Symmetricom TrueTime XL-DC GPSDO - Page 1
Forum section: electronics / projects

author: Colin1256
author_rank: Newbie
timestamp: January 15, 2016, 11:28:28 am
content: Hey all,I've gotten myself a Symmetricom TrueTime XL-DC GPSDO (Model 151-602, with the large backlit time display) that I plan to use as my lab Frequency Standard. The Seller (eBay) indicated that it has 1 MHz, 5MHz and 10 MHZ Frequency outputs in addition to the 1PPS-Pulse and an IRIG-B Output; so it's got everything I want to have in terms of outputs and also looks cool.I've cracked it open yesterday and had a look inside. Very clean design, I think. I also made sure it powers up properly. I'm still waiting for the 12V-rated antenna, so I can't test the GPS-Side of it just yet.There's a number of BNC connectors in the back, three are fixed (labeled Antenna, PPS and IRIG-B), whereas the other five are unlabeled. Thesy are connected to the 87-6XX Mainboad using jumper-wires and it would appear that they can be configured for various things as per personal preference.Unfortunately, there is little labeling on the boards; just the regular Component-Designators.I'm planning to change a few things on this particular unit:For instance, it currently relies on an internal TCXO. Being in an urban area with plenty of higher buildings and no roof-access, I'm not sure if it will be able to see enough satelites for a reliable GPS-lock at all times; so I'd like to increase the precision of the unit when GPS is not available.It seems like Symmetricom used to manufacture add-on cards with higher accuracy (OCXO / Rubidium) frequency standards, but these seem to be very hard to come by today. Fortunately, it supports a configuration where it can be tied to an external clock that I'd like to use with an external OCXO; assuming I can wire and jumper it correctly inside.Furthermore, I'm going to add some buffer amplifiers which will allow me to connect it to a number of devices in the lab to the unit in parallel. My plan is to install these in the internal bays and just add BNC-Connectors to the currently blank slot-covers.I do have a manual for the unit, (http://glacier.lbl.gov/gtp/DOM/Support/xl-dc-manual.pdf) which refers to a "87-6XX configuration drawing". This supposedly identifies all the jumper settings and connection points of the main-PCB.Does anyone have this particular drawing or even better, a service manual for the unit that would help me get started?Thanks a lot in advance!Cheers,Colin

author: ZigmundRat
author_rank: Regular Contributor
timestamp: February 17, 2016, 05:39:32 am
content: A little late on the reply here, but hopefully this is still of value.A more complete manual is available here:https://ics-web.sns.ornl.gov/timing/151-652-893man.pdfand has the 87-6xx description/diagram. However, it's still not a complete manual. There are no schematics or service manual available.The TrueTime XL-DC although old, is still a decent unit. I have four of them - two rubidium and two with OCXO. One is a 12v unit that WAS configured for a downconverter. I modified that unit back to GPS (not for the faint of heart, believe me). Besides that conversion, I have also switched 12v units to 5v (and back), replaced the rubidium oscillator, etc.A few observations:The jumpers indicated in the above referenced doc regarding the 87-6xx configuration are not all pin jumpers. Some are 0 ohm resistors.Consider that you'll probably wind up with more than one GPS or GPSDO and need a way to feed them from one antenna. Get a DirecTV 4 way splitter ('2-2150 MHz Splitter SWM 4 Way') or something very close. This is a satellite splitter that has one DC passthrough so you can power the antenna. Put your more modern device that provides the right power to the antenna on that port. On another port (that is DC blocked) connect an inline satellite antenna amplifier and your 12v XL-DC to that. The DBS inline amps need more than 5v to work right and they work great with the XL-DC. DONT go looking for the maximum gain amp - just a regular one will do. Although the XL-DC GPS is usually a little deaf you don't want to swamp it either - the performance will go DOWN. More is not always better.You can convert from 12v to 5v antenna without too much trouble - but you may not want to. OR at least it's not a big deal. But 5v antennas are easier to come by.Firmware is in ROM. Different revisions XL-DC have different firmware of course, and the rubidium appears different than the OCXO. The DAC slopes are different between the rubidium and the OCXO. There are several different GPS engines used in these, but all Trimble I think. Haven't seen anything else. I believe they started with the SV6, some have SV6-CM3, maybe SV8, and I have one with an ACE (I forget whether I, II, or III) which uses a daughter card with FPGA to do sentence translation making it backward compatible.As for other cards, they are sometimes available. You just have to watch for them.I don't know if it's possible to easily get a unit to work with an external OCXO. This is labeled and 'option' and I don't know what's required to enable it. It could be as simple as making the right jumper options (as on the 87-6XX document) but it's note entirely clear what those are. But these units also have NV storage, and I suspect that there are flags in there which determine the enabled options. Don't know for sure - just guessing. If you have figured out how to use an external oscillator that would be good information to have.Hope this helps. Please update the thread with any progress you may make or additional XL-DC info. I'll try to do the same.Ziggy

author: pacAir
author_rank: Contributor
timestamp: February 27, 2016, 08:50:09 am
content: Hi guys! I am working towards a similar conversion on my TrueTime XL-DC (w/ onboard up-converter). I'll share a few quick scans out of one of my XL-DC manuals not only showing the jumper options but also the top and bottom artwork locations showing where all these jumpers are located. I included a short document describing a few of the initial changes I did to the circuitry towards this end (based on information in these scans and actual circuit measurements).If the system will allow me to post this way (they are not all small enough to post here):TrueTime XL-DC T/F board Bottom Jumper LocationsTrueTime XL-DC T/F board Top Jumper LocationsTrueTime XL-DC T/F board Option JumpersTrueTime XL-DC Antenna Configuration ChangesHopefully these links will work and that this info might help.SteveWN7VHF

author: pacAir
author_rank: Contributor
timestamp: February 27, 2016, 09:43:11 am
content: While I am thinking about it, I scanned a few additional pages for you. Sorry about the quality but this is the best I can do without disassembling the manual!Two pages relate to the TrueTime 142-602 downconverting bullet antenna that works with the XL-DC receivers with on-board upconverters:TrueTime 142-602 Down-Converting Bullet Antenna #1TrueTime 142-602 Down-Converting Bullet Antenna #2(Please note that this is NOT the same up/down conversion system used by the later 142-6150 external upconverter box and the 142-615 Downconverting antenna. These are using different L.O. and I.F. frequencies than those used with these internal upconverter units and the bullet antenna shown!)The final scan shows the header pin locations that the unmarked rear BNC jacks can be connected to for the various output options (Note: Some of these BNC connections require a matching option board.):TrueTime XL-DC Rear BNC Configuration Header ConnectionsSteveWN7VHF

author: ZigmundRat
author_rank: Regular Contributor
timestamp: March 03, 2016, 06:41:29 am
content: Just to provide some information on what was involved in the conversion of a down converter unit to one that uses a standard GPS antenna, I've written up some of what I had to go through. I believe it is mostly complete. In order to do the conversion I had to source a replacement GPS receiver. I found that at least some of the Placer 400 GPS units have these SV6 modules inside - and they usually go pretty cheap.For reference, I've attached a pic of the down converter receiver board - a modified Trimble SVeeSix (SV6). Notice the depopulated sections and how there are pins in place of the DB9 connector of a 'normal' SV6. In the bottom view, notice how the oscillator signal is routed from the MCX connector to the C93/R15 pins via twisted pair. Also how the left side has essentially no power supply components populated. Power is taken from a 3 pin connector near C136 (removed in this picture). One of these pins is battery backup.In the top view, i have temporarily mounted a MCX connector (this is usually on the bottom for connection to the CPU/main board) so ignore that. Notice the lack of oscillator and components in the upper left. On the right middle you can see the three holes for the power/battery connections to he CPU/main board.Doing the conversion of the standard SV6 to a version that can be used in the XL-DC involved switching the serial port configuration and line drivers, depopulating the power supply and oscillator section (the XL-DC has it on the CPU/main board), reprogramming the data stream from TAIP to TSIP, and ultimately transplanting the serial EEPROM (below the chip labeled 22880-85-B8) from one board to the other. The DB9 is missing for the second port as is the RS232 driver at U81. Instead of U81, U82 is populated and different passives are there (or not). There is also the change on the CPU/main board where a capacitor must be added and a resistor removed. This is documented in the jumpers setting PDF that was uploaded by pacAir.Once I am in a position to take my unit down fro a while, I'll try to get some picture of the replacement SV6 as modified and update the post.

author: pacAir
author_rank: Contributor
timestamp: March 12, 2016, 04:34:49 am
content: As is often the case with different generations of TrueTime gear, my up-converting receiver board looks ENTIRELY different than this!SteveWN7VHF

author: ZigmundRat
author_rank: Regular Contributor
timestamp: March 13, 2016, 03:33:52 am
content: Can you post a pic? I haven't pulled my converted unit yet (so no pics yet) as I'm STILL cleaning up my pigpen of a lab

author: jeffp8
author_rank: Newbie
timestamp: May 11, 2016, 02:41:52 am
content: Greetings.I am new to this forum. In fact I joined specifically because of this thread.I have a TrueTime model XL-DC that I acquired awhile back in non-working condition.I fixed a power supply problem and replaced a bad lithium battery and the unit "seems" to be working. I say "seems" to be, because It will never GPS lock or PLL lock.It tracks satellites and displays the correct time and position but the time display always shows the letter "A" on the far right and "unlock" on the far left.I noticed while going through the menu, the DAC is maxed at 32767. This only happens when satellites are acquired. I figured the the oscillator may have aged out since it was 20 years old, so I sent it in to Wenzel Associates for evaluation. The said it was bad and not economically repairable. I purchased a new oscillator, but the symptoms remain.Can anyone familiar with this model suggest a course of action?Thanks,jeffp8

author: ZigmundRat
author_rank: Regular Contributor
timestamp: May 11, 2016, 06:43:40 pm
content: Sorry to be blunt but:The first question is whether you are capable of doing component level repair and troubleshooting. If so there could be a further conversation.If not then this is most likely unrepairable due to cost and even finding a suitable person/shop to do the work. Your best course of action would then be to resell it as-is and try to recover some of your expense, then replace it.

author: jeffp8
author_rank: Newbie
timestamp: May 12, 2016, 03:32:34 pm
content: I am capable, I just have zero experience with GPSDOs. Until I obtained this unit, I had never heard of these. I've been reading all I can find on the subject and all I can find on the truetime product.It seems to me, since I have a new oscillator on board, that the problem lies either in the "sampled" oscillator signal, or the GPS "reference" signal accurately getting back to the microprocessor. The DAC output is reasonable at startup, around 2650. Once satellites are acquired, the DAC output goes full scale, 32767.My understanding is that schematics are unavailable for this product so I'm trying to trace this out.Any tips anyone can provide would be appreciated.Thanks

author: ZigmundRat
author_rank: Regular Contributor
timestamp: May 12, 2016, 07:17:17 pm
content: Ok, that's great to hear. At its simplest the GPSDO typically compares the 1 pulse per second from the GPS to a 1 PPS derived from the OCXO and steers it via a PLL with a long time time constant. The processor does that via the DAC output which is applied to the OCXO , either directly or indirectly.Since your XL-DC reports a DAC output change the next thing would be to make sure the DAC voltage is actually changing. You can check that directly on the OCXO EFC pin. There is also a jumper on the board that sets the DAC range to either -5 to +5 or 0-10. You should probably make sure it's set correctly. Check the earlier posts in the thread for links to docs.You mentioned that you replaced the OCXO, and I seem to recall it was from the OEM with the same model. If so, great. But if not an identical replacement the EFC polarity, slope, or range could be wrong which will of course prevent its being steered correctly by the processor.

author: jeffp8
author_rank: Newbie
timestamp: May 13, 2016, 04:26:05 am
content: I had a little time to look at this today.Confirmed jumper setting for -5/+5 control voltage. The voltage / DAC value increments about every 50 seconds for 3 intervals, then waits 90 seconds and increments again. This repeats until the voltage hits +5vdc and the DAC is at 32767.I do see a 1pps square wave on the 86-357-9 pcb.Am I correct in assuming that there should be a 1pps signal from the Trimble SV6 board on what would be pin 9 of the non-exsitant DB-9 connector?I am measuring a constant +5vdc at that point.I haven't had a chance to trace out where the 1pps signal originates yet. Looks like that trace is buried on an internal layer.Do you know where it originates?Thanks for your help.Jeff

author: ZigmundRat
author_rank: Regular Contributor
timestamp: May 13, 2016, 04:16:52 pm
content: I assume you know whether or not the -5/+5 is correct for your OCXO. The unit I have with an OCXO has it mounted on a small board behind the big LCD. As I recall it's an Oscilloquartz, the exact part number I would have to check. I will try to remember to open that unit up and check the OCXO part and the DAC jumper setting.You don't mention if you have any other option boards installed but if you do, pull them and make sure the problem persists.Which exact GPS receiver do you have? They used several - all Trimble AFAIK. At the least, there have been the SV6 and the ACE III on an adapter card with FPGA.The PPS should appear on pin 9 of the GPS receiver. However it is very short, about 10uS. You will most likely need a digital oscilloscope to see it. You won't see it on a meter and probably not on an analog scope.As for the PPS on the controller board, I have not tried to trace it so I can't help much there.

author: jeffp8
author_rank: Newbie
timestamp: May 17, 2016, 04:51:30 pm
content: Yes, -5/+5 is correct for my OCXO.No other option boards are installed.GPS receiver is TNL 22880-B. Googling that indicates it is an early Trimble SV6.Pin 9 is at a constant +5vdc. Using the Oscilloscope, I see no activity on this pin.Questions:1) Is it possible to measure your pin 9? Is it at +5vdc and pulses low, or at 0vdc and pulses high?2) Does the "A" in the left most position of your LCD go away as soon as the satellite is acquired? Mine remains regardless of how many satellite have been acquired.Thanks again for your help,Jeffp8

author: ZigmundRat
author_rank: Regular Contributor
timestamp: May 18, 2016, 02:36:18 pm
content: I just powered up my #3 XL-DC. This has OCXO, one labeled TrueTime OCXO 8666-C2S, which is really an Oscilloquartz 8666. Which btw, has a 0-10v EFC. This is attached to the little PCB behind the large LCD at the front (see pic). The other OCXO is the low phase noise option.The GPS receiver in this is an Ace III with a converter board, but it will still put out PPS on the same pin of course. I have the same SveeSix in two other units - they work.Second pic shows the 10uS negative going PPS pulse on pin 9. What kind of scope do you have? Again, you will need a storage or digital scope to see this pulse.On this particular power on, once the display went to Mode: Time 3D the A changed to flashing *, then turned off. Unlock also turned off at this time. Sometimes the timing is a little different. The A is 'acquisition' so should go off after it sees enough satellites. It may need to acquire an almanac before it goes off, not sure. Unlock should go off after it is tracking, has a good fix, and has PPS within tolerance. Note that it wants to take 90000 fixes to set its position. It is possible to have no A or * and still have unlock.I know you feel it's correct but I'm skeptical of the -5/+5 EFC you say you have. If the DAC is railed it could just be the range is wrong. What was the exact model of the original OCXO?I've updated this post to include a pic of the PPS on the SVeeSix GPS (TNL22880-B like yours) in my XL-DC #4. It's not as clean, and it's not as wide either. It's < 2uS compared to the 10uS of the other unit. Another point of reference I guess.

author: Colin1256
author_rank: Newbie
timestamp: July 15, 2016, 04:00:01 pm
content: Hello everyone!I'm sorry for having been away for a while.ZigmundRat: Thank you very much for the link to the manual, this one contains a lot more information than the one I have been able to find.My XL-DC is running happily, except that it has once lost PLL Lock and couldn't recover from that. I have since changed the internal battery and the problem hasn't returned. I think it's unlikely that this was the cause, but hey, whatever I did; it seems to have helped. :-)I did get the original Symmetricom 12V Antenna with the unit, so at this time I'm not really interested in converting my unit down to 5V, though it is good to know that it can be done this easily.Other than that, I'm still hoping that one of these days I will come across a kit or schematic that will enable me to upgrade my unit from the standard simple TCXO to at least an OCXO.Cheers everyone!Colin

author: gpsdo_nut
author_rank: Contributor
timestamp: July 16, 2016, 09:26:02 pm
content: Ran across this topic today and it piqued my interest. Though older, these XL-DC servers are solid and fun units to work with.I also have a small arsenal of XL-DC units that I swap into action from time to time - XL-DC with the standard TCXO, one with the high-stability OCXO and finally one with a rubidium. While I'm not especially versed in the technical side of these units - I've found that it appears the only real way to convert these units between different oscillators is to swap out, or reprogram the PROM chip (and I don't have expertise in PROM reprogramming). Specifically it's the chip with the software label on it on the CPU-XL board.That chip apparently holds the software for several key functionality:- Ability to communicate with the specific type of GPS receiver you have (I believe the SVEE-Six and ACEII/III speak the same language, but requires a different daughterboard to convert to the proper frequency for the internal GPS timebase)- Timing constants for your time base - for example, my XL-DC examples have the following 'Response Time':TCXO: 15 seconds maxOCXO: 200 seconds max.Rubidium: 2000 seconds max.- Volts/Hz DAC stepping to properly lock-in the oscillatorAs a fun test, I took out my TCXO XL-DC's software PROM chip, as well as my SVEE-Six + daughterboard and transplanted it directly into the CPU-XL of my OCXO unit. While the unit does perform lock, I was getting super-noisy oscillator phasing due to the low response times of 15 seconds (remember OCXO's were configured with 200s). At one point during initial locking, most likely due to the incorrect Volts/Hz stepping figure, It was having a hard time keeping the OCXO under control with the DAC wildly moving out and then back in, back out, and back in.... Eventually after locking, the DAC was being moved around like it was trying to discipline a 'noisy' TCXO...So those are the things to look out for if you're still thinking about converting timebases, a large hurdle will be the software itself. To me, probably not cost effective, and look toward eBay for a OCXO-capable unit.

author: ZigmundRat
author_rank: Regular Contributor
timestamp: July 20, 2016, 03:12:09 am
content: All in all, I think these XL-DC units are pretty good. I wish they were more tunable (ala Trimble Thunderbolt) but for all practical purposes they do fine.The firmware seems to be picky. I have low phase noise options in two of my units and I can't swap those cards between boxes. One is 'sys ver 020', 'GPS-XL V1.036' & 182-6200v002 with the other 'sys ver 030', 'GPS XL V1.047' & 182-6534v003 so apparently not the same at all. The 1.047/182-6534 unit has an ACE III GPS receiver with daughter card in it. Maybe we should start grabbing some ROM images and sending them to KO4BB. Then maybe some field upgrades from TCXO might be possible. AFAICT the Rb and OCXO both are just tacked onto the backplane. So with the proper firmware it could be possible.Some additional information for your time constants:TCXO with LPN: 2.121e+03 secondsOCXO with LPN: 2.121e+03 secondsSo... I really don't know which oscillator is getting steered or for that matter which one is output on the CPU card. The LPN card has its own outputs - but since both TCXO and OCXO have the same time constant, I would think they are both steering the LPN OCXO - not the TCXO or 'normal' OCXO. If I get ambitious I'll pull the LPN card and see if/what the value changes to.As I recall, my Rb unit has a time constant of 5000 seconds but since I'm not sure I turned it on and will update with the actual number.** Confirm 5.000e+03 for Rb

author: gpsdo_nut
author_rank: Contributor
timestamp: July 20, 2016, 04:42:45 am
content: Yeah, definitely very decent units. With additional option cards like N.1, N.8, FTMIII, external oscillator disciplining (getting close to Thunderbolt tunability) and the LPN would be an XL-DC that does it all.I'm also curious as to what happens when the LPN card is pulled... One of my units indicate a LPN status in Function+73, so I'm assuming this may be a case where it may apply new oscillator characteristics if LPN is present (and may be the only FW that supports LPN).My current house standard is my Thunderbolt which has been humming along for the last month (by the way, as of 7/19/2016 LEAP: PENDING! is present!). Because of it's tunability, I've been flirting with the idea of replacing the standard OCXO with a different unit... However, it currently ain't broke so I feel less inclined to mess with it.And I'm pretty certain you're right - the Rb standard has a TC of 5000s, not 2000s. It's been a while since I've fired mine up too.

author: ZigmundRat
author_rank: Regular Contributor
timestamp: July 22, 2016, 02:12:20 pm
content: I kind of forgot about it until I went to pull the cards, but one LPN module is 5MHz and the other one is 10MHz. The 5MHz unit is in the chassis with the 10MHz OCXO behind the front panel. The 10MHz unit is/was presumably in a plain TCXO unit (more on this).I pulled the LPN module on both units. The 'TCXO' unit with the 10MHz LPN module removed does not show the clock in the big display, so the LPN module would seem to be the clock source in that unit - not the TCXO. The other one (OCXO) with the 5MHz LPN module removed still functions normally and goes to 2.121e+03 as before. I will also swap the CPU modules to see what happens when I take the one from the chassis with no display and put it in the one with the OCXO. I bet it will come up. I will also compare both processor modules and all the 'jumpers' to see if there's any difference.All of my units have an 'auxiliary' 10MHz oscillator: either a Rb, an OCXO, or a 10MHz LPN module. So I don't know if there is a XL-DC that has ONLY the CPU card with a TCXO. My CPU modules seem to require an external 10MHz.@gpsdo_nut : Do you have an EPROM reader/burner? Is there any chance I could get ROM images? I'd be happy to trade and as I mentioned before we could post them up to KO4BB as well. I really kind of interested as none of my units have anything in Function 73 regarding LPN status (and I have two units with LPN). Do any of yours have Function 07 (external oscillator control) enabled? I have a couple of Austron 1250A that would be interesting to discipline.

author: Colin1256
author_rank: Newbie
timestamp: July 23, 2016, 11:04:12 am
content: Very interesting indeed.My XL-DC is a very "bland" one; it just has the standard 87-610 card with the GPS receiver, the other bays are empty.@ZigmundRat: you're mentioning an 'auxiliary' 10 MHz Oscillator. Could you tell me a little more about that? How did you connect it? Maybe this would be a way forward for me; use one of the two unused bays for a custom board with an OXCO and feed that back into the unit as external 10 MHz Source?Does anyone have any information on the pin-headers towards the rear of the unit? A lot of them (but not all of them) have black/white twisted-pair wires installed on them that lead to the BNC connectors (my unit is wired for 10 MHz, 5 MHz and 1 MHz Outputs, along with 1PPS Pulse). I'm curious as to what the unused pins can be used for. Any idea?Thanks!Colin

author: gpsdo_nut
author_rank: Contributor
timestamp: July 24, 2016, 06:04:47 pm
content: Quote from: ZigmundRat on July 22, 2016, 02:12:20 pmHuh. Well that's interesting... Does this particular TCXO GPS-XL board have two oscillators - or just the 16Mhz TCXO? The 10MHz TCXO would have been next to the big Xilinx chip. If you don't have it, your GPS-XL is indeed externally clocked.Quote from: ZigmundRat on July 22, 2016, 02:12:20 pmThis one baffles me too - on paper I'd assume the GPS-XL would have been disciplining the 'main' 8666-CS2 osc. while the LPN (or GPS-XL) disciplines the Wenzel against the main...Quote from: ZigmundRat on July 22, 2016, 02:12:20 pmThat's because you have nicely optioned XL-DCs.My TCXO-only unit is exactly as you described - and it has that 10Mhz TCXO next to the Xilinx chip. I suspect yours just has the part outlined and is not fitted with the TCXO.Quote from: ZigmundRat on July 22, 2016, 02:12:20 pmUnfortunately I don't - I've kind of wanted a reader/burner for a while for other projects but those never took off either. Also I lied - Function 73 LPN is available on a XLi (TCXO-unit), not XL-DC. I really meant Function 72 where I have a "LPN OK" fault flag. I'm pretty sure yours has that too.None of my units have the external osc. control ability - that would have been neat.

author: pacAir
author_rank: Contributor
timestamp: July 24, 2016, 10:49:21 pm
content: Quote from: Colin1256 on July 23, 2016, 11:04:12 amI posted a link to a page out of one of my XL-DC manuals that describes those headers in a post nearer the top of this forum page. The link is:TrueTime XL-DC Rear BNC Configuration Header ConnectionsJust be aware that some of those options are only valid if the supporting hardware plug-in is installed.Steve

author: pacAir
author_rank: Contributor
timestamp: July 25, 2016, 12:31:30 am
content: Judging from the current threads it is obvious that there is a hunger for more info regarding TrueTime products! Perhaps we may be able to answer some questions by "pooling" our resources. Namely, if everyone could document the following pieces of information regarding their unit perhaps we can learn something from comparison?This list is my starting point. I recently started documenting my own TrueTime "pile". This includes GPS-DC, XL-DC & XL-AK receivers, plus TCU-800 Time Code generators/translators, which have their own plug-in family (some models even have their own built-in GPS receiver) and a few of the LED Time Displays (RD-1, RD-2).For the XL-DC family, my initial documentation list includes:1. Model Number2. Warranty Expiration (if labeled, provides a rough date of deployment)3. TrueTime XL System Version (Shown at power on)4. GPS-XL Version (Shown at boot-up)5. EPROM Part Number (TrueTime p/n for programmed firmware chip, appended on LCD screen to #4 above)6. Antenna Type & Voltage setting (Antenna is either Standard or Down-Convert... Down Convert units have aluminum label next to Antenna Jack & the GPS Receiver board)7. GPS-XL CPU Board (Model, Firmware & Version marks)8. GPS Carrier Board (Model, Firmware & Version marks)9. GPS Receiver Daughter Board (Model, Firmware, Chip & Version marks)10. OCXO Option Board (Model & Revision) (If installed)11. OCXO Oscillator (Manufacturer and all data) (If installed)12. Type of power supply (AC, DC or both)13. List of all installed option boards (Name, Model, Firmware & Version marks)14. List of all installed options (Oscillator type, Plug-in Card Names, LCD Backlight, Power Supply, etc.)15. Revision History16. Internal & External PhotosItem 15 above is based on the multiple Assembly part numbers each particular unit went through before reaching its final configuration. Each time the unit reached a milestone it had an assembly label placed on the bottom or side of the chassis (with part number and revision). If the unit was grabbed off the shelf and modified or added to, other labels showing these steps were added. Some of my units have 6 or more of these small labels!One thing I learned about the XL-DC and XL-AK receivers is that if the Model Number has a "-1" appended to it, then that unit is equipped to use the Trimble "bullet" antenna with the built-in down-converter circuitry that is NOT compatible with the later TrueTime down-converting antenna with the separate up-converter box that it is mated to. Finding these older down-converting antennas is VERY difficult (and usually quite expensive) as they were usually left on the roof when the receivers were decommissioned and were surplussed "as-is" without them.Examples:Standard Receiver (my #1 XL-DC): Model 151-602-817-12Down-Convert Antenna Unit: (my #2 XL-DC): Model 151-602-586-1Every unit I have seen (on eBay & elsewhere) that has a "-1" at the end of its model number also has the "Down Converter Required" label next to the antenna jack and on the GPS receiver Carrier Board internally. IMHO, unless you already have the correct antenna, these are best left for spare parts or avoided altogether.Steve

author: ZigmundRat
author_rank: Regular Contributor
timestamp: July 25, 2016, 02:41:07 pm
content: First, let me clarify what I said about the two LPN modules. They are both 10MHz output, but the one with the Wenzel 5MHz OCXO has an X2 MiniCircuits frequency multiplier. So both are 10MHz output.@gpsdo_nut - To answer your questions:1) Both GPS-XL modules have the VCTCXO but appear not to use it. In both chassis, neither GPS-XL init the big clock if only the GPS-XL module is plugged in (and OCXO unplugged).2) The behavior is slightly different between the OCXO unit with it's Wenzel LPN module, and the non-OCXO unit with its Oscilloquartz LPN module.- Both GPS-XL modules work in either chassis- In the OCXO chassis, neither GPS-XL modules init the big clock with the OCXO unplugged from the backplane- In both chassis, both GPS-XL init the big clock if the Oscilloquartz LPN module is plugged in- In both chassis, neither GPS-XL init the big clock if the Wenzel LPN is plugged inI also have a LPN status in F72 - I never spent much time in the fault screens since everything worksAs for EPROM burner/reader I have found the TL-866 to be a good value (OEM page:http://www.autoelectric.cn/en/TL866_main.html- Amazon,eBay, etc.) and has worked for everything so far. You might need to get more adapters, but they aren't that expensive.@Colin1256: By 'auxiliary oscillator' I mean there is an oscillator not on the main cpu board. For example, the TCXO units apparently only have a VCTCXO can on the CPU board. No other oscillator. All of my units have an additional oscillator - an OCXO (mounted behind the big clock display), a LPN module, or a Rubidium.@pacAir: That's all good info to collect. I don't know how but maybe someone could create a shared spreadsheet or something where we can compile that information. Google docs or something? I dunno.The more I look into these the more it looks like the firmware is customized for each unit built. (Could be wrong of course.) One of the reasons I say this is because my units won't operate alone with their own VCTCXO. You'd think they would at least do that. Also, the CPU from the Rb units will not recognize the LPN modules. I am guessing that if we start collecting the info from the labels (151-...) and F18 we'll find a lot of variation.

author: pacAir
author_rank: Contributor
timestamp: July 26, 2016, 05:31:50 am
content: @ZigmundRat: I agree with your assessment regarding the high likelihood that the firmware in each unit is custom for the unit configuration at the time of shipment. Most TrueTime devices seem to be like this (based on the Model Numbers). I happen to have two XL-DC units that came from the same batch with the same model number configured exactly the same but different than any of my other XL-DC units (I have 5 or 6). I also have six TCU-800 Time Code Generator/Translator units... two of them came from the same batch with two identical model numbers (identically configured) but different than all the others.This would seem to dovetail with my observation regarding all of the chassis number labels that change over the shelf-life of each chassis until it acquires its final configuration before shipping. I do not know if the end digits in the model number are actually indicating specific features or just a sort of incrementing numeric code that must be looked up in a shipping log file. This might be determined by collecting all of the data as I laid it out and comparing. I was going to create a spreadsheet of my unit's data so if anyone wants to participate they could compile the data from their unit(s) and send them along for inclusion.To make this a bit more understandable, here are the specifications from my very first (XL-DC #1) XL-DC receiver along with relevant photos:XL-DC#11. Model Number:151-602-817-122. Warranty Expiration:No Warranty Label affixed to chassis.(However, chip date codes indicate 1999 timeframe)3. TrueTime XL System Version:TRUETIME XL SYS VER 0294. GPS-XL Version (Shown at boot-up):GPS-XL v1.0465. EPROM Part Number:182-6497 v0016. Antenna Type & Voltage setting:Standard, 12Vdc7. GPS-XL CPU Board (Model, Firmware & Version marks):87-611-139 Rev A8. GPS Carrier Board (Model, Firmware & Version marks):87-7339. GPS Receiver Daughter Board (Model, Firmware, Chip & Version marks):87-ACE3-2 Rev B, GPS RX: 39818 Rev C (USA)10. OCXO Option Board (Model & Revision) (If installed):87-399-811. OCXO Oscillator (Manufacturer and all data) (If installed):10.0 Mhz, Wenzel Associates, 500-06449 Rev D, +12Vdc, 13717-004812. Type of power supply (AC, DC or both):AC Switching (standard)13. List of all installed option boards (Name, Model, Firmware & Version marks):Network Interface / RS-232 Card, 87-6004-XL Rev A14. List of all installed options (Oscillator type, Plug-in Card Names, LCD Backlight, Power Supply, etc.):No large LCD Backlight. Oscillator, Power Supply & Option Card noted above15. Revision History(Didn't note this at the time, will have to open it up and document.)16. Internal & External Photos:GPS-XL Assembly:http://www.pacair.com/Transfer/GPS/XL-DC_1/DSCF3459.JPGPower Supply:http://www.pacair.com/Transfer/GPS/XL-DC_1/DSCF3463.JPGRear Connectors:http://www.pacair.com/Transfer/GPS/XL-DC_1/DSCF3201.JPGOCXO Board Assembly:http://www.pacair.com/Transfer/GPS/XL-DC_1/DSCF3450.JPGOCXO:http://www.pacair.com/Transfer/GPS/XL-DC_1/DSCF3461.JPGOption Card Internal:http://www.pacair.com/Transfer/GPS/XL-DC_1/DSCF3457.JPGSteve

author: Colin1256
author_rank: Newbie
timestamp: July 26, 2016, 02:44:17 pm
content: @ZigmundRat: Thank you! I believe I misunderstood you. I thought it may be possible to connect an external OCXO to two of the BNC Jacks, provided they would be connected properly within the unit. and use one of them to feed in 10 MHz and use the other to output a trimming signal.I have exactly the type you are referring to; I just have the VCTCXO on the main PCB, the area behind the large (backlit) Clock LCD is empty on mine.In an ideal world, I would find an OCXO board somewhere or design and make one myself (provided I can find some pinouts of the connectors I'd need to tie into, as well as determine if my unit's firmware supports it) and upgrade my base-unit to include it, but I could also live with connecting one externally provided the unit supports this somehow.I will open my unit up and get you the full list of what's inside, but here is the preliminary data:1. Model Number: 151-602-247-122. Warranty Expiration: No Warranty Label affixed to chassis.3. TrueTime XL System Version: TRUETIME XL SYS VER 0304. GPS-XL Version (Shown at boot-up): GPS-XL v1.0475. EPROM Part Number: 182-6225 v0026. Antenna Type & Voltage setting: Standard, 12Vdc (currently reconfigured to 5V as I am testing a different antenna)7. GPS-XL CPU Board (Model, Firmware & Version marks): don't have it recorded right now8. GPS Carrier Board (Model, Firmware & Version marks): 87-733 Rev A9. GPS Receiver Daughter Board (Model, Firmware, Chip & Version marks): 87-ACE3-2 Rev C, GPS RX: 39818 Rev C (China)10. OCXO Option Board (Model & Revision) (If installed): none11. OCXO Oscillator (Manufacturer and all data) (If installed): none12. Type of power supply (AC, DC or both): AC Switching (standard)13. List of all installed option boards (Name, Model, Firmware & Version marks): none14. List of all installed options (Oscillator type, Plug-in Card Names, LCD Backlight, Power Supply, etc.): Large LCD with Backlight.Cheers,Colin

author: ZigmundRat
author_rank: Regular Contributor
timestamp: July 28, 2016, 02:57:19 am
content: Here is the data for my XL-DC #3:1. Model Number:151-602-9222. Warranty Expiration:No Warranty Label affixed to chassis.(However, date codes indicate 1997-2000 timeframe)3. TrueTime XL System Version:TRUETIME XL SYS VER 0304. GPS-XL Version (Shown at boot-up):GPS-XL v1.0475. EPROM Part Number:182-6534 v0036. Antenna Type & Voltage setting:Standard, 5Vdc7. GPS-XL CPU Board (Model, Firmware & Version marks):87-611-40 Rev N/C8. GPS Carrier Board (Model, Firmware & Version marks):87-733 Rev A9. GPS Receiver Daughter Board (Model, Firmware, Chip & Version marks):87-ACE3-2 Rev B, GPS RX: 39818 Rev C (USA)10. OCXO Option Board (Model & Revision) (If installed):87-399-1111. OCXO Oscillator (Manufacturer and all data) (If installed):10.0 Mhz, TrueTime (Oscilloquartz) 8666-C2S, ?45.866.602 42A (label degraded), +12Vdc12. Type of power supply (AC, DC or both):AC Switching (Standard Artesyn NFS40-7608)13. List of all installed option boards (Name, Model, Firmware & Version marks):Low Phase Noise, 87-357-24 Rev C14. List of all installed options (Oscillator type, Plug-in Card Names, LCD Backlight, Power Supply, etc.):Large LCD Backlight. OCXO, Power Supply & Option Card noted above15. Revision History(None in particular noted. Various crossouts/handwritten changes)16. Internal & External Photos:GPS-XL Assembly:https://www.dropbox.com/s/d8h0su5jt3zv37h/2016-07-27%2021.37.39.jpg?dl=0Power Supply:https://www.dropbox.com/s/i7j89svxifisffn/2016-07-27%2021.38.37.jpg?dl=0Rear Connectors:https://www.dropbox.com/s/ss1sonu01q25h3c/2016-07-27%2021.40.03.jpg?dl=0https://www.dropbox.com/s/eoytanw0jfnxvjq/2016-07-27%2021.40.14.jpg?dl=0OCXO Board Assembly:https://www.dropbox.com/s/9yhhc1yxklr98iw/2016-07-26%2023.06.14.jpg?dl=0OCXO:https://www.dropbox.com/s/1g63hy8hbvc6xuz/Photo%20Jul%2027%2C%2021%2039%2018.jpg?dl=0Option Card Internal:https://www.dropbox.com/s/yshs2dknc9yc2lx/2016-07-27%2021.38.03.jpg?dl=0Added Note: The OCXO here is the same as the OCXO on the 86-357-3 Low Phase Noise module (TrueTime/Oscilloquartz 8666-C2S)

author: gpsdo_nut
author_rank: Contributor
timestamp: July 28, 2016, 05:45:06 am
content: For my (older) TCXO-only XL-DC:1. Model Number:151-602-5792. Warranty Expiration:7/20003. TrueTime XL System Version: TRUETIME Mk III SYS VER 0204. GPS-XL Version (Shown at boot-up): GPS-XL v1.0365. EPROM Part Number:182-6103 v0036. Antenna Type & Voltage setting:Standard, 5V7. GPS-XL CPU Board (Model, Firmware & Version marks):87-610 Rev H(?)8. GPS Carrier Board (Model, Firmware & Version marks):87-731 Rev 049. GPS Receiver Daughter Board (Model, Firmware, Chip & Version marks):87-CM3-3 Rev B, GPS RX: 37424-6110. OCXO Option Board (Model & Revision) (If installed):None11. OCXO Oscillator (Manufacturer and all data) (If installed):None12. Type of power supply (AC, DC or both):AC Switching (Standard Artesyn NFS40-7608)13. List of all installed option boards (Name, Model, Firmware & Version marks):NTS-XL, 87-6003-XL, 187-6009 V0006, TI sync. 87-6007TI-7814. List of all installed optionsNone15. Revision HistoryNone@ZigmundRat - the ? in your 8666-C2S is a "945..."

author: gpsdo_nut
author_rank: Contributor
timestamp: July 29, 2016, 06:54:46 pm
content: @pacair - Just out of curiosity - what's the maximum time constant configured on your Wenzel OCXO?

author: pacAir
author_rank: Contributor
timestamp: July 30, 2016, 01:31:21 am
content: @gpsdo_nut: By "Time Constant" I am assuming (by the previous messages) you are referring to "Oscillator Response Time". I cannot give you that info presently because none of my units are currently hooked-up and running (rooftop antenna was taken down for house maintenance and tree-removal recently and has not yet been put back up). When I try to use an indoor antenna it generally takes forever (if at all) to get all the way to a fully-working state at my home location. I am in the Pacific Northwest and have a somewhat limited southerly "view" to typical satellite orbits because I live on the northern face of a large chunk of dirt & trees. I had somewhat attenuated operation on both "C"-band satellite and Dish Network for this same reason. An outdoor elevated rooftop antenna works well enough, though.I checked my OCXO units to see if they stored their last known oscillator values (some specs are) but Oscillator Phase & Response Time values must be considered as "real-time" values only and are not stored for off-line reference.

author: ZigmundRat
author_rank: Regular Contributor
timestamp: July 31, 2016, 10:31:42 pm
content: And for contrast, one of my Rb units:Here is the data for my XL-DC #2:1. Model Number:151-652-699-12. Warranty Expiration:Warranty Expires 07/20013. TrueTime XL System Version:TRUETIME XL SYS VER 0274. GPS-XL Version (Shown at boot-up):GPS-XL v1.0435. EPROM Part Number:182-6222 v0066. Antenna Type & Voltage setting:Standard, 12Vdc7. GPS-XL CPU Board (Model, Firmware & Version marks):87-611-139 Rev N/C8. GPS Carrier Board (Model, Firmware & Version marks):87-733 Rev N/C9. GPS Receiver Daughter Board (Model, Firmware, Chip & Version marks):87-ACE2 Rev NC, GPS RX: PII-M1, Trimble 36576-A Rev C (USA)10. OCXO Option Board (Model & Revision) (If installed):N/A11. OCXO/Rb Oscillator (Manufacturer and all data) (If installed):FEI 5650A Options 25,29,32,42,5412. Type of power supply (AC, DC or both):AC Switching (Standard Artesyn NFS40-7608) plus Artesyn NFS40-7624 for Rb (24V)13. List of all installed option boards (Name, Model, Firmware & Version marks):T1-8, 87-6000T1 Rev A, NTS-XL 87-6003-XL FW:182-7009 v00714. List of all installed options (Oscillator type, Plug-in Card Names, LCD Backlight, Power Supply, etc.):Rb Osc., T1 and alarm card, NTS NTP server card15. Revision History(None in particular noted. Various crossouts/handwritten changes)16. Internal & External Photos:GPS-XL Assembly:https://www.dropbox.com/s/fqdkzy4tjl7wzzc/Photo%20Jul%2030%2C%2019%2056%2015.jpg?dl=0Power Supply:https://www.dropbox.com/s/cfw6bhm8wc4o8g0/Photo%20Jul%2030%2C%2019%2048%2023.jpg?dl=0Rear Connectors:https://www.dropbox.com/s/xvcjyk6ploqfqkq/Photo%20Jul%2030%2C%2019%2049%2025.jpg?dl=0https://www.dropbox.com/s/cg53a50g63i1lq3/Photo%20Jul%2030%2C%2019%2050%2024.jpg?dl=0OCXO/Rb:https://www.dropbox.com/s/ngf053df97icfja/Photo%20Jul%2030%2C%2019%2047%2051.jpg?dl=0T1 Option Card Internal:https://www.dropbox.com/s/tq2t0rqti7nfyqc/Photo%20Jul%2030%2C%2019%2051%2019.jpg?dl=0NTS-XL NTP Card Internal:https://www.dropbox.com/s/elijthay6xj7i25/Photo%20Jul%2030%2C%2019%2053%2046.jpg?dl=0Other Photos:Front Panel:https://www.dropbox.com/s/muzv5zoplqlxjg7/Photo%20Jul%2030%2C%2019%2044%2054.jpg?dl=0Overall Top View:https://www.dropbox.com/s/m573zt8byltnauk/Photo%20Jul%2030%2C%2019%2045%2026.jpg?dl=0A couple of notes on my Rb units:+) Rb was adjusted via serial port on the bench to be as close as possible to 10MHz @ 5V EFC, then replaced in the XL-DC. Reported DAC values are currently around -9000+) Note the stacking of the base unit and Rb power supplies - not a fan of that but nothing has cooked yet+) LPN module is not recognized if installed+) Temex LPFRS will work as a FE-5850 replacement, but it draws more power, and creates more heat.+) As compared to the 'slimline' 1 RU XL-DC with Rb option and another 2RU unit I've seen (where the bottom of the chassis is used as the heat sink), these have an external heat sink for the Rb. That heat sink was noticeably warmer when testing with the LPFRS, but the LPFRS was within its temp spec.

author: Raoul Duke
author_rank: Newbie
timestamp: July 31, 2016, 10:40:31 pm
content: @pacAir : do you have any protocol information for your RD-2? I just bought one on fleabay and while it is wicked cool, there is a paucity of information available for it online. And, in true Datum "Hey, let's name a bunch of incompatible things the same and be surprised when we go under" form, it looks like there are a dozen different versions. I have the RS-422 version with nine 16 segment characters and no colons. And there are 4 undocumented dip switches on the CPU board - do you know if there is any documentation on these?I would like to use the RD-2 with my 9390-6000; I have plans to stick a Raspberry Pi 2 into the expansion port to create an NTP server. (Long term plan is to remover the 19MHz resonator on the RPi and drive the SOC clock gen with the 10 MHz from the 9390-6000 so the NTP should have unmeasurable drift). The serial port of the RPi can drive the RD-2.(I also have a Datum 9100 timecode generator which I use as a rack mounted digital clock - it has the cool HP BCD decoding LED displays that look like 5x7 displays but it seems to drift at 2 - 3 seconds / week).

author: pacAir
author_rank: Contributor
timestamp: August 01, 2016, 12:37:36 am
content: @Raoul Duke: It has been awhile since I have played with my RD-2 displays so I don't remember all the info on the dip-switch settings (and mine may even differ from yours!) other than:Switch # 2: If turned ON, then the 3 leading digits (which show Days of the Year when displaying IRIG-B and a few other "time" codes... as opposed to "Range Timing" or "Countdown" displays) will be turned off and not displayed.I seem to recall that one of the switches may determine whether or not the colons are flashing (per-second) or fixed continuously "ON". Another function that comes to mind is whether the display BLANKS when signal is lost or whether it simply freezes at the last display update value. That is 3 out of 4 switches possibly.Also, I think you will find that your display does have Colon LEDs, you just can't see them until they are ON because they are not mounted against the rear of the bezel panel as the actual digit devices are. If you never see them (even if time is being displayed) perhaps that is the 4th switch function... Colons ON/OFF?As with most other gear, I believe that the RD-2 only reads the position of the DIP switches at boot-up time. So, if you want to experiment, you have to cycle power after each configuration change before the unit will "see" the changes and operate accordingly.The option switches are for configuration of features and not selection of supported input codes. Selection of codes is automatic and those that are available depend on how the board is stuffed and what firmware is in it. They may all be RD-2 displays but just like all TrueTime gear there are many custom flavors!Here is a copy of the documentation I have on the RD-2 (Operation Manual, Drawings, some parts lists, etc.):TrueTime RD-2 Manual:http://www.pacair.com/Transfer/GPS/RD-2/TrueTime_820-202.pdfI got a good laugh regarding your Datum 9000-series comments. I have had a few of their devices (older, newer, rack-mount, displays, time code generators, aircraft-mount, etc.) and all of them have 9000-series model numbers!Steve

author: Raoul Duke
author_rank: Newbie
timestamp: August 01, 2016, 07:49:47 am
content: Thanks for the information on the dip switches. Unfortunately, the 820-202 manual doesn't help much with my RD-2 which is an 820-263: it has no IRIG input, and the DB25 connector is labeled RS-422 instead of RS-232. I see no reason for 16 segment LEDs unless it can display text messages, which would be nice because I hope to alternate between time and date. I suppose I'll have to brute force it some day when I have the time.

author: pacAir
author_rank: Contributor
timestamp: August 02, 2016, 09:15:04 am
content: Doesn't your RD-2 power up with the text messages in the display? Mine comes on with "Truetime" and a "Version 3.2" (or something like that) on boot up. These displays are fully alphanumeric capable.Steve

author: Raoul Duke
author_rank: Newbie
timestamp: August 02, 2016, 12:21:06 pm
content: Yes: "TRUETIME" "560-3138" and "VER 1_3" in series after power on and lamp testing all the vertical and horizontal segments (but not the diagonals) before blanking. The EPROM on the CPU board is likewise labeled "560-3138" and "ver 1.3". Pins 3, 7 & 8 of the DB25 connector are tied to J3. These are nonsensical for RS422 as the connector is labeled but they do correspond to RXD, DSR and GND for RS232. So which is it? RS232 or RS422? Who knows?Quite frankly, Datum & TrueTime seem like they were confused 95% of the time and it must have been so painful to work with their equipment. My RD-2 is missing the IRIG code input BNC as well as T1 & R2 internally that would present the correct termination impedance for the IRIG signal, saving like what, $2? Would it really have been that hard to make a single, universal RD-2 that accepted both IRIG and serial inputs? One that could be configured by DOCUMENTED dip switches to perform any of the dozen incompatible specialized tasks, making the units interchangeable in the field? Is it really surprising that their equipment has been orphaned and the companies absorbed? I wonder if they ever actually printed service manuals for all the different variants of the same item, or did they rely on long term employee Larry who knew all the versions? Perhaps Larry retired (or went insane) and there was no one left who knew how to produce or repair the equipment.

author: Wilton
author_rank: Newbie
timestamp: June 26, 2017, 03:54:10 am
content: I know this topic hasn't been visited in a while, but maybe some of you could give some feedback.I just purchased a used XL-DC (with NTP) GPS works fine. Time works fine. IRIG-B works fine, NTP works fine.But the primary reason I got it was to serve as a 10 MHz reference for test equipment.I connected the 10 MHz out to my HP 8594E Spectrum Analyzer. It was displaying a clean carrier (happened to be another 10 MHz reference). As soon as I connected the XL-DC as a reference oscillator, the displayed carrier looked really dirty. It had noise sidebands extending out at least 500 Hz on either side almost as high as the carrier.I've evaluated a lot of thing: Tried different signal levels into the Spectrum Analyzer Reference input, using attenuators, AC coupled it. I thought maybe it didn't like the fact that it was a square wave, but I tried another square wave source I have and it caused no problem. I finally started analyzing the 10 MHz output of the XL-DC. It didn't look too bad on the spectrum analyzer, but when I put it on my digital scope and looked at it many cycles after the trigger, I could see a couple of ns of jitter. I also mixed it to zero IF and looked at the noise on the scope, using FFT. There were noise sideband spurs about 100 hz away that were only down 20 dBc. My measurement noise floor was -60 dBc. I also did the jitter test on the 1pps output, and it was clean.So my question is, is this sort of jitter on the 10 MHz output normal, or did I get a defective product? Is it not appropriate to use the 10 MHz output as a reference for precision test equipment? I assumed it was.Thanks,Wilton HelmEmbedded System Resources

author: pacAir
author_rank: Contributor
timestamp: June 27, 2017, 07:42:01 pm
content: There are MANY different configurations for the TrueTime XL-DC. For example, only two of the 5 or 6 I have are equipped with a TCXO or OCXO. I have not evaluated the 10Mhz output on each of these for comparison but I would be willing to bet the units with a full TCXO or Rubidium oscillator have better noise and phase-jitter specs.Also, there is a plug-in card for this series that provides high accuracy, high-stability and low phase-noise 10Mhz output signals. The card has a 5Mhz TXCO mounted on it. Here is one currently on eBay:http://www.ebay.com/itm/TrueTime-Symmetricom-XL-DC-86-357-24-Quad-10MHz-Card-Low-Phase-Noise-BNC-Output-/361986177463?epid=901632620&hash=item54480eb9b7:g:u8oAAOSw42dZIeo8The "TrueTime Symmetricom XL-DC 86-357-24 Quad 10MHz Card Low Phase Noise BNC Output" provides 4 BNC output ports to drive multiple receiving devices such as test gear.Steve

author: Wilton
author_rank: Newbie
timestamp: July 02, 2017, 09:37:13 pm
content: I think it is going to have to go back. I still don't know if it was defective or just never intended to meet my specs. I really don't want to spend the money for the extra plug-in card. The seller sent me a second main card to try, but it ended up not having 10, 5 and 1 MHz outs at all (and stupid me, was jumpered for 12 V so I lost an antenna).But I have learned some things, so am posting here in case it helps someone else. The 10 MHz signal comes from a different clock oscillator (I don't think it is even a TCXO). The replacement board didn't even have it populated, so it obviously isn't necessary for the functioning of the rest of the circuit. It is apparently disciplined to 1 PPS or some other signal from the GPS board. There are a lot of FPGAs in this device, and I'm sure some are frequency comparators for such things. It sort of looks like 1 PPS (or possibly some other signal) is propagated with high precision and then everything else is locked to that.

author: ZigmundRat
author_rank: Regular Contributor
timestamp: July 03, 2017, 02:03:00 am
content: FWIW I just put my unit on the spectrum analyzer, with a 1MHz span centered on 10MHz. Taking the 10MHz off the back of the main card shows nothing ugly. The worst spur is at ~9.81 MHz and is ~66dB down. There are some closer in spurs at about +/- 50kHz, I am guessing from the switching power supply. This is on an OCXO unit with a low phase noise option card. Looking at the output of the LPN module, all artifacts are down in the grass and not visible. Never looked at it before but nice to see it *is* low(er) noise.So just for giggles, I fired up my TCXO unit. Same spur on the 10MHz output, slightly different level but still about -66dB.Switching references for the analyzer (now the XL-DC square wave) and looking at the Thunderbolt OCXO, the TBolt looks reasonable. in fact, switching back to the TBolt as ref, and looking at the TBolt signal I don't see any real difference regardless of the reference used. But we could be comparing different fruits here. What were your spectrum analyzer RBW/VBW and span? I'm using an Advantest R3261 here and went down to +/- 10 kHz and 30 Hz RBW. I also have the ref oscillator going through a variable attenuator and a distribution amplifier. Input to the spectrum analyzer was around 1.9v PtP. But as you say, looking at it on the spectrum analyzer didn't reveal a lot.I don't think I'll be able to duplicate your other tests (i've got other things going at the moment), but it might be educational to do so at some point. I was wondering: did you look at your other square wave source the same way?

author: texaspyro
author_rank: Super Contributor
timestamp: May 16, 2019, 04:59:35 am
content: I am in the process of adding Truetime XL (DC and AK) support to Lady Heather. It looks like I can also support the XLi (does NTP), but the XLi manual has some vague/conflicting info for the output of these commands:F18 - versionF72 - faultsF73 - alarmsDoes anybody have an XLi and can capture the serial port output response to these command?

author: pacAir
author_rank: Contributor
timestamp: May 22, 2019, 07:35:17 am
content: I don't have an XLi but I wanted to jump in and thank you for the "Lady Heather" application! I have used it on a number of GPS devices and would LOVE to see TrueTime support added! I have a number of TrueTime XL-DC, XL-AK and several older TrueTime models in my collection.Steve

author: texaspyro
author_rank: Super Contributor
timestamp: May 22, 2019, 12:25:56 pm
content: Quote from: pacAir on May 22, 2019, 07:35:17 amA guy is loaning me an XLi, but it does not have the GPS board. I think it will answer my questions, though.My XL-DC has the FTM-III power line frequency analyzer card in it. Attached is a screen shot of it monitoring the power line freq and calculating various statistics and a histogram and ADEVs of the frequency.I have some code in there to also support the oscillator frequency measurement option, but am unable to test it.

author: Kean
author_rank: Unknown
timestamp: September 10, 2020, 05:29:28 pm
content: I know this is an old thread, but it is one of the few here mentioning TrueTime GPSDO's.Just in case anyone is following this thread and knows anything about the TrueTime GPS-DC, I make a post recently looking for more info.https://www.eevblog.com/forum/testgear/looking-for-info-on-truetime-gps-dc-416-rubidium/

author: Ulaker
author_rank: Newbie
timestamp: December 21, 2020, 10:53:41 am
content: Hello,anybody of the people familiar with TrueTime xl-dc gpsdo around? Mine does not behave as expected, it never gets lock stays in lookung for satellites status for ever even with the time and lon/lat/alt correct after a few minutes.Any help welcome,Ulaker

author: ZigmundRat
author_rank: Regular Contributor
timestamp: December 21, 2020, 02:00:03 pm
content: There could be several causes for this. Most probably:+) Do you have the right antenna? It could be 5V, 12V, or require a down-converter. This is all usually marked on the back by the antenna connector. You might include a picture of the back, and antenna details.+) GPS receiver could simply be old/defective. It’s probably a Trimble Ace, or maybe a SVee 6, and those are somewhat hard to find these days.+) You didn’t wait long enough for a fix. These receivers are not particularly sensitive, and require a good antenna placement. Also, it may take 15 minutes or more for the receiver to find the strongest satellites and then download an almanac.+) Does FN 60 ever show satellite signals?Hopefully this is some help. Let’s see where it goes.

author: Ulaker
author_rank: Newbie
timestamp: December 21, 2020, 05:08:30 pm
content: Ok fourth attempt to post a follow upTried few time to craft a followup with quotes and photos but failed to comply to the rules and regulations...I did change the battery after initial attempts to get this old horse saddled, but the fresh battery did not help, the only thing that changed is that the current year stays in the NVRAM when power cycled.Would like to believe that this antenna is the right one since date time and location do get on the displays whithin a few minutes after power on.The unit is acting quite fast within a few minutes to show on both displays the current time and on the small display the correct longitude/latitude/elevation, The status is enumerating a few integer numbers that I take to be the staelite currently in field of view. Than transits to looking for satelites and eventually not enough satellites. So far it was understandably but even after two weeks with several restart (power cycling) The FN60 does not contain tracked or bad satellites.OCXO is unfortunately missing, does that matter for satellite fix?Is the 3/4" PVC pipe stub compulsory under the antenna? Is proximity to metallic structure detrimental to signal integrity?Is the Firmware possibly obsolete? do the currently active staellites of the constellation use a newer protocoll for almanach distribution? Why is the serial port spitting out only day of year and current hour minute second? Not reacting to any input?Is there a unlock procedure for the serial port?Questions over questions to which I am more than happy to have somebody to talk about.Thanks for helping solve this puzzle,Greetings from Germany,Ulaker

author: ZigmundRat
author_rank: Regular Contributor
timestamp: December 21, 2020, 11:56:49 pm
content: Yeah, that looks like the down converter antenna, lucky you were able to get it. And I see the receiver is marked as 'Downconverter required'. So you're off to a good startIt's possible to convert the board to standard GPS (no downconverter) but it's not easy, and you need another receiver (practically unobtanium).You say that it does track for a while and then loses the satellites. (And yes, those integer numbers on the bottom line are the tracked satellite numbers.) Apparently something is warming up and drifting, causing it to lose lock. I don't think the OCXO is required for GPS to get satellite fixes, but it would of course never go to locked state. FYI: All of my units have OCXO or Rb options and require them to be present or the system does not initialize. So I think you must have the TCXO version since it starts up OK.Question: How do you know you are missing an OCXO?Answers:+) No, the PVC stub is not an absolute requirement.+) Yes, proximity to metallic objects is detrimental to signal integrity. Best to place above and away from them, best as you can.+) Yes, the firmware is obsoleteWe're talking mid-90s here. That said, the unit should work (I have 4 of them, different build options) with the only real effect of the date/time being wrong, which you can fix with the FN68.+) There are no changes to the almanac distribution+) The default is to send the time every second+) You probably aren't sending it the right commands. Have you read the fine manual?+) AFAIK, there is no serial port lockout, but you can lock the keypad.I doubt its the cause, but check FN65 and make sure all satellites are enabled.If you're feeling adventurous, you could check the oscillators on the CPU board. These are under the GPS board. Actually there should be two. One a 16.368 MHz for the GPS clock, and a 10MHz TCXO. It's possible if the 16.368 oscillator is off frequency enough, it could cause poor sensitivity and other symptoms. I don't exactly recall 100% but I *think* the MCX connector closest to the board edge has this signal on it, the other one goes to the GPS antenna connector.I also notice you have the NTP card. Are there other modules installed?

author: Ulaker
author_rank: Newbie
timestamp: December 22, 2020, 09:51:18 am
content: Question: How do you know you are missing an OCXO?The dangling connector stub between the receiver & NTP card and the display would have been my guess that it is for the OCXO it has supplyand coax as well as wires that I deemed to be the control/adjustment to trim the 10MHz to track the GPS time. I do not really know, it is a guess.I locatet the 16.368MHz signal path and it is 16.3860517 is it close enough? Should it be tweaked closer to 16.368000?There is provision to adjust the frequency in the can of the oscillator of but with the stacked board in place not accessible.Not really clever design.The serial communication is still a bit of a mystery to me at this time since my naive expectations to interact with the module did not produceany gain of insight. Maybe need to really closer verify that the Rx/Tx is really what I think it should be. The PC terminal emulation is receivingthe datagram for DOY.HH.MM.SS followed by a "?" nothing more than that and any keys I attempt to send to the device are not producing anychange in behavior. The stream of DOY.Time is coming steady. Only at the beginning it is counting from zero then when it gets the decodedsignal from the first Satellite it changes to the correct current DOY and time.I will try to reposition the antenna to be a bit further away from metallic structure, so maybe the signal/noise improves and the normal sturt upprocedure completes.No other modules and I have not yet checked if the NTP card is responsive, I still needs a converter to talk to it over the LAN port. If the sturtup ever completesthe next step might be to illuminate the large display and if I get to attach the NTP card to the LAN will try to set up a local NTP service?I am doing this just as a challenge to see if I still can get old stuff to work again.Thanks once more for assistance,Ulaker

author: Ulaker
author_rank: Newbie
timestamp: December 23, 2020, 07:55:31 pm
content: Reply to myself, the 16.368 adjustable oscillator is hard to reach and requires repetitive disassemble of the stacked boards. If it is the way to achieve bit lock and/or phase lock I had no successful iteration of adjustment and proof of concept in doing it.The rs-232 is either broken or misconfiguration of sorts. The tx pin is functional the rx is stuck on mark level so no way to input the ctrl-c and obviously none of the further interactin instructions on this path.So question: is the manual of this board available or at least reverse eng of the rs-232 port path, possibly jumpers or driver chips already figured out? The rs-232 port is probably talking to the 80c186, so need to find out how the uart functionality is implemented. If it was a static jolt that destroyed a protection diode or rx driver IC in the proximity of the 9pin connector maybe the component could be replaced and functionality restored?Thanks for help and season greetings from Germany,Ulaker

author: ZigmundRat
author_rank: Regular Contributor
timestamp: December 24, 2020, 04:16:13 am
content: If you've set it on frequency, that's all you can do. Adjusting it after that isn't going to help. But I think you may have a bigger problem: The down converter antenna could be the wrong one.The manual references a 142-603 model - @pacAir (and others) have indicated that the 140-615 you have has a different IF frequency and is incompatible. That would explain alot. Besides the 142-603 referenced in the manuals, there is also the 142-401, 142-602, and 142-610 which may also be compatible. I also just read: "It will not work with receivers matched to the "bullet" style downconverters (eg. XL-AK, XL-DC etc)." in an eBay listing from a guy who has been doing this for a long time. So I think that's accurate, sorryRegarding the serial port: @pacAir in the 2nd reply at the top of this thread posted a PDF of the option jumpers. J26 and J27 determine RS232/RS422. You might start tracing there and see what you find. My one unit I have open now has an LTC491 driver chip (differential driver) and a Sipex SP310 (RS232 driver). I haven't traced them out to see what's connected where (there's also a 75179 on the GPS board, that could be the reason for the LTC491).

author: Ulaker
author_rank: Newbie
timestamp: December 24, 2020, 05:18:49 pm
content: Thank you for guidance, I lack knowledge of the inner cogwheel mechanism that is buried inside the receiver board. Is there any description i.e. theorie of operation that explains the approach that the cavemen of gps technology have chosen to implement a signal processing to recover frequency and phase over this convoluted extraterestrial path with the components available four decades ago? Why two cpu architectures, 80c186 and 68000, completely different designs of data processing engines engaged in the task? Appearantly different groups with different taste and decision making choice required to skin the cat? If I understand it right part of the coarse aquisiton demodulation seems to work despite the incorrect front end? The gps derived solutions to date, time, longitude, latitude and elevating computation produces correct results. The tracking of satelites never gets to classify good or bad satellites, (the lists are empty even fter manny hours) despite the 2d time enumeration of recognizer satelites in field of view of the antenna.Not sure how long it will take me to find time to trace the path of the rs-232, (maybe the faulty part can be bypassed) I expect to get more insight into the inner workings of this gps engine if it can be explored via the responses and monitoring parameters.Merry Xmas,Ulaker

author: ZigmundRat
author_rank: Regular Contributor
timestamp: December 25, 2020, 02:56:56 pm
content: I also lack knowledge of the inner workings of GPS navigation and timing. I found this:http://www.nbmg.unr.edu/staff/pdfs/blewitt%20basics%20of%20gps.pdfto be a very readable description of the system. 40 years ago or today, the system basically works the same way. The main differences are in time to first fix, simultaneous satellites tracked, etc.The reason for different processor architectures is the GPS is made by Trimble, the clock generator/disciplined oscillator by Datum. It is not a surprise that they would be different.I can’t explain why (if the down converter is the wrong one) it would ‘half work’. I agree, it appears that C/A signal can be initially recovered but after that, it goes to another state where it can’t proceed.If you want to talk to the GPS engine directly, you should be able to do so by carefully connecting to the serial port. Keep in mind the electrical signal levels if you do this. I used this method to capture the traffic between GPS module and the system board. The GPS is setup is TSIP mode so you will need to decode it. You might also need/want to see if you can find the software to talk to these old Trimble receivers. I think it was called TSIPCHAT, I will have to look in my old stuff for it.Frohe Weihnachten Ulaker!

author: ZigmundRat
author_rank: Regular Contributor
timestamp: December 27, 2020, 04:14:28 am
content: Just a bit more info for you. Just to illustrate the variety of parts used in these, I've included a picture of another GPS receiver which they used, an ACE-II model, again by Trimble.But it wasn't 100% compatible, so they built a FPGA converter board and placed it between the system board and the GPS. These boxes were widely varying in their options and builds. I don't think I've run into two units with exactly the same firmware either. It's almost like the firmware was custom burned for each box shipped, depending on the options.With regard to the OCXO: I also include here two pictures of my OCXO unit. One showing the cable routing and where the OCXO is mounted (2nd pic).The OCXO itself is a Oscilloquartz 8666-CS, which is mounted on a little carrier card. I provided a picture of that board alone for reference (3rd pic). There's no magic there, just a regulator and an op-amp buffer for the output. It wouldn't be that hard to lay out a new board to match. If you decide to do this, and can't read some component values let me know. Likewise for dimensions. Good luck with your unit!Cheers!

author: Ulaker
author_rank: Newbie
timestamp: December 27, 2020, 07:01:14 pm
content: thank you for bringing more light into the evolution history of the beginnings of GPS technology.Looks more like prototype or development studies than series fabrication. A long way between these and ublox neo m8p.Did you never replace the NVRAM lithium-thionylchloride cell? I checked it and it was around 1V, so I replaced mine with a 3032 button cell since the original is hard to get and mighty expensive without even considering shipping cost.What is the switch on the receiver board supposed to do? Usability in the same class as the trimmer on the 16.368 oscillator.This gadget is a textbook collection of solutions on how not to design equipment.Did not find time to further fiddle around but the few restarts seem to have a reproducible behavior, the date, time and location reliably decoded and the status changes initially between looking for satellites and note enough satellite in between the 2d solution for several sat numbers is briefly displayed finally it decides to stay solid on not enough satellites and nothing more seems to happen on the status. Maybe peeking into the messages exchange between the two boards reveals weather it still continues to demodulate satellite signals, and if yes which ones.Cheers!

author: gpsdo_nut
author_rank: Contributor
timestamp: December 27, 2020, 10:16:39 pm
content: Great to see the TrueTime XL-DC thread still ticking on! My Racal Dana 1992 counter power supply apparently took a dumper the other day so posed a question in the Repair section....and noticed new posts here!@Ulaker - If I remember correctly, TrueTime customizes the Trimble GPS receivers to accept a scaled-down LO frequency from the 10MHz reference to something like 16.384kHz, which replaces the native 16.384KHz crystal that usually accompanies these Trimble receivers. When your unit eventually loses lock on the original satellites, what does your XL-DC DAC value read (FN+71, up/down arrow to DAC page)? Make sure it isn't pegged onto either end of the 16-bit DAC range (I think -32768 to +32767). Do you have a frequency counter with a good reference to determine how far off to true 10Mhz your XL-DC is giving out?Also make sure your receiver isn't stuck in TIME mode when you power on your unit. Stick it in AUTO for the time being.

author: Ulaker
author_rank: Newbie
timestamp: December 28, 2020, 05:32:11 am
content: Hello, thank you for suggestions.The mode is Auto, upon power up it seems to iterate a few steps of the state machine giving Mode Auto and 1sat values like 22 and 4 etc in between messages like No usable satellites yet and looking for satellites.I would like to believe, but do not remember exactly, some 2d messages among the sturtup strings.After a while it seems to get stuck in looking for satellites.The fact that it stays in the looking for satellites may be indicative that the demodulator does not recognize sync or idle pattern which should translate usable signal and that to satellite in field of view.The FN71 values change during the initial aquisiton steps, and stop when the looking for satellites is reached.Is there some way to check signal to noise ratio anywhere? Any test points on the board with known healthy patterns for analog scope or digital status like carrier detection or bit lock, frame lock, etc? In these early design they sure must have hardware for signal processing so some partial tell tale points reachable on the board.The steady state values given by FN71 are:Dac -15098,Response Time 6.250e+00sOsc Phase -3.462e-06sOsc Offset -7.362e-07Osc Drift -1.750e-06/dayNo idea weather these values are indicative of something. I never checked them before nor do I know where to look for healthy range values for a nominal operating device.Season greetings,Ulaker

author: gpsdo_nut
author_rank: Contributor
timestamp: December 28, 2020, 09:06:07 am
content: Your DAC value looks to be in the proper range.Quote from: Ulaker on December 28, 2020, 05:32:11 amYes, if the receiver thinks it has enough satellites to form a 2D solution it'll briefly enter that state while continuing to search the sky to eventually (hopefully) enter 3D positioning mode. As ZigmundRat may have hinted, it's still very possible the demodulator for the downconverter section to not be 100% compatible with your unit.Quote from: Ulaker on December 28, 2020, 05:32:11 amYou can check the C/NO values of each satellite in FN60 - I have a Trimble SVee 6 model (old) and reports in Trimble's own AMU units. I think anything above like an '8' is pretty good. Newer models may report differently. As for test points, not certain; the RF and digital domain stuff is done inside the Trimble GPS board, which is a modified COTS product but I wouldn't expect any real TPs for things like that - someone else can correct me if I'm wrong.As I type this, you can also issue a F79 and do a COLD reset of the GPS module and see if it starts up and holds on to satellites better. You also did mention changing the 3V lithium NV memory battery which should have done the same thing...but do try F79 COLD Start a try for grins.

author: Ulaker
author_rank: Newbie
timestamp: December 28, 2020, 02:37:35 pm
content: Set FN79 selected to yes, does not seem to provoke reaction, or does it apply this selection on next power cycle?FN60 is and stays unpopulated, neither tracking nor bad show any entry, in other word end of list when it should display the sat numbers and possibly characterization their signal condition.Might be that the front end down converter implementation or its current bandwidth is no perfect harmony for the processors in the unit, still it does some corse aquisiton steps. There possibly is a different demodulator for parts of the signalling stream. Intrigueing that partial functionality. I guess it is perfectly explainable with better understanding of the coreography and orchestrations in these boards. It must have worked once upon a time but something changed since than. It might be a unmatched front end....At this time I have little inclination to procure another front end section, maybe after the rs232 rx path is functional.Possibly the event that fried the rs232 input also impacted the antenna associated circuitry in some way detrimental signal integrity.

author: looney
author_rank: Newbie
timestamp: January 07, 2021, 10:29:17 am
content: I also received a XL-DC (Symmetricom branded) in the mail today, pictures and more info will follow later.But I can tell you right now that it's a very basic unit, just a PSU and GPS board, 12 Symmetricom antenna, no other I/O, no Rb and no OCXO.This leads to my question, is it possible to fit an OCXO even when there is no wire harness for it?On the pictures in this topic I see that the power and coax go somewhere under the ribbon cable connecting the backplane and the front panel but it's not clear where they connect.I'm also not sure if the option would need to be enabled in software.I guess it's always a possibility to replace the TCXO on the GPS board with an OCXO or Rb?Again, I will post picture and info according to the template later this week but I thought it was wise to ask this question first in case there is something in particular I need to look for that might not be included in the templatePS: The unit, as bare as it is, does function perfectly, 3d time fix in a few minutes and so far it seems within spec compared to my Rb optioned Oscilloquartz OSA 5230 receiver.

author: Ulaker
author_rank: Newbie
timestamp: January 07, 2021, 09:36:47 pm
content: Happy to hear that thre are more electronics archeologists digging into the evolution of the time keeping technology.As far as I was able to gather info there is no repair manual or schematic circulating in the open. Everithing I have seen sofar is descriptors experience. Modifications of the tcxo to ocxo or rubidium is definitely possible since symmetricom didit a long time ago already. They used two or more receiver modules and middleware to translate message sentencesderive time and location to adjust the different options of local time keeper. The core peace of the processing is achieved on two cpu, one 68000 and one 80c186.Depends on your determination and skills to reverse engineering and weather economics do not play significant part of the ecuation. The slope and loop time to control the local oscillator varies for each technology approach. At this time it is not clear to me weather different firmware versions existed for tcxo ocxo and rubidium or jumper configuration determined the discipline of the slave oscillator present.Happy new Year and fun with your new aquisition,Ulaker

author: ZigmundRat
author_rank: Regular Contributor
timestamp: January 08, 2021, 04:22:57 pm
content: In our collective experience so far, it almost seems that each unit was built to order. The specific firmware version appears to be very much tied to the exact build options. So far, I haven't found any software setting or hardware strapping which sets the oscillator type. It appears that TCXO, OCXO, and Rb all have their loop parameters in ROM. This means that you will not readily be able to change out the TCXO for an OCXO, or Rb option. The only other option would be if you had the 'external oscillator option', which is the only way you can set any of the control loop parameters.I guess we could start collecting ROM images and info on specific version, model number, GPS, and installed options. I have two Rb units, an OCXO with added low phase noise option, and a TCXO version with added low phase noise option. They two Rb units identify with the same model number (182-6222v006) and the same version (1.043) but the SYS version (027) is SV6 on one and ACE on the other. I don't know if both GPS engines are supported in the same ROM and are identified at startup, or if it's another case of unique firmware.

author: salvateur2012
author_rank: Newbie
timestamp: June 28, 2021, 11:13:34 am
content: bnjr ma betterie typê keeepers 3.5 volt a exploser du coup court cicruit jaimerais savoir le role de cette pile et cause possible merci

author: ZigmundRat
author_rank: Regular Contributor
timestamp: June 28, 2021, 12:29:33 pm
content: The battery allows the saving of current location, almanac data, and clock to keep time when powered off. This makes future startup times faster, but is not required for operation.There is no normal reason the battery shouldexplode. I suppose given their age an original battery could leak, but none of my units did. Please note that this is a special non-rechargeable lithium thionyl chloride long life battery, and must be replaced correctly and with the correct type! If the original were replaced with something different or the circuitry were altered, then there could have a problem.(I’m sorry, I do not read French, so used a translation to understand the question.)

author: gmilliorn
author_rank: Contributor
timestamp: September 18, 2022, 06:29:48 pm
content: I purchased an XL as not working, the seller artfully hid the following in the shadows. This appears to bethe original battery type, so they do leak for some reason.I suppose that is what the previous poster was referring to. This is truly a parts unit now I guess.

author: gmilliorn
author_rank: Contributor
timestamp: October 29, 2022, 08:10:28 pm
content: The GPSDO seems unsalvageable, but the OXCO is OK and chassis, despite some lithium corrosion is fine. I hadthought to marry this with a Trimble GPSDO but schematics seem unavailable, at least as far as I can tell.So I've reverse engineered the display/keyboard and some of the backplane, at least well enough to talk to thefront panel, using an Arduino. That's probably not sufficient to manage the Trimble I assume, based on whatothers are using (the M1DST code looks interesting).I can post the schematics if that is of interest. It is not the TrueTime GPSDO board, though.

author: gmilliorn
author_rank: Contributor
timestamp: October 30, 2022, 01:53:23 am
content: Here's the schematics if they're of interest.I don't know anything about TrueTime's products, soall the names are based on assumptions. It's enough foran Arduino to talk to, at least.

author: ZigmundRat
author_rank: Regular Contributor
timestamp: October 30, 2022, 04:12:23 am
content: Definitely of interest, thanks for sharing your work. Repurposing the chassis is a great idea, and now that you’ve got the backplane connections figured out you’re well on your way. In the original product, the front panel is little more than a clock plus a keypad and smaller LCD for configuration and some status displays. I would think that you could turn this into a display/control pad for the Trimble/UCCM type GPSDOs (or Thunderbolt). You would need to parse the serial output and send serial commands, but this is not especially difficult, just annoying as the output is mostly meant to be human readable. There are a variety of projects which provide displays for these units which you could leverage. Some simple, some more complex. The M1DST project is interesting (C# and .NET on a micro) but there are many other platforms which could be used (Teensy, ESP32, etc).If you wouldn’t mind posting some code examples that would really complete the package.Thanks again for sharing.

author: Kean
author_rank: Unknown
timestamp: October 30, 2022, 01:07:34 pm
content: Indeed. I have a similar unit, the TrueTime GPS-DC (2RU version) and I've not had any luck getting it to do anything due to the lack of any docs.The idea of repurposing the front panel and chassis is appealing, and maybe even some of the output cards. The front panel is slightly different on my model, but probably implemented in a similar fashion. I suspect just the keyboard layout changed slightly between models.

author: gmilliorn
author_rank: Contributor
timestamp: October 30, 2022, 07:09:03 pm
content: Here's the arduino code for probing/controlling the system. It hasdetails on the clock display, which is basically a 96-bit shift register,one bit per LCD segment.The keyboard debouncing is poor, I've not spent much time onit as I think I probably need to switch to a raspberry pi if I want to runan NTP service on it.

author: NA5B
author_rank: Contributor
timestamp: March 05, 2024, 06:06:23 pm
content: Hello all, I would like to use the Lady Heather with my Truetime XL-DC but it is not listed in the supported devices. I tried all the commands listed for various devices. Anyone running the Lady Heather with Truetime XL-DC? I see that Texaspyro has a picture shared here using the same unit with the software. I also have a Fei-Zyfer Nanosync and have no problem running it with the Lady Heather with /rx3 command. Thank you.