[time-nuts] TPLL secret reveled

Steve Rooke sar10538 at gmail.com
Thu Jun 10 01:05:26 EDT 2010


Warren,

>From what I hear you say, the calculation of ADEV requires frequency
measurements spaced at accurate Tau intervals. It is also evident
that, although frequency is the reciprocal of period, the spacing of
frequency data thus converted from phase data would not be accurately
spaced at Tau intervals and attempts to correct for that
mathematically is only an interpolation therefore accurately spaced
frequency measurements should give the best results. The one thing
that is somewhat concerning with your claims is that you are
suggesting your able to obtain time slice measurements down to 1
femtosecond accuracy. I am aware that you have been using an off the
shelf A2D DAQ and I find it hard to believe that this instrument is
able to repeatedly take measurements at that accuracy. This would
require some form of internal clock which is accurate to 10^-15 and is
most probably far more accurate than any reference oscillator you have
on site. A DAQ with such accuracy of repeated methods would most
likely cost well in excess of a TSC in the first place.

I am also aware that you do not have the time to produce a polished
drafted schematic of your simple TPLL circuit so you have been
annotating existing TPLL block diagrams but would it be possible for
you to draw the actual circuit on a plain piece of paper with a pencil
and then photograph it so to include it with a future posting please.
I personally do not require anything highly polished in some  fancy
CAD program and would be very happy with a hand drawn annotated
circuit.

Best regards,
Steve

On 10 June 2010 16:05, WarrenS <warrensjmail-one at yahoo.com> wrote:
>
> There has been speculation on why the low cost, simple, TPLL tester compares
> so favorably with the TSC 5120A over a wide range of taus, even when  using
> different Oscillators. The theories range from pure luck to some special
> secret magic hardware.
>
> If I was that lucky, I'd be doing Lottery and not ADEV.
> And If I could build some secret simple Hardware, and was able to adjust it
> to give some desired effect on future random noise, I'd be in politics or
> the stock market, not making ADEV Breadboards.
> There is another more likely explanation that is within my limited
> capabilities, that many refuse to consider.
> That is this method just works correctly without doing anything very special
> at all.
>
> The reason that the simple TPLL works so good but is hard for some "experts"
> to accept, seems to come down to the fact that this method uses Frequency
> and not Phase to make the raw data log used to then calculate ADEV data.
>
> Most if not all other methods depend on Phase differences (i.e time
> differences) to calculate the Frequency difference.
> The simple analog TPLL method holds the Phase difference to zero (with-in 1
> femtosecond) and calculates the average Frequency differences by  measuring
> the voltage on the EFC of the reference Oscillator. That way no variable
> phase is involved.
> This filtered Frequency data log can then be used to calculate ADEV without
> first needing to convert from or to phase.
> The fact that average Frequency differences do not start out as wide
> bandwidth Phase, means that all the fancy write-ups that tell how best to do
> that, do not apply.
>
> Some have argued that Phase and freq are the same thing, so the fact that
> this uses freq would make no difference.
> Others have argued that one can not average Freq, so you have to convert to
> phase first.
> Both have a basis of truth for some methods, but neither is correct here, as
> proven by the end results.
> (unless one wants to also assume that I'm either the luckiest or smartest
> person in the universal for getting it right the first time.)
>
> While it is true that the TPLL Freq data can be turned into accurate
> controlled Bandwidth Phase data, Wide band phase data can not be so easily
> turned into controlled limited Bandwidth, zero dead time, integrated Freq
> data, which is the thing that is needed to get good ADEV results.
> The reason is, to get high resolution, such as 1 femtosecond (1e-15) phase
> data, it takes a  wide bandwidth, which means high noise and many other
> problems. To get 1e-15 freq data from the EFC (limited by the ref osc), this
> can be done with the B/W equal to tau0.
>
> The short Over simplified summery is:
> At 1sec Tau0, the up to 1e15 to one difference in bandwidth between Phase
> and Frequency measurements makes a big difference that some seem to be
> missing. (think Phase trigger jitter)
> The simple TPLL has No secrets, just some basic differences that seem to of
> been forgotten or not considered.  The way that frequency is measured is
> what is different between the TPLL frequency method and the other more
> popular phase methods.
>
> The fact is, that the simple TPLL in spite of it limitations, has been shown
> to work just fine in the real world.
> If one can not understand or accept that measuring frequency without needing
> to first measure phase is the real secret reason why the TPLL works so good,
> without needing any special H/W or S/W 'adjustments', then feel free to
> propose a better reason besides Luck.
>
> ws
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein




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