MJ
Matthias Jelen
Tue, May 23, 2017 7:40 AM
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
MD
Magnus Danielson
Tue, May 23, 2017 9:40 AM
Hi Matthias,
I seem to recall a similar issue and as I recall it, I could see
"wobbles" on the output, which I presume is from the rubidium lamp
RF-generation. It was quite obvious when looking at the output with a
scope. I am quite sure it was a LPFRS-01.
Cheers,
Magnus
On 05/23/2017 09:40 AM, Matthias Jelen wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
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Hi Matthias,
I seem to recall a similar issue and as I recall it, I could see
"wobbles" on the output, which I presume is from the rubidium lamp
RF-generation. It was quite obvious when looking at the output with a
scope. I am quite sure it was a LPFRS-01.
Cheers,
Magnus
On 05/23/2017 09:40 AM, Matthias Jelen wrote:
> Hello Time-Nuts,
>
> i´ve been playing with some Rbs recently.
>
> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>
> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>
> Any hints are appreciated.
>
> Regards,
>
> Matthias
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
CS
Charles Steinmetz
Tue, May 23, 2017 10:53 AM
one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump.
My first guess would be a problem in the control loop locking the VCXO to the Rb
Good guess. The most likely explanation is that the loop is unstable or
marginally stable over a range of frequencies. This could be due to
wrong component values in the loop filter due, for example, to component
value drift (probably a capacitor, maybe a resistor) or installation of
wrongly valued parts at the time of assembly, OR unexpectedly high f/V
sensitivity of the EFC characteristic of the VCXO.
It could also be a problem with the power supply to the loop filter, or
frequency modulation in the Rb physics package, but both of those are
much less likely than instability of the VCXO locking loop, IMO.
Best regards,
Charles
Matthias wrote:
> one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump.
>
> My first guess would be a problem in the control loop locking the VCXO to the Rb
Good guess. The most likely explanation is that the loop is unstable or
marginally stable over a range of frequencies. This could be due to
wrong component values in the loop filter due, for example, to component
value drift (probably a capacitor, maybe a resistor) or installation of
wrongly valued parts at the time of assembly, OR unexpectedly high f/V
sensitivity of the EFC characteristic of the VCXO.
It could also be a problem with the power supply to the loop filter, or
frequency modulation in the Rb physics package, but both of those are
much less likely than instability of the VCXO locking loop, IMO.
Best regards,
Charles
BK
Bob kb8tq
Tue, May 23, 2017 11:28 AM
Hi
It could be a DDS based coarse tune loop and you just happen to be unlucky on one unit.
You can (with bad luck) get a fairly significant spur out of a DDS quite close to carrier. That
will give you “ripples” in the ADEV plot.
Bob
On May 23, 2017, at 3:40 AM, Matthias Jelen Matthias.Jelen@gmx.de wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
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and follow the instructions there.
Hi
It could be a DDS based coarse tune loop and you just happen to be unlucky on one unit.
You can (with bad luck) get a fairly significant spur out of a DDS quite close to carrier. That
will give you “ripples” in the ADEV plot.
Bob
> On May 23, 2017, at 3:40 AM, Matthias Jelen <Matthias.Jelen@gmx.de> wrote:
>
> Hello Time-Nuts,
>
> i´ve been playing with some Rbs recently.
>
> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>
> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>
> Any hints are appreciated.
>
> Regards,
>
> Matthias
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
A
Angus
Tue, May 23, 2017 7:44 PM
Hi,
If you've not already looked, it would be worth checking on the
EEVblog since there were some discussions there on faults in these
units - particularly the capacitor and lamp voltage issues.
One of the temperature controllers could be a little unstable too.
Angus.
On Tue, 23 May 2017 09:40:26 +0200, you wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Hi,
If you've not already looked, it would be worth checking on the
EEVblog since there were some discussions there on faults in these
units - particularly the capacitor and lamp voltage issues.
One of the temperature controllers could be a little unstable too.
Angus.
On Tue, 23 May 2017 09:40:26 +0200, you wrote:
>Hello Time-Nuts,
>
>i´ve been playing with some Rbs recently.
>
>I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>
>Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>
>Any hints are appreciated.
>
>Regards,
>
>Matthias
>
>_______________________________________________
>time-nuts mailing list -- time-nuts@febo.com
>To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.
MJ
Matthias Jelen
Thu, May 25, 2017 8:12 AM
Hi Angus,
thanks for the hint. I read through this fairly long thread - the
baseline seems to be: Replace the caps.
Best regards,
Matthias
Am 23.05.2017 um 21:44 schrieb Angus:
Hi,
If you've not already looked, it would be worth checking on the
EEVblog since there were some discussions there on faults in these
units - particularly the capacitor and lamp voltage issues.
One of the temperature controllers could be a little unstable too.
Angus.
On Tue, 23 May 2017 09:40:26 +0200, you wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
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and follow the instructions there.
Hi Angus,
thanks for the hint. I read through this fairly long thread - the
baseline seems to be: Replace the caps.
Best regards,
Matthias
Am 23.05.2017 um 21:44 schrieb Angus:
> Hi,
>
> If you've not already looked, it would be worth checking on the
> EEVblog since there were some discussions there on faults in these
> units - particularly the capacitor and lamp voltage issues.
> One of the temperature controllers could be a little unstable too.
>
> Angus.
>
>
> On Tue, 23 May 2017 09:40:26 +0200, you wrote:
>
>> Hello Time-Nuts,
>>
>> i´ve been playing with some Rbs recently.
>>
>> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>>
>> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>>
>> Any hints are appreciated.
>>
>> Regards,
>>
>> Matthias
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
BK
Bob kb8tq
Thu, May 25, 2017 10:46 AM
On May 25, 2017, at 4:12 AM, Matthias Jelen Matthias.Jelen@gmx.de wrote:
Hi Angus,
thanks for the hint. I read through this fairly long thread - the baseline seems to be: Replace the caps.
Best regards,
Matthias
That’s what worked for mine ….. (at least most of them). In my case they arrived dead.
Bob
Am 23.05.2017 um 21:44 schrieb Angus:
Hi,
If you've not already looked, it would be worth checking on the
EEVblog since there were some discussions there on faults in these
units - particularly the capacitor and lamp voltage issues.
One of the temperature controllers could be a little unstable too.
Angus.
On Tue, 23 May 2017 09:40:26 +0200, you wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Hi
> On May 25, 2017, at 4:12 AM, Matthias Jelen <Matthias.Jelen@gmx.de> wrote:
>
> Hi Angus,
>
> thanks for the hint. I read through this fairly long thread - the baseline seems to be: Replace the caps.
>
> Best regards,
>
> Matthias
That’s what worked for mine ….. (at least most of them). In my case they arrived dead.
Bob
>
> Am 23.05.2017 um 21:44 schrieb Angus:
>> Hi,
>>
>> If you've not already looked, it would be worth checking on the
>> EEVblog since there were some discussions there on faults in these
>> units - particularly the capacitor and lamp voltage issues.
>> One of the temperature controllers could be a little unstable too.
>>
>> Angus.
>>
>>
>> On Tue, 23 May 2017 09:40:26 +0200, you wrote:
>>
>>> Hello Time-Nuts,
>>>
>>> i´ve been playing with some Rbs recently.
>>>
>>> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>>>
>>> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>>>
>>> Any hints are appreciated.
>>>
>>> Regards,
>>>
>>> Matthias
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
> _______________________________________________
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> and follow the instructions there.
TS
Tim Shoppa
Thu, May 25, 2017 11:27 AM
Matthias, are the units all over in the same thermal environment when you test them?
A period of 150s or so in a wobble sounds like a not perfectly damped thermal cycle time of a lightweight oven or lamp.
Reminds me a little of the unit to unit variation in HP Wien Bridge oscillator amplitude stability (also a lamp!)
Tim N3QE
On May 23, 2017, at 3:40 AM, Matthias Jelen Matthias.Jelen@gmx.de wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Matthias, are the units all over in the same thermal environment when you test them?
A period of 150s or so in a wobble sounds like a not perfectly damped thermal cycle time of a lightweight oven or lamp.
Reminds me a little of the unit to unit variation in HP Wien Bridge oscillator amplitude stability (also a lamp!)
Tim N3QE
> On May 23, 2017, at 3:40 AM, Matthias Jelen <Matthias.Jelen@gmx.de> wrote:
>
> Hello Time-Nuts,
>
> i´ve been playing with some Rbs recently.
>
> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>
> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>
> Any hints are appreciated.
>
> Regards,
>
> Matthias
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
MJ
Matthias Jelen
Thu, May 25, 2017 12:12 PM
Hi Tim,
yes, both units on my workbench, same setup, same power supply.
I´ll exchange the caps.
I wonder why they made efforts to design a physics package with 20 years
lifetime, just to put wet electrolytic caps into such a hot environment.
Regards,
Matthias
Am 25.05.2017 um 13:27 schrieb Tim Shoppa:
Matthias, are the units all over in the same thermal environment when you test them?
A period of 150s or so in a wobble sounds like a not perfectly damped thermal cycle time of a lightweight oven or lamp.
Reminds me a little of the unit to unit variation in HP Wien Bridge oscillator amplitude stability (also a lamp!)
Tim N3QE
On May 23, 2017, at 3:40 AM, Matthias Jelen Matthias.Jelen@gmx.de wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
Hi Tim,
yes, both units on my workbench, same setup, same power supply.
I´ll exchange the caps.
I wonder why they made efforts to design a physics package with 20 years
lifetime, just to put wet electrolytic caps into such a hot environment.
Regards,
Matthias
Am 25.05.2017 um 13:27 schrieb Tim Shoppa:
> Matthias, are the units all over in the same thermal environment when you test them?
>
> A period of 150s or so in a wobble sounds like a not perfectly damped thermal cycle time of a lightweight oven or lamp.
>
> Reminds me a little of the unit to unit variation in HP Wien Bridge oscillator amplitude stability (also a lamp!)
>
> Tim N3QE
>
>> On May 23, 2017, at 3:40 AM, Matthias Jelen <Matthias.Jelen@gmx.de> wrote:
>>
>> Hello Time-Nuts,
>>
>> i´ve been playing with some Rbs recently.
>>
>> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>>
>> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>>
>> Any hints are appreciated.
>>
>> Regards,
>>
>> Matthias
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
BK
Bob kb8tq
Thu, May 25, 2017 12:59 PM
Hi
Even more to the point, why did they put in 5,000 hour caps and run them right at
maximum temperature? No derating the voltage or anything …. It looks very much
like a design decision made by the purchasing department :)
Bob
On May 25, 2017, at 8:12 AM, Matthias Jelen Matthias.Jelen@gmx.dewrote:
Hi Tim,
yes, both units on my workbench, same setup, same power supply.
I´ll exchange the caps.
I wonder why they made efforts to design a physics package with 20 years lifetime, just to put wet electrolytic caps into such a hot environment.
Regards,
Matthias
Am 25.05.2017 um 13:27 schrieb Tim Shoppa:
Matthias, are the units all over in the same thermal environment when you test them?
A period of 150s or so in a wobble sounds like a not perfectly damped thermal cycle time of a lightweight oven or lamp.
Reminds me a little of the unit to unit variation in HP Wien Bridge oscillator amplitude stability (also a lamp!)
Tim N3QE
On May 23, 2017, at 3:40 AM, Matthias Jelen Matthias.Jelen@gmx.de wrote:
Hello Time-Nuts,
i´ve been playing with some Rbs recently.
I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
Any hints are appreciated.
Regards,
Matthias
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Hi
Even more to the point, why did they put in 5,000 hour caps and run them right at
maximum temperature? No derating the voltage or anything …. It looks very much
like a design decision made by the purchasing department :)
Bob
> On May 25, 2017, at 8:12 AM, Matthias Jelen <Matthias.Jelen@gmx.de>wrote:
>
> Hi Tim,
>
> yes, both units on my workbench, same setup, same power supply.
>
> I´ll exchange the caps.
>
> I wonder why they made efforts to design a physics package with 20 years lifetime, just to put wet electrolytic caps into such a hot environment.
>
> Regards,
>
> Matthias
>
> Am 25.05.2017 um 13:27 schrieb Tim Shoppa:
>> Matthias, are the units all over in the same thermal environment when you test them?
>>
>> A period of 150s or so in a wobble sounds like a not perfectly damped thermal cycle time of a lightweight oven or lamp.
>>
>> Reminds me a little of the unit to unit variation in HP Wien Bridge oscillator amplitude stability (also a lamp!)
>>
>> Tim N3QE
>>
>>> On May 23, 2017, at 3:40 AM, Matthias Jelen <Matthias.Jelen@gmx.de> wrote:
>>>
>>> Hello Time-Nuts,
>>>
>>> i´ve been playing with some Rbs recently.
>>>
>>> I compared two LPFRS-01 to a PRS-10. One seems to behave quite well (compared to the specs given here: http://www.spectratime.com/uploads/documents/isource/iSource_LPFRS%20Spec.pdf) - short term stability specs are met), the other one shows quite some phase ripple (appx. 1 ns RMS with a frequency around 0.007 Hz) which spoils ADEV in the 60 - 200s range, very similiar to the typical GPSDO bump. Long term stabilty is OK.
>>>
>>> Unfortunatly I didn´t find any schematics on the web. Has anyone encountered a similiar problem with this unit? Any idea were this might come from? My first guess would be a problem in the control loop locking the VCXO to the Rb, but I have no clue which time constants are used in the PLL.
>>>
>>> Any hints are appreciated.
>>>
>>> Regards,
>>>
>>> Matthias
>>>
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