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[Question] CTI OSC5A2B02 OXCO module high precision frequency reference project

 

As a consequence of a completely unrelated conversation I got the idea of comparing the OXCOs to a GPSDO or another OXCO by filtering out the harmonics, mixing with a GPSDO, filtering out everything above a few Hz and timing the interval between zero crossings of the difference frequency which should be in the milliHertz range. By using higher harmonics the measurement period can be reduced from 100 s as desired.

Has anyone tried or heard of someone using such a technique? Given the long history of frequency comparisons I should expect it's been done by many others prior to the advances in the '70s and '80s in semiconductor technology.

Have Fun!
Reg
 

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Have you run a phase noise test on them?

?

From: Reginald Beardsley via groups.io
Sent: Wednesday, August 9, 2023 4:04 PM
To: [email protected]
Subject: Re: [qex] [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project

?

As a consequence of a completely unrelated conversation I got the idea of comparing the OXCOs to a GPSDO or another OXCO by filtering out the harmonics, mixing with a GPSDO, filtering out everything above a few Hz and timing the interval between zero crossings of the difference frequency which should be in the milliHertz range. By using higher harmonics the measurement period can be reduced from 100 s as desired.

Has anyone tried or heard of someone using such a technique? Given the long history of frequency comparisons I should expect it's been done by many others prior to the advances in the '70s and '80s in semiconductor technology.

Have Fun!
Reg

?

9D0D469BA24942CCABE219B630BB0F6A.png

 

I am just starting on this project. So far all I have done is test 4 of the trimmer next to OXCO PCBs and measured the voltage required to set 10 bare OXCOs to 10 MHz.

Tests on the first two PCB units set them set to 10 MHz and showed 0.1 ppb over a couple of days comparing the OXCOs to a GPSDO and the OXCO in my HP 5386A and timing how long it took
for the OXCOs to vary by a cycle or half cycle relative to GPSDO on a 4 channel DSO.

That is all the testing I have done. It was very informal and was solely for the sake of determining whether I wanted to buy more. I ordered 3 more PCBs and 10 bare OXCOs.

Of the 3 PCBs one had a cap broken off which I've not dealt with yet and the other two would not tune to 10 MHz. That alerted me to the drift of the voltage required to set the OXCO to 10 MHz. So when the 10 bare OXCOs arrived I adjusted them to as close to 10 MHz as I could with a lab supply and noted the voltage and frequency as reported by the 5386A using the GPSDO as the reference. I am still waiting for the 2nd batch of 10 bare OXCOs to arrive.

I have only done qa very preliminary error budget assessment focused solely on the PS to the LM399 and OXCO. The most basic steps for such an endeavor are not complete. I've only gotten far enough to know that the PS will have to be *very* much more stable and accurate than anything I currently have in functional form.

I have lots of nice T&M kit, but nothing in the 0.001 ppb range, so I'll have to build that. While retrieving an ancient CB radio PSU to repurpose for this effort I found a Sola Constant Voltage ferroresonant transformer which will accept 90-130 Vac and output 118 Vac.

The net result is I now have 2 different PS designs for feeding the LM399 and AD8429 to test:

Sola and single LM317

Dual LM317

I'm busier than the proverbial one armed paper hanger with hives. I'm building a rack and bench to hold all the T&M gear which has never all been in operation at the same time, managing 16,000 sq ft of commercial space comprised of 4 discrete buildings and attempting to dispose of a staggering volume of stuff my Dad left ranging from WW II surplus electronics parts to an NOS Montgomery Ward cement mixer still on the pallet. Add to that multiple pieces of T&M kit, cables and adapters, etc arriving which need to be checked within the return period.

The PS for this project is the absolute limit of what I have time for.

Have Fun!
Reg

 

¿ªÔÆÌåÓý

This person named Adrian Rus, pretty sharp engineer and entrepreneur, (co-authored some papers with Ulrich) said (and we tested it) that you should have a minimum of 15,000uf on an individual oscillator for references.? Also, and I tested this for him, we switched to lt3045 regulators as they were proven to be exceptionally low-noise and cleaned-up even dirty power supplies.? We used these modules and others like them:

?

?

For testing, I used a 60dB amp that tapped off the residual noise and A/C from the DC voltage and then fed that into my low frequency spectrum analyzer and the noise reduction was amazing.

?

Andrew Holme, who authored our phase noise test set, used a capacitance multiplier circuit with large caps on it.? I tested it and then fed it into the lt3045s and it was pretty clean.? You can stack the lt3045s for more current and also in series to reduce noise.

?

Big problem turned out to be shielding when testing very low PN oscillators in the -180 dBc range so for testing I switched to Dewalt 20V power tool batteries followed by the lt3045 regulators.? When using batteries and 15kuf caps though, I first used the LM317 regulators and didn¡¯t see much difference but running off of mains, the lt3045s made all the difference.? Every noise spike we found later was related to external energy.

?

If I was building a bench, I think I would have a rack of the lt3045s with a switch that fed them from batteries or from mains.

?

?

?

?

Sent from for Windows

?

From: Reginald Beardsley via groups.io
Sent: Thursday, August 10, 2023 11:15 AM
To: [email protected]
Subject: Re: [qex] [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project

?

I am just starting on this project. So far all I have done is test 4 of the trimmer next to OXCO PCBs and measured the voltage required to set 10 bare OXCOs to 10 MHz.

Tests on the first two PCB units set them set to 10 MHz and showed 0.1 ppb over a couple of days comparing the OXCOs to a GPSDO and the OXCO in my HP 5386A and timing how long it took
for the OXCOs to vary by a cycle or half cycle relative to GPSDO on a 4 channel DSO.

That is all the testing I have done. It was very informal and was solely for the sake of determining whether I wanted to buy more. I ordered 3 more PCBs and 10 bare OXCOs.

Of the 3 PCBs one had a cap broken off which I've not dealt with yet and the other two would not tune to 10 MHz. That alerted me to the drift of the voltage required to set the OXCO to 10 MHz. So when the 10 bare OXCOs arrived I adjusted them to as close to 10 MHz as I could with a lab supply and noted the voltage and frequency as reported by the 5386A using the GPSDO as the reference. I am still waiting for the 2nd batch of 10 bare OXCOs to arrive.

I have only done qa very preliminary error budget assessment focused solely on the PS to the LM399 and OXCO. The most basic steps for such an endeavor are not complete. I've only gotten far enough to know that the PS will have to be *very* much more stable and accurate than anything I currently have in functional form.

I have lots of nice T&M kit, but nothing in the 0.001 ppb range, so I'll have to build that. While retrieving an ancient CB radio PSU to repurpose for this effort I found a Sola Constant Voltage ferroresonant transformer which will accept 90-130 Vac and output 118 Vac.

The net result is I now have 2 different PS designs for feeding the LM399 and AD8429 to test:

Sola and single LM317

Dual LM317

I'm busier than the proverbial one armed paper hanger with hives. I'm building a rack and bench to hold all the T&M gear which has never all been in operation at the same time, managing 16,000 sq ft of commercial space comprised of 4 discrete buildings and attempting to dispose of a staggering volume of stuff my Dad left ranging from WW II surplus electronics parts to an NOS Montgomery Ward cement mixer still on the pallet. Add to that multiple pieces of T&M kit, cables and adapters, etc arriving which need to be checked within the return period.

The PS for this project is the absolute limit of what I have time for.

Have Fun!
Reg

?

DE402535D0F8445590634EA13265E995.png

 


Jerry,

Thanks as always. That's very helpful, though ti adds a 3rd option to test.. This seems like a good application for 1-2 Farad caps on all the DC lines adjacent to the device being powered.

That should yield sub 1 Hz RC time constants. As Ken Thompson said, "When it doubt, use brute force."

One of the things that scares me is EMI. A "make before break" relay to switch between mains supply and a battery for measurements.

At the moment I'm swamped by the consequences of a buying binge arriving.

Have Fun!
Reg


On Friday, August 11, 2023 at 11:59:02 AM CDT, Jerry <jerry@...> wrote:


This person named Adrian Rus, pretty sharp engineer and entrepreneur, (co-authored some papers with Ulrich) said (and we tested it) that you should have a minimum of 15,000uf on an individual oscillator for references. Also, and I tested this for him, we switched to lt3045 regulators as they were proven to be exceptionally low-noise and cleaned-up even dirty power supplies. We used these modules and others like them:



https://www.ebay.com/itm/274137165726?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=pX50eYVtSOq&sssrc=2047675&ssuid=UQSWHCvkTY2&widget_ver=artemis&media=COPY



For testing, I used a 60dB amp that tapped off the residual noise and A/C from the DC voltage and then fed that into my low frequency spectrum analyzer and the noise reduction was amazing.



Andrew Holme, who authored our phase noise test set, used a capacitance multiplier circuit with large caps on it. I tested it and then fed it into the lt3045s and it was pretty clean. You can stack the lt3045s for more current and also in series to reduce noise.



Big problem turned out to be shielding when testing very low PN oscillators in the -180 dBc range so for testing I switched to Dewalt 20V power tool batteries followed by the lt3045 regulators. When using batteries and 15kuf caps though, I first used the LM317 regulators and didn¡¯t see much difference but running off of mains, the lt3045s made all the difference. Every noise spike we found later was related to external energy.



If I was building a bench, I think I would have a rack of the lt3045s with a switch that fed them from batteries or from mains.









Sent from Mail for Windows
 

FYI I just ordered 4 from this seller:

https://www.ebay.com/itm/115745541000

Which was about 1/4 of the other seller's prices. Makes them suspect, but Shenzen is truly the Wild West and Far East.

I'll test and post results when they arrive.

Have Fun!
Reg

BTW Trimming everything after the "?" deletes ebay's tracking information. I alsways test the link after the edit to verify I didn't drop a digit.
-------------------------------------------------------------------------------------------------------------------------------------


On Friday, August 11, 2023 at 11:59:02 AM CDT, Jerry <jerry@...> wrote:


This person named Adrian Rus, pretty sharp engineer and entrepreneur, (co-authored some papers with Ulrich) said (and we tested it) that you should have a minimum of 15,000uf on an individual oscillator for references. Also, and I tested this for him, we switched to lt3045 regulators as they were proven to be exceptionally low-noise and cleaned-up even dirty power supplies. We used these modules and others like them:



https://www.ebay.com/itm/274137165726?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=pX50eYVtSOq&sssrc=2047675&ssuid=UQSWHCvkTY2&widget_ver=artemis&media=COPY

[snip]
 

Not so much design as a hobby, but my noise floor really shrunk when I powered my station with a deep cycle battery.? Wonder what the equivalent capacitance is on a group 24??? ;-)? the switching smart charger is not noticeable with the battery in line.

On Aug 11, 2023 10:50, "Reginald Beardsley via groups.io" <pulaskite@...> wrote:

Jerry,

Thanks as always. That's very helpful, though ti adds a 3rd option to test.. This seems like a good application for 1-2 Farad caps on all the DC lines adjacent to the device being powered.

That should yield sub 1 Hz RC time constants. As Ken Thompson said, "When it doubt, use brute force."

One of the things that scares me is EMI. A "make before break" relay to switch between mains supply and a battery for measurements.

At the moment I'm swamped by the consequences of a buying binge arriving.

Have Fun!
Reg

On Friday, August 11, 2023 at 11:59:02 AM CDT, Jerry <jerry@...> wrote:


This person named Adrian Rus, pretty sharp engineer and entrepreneur, (co-authored some papers with Ulrich) said (and we tested it) that you should have a minimum of 15,000uf on an individual oscillator for references. Also, and I tested this for him, we switched to lt3045 regulators as they were proven to be exceptionally low-noise and cleaned-up even dirty power supplies. We used these modules and others like them:



https://www.ebay.com/itm/274137165726?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=pX50eYVtSOq&sssrc=2047675&ssuid=UQSWHCvkTY2&widget_ver=artemis&media=COPY



For testing, I used a 60dB amp that tapped off the residual noise and A/C from the DC voltage and then fed that into my low frequency spectrum analyzer and the noise reduction was amazing.



Andrew Holme, who authored our phase noise test set, used a capacitance multiplier circuit with large caps on it. I tested it and then fed it into the lt3045s and it was pretty clean. You can stack the lt3045s for more current and also in series to reduce noise.



Big problem turned out to be shielding when testing very low PN oscillators in the -180 dBc range so for testing I switched to Dewalt 20V power tool batteries followed by the lt3045 regulators. When using batteries and 15kuf caps though, I first used the LM317 regulators and didn¡¯t see much difference but running off of mains, the lt3045s made all the difference. Every noise spike we found later was related to external energy.



If I was building a bench, I think I would have a rack of the lt3045s with a switch that fed them from batteries or from mains.









Sent from Mail for Windows
 

Grif,

Thanks for your very interesting and insightful question. I've never thought about that, but it suggests an excellent experiment.

The effective capacitance at a particular discharge rate should be measurable using a DSO in single shot to measure the voltage across the battery when a load is applied and then solving for C.

I don't know enough about battery behavior to offer anything more than a SWAG that the effective capacitance varies with the applied load.

This might be an excellent case for a battery of Edison cells for a low noise PSU.

Have Fun!
Reg




On Friday, August 11, 2023 at 03:00:12 PM CDT, Grif Griffith <grif615@...> wrote:


Not so much design as a hobby, but my noise floor really shrunk when I powered my station with a deep cycle battery. Wonder what the equivalent capacitance is on a group 24??? ;-) the switching smart charger is not noticeable with the battery in line.

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