2 digit DVM. That plus the rather low ratio between warming up and on temperature heater current readings (280:200mA) left me wondering whether it actually was a 5 volt part or a 12 volt one so I tested it with a 6.9 volt supply (6.5v after losing voltage in my moving coil multimeter's shunt circuit on the 600mA scale).

 I noticed that the heat up current was limited to 280mA and the output voltage rose to around the 4.5Vpp mark rather than remain confined to a TTL level from a 5v internal regulator circuit. I temporarily held a 1.3v NiMH cell in series with the 6.9v (6.5v) noting the same 280mA current limit and an even higher output voltage on the 'scope. I didn't dawdle at this voltage (7.8v) for fear of burning out a 5 volt part with an absolute maximum overvolting stress figure of only 7 volts. I guestimated a trend towards a 10Vpp at 12v which seemed a rather improbable specification for even a 12v part.

 This and subsequent testing strongly suggests that, contrary to my initial expectations, this must be a 5 volt part after all, rather than a 12 volt part that has a freakish ability to generate stable on frequency output off a 4.88v supply. The key aspect that led me to even consider the 12 volt possibility being that of the rather low 1.4:1 ratio of warm up to warmed up heater current levels. Most of the OCXO data sheets I've looked at generally show a ratio of 2:1 or even 3:1, hence my "Dicing with death" supply voltage experiment.

 I've already sought advice on this OXCO in my "Ublox-NEO-M8N GPS navigation signal amplify module for arduino Rasppery PI" thread but, after two days, not had any takers. Since there is rather more interest being shown in OCXOs in this thread, I've attached the same set of images I'd posted in the other thread in the hope that someone may recognise the particular OCXO module that I've currently got lashed up to a couple of NB3N502 clock multiplier chips with a 74193 slung between them as a divide by 13 circuit to generate 10MHz from this 13MHz OCXO.

 The unit appears to be unused NOS (the pin out markings were done by me in accordance with the pin out data in the last image showing the Vectron data sheet page).

JBG

[jpb]

There are quite a few 13MHz OCXOs around - I guess because they were used in GSM (?). I bought several MTI ones (new old stock) a while ago simply because they were good OCXOs even though the frequency is a little awkward.

I also bought a couple off this seller (Aspen electronics) who is UK based:
https://www.ebay.co.uk/itm/OCXO-Vectron-13MHz-High-Stability-Oven-Oscillator-New-old-Stock/272806056479
I didn't pay the full £9 as (at the time at least) they were open to offers.
I've not extensively tested it but it seemed to work ok (the frequency varied about the right value when the control voltage was varied.
Looking at your datasheet it seems the same as the Aspen one (on their ebay listing) and does correspond to what they are selling I think but rather different from the OCXO you show in your photo.

Incidentally I also bought a N-type connector Surge supressor off Aspen electronics which they are still selling and are good value - especially as there was a muddle up and they ended up sending me two, I offered to send it back if they would pay the postage but they just told me to keep it.

[Johnny B Good]

There are quite a few 13MHz OCXOs around - I guess because they were used in GSM (?). I bought several MTI ones (new old stock) a while ago simply because they were good OCXOs even though the frequency is a little awkward.

I also bought a couple off this seller (Aspen electronics) who is UK based:
https://www.ebay.co.uk/itm/OCXO-Vectron-13MHz-High-Stability-Oven-Oscillator-New-old-Stock/272806056479
I didn't pay the full £9 as (at the time at least) they were open to offers.
I've not extensively tested it but it seemed to work ok (the frequency varied about the right value when the control voltage was varied.
Looking at your datasheet it seems the same as the Aspen one (on their ebay listing) and does correspond to what they are selling I think but rather different from the OCXO you show in your photo.

Incidentally I also bought a N-type connector Surge supressor off Aspen electronics which they are still selling and are good value - especially as there was a muddle up and they ended up sending me two, I offered to send it back if they would pay the postage but they just told me to keep it.

 Yeah, the data sheet is identical, right down to the incorrectly stated 36.1mm width (I guess it should have read 26.1 afaicr from my own measurements).  If you look past the label, I think you'll see a very strong resemblance to mine.

 Just out of interest, were your units 12 or 5 volt ones? Mine, afaict, seems to be a 5 volt unit. The warm up period seems very protracted. Almost eight minutes when I thought to time it with a stopwatch this morning after leaving it off overnight followed by accidentally stopping the watch prematurely after just two or three minutes when I overreacted to what I thought was the appearance of the stable 10MHz waveform on my 'scope which resulted in my switching it off for a ten or fifteen minute cool down before starting another warm up timing test.

 I don't suppose the mere 4.8v that manages to reach the OCXO via the solderless breadboard is helping this situation in any way. However, the fact that even at this low a voltage it's managing to warm up and start producing a stable 13MHz 3Vpp square wave bodes well for it being an actual 5 volt part, rather than just a freak 12v part which can manage to produce the goods even at such a low voltage, which can prove very useful in eliminating the need to have an additional 12v supply accompanying the existing 5 volt supply needed to power my planned GPSDO project.

 Powering from a 5.25v rail should reduce the warm up to something nearer to the more acceptable 5 minute mark and probably reduce the warmed up heater demand current from 200 to 170mA. I've tried the effect of packing foam rubber pieces top and sides as insulation which knocks around 30mA off its 4.8v current consumption so a reduction to 150mA on the higher voltage supply looks low enough that I might be able to use a 10MHz variant with a NB3N502 multiplier to substitute the 50MHz smd XO chip (currently substituted with a 0.1ppm TCXO module) in my cheap as chips FY6600 signal generator.

 I'd only considered using a TCXO as an upgrade to the execrable 50ppm smd XO chip Feeltech had planted just one centimetre from a bunch of three LDO regulator chips generating 70 deg C temperatures which kept it running at 50 deg C . I'd bought the TCXO as a module simply because it was the cheapest way to get my hands on a 0.1ppm 50MHz TCXO but once I realised how bad an idea it was to transplant the DIP14 oscillator into the original XO location, I simply mounted the TCXO module well away and wired its output via a short length of co-ax to where the smd XO had been.

 The use of an OCXO had originally been discounted on the grounds of its much higher energy consumption not only due to the additional heat load but also the demand for a separate PSU of its own to boot. Now, suitably thermally insulated, not only is the consumption looking low enough for the existing PSU to handle, the extra heat (circa 1 watt or less) is not going to be a problem either.

 Of course, this all assumes that I can get hold of a 10MHz version of this OCXO since the additional ICs needed to generate 10MHz from a 13MHz OCXO draw around another 70 to 80mA which may prove to be the final straw for the much put upon smpsu board during the warm up phase when the heater current is at its maximum limit of 280mA. Still, it's fairly straight forward to test the limits of the FY6600's PSU before committing to such an upgrade should I be so lucky as to get hold of a 10MHz version to play with.

 In the meantime, I guess my next step is to rehome my rat's nest wired prototype concoction onto vero board so I can do more meaningful stability tests and have something that I can shoehorn into a petite case alongside of my u-blox GPS module and some more ICs and/or that Arduino Nano I speculatively purchased when I bought the GPS module some three months ago. At any rate, I'll be able to prototype some PLL designs once I've freed up my solderless prototyping board for further experiments.

 Oh, and just to reiterate, what voltage were those OCXOs of yours? 12 or 5 volts?

JBG

[jpb]

It took me a little while to dig them out (it was about 2 years ago when I bought them).

They are 12V ones (which is stated on the data sheet).

I connected one up as can be seen in the attached pictures - I didn't allow much time for warming up and anyway my counter is in use currently as I'm trying to do some long term ADEV measurements.

The counter on my scope normally reads a little low (it reads 9.99998 MHz at 10MHz) so the frequency is a bit high (reading exactly 13MHz) when it should be a bit low normally with VC not set but as I say, I didn't allow any warm up.
I did check them when I got them.
The control should be between +/-1000 to +/-3000 ppb with the control voltage being between 0 and 10V so it should be changing between 13 and 39 Hz and unfortunately my scope counter is only six digits so doesn't quite extend far enough.

EDIT: I should have added that the voltage is only 2.2V because I'm loading it with 50 ohms - it is above 6V on 10Mohm setting but the waveform is rather ugly. The best load I guess is 600 ohms or so but this was just a quick demo to give you some info.

[jpb]

By the way - if you're after low power these are only 120mW !! :

https://www.ebay.com/itm/CTS-16-384MHz-OCXO-3-3V-Oven-Controlled-VFControl-50ppb-120mW-VFOV405-TCEDH/113700631221

I bought one to play with. Unfortunately they are 16.384MHz which is good for a clock but not so handy for a 10MHz reference.

[Johnny B Good]

It took me a little while to dig them out (it was about 2 years ago when I bought them).

They are 12V ones (which is stated on the data sheet).

I connected one up as can be seen in the attached pictures - I didn't allow much time for warming up and anyway my counter is in use currently as I'm trying to do some long term ADEV measurements.

The counter on my scope normally reads a little low (it reads 9.99998 MHz at 10MHz) so the frequency is a bit high (reading exactly 13MHz) when it should be a bit low normally with VC not set but as I say, I didn't allow any warm up.
I did check them when I got them.
The control should be between +/-1000 to +/-3000 ppb with the control voltage being between 0 and 10V so it should be changing between 13 and 39 Hz and unfortunately my scope counter is only six digits so doesn't quite extend far enough.

EDIT: I should have added that the voltage is only 2.2V because I'm loading it with 50 ohms - it is above 6V on 10Mohm setting but the waveform is rather ugly. The best load I guess is 600 ohms or so but this was just a quick demo to give you some info.

 Thanks JPB.

 The data sheet obviously matches those OCXOs of yours but I'm not so sure it's an exact match to mine. It looks like the one I got must be a later 5 volt version - the rest of the info, pin out and dimensions (width typo excepted) matches but not the tuning voltage spec unless my unit is indeed a 12 volt unit that freakishly also manages to work from as low a voltage as 4.79 volts (perilously close to the lower 5% tolerance limit for a 5 volt part).

 I rather think the reason for the 8 minutes and 21 seconds warm up before mine springs into life (retested it again this morning) is probably on account the 430mA warm up current drags the voltage down below the -5% tolerance limit. I didn't think to check the voltage but since just a few seconds disconnection from supply leads to tens of seconds of another warm up phase, it's easy enough to run a quick voltage check... which reveals a further one tenth of a volt drop but there are so many iffy connections, the slightest disturbance to the USB connectors can vary this by +/- 0.1v making it rather difficult to verify whether an out of tolerance voltage condition is really the cause of this delayed output phenomena[1].

 The fact that a control voltage of 3.31 tunes it exactly to 13MHz, and that it can produce a 3Vpp square wave from a 4.8v supply and the output voltage is raised by the same voltage boost over and above this 4.8 volts (i.e. 6.5v supply produces a 4.5Vpp signal) leads me to the conclusion that it's a 5 volt rather than a 12 volt OXCO in spite of the quite protracted warm up period before it even produces any sensible output at all.

 It's not merely a case of a 3Vpp at slightly the wrong frequency during the warm up, it's a complete lack of output other than a low amplitude unstable high frequency riding on top of a much lower frequency square wave, possibly the fundamental of a 3rd overtone SC cut crystal. If I'm correct in my assessment, then applying 12v is guaranteed to destroy my 4 quid bargain in an instant. Since, aside from the protracted warm up period, it seems to be working just fine off a 4.8v supply, it seems my best bet is to assume that it is a 5 volt part that is best not subjected to a 12v supply.

 The best I can hope for is for someone who has been running a seemingly identical OCXO off a 12v supply for months or even years, to decide, purely out of curiosity you understand, to test them with a 5 volt supply to see whether they'll display the same or similar behaviour as my particular (peculiar?) example.

 Apropos of those ultra low power (by the conventional standard of OCXOs) 16.384MHz clock OCXOs, nice as that is, ultra low power is at the bottom of my list of priorities in my current GPSDO project. I only mentioned the relatively modest power requirement of that 13MHz bargain buy on account of the possibility of now being able to use a 10MHz example in my Feeltech FY6600 without having to add a second dedicated PSU board as would have been required to power a 12v 3W (warmup demand current rating) OCXO module which complication led me to choose that 0.1ppm 50MHz clock power module as a low power requirement compromise between the existing low quality smd XO chip and the ultimate in OCXO accuracy and stability.

[1] ... Several hours later:

 I decided to power the YwRobot Breadboard Power Supply from a 9v wallwart instead of via its USB port, only to discover that the AMS1117-5 was only producing 4.81v    I was no better off so I perused the 1117's data sheet and lifted its ground/ref pin, bunged a 33R in series and, after an initial test to determine that I needed to add a 370R between the output and the Gnd/Ref pin to raise the voltage by almost another half volt, got the soldering iron warmed up again and completed the modification.

 Now I'm getting 5.31 to 5.39 volts depending on how hot the regulator chip gets - much better to be on the high side than on the low side - less waste heat in the LDO regulator for a start and I now see a 13MHz output (initially slightly off frequency of course!) within seconds of powering it up. This is more like it!

 Almost instant, though slightly off frequency, output followed by the warm up phase onto frequency more typical of normal OCXO startup behaviour. I guess my NOS example must be far less ancient than that 1997 data sheet would imply after all. 

JBG

[Johnny B Good]

It took me a little while to dig them out (it was about 2 years ago when I bought them).

They are 12V ones (which is stated on the data sheet).

I connected one up as can be seen in the attached pictures - I didn't allow much time for warming up and anyway my counter is in use currently as I'm trying to do some long term ADEV measurements.

The counter on my scope normally reads a little low (it reads 9.99998 MHz at 10MHz) so the frequency is a bit high (reading exactly 13MHz) when it should be a bit low normally with VC not set but as I say, I didn't allow any warm up.
I did check them when I got them.
The control should be between +/-1000 to +/-3000 ppb with the control voltage being between 0 and 10V so it should be changing between 13 and 39 Hz and unfortunately my scope counter is only six digits so doesn't quite extend far enough.

EDIT: I should have added that the voltage is only 2.2V because I'm loading it with 50 ohms - it is above 6V on 10Mohm setting but the waveform is rather ugly. The best load I guess is 600 ohms or so but this was just a quick demo to give you some info.

 Thanks JPB.

 The data sheet obviously matches those OCXOs of yours but I'm not so sure it's an exact match to mine. It looks like the one I got must be a later 5 volt version - the rest of the info, pin out and dimensions (width typo excepted) matches but not the tuning voltage spec unless my unit is indeed a 12 volt unit that freakishly also manages to work from as low a voltage as 4.79 volts (perilously close to the lower 5% tolerance limit for a 5 volt part).

====snip====

 The best I can hope for is for someone who has been running a seemingly identical OCXO off a 12v supply for months or even years, to decide, purely out of curiosity you understand, to test them with a 5 volt supply to see whether they'll display the same or similar behaviour as my particular (peculiar?) example.

 Apropos of those ultra low power (by the conventional standard of OCXOs) 16.384MHz clock OCXOs, nice as that is, ultra low power is at the bottom of my list of priorities in my current GPSDO project. I only mentioned the relatively modest power requirement of that 13MHz bargain buy on account of the possibility of now being able to use a 10MHz example in my Feeltech FY6600 without having to add a second dedicated PSU board as would have been required to power a 12v 3W (warmup demand current rating) OCXO module which complication led me to choose that 0.1ppm 50MHz clock power module as a low power requirement compromise between the existing low quality smd XO chip and the ultimate in OCXO accuracy and stability.

====snip====

 Now I'm getting 5.31 to 5.39 volts depending on how hot the regulator chip gets - much better to be on the high side than on the low side - less waste heat in the LDO regulator for a start and I now see a 13MHz output (initially slightly off frequency of course!) within seconds of powering it up. This is more like it!

 Almost instant, though slightly off frequency, output followed by the warm up phase onto frequency more typical of normal OCXO startup behaviour. I guess my NOS example must be far less ancient than that 1997 data sheet would imply after all. 

JBG

 Further developments in my cheap OCXO saga:

 I've more or less determined that my bargain of the century 13MHz OCXO acquisition last month is in fact a 5 volt part after all. Disappointingly, those 10MHz versions that I was alluding to turned out to be 12 volt parts (they were identical in appearance to my 13MHz example but as everyone knows, looks can be deceiving).

 One of the results of my search for a definitive data sheet for that 13MHz OCXO was the discovery of a very cheap source of 10MHz versions of this CQE branded OCXO from a UK supplier who, unbelievably, CBA to test them or track down a data sheet so was selling them off for a mere £4.99 each (plus £2.00 P&P one off or £1.0 per additional unit on a multiple order), claiming them to be unused NOS.

<https://www.ebay.co.uk/itm/CQE-CRYSTAL-OSCILLATOR-10MHz-REDUCED-TO-CLEAR/253081992039?hash=item3aecdcbb67:g:x1gAAOSw~qNZh2rl>

<https://tinyurl.com/y6pl2xvk>

 At the time, I'd already ordered a set of three and was waiting on their delivery. I didn't want to mention this source for fear of him being inundated with orders and the stock drying up. Those first three cost me 4 quid in postage but I didn't want to order a "Lifetimes's Supply" in one go just to save a couple of quid in case they turned out to be not such a wise investment after all. As it turned out, all three performed just fine although I was a little suspicious about the claim for them being unused NOS (the pins didn't seem to be quite as pristine looking as my initial 13MHz rally purchase).

 Since I now had a 10MHz OCXO plus a couple of spares, after testing them out on a 5.33v supply and discovering after several minutes delay a 10MHz 600mVpp sine wave output finally putting in an appearance, I decided it would be well worth the risk of applying 12 volts to the Vdd pin to prove my, by then, very strong suspicion that these were the more usual 12 volt parts. The risk taken paid off handsomely. I've also been able to ascertain that, apart from an ac coupled 4Vpp sine wave output, the 13MHz Vectron data sheet I posted pretty much applies to these 10MHz CQE branded clones (including the 0 to 10 volt tuning range with positive sense).

 Once I had satisfied myself as to the worth of ordering more of these OCXOs, I placed an order for another four to secure myself a bargain basement lifetime supply. I've since used one of them (with a NB3N502 clock multiplier chip) to upgrade the TCXO upgrade to my FY6600's original 50MHz SMD XO chip. Of course, this involved adding a 12v 300mA smpsu (extracted innards from a wallwart) to power the OCXO board - the existing +12v rail has insufficient reserve to handle such abuse.

 However, the nice thing about this extra psu complication that I'd initially hoped to avoid is that I can shut the generator off rather than just put it into standby to keep the OCXO up to temperature since its smpsu is wired directly to the IEC C6 mains inlet socket to stay powered up whilst it remains plugged into a mains supply (it only takes 1.3W once up to temperature). Placing the generator into standby only drops the consumption from circa 7 to 9.7 watts down to 5 watts (plus the 1.3W of the OCXO), so I gain an advantage from my pain of adding a second smpsu to the box as well as a very slight reduction in the loading on the original 3 rail smpsu board. What's not to like about a mod like this? 

 Incidentally, my suspicions about these 10MHz CQE OCXOs being unused NOS were confirmed when I received the last four units. A couple of them had the remnants of a through plated hole on a pin each disproving the 'unused NOS' claim. However, since they tested good with tuning voltage settings for exactly their 10MHz frequency ranging from a low of 2.32 to a high of 4.51 volts out of a 0 to 10 volt tuning range, at a penny shy of a fiver each, I could hardly complain at this modest bit of mendacity on the part of the seller.

 However, I can certainly question the need to mislead. The question in this case being why he felt the need to disguise the fact of them being used items at the price he was asking in the first place when such readily evident mendacity could only undermine his credibility. Still, at least you can be on your guard over this aspect of their condition if you decide to take a chance on such a cheap and local (for UK citizens at least) source of 10MHz OCXOs. 

 I still have to lash my GPS up to one of these OCXOs to create a GPSDO better suited to calibrating the FY6600's OCXO upgrade but I thought it best to apply the OCXO upgrade to the FY6600 first before sorting the GPSDO project out since its enhanced frequency stability over the initial TCXO upgrade makes it an even more useful test tool for the next stages in this project.

 Another contributor to the FY6600 thread, 'Arthur Dent', had added a 10MHz OCXO with a NB3N502 clock multiplier chip to his FY6600 over a year ago and included an external 10MHz reference socket with a change over switch. I plan to do almost the same modification but without the complication of a change over switch.

 I recently spotted a reference to the use of injection locking a Wien bridge oscillator (very low harmonic distortion and spurious free sine wave oscillator) to a high stability XO and discovered literature on the use of such injection locking being used to synchronise XOs although I couldn't find any examples of the technique being applied to real world OCXOs.

 However, as far as I can see, it shouldn't be too difficult to injection lock a free running OCXO to an external reference source that's within 1ppb of its frequency. In my case, I'd expect my OCXO to be well within half a part per billion so quite amenable to this technique of getting it to lock into sync with an external 10MHz GPSDO reference without the need for a change over switch or the risk of any 'hand over glitches' that may crash the FY6600's FPGA logic during such transitions back and forth between its internal and external 10MHz reference sources (and fall back gracefully onto its internal source should the external reference fail unexpectedly for any reason whatsoever).

 I started a new thread yesterday called " Injection locking the 10Mhz OCXO to external reference (upgrading a FY6600)" but so far haven't had any takers despite my two attached photos having been viewed 14 and 13 times. It rather looks like I'll have to run my own experiments to find the best method of injection locking the internal TCXO to the 10MHz external source.

 Mention of those photos reminds me that it would be worth attaching them here for a bit of light entertainment. The first will be obvious but the second needs an explanation. Basically, out of frustration with having to make do with just the raw 10MHz PPS output as a calibration reference with all the non integer divisor induced jitter as well as the distracting effect of the sawtooth corrections applied by the GPS module to keep synced with GPS time, I made up a crude crystal and resistor filter using a couple of 10MHz crystals I'd bought at that radio ham rally last month to try and filter out the worst of the jitter on the raw PPS output.

 Rather surprisingly, it worked better than I'd had any right to expect. The picture shows the setup with just sufficient resolution to reveal the details and the effect on the scope traces. However, the still image can't convey the ever present though very toned down sawtooth effect which is now less of a jitter and more a swaying effect. It makes it just that little bit easier to adjust the OCXO to within 100ppt.

 However, since it is a direct output from the GPS's PPS line, it does suffer from variations in phase as reflected by the deviation map plot variations of +/-3 or 4 metres in the u-centre app which equates to some +/- 10 to 12ns phase shifts which makes trying to calibrate an OCXO to within 50ppt rather problematical (also, the sawtooth doesn't help either). As things stand right now, it's largely a matter of luck getting the OCXO tighter than 50ppt. I need a GPSDO source before I can do any better and get a more accurate idea of the ageing drift rate of these OCXOs. Hopefully, it won't be much longer before I finally get my GPSDO project completed sufficiently enough to properly calibrate and check these OCXOs but for now, I'm having to make do with a filtered 10MHz PPS signal.

JBG