OCXO Stable Reference and Control Voltages? - Page 1
Forum section: electronics / projects

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 01, 2016, 06:54:19 am
content: Hi,What do you folks think is best practice for the reference and control voltages for fine tuning an OCXO? Is a passive divider network off VCC sufficient, or should I be looking at a reference IC, and then a passive divider off the reference? Or something else entirely?The oscillator itself is quite stable, but if the voltages drift (relative to one another) then any tuning is not so useful.I'd like to maximize long term accuracy, and have to recal only a couple times a year.The OCXO is this guy:http://www.ctscorp.com/wp-content/uploads/2015/12/OCXO196.pdfThanks in advance.

author: AdamHi
author_rank: Contributor
timestamp: March 01, 2016, 04:14:06 pm
content: I've always assumed that you'd want to divide off a stable separate voltage source - but you got me thinking that maybe i'm wrong! If you find the answer elsewhere, please keep this post updated.BTW - where are you sourcing this OCXO? eBay?--adam

author: grumpydoc
author_rank: Super Contributor
timestamp: March 01, 2016, 04:59:19 pm
content: Depends of the accuracy that you need (or can "calibrate" to).The tuning range is 7x10-7, therefore 5% change in your VFCwill be 3.5x10-8(35ppb).Only if you can measure to better than that is worring about VFCto better than 5% going to do you any good.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: March 01, 2016, 05:03:48 pm
content: Maybe you could watchThat's the design I plan to use if I ever get around to adding an OCXO to my Racal Dana 1999.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: March 01, 2016, 05:07:57 pm
content: OCXOs typically provide their own reference designed for this purpose. The pdf you linked shows it's on pin 2. Use that reference with a voltage divider or similar, and feed the control voltage back into pin 1.

author: Cerebus
author_rank: Super Contributor
timestamp: March 01, 2016, 05:25:25 pm
content: The hint is in the datasheet for the part. There's an option - option R - to get this OCXO with a reference voltage output. If they are going to bother to make a part that provides a reference voltage output I'd take that as a hint that it might be a good idea. If you do the calculations on the tuning range (+/- 0.7ppm) versus the Allan deviation (0.01 ppb @ 1.0 sec) you'll get an idea of the voltage stability needed - 1 part in 140,000 (~7 ppm) would introduce an error equivalent to the Allan deviation.Moreover, I'd hope that they arranged the drift of the vref output to follow the oscillator drift (with respect to tempco, power etc) in a compensatory fashion - making it a more attractive option than providing your own reference.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 01, 2016, 06:54:43 pm
content: Quote from: suicidaleggroll on March 01, 2016, 05:07:57 pmAhhhhh! I misunderstood how it worked. I thought I was supposed to *apply* 4.0V to that VRef pin, and then apply the correction voltage to the VC pin. This makes much more sense...Hopefully I did not damage the unit, but it doesn't look like I did on the scope (and in comparison to the other OCXO unit).Thanks.

author: Vgkid
author_rank: Super Contributor
timestamp: March 01, 2016, 07:19:10 pm
content: The internal ocxo voltage is generally rather stable. I have a few that are of similiar size to your CTS unit.If you want, I can power one up(NOT A CTS, a C-MAC), and record its stability for you. Will not be the greatest, as will have only been running for a few hours before measure>.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 01, 2016, 09:15:19 pm
content: Quote from: Vgkid on March 01, 2016, 07:19:10 pmI appreciate the offer. I am trying to learn about these things. You are referring to recording the change in voltage of the Vref over time? I could do that with my bench meter as well.Or are you talking about recording the frequency drift? I don't believe I personally have any tools to do that. The bench meter (which does logging) can only go to about 300kHZ (and does not have an external clock), and my frequency counters cannot record things (and they are not even oven controlled, which is why I am messing with these OCXOs.)

author: NivagSwerdna
author_rank: Super Contributor
timestamp: March 01, 2016, 10:23:49 pm
content: Quote from: Cerebus on March 01, 2016, 05:25:25 pmYes but the OP didn't state they had option R. In the absence of option R then the solution might depend on your budget..... if you are not price sensitive then a voltage ref ic would work (that's what I'm planning to do) (I think that's what was done in the video I referenced)

author: Vgkid
author_rank: Super Contributor
timestamp: March 01, 2016, 11:15:17 pm
content: @ Flying hacker: correct. Still will post anyway.if you want to seethe long term stability check my 'Allen Deviation' thread in the beginners section.Somthing is not going good with my setup, if you look at the aldev graphs.@ NivagSwerdna: I agree. A rather decent 5v ref chip will work out good.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 02, 2016, 01:40:20 am
content: Quote from: NivagSwerdna on March 01, 2016, 10:23:49 pmYes, as the OP I do indeed have option R. So that will work great. Thanks. I misunderstood the application.Vgkid: I will check that thread. Thanks.

author: uncle_bob
author_rank: Unknown
timestamp: March 02, 2016, 02:44:17 am
content: Quote from: FlyingHacker on March 01, 2016, 06:54:19 amHiIf you are looking at that specific CTS OCXO on eBay right now ... beware ... the current drop is defective. They have an internal spurious oscillation. The suspicion is that they sent them to the dump as scrap and they wound up on eBay instead.Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 02, 2016, 04:41:40 am
content: Quote from: uncle_bob on March 02, 2016, 02:44:17 amHmm. The two I got seem pretty stable. with 20MHz BW limit it looks like a perfect sine. At 300MHz it has a little distortion, but rock solid. How would one identify this problem? I don't have a spectrum analyzer/FFT. My scopes are old school Tek gear.

author: Theboel
author_rank: Frequent Contributor
timestamp: March 02, 2016, 05:08:22 am
content: Quote from: uncle_bob on March 02, 2016, 02:44:17 amCan You more detail about your information Sir. I need a few of this ocxo.

author: Vgkid
author_rank: Super Contributor
timestamp: March 02, 2016, 05:18:32 am
content: Quote from: FlyingHacker on March 02, 2016, 01:40:20 amIf you read through it and find something that interests you, I can post the image of the graph(you most likely don't have TimeLab)or anything else that you want, as I still have the files, or atleast I could download them.-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_In some documents they suggest using trimmers with tempco's better than 50PPM, but that can get expensive, just use a string of nice resistors, with a pot for trimming.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 02, 2016, 05:31:32 am
content: Quote from: Vgkid on March 02, 2016, 05:18:32 amTimeLab looks interesting. Do you then have a TimePod to connect to? This is all stuff beyond my hobby budget for now (and I need a Spectrum Analyzer first anyway).I checked the thread. It may be a little too academic for my uses (read that as, I don't have the time to dedicate to figuring most of it out) It is interesting to read, though. Thanks.

author: Cerebus
author_rank: Super Contributor
timestamp: March 02, 2016, 01:43:32 pm
content: Quote from: NivagSwerdna on March 01, 2016, 10:23:49 pmYes, but that's kind of irrelevant in the context of the availability of the option suggesting that such a thing might be useful in conjunction with this part.

author: uncle_bob
author_rank: Unknown
timestamp: March 02, 2016, 11:04:44 pm
content: Quote from: Theboel on March 02, 2016, 05:08:22 amHiMultiple people who have purchased these OCXO's on eBay over the last few weeks have all reported a spurious signal on the output at a level high enough to make the useless for their needs. The signal is broadband and show up as a series of spurs all at about -100 dbc spaced at a uniform interval of 40 to 80 Hz (depending on the exact unit tested).Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 02, 2016, 11:15:15 pm
content: Quote from: uncle_bob on March 02, 2016, 11:04:44 pmThanks. I don't have a spectrum analyzer, but these look solid on a 300MHz scope. I will slow the scope down and see if I see anything. Does this look like AM modulation, what?They also seem to work fine as an input to at least two frequency counters. I ordered mine about a month ago. They were bought from a seller selling them in pairs.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 02, 2016, 11:38:41 pm
content: I can trigger off some kind of harmonic at around 333 Hz. Not sure what that is.

author: uncle_bob
author_rank: Unknown
timestamp: March 02, 2016, 11:53:09 pm
content: Quote from: FlyingHacker on March 02, 2016, 11:15:15 pmHiIt shows up as phase modulation. With a *lot* of care, you can catch it on a scope. You sort of need to know the modulation frequency first and then adjust the scope's trigger to duplicate it.Bob

author: uncle_bob
author_rank: Unknown
timestamp: March 02, 2016, 11:54:45 pm
content: Quote from: FlyingHacker on March 02, 2016, 11:38:41 pmHiYou may be triggering off of a spur that is at 333/N where N could be 4,5,6,7 ... who knows.Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 03, 2016, 02:17:23 am
content: Yeah, I don't think I would be able to tell if these are affected without a spectrum analyzer.Anyone have one of the bad ones on a scope?

author: uncle_bob
author_rank: Unknown
timestamp: March 03, 2016, 02:40:24 am
content: Quote from: FlyingHacker on March 03, 2016, 02:17:23 amHiIf you bought them in the last month or so, it's just about certain they are out of the defective lot. They show up in singes, pairs, and trays of 40 or so. There are a variety of seller names. I doubt there are very many real sellers behind all those names.Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 03, 2016, 03:08:20 am
content: Were there other people, besides the two people on time-nuts (where only some units were defective) who had defective units?I mean is there evidence to show that this is widespread?

author: Vgkid
author_rank: Super Contributor
timestamp: March 03, 2016, 03:28:32 am
content: Over 27 hoursMin: 7.03573,max: 7.03588, 150uVP-P, mean:7.03581Variance : .449580E^-9.Most likely more stable then some 5.5 digit multimeters.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 03, 2016, 04:28:30 am
content: Quote from: Vgkid on March 03, 2016, 03:28:32 amThanks. I saw similar performance on the CTS, and I was lagging the voltage after my cheap trim pot divider.So it seems like these reference voltages are designed for stability, which would make a lot of sense given their intended use.

author: uncle_bob
author_rank: Unknown
timestamp: March 03, 2016, 12:36:57 pm
content: Quote from: FlyingHacker on March 03, 2016, 04:28:30 amHiThe reference is just a 4.1V zener hooked to the +5 rail through a resistor.Bob

author: uncle_bob
author_rank: Unknown
timestamp: March 03, 2016, 12:42:52 pm
content: Quote from: FlyingHacker on March 03, 2016, 03:08:20 amHiWhen you have multiple "tray full" buyers each find that all the ones in the tray have the same issue .... that's cause for concern. These all appear to have come from the same "sale" (same part number / same pictures / same time on eBay) somewhere in China.Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 03, 2016, 04:43:07 pm
content: Quote from: uncle_bob on March 03, 2016, 12:36:57 pmIt seems to be a pretty decent zener and resistors ;-) Also since they remain at the same temp as the rest of the OCXO I assume that helps as well. I suspect the stable temperature is the most useful aspect.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 03, 2016, 04:46:44 pm
content: Quote from: uncle_bob on March 03, 2016, 12:42:52 pmAh. Thanks. I did not see that there were trayfulls defective. All I saw in a web search was a couple people with defective units on time-nuts. I either didn't find the right place in that thread, or this is someplace else.The two I got are from Hong Kong, BTW. Of course they could have walked across the border. Need to find a friend in St. Louis with a spectrum analyzer.

author: uncle_bob
author_rank: Unknown
timestamp: March 04, 2016, 12:17:46 am
content: Quote from: FlyingHacker on March 03, 2016, 04:46:44 pmHiIf you go the spectrum analyzer route, you need one that will go down -120 dbc. That's a really good analyzer. A phase noise test set is a much easier way to look for this stuff.More than you ever wanted to know about what is inside:http://syncchannel.blogspot.com/2016/03/schematic-of-cts-1960017-10mhz-ocxo.htmlBob

author: John Heath
author_rank: Frequent Contributor
timestamp: March 05, 2016, 08:18:34 pm
content: Quote from: FlyingHacker on March 01, 2016, 06:54:19 amHi FlyinHackerFrom one hacker to another stay away from carbon resisters. I knew a guy who used a 1K carbon at 5 volts to generate a 400 Hz tone with nothing but band pass filters for a lunch time alarm in factory. This had my antenna up so I asked him why he would use such a esoteric approach to generate a 400 hertz tone. He said just to make a point as there is so little to do. With this in mind I would go with a constant current source and zener diode with a op-amp voltage follower if precision is a concern. Failing this a 12 volt source then 7808 followed by a 7805 is about a stable as it is going to get assuming temperature is constant. Did not want to probe but what are you on to with long term precise time measurements?

author: uncle_bob
author_rank: Unknown
timestamp: March 06, 2016, 01:39:56 am
content: Quote from: John Heath on March 05, 2016, 08:18:34 pmHiGiven that you can now see the schematic of what's in the OCXO, just put a very normal multi turn pot between the Vref and ground. Attach the wiper to the EFC pin and you have the best you possibly can have. It's referenced to and tracking to the internal bias as best you can. That (and the "zero TC" of a normal pot) will do as good as anything you can do.Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 06, 2016, 01:54:04 am
content: Quote from: uncle_bob on March 06, 2016, 01:39:56 amThis is exactly what I did as soon as I figured out that the vRef was an output not an input! Doh!I ran some tests, and it was quite stable for a few days.John Heath: I may have misspoke in terms of "long term." I am really looking to make a lab frequency standard. However, one of the cheap GPSDO from ePay may be a better option (into some distribution amp).

author: suicidaleggroll
author_rank: Super Contributor
timestamp: March 06, 2016, 03:18:57 am
content: Use that vref to reference a dac and run it off an MCU or CPLD that's also measuring the output frequency vs a GPS PPS and you have an easy GPSDO.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 06, 2016, 06:24:03 am
content: Quote from: suicidaleggroll on March 06, 2016, 03:18:57 amI was wondering about something like this. Do you think a nav grade GPS would be sufficient with a long gate time? I think one of the other threads had something about this.

author: uncle_bob
author_rank: Unknown
timestamp: March 06, 2016, 07:02:26 pm
content: Quote from: FlyingHacker on March 06, 2016, 06:24:03 amHiSimple answer -- no.More complicated answer: On a nav grade receiver, time is an afterthought. They don't put much work into it. The result is that the error in the timing solution gets pretty high. As the constellation shifts around that error moves plus and minus at a 1 to 12 hour-ish rate. If it's a few microseconds of error (as it is on some parts), that's a big deal.With LEA-6T's dirt cheap, why not use the "right part"?Bob

author: Cerebus
author_rank: Super Contributor
timestamp: March 06, 2016, 10:24:37 pm
content: Quote from: uncle_bob on March 06, 2016, 01:39:56 amI did a bit of experimenting recently with inexpensive multiturn pots (i.e. not the £20 a piece Vishay ones but ordinary Bourns et. al.). With the pots adjusted to mid scale I was seeing a worst case tempco on the ratio of voltage applied to the voltage at the wiper of about 25% of the tempco of the end to end resistance. e.g. For a 200 ppm track tempco I was seeing a ratiometric tempco of 50ppm. This is only a small sample (I had about 5 different pots to try) but it does suggest that you can't rely on the assumption that using a variable resistor as a potentiometer will cancel the temperature coefficient of the track.

author: DimitriP
author_rank: Super Contributor
timestamp: March 06, 2016, 11:16:06 pm
content: QuoteDue to "out of sight out of mind disease".Probably because most can't measure the difference and if they dont' see it, it doesn't exist.

author: DimitriP
author_rank: Super Contributor
timestamp: March 06, 2016, 11:44:46 pm
content: Quote from: FlyingHacker on March 06, 2016, 06:24:03 amYes or no will depend on your requirements and definition of "Sufficient"."Sufficient", depends on how many decimal digits your counter can display past 10000000 Hz

author: uncle_bob
author_rank: Unknown
timestamp: March 06, 2016, 11:52:48 pm
content: Quote from: Cerebus on March 06, 2016, 10:24:37 pmHiBased on tests by the guys who make them (and that repeat when done in the field) the radiometric numbers on a properly made wire wound 20 turn is nearly zero (< 5 ppm). A properly done 20 turn cermet part with a TC of 100 ppm / C will come in below 10 ppm. In both cases it has to be a linear (not a log taper) part. It also assumes you have zero current through the wiper and that the pot is in good shape.Bob

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 07, 2016, 03:42:45 am
content: Quote from: uncle_bob on March 06, 2016, 07:02:26 pmI was (apparently erroneously) thinking the LEA-6T was a nav grade receiver. That was the one I was thinking of using, and yes they are cheap. I have not done much research into the topic yet, as I am sure is obvious.I was going to order a LEA-6T and give it a shot. How much advantage is there to disciplining an OCXO with that GPS source vs. simply using the GPS source itself? Some of the models appear to use TCXOs. I get that OCXOs are more accurate, but the GPS model would be running off TCXO anyway.I suppose you have to look at the GPS lock status and stop any disciplining of the OCXO when the GPS is not locked? But what feedback voltage would you apply to the OCXO vC at those times when the GPS was not locked? The last voltage before you lost the lock, or some predetermined middle ground setting, or what? I am guessing the last voltage before you lost the lock, or a (decaying?) moving average of recent values.Sounds like fun.

author: DimitriP
author_rank: Super Contributor
timestamp: March 07, 2016, 06:46:42 am
content: QuoteHere is the short version pasted fromhttp://www.ko4bb.com/Timing/FAQ-2.phpQuoteThere are plenty of designs out there, attempting to meet various degrees of "sufficiency".

author: Vgkid
author_rank: Super Contributor
timestamp: March 07, 2016, 09:20:36 pm
content: GPSDO circuits.1pps:Brooks Shera(PLL);http://home.teleport.com/~oldaker/10mhz_construction.htmhttp://www.rt66.com/~shera/index_fs.htmVe2zaz(FLL):http://ve2zaz.net/GPS_Std/GPS_Std.htmZL1BPU(PLL) ;http://www.qsl.net/zl1bpu/MICRO/SIMPLE/SimpleGPS.htmKE0FF (PLL);http://www.rollanet.org/~joeh/projects/GPSlave_writeup.pdf10khz inputJ.R. Miller(PLL) ;http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm____________________Heres one I just stumbled upon, will read it later.https://hackaday.io/post/21322

author: DimitriP
author_rank: Super Contributor
timestamp: March 07, 2016, 09:51:41 pm
content: Since we are posting listshttp://www.jackson-labs.com/index.php/products/furyhttp://www.jackson-labs.com/index.php/products/lte_liteFor anyone building one primarily for educational purposes, I believe nothing beats the Miller GPSDO for simplicity ,ease of construction , performance and price (if you are into that sort of thing) .Here is a comparison to put things in perspective:http://www.leapsecond.com/pages/gpsdo/

author: edpalmer42
author_rank: Super Contributor
timestamp: March 07, 2016, 10:04:15 pm
content: Quote from: FlyingHacker on March 07, 2016, 03:42:45 amA bare GPS receiver (even a timing-grade one) will wander around in the e-8 area when averaged over 1 sec. So a 10 MHz output might change by 0.1 Hz. If you average over 10 sec., you're now in the e-9 area and so on. A reasonably good OCXO will get you to the e-11 range at 1 sec. The GPSDO merges these two as described in the quote from KO4BB.GPSDOs behaviour during a loss of lock vary depending on the sophistication of the design. The smartest ones learn the drift rates of the OCXO and shift the EFC voltage accordingly. Less sophisticated ones freeze the voltage. Some DIY versions (often analog-based circuits without a processor) don't take any special action. But remember that a timing-grade GPS receiver typically only needsonesatellite to maintain lock.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 07, 2016, 11:50:41 pm
content: Great info, everyone! Thank you.

author: uncle_bob
author_rank: Unknown
timestamp: March 08, 2016, 12:19:03 am
content: HiJust in case anybody else has missed the uBlox "magic code":A LEA-6 is a nav receiver *unless* it is a LEA-6T. The LEA-6T is a timing receiver. The same convention applies to other parts in their lineup in the same fashion.The "T" enables a number of features. It is *not* clear that it changes the basic function of the unit. The features it enables make it much easier to use in a GPSDO or other precise timing (sawtooth corrected) application. The net result is that you are below 1x10^-9 at one second rather than up around 1x10^-8 at 1 second.Bob

author: lars
author_rank: Regular Contributor
timestamp: March 08, 2016, 01:49:17 pm
content: Quote from: uncle_bob on March 08, 2016, 12:19:03 amI enclose two charts showing my results with NEO-6M (naviagation only and about 10USD on ebay) and LEA-6T (about 30USD on ebay). I have tested both with a patch antenna in-house that gave about 30db C/N (=int on chart) and an small patch antenna on the roof that gave about 50dB C/N (=ext). For the LEA-6T I also have set mode 0 that is mobile mode (=nf on chart) and also done a survey and set mode 2 fixed (=f on chart). A note: I have default mask angle 5 degrees and maybe a higher value should have given better results especially as I am in Sweden that is quite far north.If you use the GPS module standalone the ADEV give a good indication of what you can get if you test for example a counter. If you have 1E-8 at 1sec you can get about 8digits average and 7digits with normal measurement confidence at 1sec gate time (Frequency plots often seems to jump about a factor ten more than the ADEV). At 100 sec ADEV is 1E-10 and for 100sec gate time you get 10digits average and 9digits with confidence.For using a GPS module standalone I haven´t seen any DIY designs of hardware sawtooth correction. Otherwise sawtooth correction probably gives an extra digit.I enclosed the MDEV chart as I think MDEV is useful to see possible limits when designing GPSDO controllers with PI-loops and a Pre-filter that take away part of the sawtooth errors.At short time constants (10-100secs) sawtooth correction probably is very useful for a GPSDO. At long time constants (1000-10000secs) a pre-filter probably is nearly as efficient I think. I have never seen a hanging bridge longer than 300secs. Also at Tau longer than 1000sec the GPS errors (changing satellites, ionosphere etc) starts to get in the same region as the filtered GPS module errors I think.My own rule of thumb is also that AT cut OCXO´s (and good VCTCXO as DOT050V) need time constants in the GPSDO of about 10-100secs, SC cut OCXO 100-1000secs and Rubidium 5000-20000secs to match good GPS receivers.Lars

author: lars
author_rank: Regular Contributor
timestamp: March 08, 2016, 02:32:47 pm
content: Quote from: Vgkid on March 07, 2016, 09:20:36 pmMy observations:The Shera design is blamed for its 42ns TIC (Time Interval Counter) but gave good results with an HP10811 (not so common available anymore?) if I remember correct.The VE2ZAZ uses a FLL and 100ns TIC if I understand correct and ADEV curves is not impressive.ZL1BPU is not open source as I see and also 100nS TIC.KE0FF seems promising but difficult to see result as no good results presented. Also requires to solder a CPLD and programming.Nick Sayers also have 100ns TIC and not so impressive ADEV.The Miller design relies on the Jupiter module being very good, but obsolete? Has anyone showed the same performance with another module with 10kHZ, eg uBlox. I haven´t seen any such results yet.So except the Miller the Shera still seems best. But some components are obsolete. Another drawback of the Shera maybe that it is only designed for a 45ppb span of the OCXO.Isn´t it any modern DIY design that uses an optimized design? With a TIC with better resolution than the sawtooth-ripple and a well designed PI-loop and pre-filter as Sheras design?For a better TIC I have a used my simple design with 1nS resolution that was described in timenuts forum in feb 2014. It uses an Arduino but the software is not enough good for the complete GPSDO (even if I use it to discipline a LPRO and earlier an OCXO).Lars

author: DimitriP
author_rank: Super Contributor
timestamp: March 08, 2016, 07:31:06 pm
content: QuoteWhich 10Mhz output did you measure? Did you use the 10Mhz out of the LEA or was it disciplining an external OCXO?If the former, it would be interesting to compare ADEV plots for the LEA (M & T ) producing 10KHzQuoteNow that would be something!I'm hoping someone with equipment capable of producing ADEV plots will build one someday and publish the results.

author: lars
author_rank: Regular Contributor
timestamp: March 08, 2016, 07:57:19 pm
content: Quote from: DimitriP on March 08, 2016, 07:31:06 pmI have only compared with 1PPS out from the NEO/LEA against a divided down rubidium. My setup with the HP5370 is not enough fast to compare 10kHz signals. If so I probably have to use an XOR (that is build a Miller GPSDOLars

author: ve7xen
author_rank: Super Contributor
timestamp: March 08, 2016, 08:16:53 pm
content: Quote from: lars on March 08, 2016, 02:32:47 pmI have been toying with the idea of using theTDC7200TIC (55ps resolution TIC designed for ultrasonic flow measurement) to design a GPSDO. The part should be able to measure the 1PPS vs. 10MHz directly without any external dividers, though I am not sure this is a good idea from a performance point of view... Trying to learn more of the control theory and think it will be an interesting project, though I don't really have any good way to measure the loop performance. If I get around to implementing a working design I guess it will be time to set up a collection of Rubidiums and TICs to log data... Only in the planning stages at this point, but I think this is a viable and relatively easy / low part count option to get my feet wet.I had previously considered re-implementing the design of thePICTICon something other than PIC and using it as the phase detector for a GPSDO, but that complicates the hardware quite a bit.Sorry for the noise.

author: DimitriP
author_rank: Super Contributor
timestamp: March 08, 2016, 09:46:16 pm
content: QuoteYou could , instad of measuring 1PPS coming out of the LEA, set it to produce 10KHz, and divide it down to 1PPS.Other than the divide by 10 the rest of the setup would be the same as what you have already measured.

author: uncle_bob
author_rank: Unknown
timestamp: March 08, 2016, 11:17:39 pm
content: Quote from: lars on March 08, 2016, 01:49:17 pmHiIf you use the sawtooth correction out of the 6T to take out the sawtooth issues, the ADEV plot drops down well below 1x10^-9 at 1 second.Bob

author: lars
author_rank: Regular Contributor
timestamp: March 09, 2016, 06:24:28 pm
content: Here is my ADEV and MDEV with sawtooth correction on the LEA-6T module. I used the HP5370B and subtracted the values I got from uCenter for TPerror afterwards. I also did ADEV and MDEV curves for the values on TPerror from uCenter as I saw wiggles on the sawtooth corrected curve. The wiggles is also seen in the correction data, I don´t know why.Lars

author: DimitriP
author_rank: Super Contributor
timestamp: March 09, 2016, 07:12:53 pm
content: Great stuff!As for the wiggles, we had them appear at another thread (Hi Ed and VGkid) and we couldn't get rid of them no matter what was suggested and tried .. Consider yourself lucky they only appeared once !Hopefully you'll never see them again.

author: uncle_bob
author_rank: Unknown
timestamp: March 09, 2016, 11:08:52 pm
content: Quote from: lars on March 09, 2016, 06:24:28 pmHiDon't ask how many times I've run down this list:1) Sawtooth is either on the edge I just got or on the next one2) Sawtooth either subtracts from the reading or adds to the readingYes, one would *think* that going through all 4 combinations would not be required to figure out which combo was correct....Bob

author: Vgkid
author_rank: Super Contributor
timestamp: March 09, 2016, 11:36:24 pm
content: Those aren't wiggles, these are wiggles. Actually it is a pretty good oscillation.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 09, 2016, 11:56:18 pm
content: I'll fix those stupid wiggles. Where's my C-4?

author: uncle_bob
author_rank: Unknown
timestamp: March 10, 2016, 12:03:36 am
content: Quote from: Vgkid on March 09, 2016, 11:36:24 pmHiThose wiggles are from a spur at 0.09 Hz off carrier.Bob