[time-nuts] ensemble oscillators for better stability

Said Jackson saidjack at aol.com
Mon Dec 31 02:36:02 UTC 2012


If the math works out, then I guess it must work.. If one has the time to wait..


Sent From iPhone

On Dec 30, 2012, at 16:23, "John Miles" <jmiles at pop.net> wrote:

>> Bruce,
>> The Tsc5125A and miles Timepod show a phase noise floor 3dB above the
>> noise floor of the two oscillators (if two are used with identical noise
> floors).
> Bruce is actually talking about a semi-undocumented trick with the TimePod
> that allows it to act like an E5052 or TSC 5120A-01 with two internal
> references.  Basically, you remove the SMA jumpers from the TimePod's input
> jack panel and feed two independent reference sources that are very close to
> the same frequency to the Ch0 IN and Ch2 IN jacks.  Then you connect your
> DUT to the REF IN jack, and flip the channel equations from "0-1" and "2-3"
> to "1-0" and "3-2" to reverse the roles of the input and reference sources. 
> That allows the cross-correlation algorithm that normally removes the ADC
> noise from a PN measurement to remove the uncorrelated noise from your two
> references as well.  It's a nifty technique, but it is important that the
> two references be close to the same frequency for various reasons, some of
> which I haven't adequately investigated.   So it falls into the "Unsupported
> technique/Use at your own risk" category.
>> It would be nice if that worked, then we all could use $10 TCXOs instead
> of
>> $1000 Wenzel references.
> That's basically how the E5052A/B and TSC 5120A-01 work -- if you look at
> their phase noise floor specs, they are much better than what can be
> obtained from any one reference source.  The E5052A/B instruments actually
> use the technique to remove the noise from two VHF-microwave downconverters.
> That was my original intent in adding those SMA jacks -- see
> http://www.miles.io/timepod/VHF_test_jig.jpg and
> http://www.miles.io/timepod/VHF_example_400_MHz.png , where a pair of HP
> 8662A synthesizers is used to downconvert a much quieter 400 MHz source for
> measurement at 9 MHz.
> In principle you can indeed use a pair of $10 TCXOs as references to measure
> arbitrarily low-noise DUTs, but you may need to run the measurement for days
> or weeks.  Measurement time is the price of the free lunch in this case.
> -- john
> Miles Design LLC
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