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

Magnus Danielson magnus at rubidium.dyndns.org
Sun Jun 13 22:46:54 UTC 2010

On 06/13/2010 07:29 PM, WarrenS wrote:
> Magnus Posted
>> "The TPLL is a mid-tau stability test, since it's sweet-spot is in the
>> 0,1 - 1000 s range. Short-term is better handled in LPLL phase-noise
>> measurements."
> Mostly agree, it is a mid-tau device, but also consider:
> The simple TPLL can be used to find the 1ms to 10 ms ADEV as good and
> maybe? better than ANYthing else.
> AND I use it to find the drift and ADEV of my dual oven HP 10811's out
> to weeks, so there is no long term limit.
> (the trick is to control the DUT and not the Reference when doing long
> term testing)
> I find the TPLL method is useful for MUCH more than just getting ADEV data.
> As such it's "sweet spot" extends from below 0.004 ms (250 Hz)
> all the way up to >> weeks, when the DUT is the controlled Osc.

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.

One rarely sees plots below 100 ms. I think you ment 4 ms, as it would 
correspond to 250 Hz.

> ALSO the simple TPLL is very Good and useful for seeing and measuring
> the effects of temperature, line noise, vibration, PS, load, and just
> about everything else that effects the frequency stability of an
> oscillators below 1 KHz or so.

For the price-tag, it could very well be an interesting alternative.

> 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 still in doubt about some of the TPLL's other high end performance
> capabilities, try the swinging osc test with ANYthing else and see if
> you can match the simple TPLL's performance.
> If one would make a list for the non ADEV uses and advantages of the
> simple TPLL
> It would indeed be very long list, and it does not take any fancy write
> up to see that, just a bit of open minded thinking.
> 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.


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