The hump is the DAC update frequency measure: fast update -> hump towards the left, slow update -> towards the right. Better update fast or slow: recently it was pointed out that fast should be better and this will shift the hump in the 1 to 10 seconds range.
On Mon, Oct 22, 2012 at 1:32 PM, Tom Van Baak <[email protected]> wrote: > Hi Bert, > > Not sure about the range/resolution. That would depend on how the standard > is used and what its frequency drift rate is. The stability doesn't have to > be too much better than the standard itself. > The Austron 2055 resolution is 1e-14, IIRC. The Symmetricom AOG is 1e-19 > (overkill). > > What I've found in some GPSDO and passive atomic standards (e.g., Rb or > Cs) is that as soon as you turn on the DAC and enable the loop, you get > more short-term noise, say in the range of 1 to 100 seconds. That's why for > best stability you always switch off the loop during a sensitive > measurement. Many older Cs had a "Cs off" switch for this. Not only did it > conserve cesium but it also means you're running straight off the > high-quality OCXO. This is also true for GPSDO, like the TBolt which allows > you to turn off disciplining with a s/w command. > > In general, when you discipline a OCXO you get that characteristic ADEV > "hump". This is expected, a natural byproduct of combining two unknowns, > one that's assumed to be better at short tau and worse at long tau (e.g., > OCXO) and one that's assumed to be better at long tau and worse at short > tau (e.g., Rb cell, or Cs beam, or GPS receiver). At some point there is a > cross-over and you know/assume that at that point each must be contributing > 1/sqrt(2) of the noise. > > To see the humps in living color, refer to: > http://www.leapsecond.com/pages/gpsdo/ > > To answer your question about short/medium/long, I guess in this case > short is tau left of the hump; medium is the hump, and long is tau to the > right of the hump. > > /tvb > > ----- Original Message ----- > From: <[email protected]> > To: <[email protected]> > Sent: Monday, October 22, 2012 4:04 AM > Subject: Re: [time-nuts] Adjusting HP 5065A frequency > > > Tom > I have two questions what should the range, resolution and stability of > the delay generator be and how much do you think a digital loop driven by a > Tbolt would degrade short and medium precision. What is your definition of > short and medium? > Bert Kehren > > > In a message dated 10/22/2012 12:25:08 A.M. Eastern Daylight Time, > [email protected] writes: > > Three companies come to mind for phase microsteppers. A popular one > decades ago was made by Austron (model 2055A). I got mine on eBay but > they are > not as common now as ten years ago. > > The current models by Symmetricom and Spectra Dynamics are extremely > high-end (expensive) and overqualified for use with a vintage rubidium > oscillator. If you visit NIST or USNO you will see these impressive units. > > It would be a very fun project to make your own. I suspect other group > members could either help you or would eagerly employ your design for > their > own use. > > But -- before you decide on a hardware solution see if you can do it in > software. > > An analogy is what we do with GPS 1PPS sawtooth errors. There are two ways > to deal with this. One is to capture the correction message over RS232, > measure the DUT vs. GPS 1PPS with a TIC, and then numerically apply the > sawtooth correction with one line of code. Several of the popular GPS > monitor > programs do this automatically for you (TBoltmon and TAC32, for example). > The > software solution is perfect to the granularity of the sawtooth message, > typically 1 ns. > > The hardware implementation usually involves a PIC and a programmable > delay generator. The PIC listens for the correction message over RS232 > and then > has plenty of time (up to one second) to program the delay chip. When the > hardware 1PPS arrives it is delayed to compensate for the aforementioned > sawtooth error. The result is a hardware 1PPS that's quite close to the > ideal > 1PPS, limited again by the granularity of the message, as well as offset > or linearity errors in the delay chip. > > So that's the analogy. To apply this to your rubidium, ask yourself which > instruments or measurements or users are downstream of your 5065A 10 MHz > output. Can they deal with daily software corrections to a stable but > slightly imprecise frequency, or do they really need the frequency to be > as > accurate as possible at all times. > > There's a third alternative as well. You might consider using your 5065A > as the LO in a GPSDO. This will sacrifice some short- and mid-term > precision > due to additive noise, but it will guarantee the best possible long-term > accuracy. > > /tvb > > ----- Original Message ----- > From: Edgardo Molina > To: Tom Van Baak ; Discussion of precise time and frequency measurement > Sent: Sunday, October 21, 2012 8:49 PM > Subject: Re: [time-nuts] Adjusting HP 5065A frequency > > > Dear Tom, > > > Good evening. In relation to your last comments on this and other subjects, > I am sharing some thoughts and experience about it. I took the liberty to > separate the topics as to ease the interested parties to follow up > accordingly. TNX. > > > > > a. Information you kindly provided and the index for newbies: > > > Thank you! You just provided me with lots of new ideas and information on > the subject. You have very valuable information in your web site. As Hal > was saying, an index should be done anywhere so it could be easier for the > rest of us to locate the information. I am planning soon to build a web > page > for my lab. In english of course for everybody to share my experiences. I > could work on an index to point out to the various sources of information > and topics that are difficult to find. That I think could expedite things > a > little bit. > > > b. Phase Micro steppers: > > > I saw the phase micro steppers working at CENAM time scale. I was > wondering that the technique could be translated to my 5065As and not > trying to > touch them so often. If I am assuming correctly and the technique could be > used with the HP Rb standards. Are those phase micro steppers easy to > find? I > mean, affordable in the second market? If there is one of course. I saw > the > ones used at CENAM are produced by SpectraDynamics in Colorado. According > to Mike Lombardi it is a small highly specialized company with a small > market to serve. I could translate it as "expensive and exotic" : ) Am I > correct? > > > c. Thunderbolt and my will to share initial experiences: > > > I am gathering a lot of information on the Thunderbolts as I am using them > in my thesis work. I bought a couple of them. If my information or novice > experience with these receivers is good for anybody, I would be more than > glad to share it. > > > Thank you. > > > Kind regards, > > > > > > > Edgardo Molina > Dirección IPTEL > > > www.iptel.net.mx > > > T : 55 55 55202444 > M : 04455 20501854 > > > Piensa en Bits SA de CV > > > > > > > Información anexa: > > > > > > > > > CONFIDENCIALIDAD DE INFORMACION > > Este mensaje tiene carácter confidencial. Si usted no es el destinarario > de este mensaje, le suplicamos se lo notifique al remitente mediante un > correo electrónico y que borre el presente mensaje y sus anexos de su > computadora sin retener una copia de los mismos. Queda estrictamente > prohibido > copiar este mensaje o hacer usode el para cualquier propósito o divulgar > su en > forma parcial o total su contenido. Gracias. > > > > > NON-DISCLOSURE OF INFORMATION > > This email is strictly confidential and may also be privileged. If you are > not the intended recipient please immediately advise the sender by > replying > to this e-mail and then deleting the message and its attachments from your > computer without keeping a copy. It is strictly forbidden to copy it or > use it for any purpose or disclose its contents to any third party. Thank > you. > > > > > > > > > > On Oct 21, 2012, at 7:29 PM, "Tom Van Baak" <[email protected]> wrote: > > > Hi Edgardo, > > What you'll find is that many labs do not periodically adjust the C-field > of their 5061A or 5065A at all. > > Instead, any phase or frequency adjustment is done with phase > microsteppers or simply done in software with time and rate adjustments to > the raw > data. These methods avoid all possible physical side-effects of changing > voltages, currents, and fields. It also makes it possible to gather > long-term > data to show how the standard is operating (if you make mechanical rate > adjustments it complicates data that you have already collected). > > The other point is that when making stability measurements, there is no > requirement that the reference (e.g., 5065A) be perfectly on-frequency. So > this removes motivation for physically touching and possibly perturbing > the > operation of the reference. > > Please also take the time to read these pages. > > "HP 5065A Rubidium C-Field Resolution" > http://leapsecond.com/pages/hp-5065a-cfield/ > > "Rubidium Oscillator Stability" > http://leapsecond.com/images/4rb.gif > > "Stability and Noise Performance of Various Rubidium Standards" > http://www.ke5fx.com/rb.htm > > "Performance of Low-Cost Rubidium Standards" > http://febo.com/pages/oscillators/rubes/ > > "A close look at a drifting HP 5065A Rubidium Frequency Standard" > http://leapsecond.com/pages/doug-rb/ > > /tvb > > > _______________________________________________ > 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. > _______________________________________________ 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.
