[time-nuts] Advantages & Disadvantages of the TPLL Method

Magnus Danielson magnus at rubidium.dyndns.org
Mon Jun 14 04:45:40 EDT 2010


Steve,

On 06/14/2010 04:49 AM, Steve Rooke wrote:
> On 14 June 2010 10:46, Magnus Danielson<magnus at rubidium.dyndns.org>  wrote:
>
>> Still puts it in the mid-tau range as a method. The useful range and
>> precision of a particular implementation of the method will vary.
>
> By putting a GPSDO in the usual place of the DUT and putting the 10811
> in place of the reference oscillator it could work well beyond the
> 1000s point. CAVEAT: this only works for a DUT that has an EFC that is
> reasonably linear.

EFC linearity will remain an issue for analog oscillators. The 
oscillator gain will differ depending on offset voltage and temperature.

>>> So if you are just thinking about the TPLL for taking ADEV data from 0.1
>>> to 1000 sec, then you're are missing 90% of the other useful stuff it
>>> can do as good or better than most anything thing else out there, and
>>> all for the same $10 (my cost).
>>
>> The typical price-tag of a 10811 is in 100-150 USD. I think it is reasonable
>> to assume that a TPLL weighs in at about 200 USD with all support mixers,
>> amplifiers, ADCs etc. It's not bad, but if you don't have the parts that's
>> about what you need to spend at least.
>
> If you really wanted to be a scrooge, you could open the case on one
> of those plethera of HP intruments and temporarily borrow that 10811
> that is just sitting there. As for something like a ADC, you could
> find a DAQ on fleeBay which could do duty here and also be a useful
> tool for general purpose use. Heck, you can use your sound card to
> digitize the EFC, provided it is DC coupled.

If you don't have the parts, then it will set you back with at least 
that number. If you have the parts, you have already invested in them 
and payed for them that way. You may be lucky to be given the 
oscillator, but honestly you can't rely on that. I just want the cost 
numbers to be more reasonably given. It is still a fairly cheap solution.

>>> BTW, with a couple of minor configuration changes, the TPLL BreadBoard
>>> can be transformed into a LPLL,
>>> so the usefulness of the basic Universal TPLL BB circuit has even more
>>> possibilities.
>>> In fact one could make yet another list of all the additional things it
>>> can do with no added cost,
>>> just by changing a few jumpers and values.
>>> But those things are for later discussions, one windmill at a time.
>>
>> Measurement of phase noise is what the LPLL is good at, especially when done
>> in cross-correlation mode. Interferometric setups use the mixers better.
>> Both these techniques could be used for LPLL and TPLL measures.
>
> Do you have some pointers to these setups please Magnus?

Look at Enrico Rubiolas site where his publications and presentations 
should be inspirational. His focus is on LPLLs. but the methodology of 
cross-correlation and interferometric setup should be as viable in the 
TPLL world.

Cheers,
Magnus





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