[time-nuts] Timenoob - Cheap and simple 10MHz reference

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Dec 28 20:27:42 UTC 2009


Giuseppe Marullo wrote:
> Robert,
>
>> Welcome to the group.
> Thank you and all the others, you are giving me a lot of informations. 
> BTW, my provider retrieved my emails so I am fully operational (at 
> least I hope).
>
> while I did not originally envision building this kind of equipment, I 
> could do it while it lies well within the digital domain, I have some 
> test gear (frequency counter, DMM, analog scope, BF frequency 
> generator, LA and some FPGAs with 100+Msamples ADC) but...I will have 
> to trust it so I am back at square one, until I have a reliable 
> source... I would like a GPSDO, possibly ready to run, then I will 
> start building something that I could actually check against the GPSDO.
>
> Maybe a GPSDO myself, who knows...wondering if this could be done all 
> digital, without using a DAC, without using a driving voltage for a OCXO.
>
> Giuseppe
>
Giuseppe

One can use a DDS or equivalent phase continuous high resolution 
sysnthesizer to produce a corrected output frequency using the OCXO 
frequency as an input, however the DDS itself uses a DAC and you will 
probably need to use a few cascaded mix and divide stages to reduce the 
spur amplitude to an acceptable level.
This has the advantage that one can use an OCXO that either doesnt have 
an EFC input or one that has drifted beyond the adjustment range (via 
EFC and/or mechanical trimmer) but is otherwise quiet and stable.

Bruce





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