Hi As far as I can see on the e place, they made quite a few of the Z3811 assemblies. They actually have them (clearly labeled MTI 260 OCXO assembly) with OCXO's made by CTS on them. They apparently made enough to find a second source for the OCXO.
Bob On Feb 18, 2013, at 11:29 PM, Ed Palmer <[email protected]> wrote: > Hi Bob, > > On 2/18/2013 6:19 PM, Bob Camp wrote: >> Hi >> >> The -Z3811 is indeed a part out of a HP GPSDO. HP is a big enough customer >> that the part they get *may* have little relation to the standard part. > > True, but it doesn't look like there were many Z3811s made. The order > wouldn't have been that large. Maybe there were enough other orders from HP > that they wanted to keep them happy. > >> If they all started out at the same temperature, then the noisy ones finish >> warmup quicker than the quiet ones. Take a look at when the final "glitch" >> happens in the warmup process. It's definitely happening earlier on the >> noisy parts. If warmup finishes quicker - the part is running at a lower >> temperature. That of course is only the time between the cutback from full >> current to the glitch. It may not mean it's running cooler. > > Between possible temperature differences due to crystal tuning and component > tolerances that affect the internal voltage regulators ( and therefore affect > the maximum current available to the oven ), I don't know what, if any, > conclusions can be drawn for such a small number of samples. But when I > rechecked the startup current, it looks like the noisy oscillators draw a few > milliamps ( up to 10 ) more than the quiet one. That might allow them to > warm up quicker. > > Thanks, > Ed > >> Bob >> >> On Feb 18, 2013, at 5:32 PM, Ed Palmer <[email protected]> wrote: >> >>> Hi Bob, >>> >>> On 2/18/2013 2:42 PM, Bob Camp wrote: >>>> Hi >>>> >>>> Like any control loop, gain, bandwidth and noise are all related. In a >>>> DOCXO you have two control loops and they do interact. That said, there's >>>> nothing grossly wrong with the four OCXO's. The noisy parts have a bit >>>> more gain in the controller. The quiet parts have a bit less gain. The >>>> easy way to see this is the ringing after the current changes. >>> Yes, when I zoom in on the ringing after the first step change, they all >>> show a period of ~9 seconds. The blue trace (the quiet one) has a nice >>> smooth damped sine wave while the other ones have varying amounts of noise >>> superimposed on the sine wave. The amplitude of the ringing on the noisy >>> ones is greater than the amplitude of the quiet one. In one case, more >>> than twice as big. >>> >>>> Without ADEV numbers there's no way to know which one is good (or better) >>>> and which one is bad (or worse). The noisy parts may be responding to the >>>> ambient temperature rumble (thus correcting for it) and the quiet ones may >>>> be ignoring it (allowing it to hit the crystal). >>> I hadn't thought of that possibility. Thanks for that! >>> >>>> It's also possible that the noisy ones have an electrical issue in the >>>> loop that generates the noise. >>> I was thinking of maybe a dead filter capacitor - hence the noise. >>> >>>> If all the ovens started from the same temperature, there is a variance in >>>> the oven set points. Some take longer to warm up than others. You don't >>>> mention if they started the same, so that may or may not be significant. >>> They all started at the same temperature. Any apparent difference in >>> warmup time is mostly due to the arbitrary offset of the traces. The offset >>> was just so you could see all four traces clearly. However, isn't it also >>> likely that each oscillator has had it's oven tweaked to match that >>> particular crystal? >>> >>>> To further complicate things, in a double oven, you can have a noisy outer >>>> oven that gets suppressed by the inner oven. Are your specific 260's >>>> double ovens? No way to be sure without tearing one open. The second >>>> "step" in the current plot could be an inner oven cutting back. >>> I wondered about that second step. The period of the ringing on the second >>> step is about 1 sec. longer than the ringing on the first step so it's >>> apparently a different circuit. The 260 series datasheet does NOT say >>> anything about it being a double oven. They talk about customizing the >>> unit to suit the customer, but that seems a bit extreme. >>> >>> By the way, I purchased these oscillators from our favorite auction site. >>> If anyone's interested, the 260 series includes both AT and SC crystals. >>> Since these start out ~150 Hz low, they appear to be SC cut. The output is >>> a 5 MHz sine wave @ ~+7 dBm into 50 ohms. They work fine with a 12V power >>> supply. They have no mechanical frequency adjustment (unless it's under a >>> suspicious spot of solder on the case) but my 4 were all adjustable to 5 >>> MHz via EFC. They were apparently removed from Z3811 GPS receivers. They >>> each have a sticker on the side that says "Z3811-80010". There doesn't seem >>> to be much info available on the Z3811. I have no relationship to the >>> vendor - just a customer. >>> >>> So it sounds like the proper thing to do is file this information and carry >>> on. After making some Allan Deviation measurements, review everything to >>> see how, or if, oven 'noise' correlates to Allan Deviation results. >>> >>> Thanks Bob, >>> >>> Ed >>> >>>> Bob >>>> >>>> >>>> On Feb 18, 2013, at 2:40 PM, Ed Palmer <[email protected]> wrote: >>>> >>>>> I know that when making AC measurements on various OCXOs of the same >>>>> type, you have to expect wide variations in the results. e.g. TVB's >>>>> Allan Deviation measurements on a selection of 10811A oscillators at >>>>> http://www.leapsecond.com/pages/z3801a-osc . But what about DC current >>>>> measurements? How much variability should you expect? >>>>> >>>>> I recently bought 4 MTI 260 oscillators with thoughts of doing some >>>>> 3-cornered hat experiments. I thought I'd use the best 3 of 4. One test >>>>> I always do on an OCXO is to measure the DC current drain as it warms up. >>>>> Nothing radical - I have an HP 6622A GPIB-equipped linear power supply. >>>>> I just do GPIB queries as fast as I can and log the results. I get about >>>>> 6 readings per second. More than enough for my needs. >>>>> >>>>> This time, I was surprised by the results of this test. The attached >>>>> picture shows why. I've offset the traces horizontally and vertically >>>>> for clarity so I deleted the axes. The horizontal lines are 200 ma >>>>> apart, but the position of each trace is arbitrary. All four oscillators >>>>> start at a current-limited value of ~1 Amp and have a steady-state >>>>> current drain of ~230 mA. The length of the graph is ~20 minutes. >>>>> >>>>> Although the family resemblance is obvious, I was surprised by the >>>>> different noise levels. I let one of the noisy units run for a day to >>>>> see if it would settle down, but there was no improvement. Are these >>>>> results reasonable, or do I have one oscillator with a good oven (blue >>>>> trace), one marginal (purple), and two rather poor ones (red and green)? >>>>> I'm thinking that the noise on the oven could affect the Allan Deviation >>>>> due to either or both of the thermal inconsistencies or varying load on >>>>> the power supply. >>>>> >>>>> Any thoughts? >>>>> >>>>> Thanks, >>>>> Ed > > _______________________________________________ > 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.
