[time-nuts] Re: Commercial solution - 122.88 Mhz low noise source

[Jeff Blaine]

It looks like the XO version is mounted on the PCB.  But there is a VCXO 
version which would run about +/- 35 PPM/3.3V typical and that's 
(amazingly) available.

Since this EFT is not an on-board capability, at the moment, I'm 
thinking to mount the VCXO - and associated goodies to slave it to the 
10 Mhz GPSDO feed - in a separate enclosure that could allow the VCXO to 
be thermally insulated.  The temp swing vs. time will move very slowly 
and that would allow a very damped PLL loop to apply corrections.

I've not done anything with a PLL before but I don't envision this as 
being too complicated.  And it would be a pretty cool project.  Don't 
need true "phase" lock, but rather "frequency control" without degrading 
the noise characteristics of the VCXO.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com


On 4/3/22 7:38 PM, Lux, Jim wrote:
> On 4/3/22 5:09 PM, Bob kb8tq wrote:
>> Hi
>>
>> Does the Abricon have an EFC input? If so, rigging up a PLL to lock
>> 122.88 to 10 MHz is probably the best option.
>>
>> Bob
>
>
> And what about moving off the board - so you don't have to chase the 
> temperature swings.
>
>
>>
>>> On Apr 3, 2022, at 7:57 PM, Jeff Blaine <KeepWalking188 at ac0c.com> 
>>> wrote:
>>>
>>> I've got a couple of Red Pitaya 122-16 SDR and want to discipline 
>>> them to an external low noise GPSDO source.  Wanted to see if there 
>>> were some easy solutions that fell into this category.
>>>
>>> For the prior generation (QS1R), I had built a homebrew OCXO based 
>>> on a custom low noise crystal from ICM and that worked great for the 
>>> 125 Mhz application.  Unfortunately this Pitaya is a bit removed in 
>>> Fc and ICM has been out of biz for several years now.
>>>
>>> The RP's on-board oscillator is the respectable Abracon ABLNO 122.88 
>>> which runs about -115 dBc/hz at 100 Hz spacing and that's probably 
>>> not a limitation for the unit.  Unfortunately the OSC is a bit too 
>>> sensitive to external temp and wanders around quite a lot (+/- 5 
>>> PPM) compared to the homebrew OCXO - over the annual ambient temp 
>>> range of (10-35C) (all datasheet referenced values). The Abracon 
>>> unit is mounted on the board with the FPGA and sees additional temp 
>>> range depending on other heat generation factors (FPGA loading).
>>>
>>> I have a couple of commercial GPSDO on the bench now, so a pretty 
>>> clean 10 Mhz GPSDO reference is available now.  And I've seen enough 
>>> board discussion to know that a homebrew GPSDO solution is one of 
>>> those "it's harder than it looks" things.  Hence the desire just to 
>>> buy whatever is the silver bullet, as long as it does not require 
>>> too much silver.  ha ha
>>>
>>> Appreciate any suggestions.  TKs!
>>>
>>> 73/jeff/ac0c
>>> alpha-charlie-zero-charlie
>>> www.ac0c.com
>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe 
>>> send an email to time-nuts-leave at lists.febo.com
>>> To unsubscribe, go to and follow the instructions there.
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe 
>> send an email to time-nuts-leave at lists.febo.com
>> To unsubscribe, go to and follow the instructions there.
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe 
> send an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.