[time-nuts] Digital tight PLL method

Bob Camp lists at rtty.us
Wed May 26 10:56:43 UTC 2010


Sounds like your bill of material was a bit above $10.


On May 26, 2010, at 4:42 AM, Ulrich Bangert wrote:

> Warren,
> you are not the only person to have ideas like this!
> I managed to get me a Stanford Research DS345 generator which gives 1E-6 Hz
> frequency resolution for any frequency below 30 MHz (Can be locked to any 10
> MHz reference). At 10 MHz this resembles a relative resolution of 1E-13. I
> used this generator in a digital pll where the phase error was measured by a
> DBM and a a HP3457. The digital PLL was a simple script written with my
> EZGPIB utility which controlled the DS345 and read the HP3457 via IEEE488.
> The main difference to your analogue solution is that it delivers a
> frequency measurement value immediately (= the current setting of the DS345)
> without any knowledge needed about the mixer's phase gain properties. And it
> is not limited to a certain frequency. Of course, the generator may be
> exchanged by an DIY DDS and the multimeter may be exchanged against a DIY
> A/D converter. Injection locking is not a topic with the DDS circuit.
> Nevertheless my measurement were not exactly encouraging. May be that I
> missed to apply the important math that Bruce has been suggesting in the
> discussion with you. All the stuff is on my workbench and is ready to use.
> May be I give it another try.
> Best regards
> Ulrich Bangert   
>> -----Ursprungliche Nachricht-----
>> Von: time-nuts-bounces at febo.com 
>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von WarrenS
>> Gesendet: Montag, 24. Mai 2010 18:49
>> An: John Miles; Tom Van Baak; Discussion of precise time and 
>> frequency measurement
>> Betreff: [time-nuts] Digital tight PLL method
>> Concerning the simple, $10, Low cost, Tight PLL method of doing ADEV.
>> "If you accept that the measurement is going to be limited by 
>> the Reference 
>> Osc,
>> Then for Low COST and SIMPLE, with the ability to measure 
>> ADEVs at very low 
>> levels,
>> Can't beat a simple analog version of  NIST's "Tight 
>> Phase-Lock Loop Method 
>> of measuring Freq stability".
>> http://tf.nist.gov/phase/Properties/one.htm#oneone    Fig 1.7"
>> Here is some more information on the subject that may help 
>> inspire some of 
>> the great minds out there.
>> In spite of all the unjustified criticism, the latest test 
>> will show, at 
>> least to the more open minded nuts,
>> There is NOTHING inherently wrong with the tight PLL method 
>> as I have done 
>> it. It gives about as good of answers as anything out there.
>> As I've implemented it, there are some disadvantages, because 
>> there is just 
>> so much one can do with a single Op amp design.
>> If one does the calculation they will also see the OP amp is 
>> not a limiting 
>> factor in the performance of this method.
>> AS I have said before, the disadvantage of my simple BB 
>> version that was 
>> tested, is that it is limited by the Ref Osc and the way it's freq is 
>> modified.
>> The accuracy is limited by the fact the first simple BB 
>> version I built is 
>> an all analog system.
>> That is solely because the frequency control I used on the 
>> simple version is 
>> the analog EFC input of the reference Osc.
>> I've also pointed out, that is not a limitation of the 
>> method, there are 
>> solutions for that.
>> Now I'm amazed that no one has had a New inspiration.
>> Maybe a more direct approach will help some to see the next 
>> logical step. Using the same basic tight PLL method, make 
>> some of the unit digital. Do not modify the freq of the 
>> reference osc with analog,  GET it yet? That way the device 
>> would be half digital without any of the analog 
>> shortcoming or the need to physically change the reference 
>> freq. Do I really need to explain more?
>> Have fun
>> ws
>> ***************
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