Hi With most 10811 range oscillators the impact of a simple bandpass filter is low enough to not be a major issue. That's for normal lab temperatures with the circuitry in a conventional die cast box. No guarantee if you open the window and let the fresh air blow in during the run.
That's true with a heterodyne. I can see no obvious reason it would not be true on DMTD. Bob On Feb 6, 2010, at 5:12 PM, Bruce Griffiths wrote: > The only major issue with DMTD systems is that they undersample the phase > fluctuations and hence are subject to aliasing effects. > The low pass filter has to have a bandwidth of the same order as the beat > frequency or the beat frequency signal will be significantly attenuated. > Since the phase is only sampled once per beat frequency period the phase > fluctuations are undersampled. > Various attempts to use both zero crossings have not been successful. > > In principle if one can overcome the increased phase shift tempco associated > with a bandpass filter, using a bandpass filter can in principle ensure that > the phase fluctuations are oversampled. > > > Bruce > > Bob Camp wrote: >> Hi >> >> A straight heterodyne system will get you to the floor of most 10811's with >> a very simple (2 stage) limiter. As with the DMTD, the counter requirements >> aren't really all that severe. >> >> Bob >> >> >> On Feb 6, 2010, at 4:24 PM, WarrenS wrote: >> >> >>> >>>> "It's possible / likely for injection lock ... to be a problem ..." >>>> >>> Something I certainly worried about and tested for. >>> What I found (for MY case) is that injection lock is NOT a problem. >>> The reason being is that unlike most other ways, where the two OSC have to >>> be completely independent, >>> The tight loop approach forces the Two Osc to "Lock with something like 60 >>> + db gain, >>> so a little stray -80db injection lock coupling that would very much limit >>> other systems has >>> no measurable effect at e-13. Just one of the neat little side effects that >>> make the tight loop approach so simple. >>> >>> >>>> "then a part in 10^14 is going to be at the 100 of nanovolts level." >>>> >>> For that example, just need to put a simple discrete 100 to 1 resistor >>> divider >>> in-between the control voltage and the EFC and now you have a nice workable >>> 10uv. >>> BUT the bigger point is, probable not needed, cause you are NOT going to do >>> any better than the stability of the OSC with a grounded shorted EFC input. >>> >>> as you said and I agree is so true: >>> >>>> "There is no perfect way to do any of this, only a lot of compromises ... >>>> you need to watch out for". >>>> >>> But you did not offer any easier way to do it, which is what the original >>> request was for and my answer addressed. >>> This is the cheapest easiest way BY FAR to get high performance, at low >>> tau, ADEV numbers that I've seen. >>> >>> ws >>> *************** >>> >>> ----- Original Message ----- From: "Bob Camp"<[email protected]> >>> To: "Discussion of precise time and frequency >>> measurement"<[email protected]> >>> Sent: Saturday, February 06, 2010 12:09 PM >>> Subject: Re: [time-nuts] ADEV vs MDEV >>> >>> >>> >>>> Hi >>>> >>>> It's possible / likely to injection lock with the tight loop approach and >>>> get data that's much better than reality. A lot depends on the specific >>>> oscillators under test and the buffers (if any) between the oscillators >>>> and mixer. >>>> >>>> If your OCVCXO has a tuning slope of 0.1 ppm / volt then a part in 10^14 >>>> is going to be at the 100 of nanovolts level. Certainly not impossible, >>>> but it does present it's own set of issues. Lab gear to do it is >>>> available, but not all that common. DC offsets and their temperature >>>> coefficients along with thermocouple effects could make things exciting. >>>> >>>> There is no perfect way to do any of this, only a lot of compromises here >>>> or there. Each approach has stuff you need to watch out for. >>>> >>>> Bob >>>> >>>> -------------------------------------------------- >>>> From: "WarrenS"<[email protected]> >>>> Sent: Saturday, February 06, 2010 2:19 PM >>>> To: "Discussion of precise time and frequency >>>> measurement"<[email protected]> >>>> Subject: Re: [time-nuts] ADEV vs MDEV >>>> >>>> >>>>> Peat said: >>>>> >>>>>> I would appreciate any comments or observations on the topic of >>>>>> apparatus with demonstrated stability measurements. >>>>>> My motivation is to discover the SIMPLEST scheme for making stability >>>>>> measurements at the 1E-13 in 1s performance level. >>>>>> >>>>> >>>>> If you accept that the measurement is going to limited by the Reference >>>>> Osc, >>>>> for Low COST and SIMPLE, with the ability to measure ADEVs at that level, >>>>> 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 >>>>> >>>>> >>>>> By replacing the "Voltage to freq converter, Freq counter& Printer with >>>>> a Radio shack type PC data logging DVM, >>>>> It can be up and running from scratch in under an Hr, with no high end >>>>> test equipment needed. >>>>> If you want performance that exceeds the best of most DMTD at low Tau it >>>>> takes a little more work >>>>> and a higher speed oversampling ADC data logger and a good offset voltage. >>>>> >>>>> I must add this is not a popular solution (Or a general Purpose one) but >>>>> IF you know analog and have a GOOD osc with EFC to use for the reference, >>>>> as far as I've been able to determine it is the BEST SIMPLE answer that >>>>> allows High performance. >>>>> Limited by My HP10811 Ref OSC, I'm getting better than 1e-12 in 0.1 sec >>>>> (at 30 Hz Bandwidth) >>>>> >>>>> Basic modified NIST Block Diag attached: >>>>> The NIST paper sums it up quite nicely: >>>>> 'It is not difficult to achieve a sensitivity of a part in e14 per Hz >>>>> resolution >>>>> so one has excellent precision capabilities with this system.' >>>>> >>>>> This does not address your other question of ADEV vs MDEV, >>>>> What I've described is just a simple way to get the Low cost, GOOD Raw >>>>> data. >>>>> What you then do with that Data is a different subject. >>>>> >>>>> You can run the raw data thru one of the many ADEV programs out there, >>>>> 'Plotter' being my choice. >>>>> >>>>> >>>>> Have fun >>>>> ws >>>>> >>>>> ************* >>>>> >>>>> [time-nuts] ADEV vs MDEV >>>>> Pete Rawson peterawson at earthlink.net >>>>> Sat Feb 6 03:59:18 UTC 2010 >>>>> >>>>> Efforts are underway to develop a low cost DMTD apparatus with >>>>> demonstrated stability measurements of 1E-13 in 1s. It seems that >>>>> existing TI counters can reach this goal in 10s. (using MDEV estimate >>>>> or 100+s. using ADEV estimate). The question is; does the MDEV tool >>>>> provide an appropriate measure of stability in this time range, or is >>>>> the ADEV estimate a more correct answer? >>>>> >>>>> The TI performance I'm referring to is the 20-25 ps, single shot TI, >>>>> typical for theHP5370A/B, the SR620 or the CNT81/91. I have data >>>>> from my CNT81showing MDEV< 1E-13 in 10s. and I believe the >>>>> other counters behave similarly. >>>>> >>>>> I would appreciate any comments or observations on this topic. >>>>> My motivation is to discover the simplest scheme for making >>>>> stability measurements at this performance level; this is NOT >>>>> even close to the state-of-the-art, but can still be useful. >>>>> >>>>> Pete Rawson >>>>> >>>>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >>> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
