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.
