[time-nuts] Best way for generating 8994.03 MHz from 2899.00042272.....MHz?

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Sat Aug 15 04:36:02 UTC 2009




On 8/14/09 7:17 PM, "Rick Karlquist" <richard at karlquist.com> wrote:

> Lux, Jim (337C) wrote:
>> These days, you might want to consider using the GaAs VCOs from Hittite,
>> rather than the DRO. DROs are SUCH a pain to build and tune, being a
>> mechanical resonator in a cavity.  Everything you do seems to adversely
>> affect the DRO.  The MMIC VCO is just a die (or a die in a package) and
>> it's
>> pretty much immune to external effects, since the resonator is built into
>> the oscillator.
>> 

> 
> We've used both.  The DRO has much better open loop phase noise, and this
> synthesizer is for a single frequency, so the DRO only needs enough
> tuning to make up for drift.  I was assuming the original poster
> would purchase a DRO.  I agree that they are not something you
> want to build.  We had no trouble with the ones we purchased
> from various vendors.  BTW, the 5071A cesium frequency standard
> uses a DRO to help generate the 9192... MHz signal that
> excites the CBT, as explained in my FCS paper in the early
> 90's.
> 
> I don't understand how you got worse phase noise with a DRO
> than a VCO, unless you used a narrow loop bandwidth for the
> DRO and a wide loop bandwidth for the VCO.

Same basic loop for both.. (well, adjusted so the in-loop noise blends into
the outside the loop noise..but the turnover was pretty similar)

http://tmo.jpl.nasa.gov/progress_report/42-166/166A.pdf is probably the only
published data readily available.



> 
> Perhaps the original poster should start with a VCO and see
> if the phase noise is good enough, then go to a DRO if necessary.

Sure is easier with the MMIC.




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