HP5385A OCXO Timebase - Page 1
Forum section: electronics / testgear

author: Miti
author_rank: Super Contributor
timestamp: September 06, 2018, 03:16:31 am
content: Being obsessed with the stability of the time base in my instruments (does it sound familiar?) I decided to make an OCXO oscillator for my HP5385 frequency counter (the TCXO oscillator that was installed is ridiculous) until I find the time to put together a GPSDO. It is nothing too crazy, a used OSC5A2B02 OCXO from Ebay, a MAX6126AASA21 and a potentiometer. So I made a board, got it done in China by PCBWay and installed it today. All I can say is that the difference is huge. I calibrated it using another 10MHz OCXO manually disciplined to a GPS module using my Tek TDS210 scope and a programmable power supply for VFC.

author: metrologist
author_rank: Super Contributor
timestamp: October 17, 2018, 07:13:26 am
content: Are you offering these populated minus the clock? Do the pins connect to the counter's board as a drop-in replacement?

author: Miti
author_rank: Super Contributor
timestamp: October 18, 2018, 12:20:22 am
content: I'm offering the bare boards only as I don't have the time to populate them and don't think I'd make any geschaft.The board is a drop in replacement for option 004, you'll need to do the following beside populating this board:1. Remove the TCXO.2. Populate a ferrite bead and a 10 - 100nF capacitor that are left out on the counter board.3. Move a jumper from one location to another.4. Solder the new board in the place of OCXO, drop in as I said.5. Let it run for few hours and then calibrate.It is a dramatic improvement.

author: DC1MC
author_rank: Super Contributor
timestamp: November 23, 2018, 09:28:16 pm
content: Hi Miti, do you still have some boards, how much will cost to post one to Germany in a padded envelope ?Cheers,DC1MC

author: DC1MC
author_rank: Super Contributor
timestamp: December 16, 2018, 07:43:35 pm
content: The board from Miti arrived nicely and the OCXO as well (I've got tow of each type, they are compatible).Because of a brain fart, I've posted pictures in this thread:https://www.eevblog.com/forum/testgear/hp-5385a/Bit promise that when the board is done, I'll post the final result here.Cheers,DC1MCEdit: Added a picture to the Miti PCB, OCXO and a DIP16 socket for referenceAlso a datasheet PDF oft the CTI oscillator.

author: Miti
author_rank: Super Contributor
timestamp: December 16, 2018, 11:54:25 pm
content: After more than one month of running continuously, with the OCXO timebase and the 10MHz GPSDO at the input, my frequency counter drifts about +/- 400ppt maximum, probably due to ambient temperature changes. Impressive, eh?

author: texaspyro
author_rank: Super Contributor
timestamp: December 17, 2018, 02:57:46 am
content: An OCXO that has been powered off for a long time can take over a month for the drift to level off and stabilize. Here is what the 8663 DOCXO did when I put it in an HP58132A counter.UTC 8663 mounted on Sweeny DOCXO card in a HP 53132A counter. The 8663 hadnot been powered up for over 10 years. Below is the frequency drift per dayas the 8663 aged in. THe 8663 is spec'd at 1E-10 (1 mHz) per day aging. Frompast experience, they are capable of much better than that (1E-11 to 1E-12 perday). They seem to be limited in this application by the EFC DAC / VREFperformance.The 8663 was mounted on the Gerry Sweeny aftermarket OCXO board for the 531xxcounters. For the first 30 days, the board was configured for the 0 .. 10VEFC DAC range. The Sweeny board powers the DAC with +/- 12V which is a bitout of the spec'd minimum +/- 13.5V required for optimum performance onthe 0 .. 10V range.The Sweeny OCXO board is based up on the HP design with a couple of nice mods.First it has footprints for several common OCXO modules. Second, it allowsthe DAC range to be configured for 0 .. 5V, 0 .. 10V, and +/- 5V.The circuit feeds the OCXO output through a differential line driver. The linedriver sends the OCXO to the HP counter mother board through a ribbon cable.The motherboard makes the OCXO output available on a BNC on the counterback panel. Checking the ADEVs of the raw OCXO outout and the counter outputshows that the 53132A degrades the DOCXO output by around 1.5E-12 (raw DOCXOvalue around 5.1E-12 at 200 seconds, counter 10 MHz output BNC around6.5E-12)For the first 30 days the EFC DAC reading was recorded and the HP53132A wasthen auto-cal'd and the new EFC DAC output was recorded. (The DAC readingsfor the first 10 days were lost when a momentary power failue occured and thesystem was not shut down cleanly).The initial 30 day run was done with the Sweeny board DAC configuredfor the 0 .. 10V range. Given the DOCXO EFC sensitivity (around 0.75 V / Hz)and the 12-bit DAC, the minimum auto-cal resolution is 0.002 Hz. Severalauto-cal cycles were performed each morning until one was within 0.001 Hz.DAC readings were made by a Tektronix DMM914 4.5 digit DMM, not the best toolfor the task, but it was available.drift (Hz/day) DAC (after cal -> 24 hrs later)day 1: .298000 Hzday 2: .057000 Hzday 3: .033000 Hzday 4: .022000 Hzday 5: .017000 Hzday 6: .011800 Hzday 7: .009640 Hz 4.471Vday 8: .008400 Hz 4.458Vday 9: .006380 Hz 4.451Vday 10: .003880 Hz 4.443Vday 11: .002840 Hz 4.446V -> 4.438V // power glitch caused resetday 12: .003470 Hz 4.437V -> 4.437Vday 13: .002100 Hz 4.432V -> 4.433Vday 14: .001590 Hz 4.430V -> 4.430Vday 15: .001380 Hz 4.426V -> 4.428Vday 16: .001660 Hz 4.424V -> 4.426Vday 17: .000526 Hz 4.422V -> 4.423Vday 19: .000284 Hz 4.421V -> 4.423Vday 20: .000038 Hz 4.423V -> 4.424Vday 21: .001019 Hz 4.420V -> 4.420Vday 22: .001350 Hz 4.417V -> 4.418Vday 23: .000402 Hz 4.417V -> 4.417Vday 24: .000953 Hz 4.418V -> 4.419Vday 25: .000304 Hz 4.417V -> 4.416Vday 26: -.000441 Hz 4.417V -> 4.418Vday 27: .000214 Hz 4.415V -> 4.415Vday 28: .000517 Hz 4.415V -> 4.416Vday 29: -.000998 Hz 4.415V -> 4.415Vday 30: .001300 Hz 4.415V -> 4.414Vday 31: .000423 HzPowered down, replaced 53132A fan, changed DAC range to 0 .. 5V, andthe 53132A was put back into case (hence no more DAC readings). The 0 .. 5VDAC range reduced the auto-cal minimum step size to 0.001 Hz. Hopefullyit should also improve the DAC stability.Warmup frequency error after power up:1 Hz - 3m0.1 Hz - 3m 25s0.01 Hz - 5m 45s0.001 Hz - 6m 15sAfter 24 hours the unit was auto-cal'd once and left alone. The frequencyerror for the next week:day 32: .000152 Hz (0.00009 Hz/day for last 18 hours)day 33: -.000825 Hzday 34: -.000730 Hzday 35: -.000287 Hzday 36: -.000144 Hzday 37: -.000086 Hzday 38: -.000083 Hz

author: cncjerry
author_rank: Unknown
timestamp: December 17, 2018, 04:20:56 am
content: Mark, I sent you a note the other day asking how you are using Lady Heather to do these plots. I was thinking that once I had my Rb standard tuning word set, couldn't I use another 1PPS signal against the now stable Rb 1PPS to do ADEV in LH? How are you reading both the Tek meter and frequency counter in LH? Or am I missing something simple?ThanksJerry

author: texaspyro
author_rank: Super Contributor
timestamp: December 17, 2018, 05:02:02 am
content: No Tek meter involved...I was using a TAPR TICC dual channel interval counter clocked by an HP-5071A. For the HP counter, I connected the counter freq ref output to the TICC via a TAPR TADD2-Mini divider (divides 10 MHz down to 1Hz). Heather is configured with the TICC as the input device.

author: cncjerry
author_rank: Unknown
timestamp: December 17, 2018, 07:54:04 am
content: That TICC shows up a lot in time nut projects and I assume heather supports it. Isn't the sampling rate limited to >1sec though? I have to go read the manual. I've been looking for a new counter and have been considering the PM6681 or a TICC. I have a TADD2 and I guess you use that to make up for the sampling rate in the TICC, correct? I've been reading up on the Tight PLL method of measuring ADEV and was planning to start there and maybe build the mini Dual Mixer Time Difference setup. But if you get acceptable results using the TICC maybe I should just buy one already and try it out.ThanksJerry

author: texaspyro
author_rank: Super Contributor
timestamp: December 17, 2018, 07:08:33 pm
content: The TICC can handle over 100 Hz. With some firmware mods the hardware can probably do 1 kHz... hence the use of input dividers. The serial port data rate is one limitation.If you want to do independent two-channel measurements on the TICC you need to have a good input clock source. If you are doing differential measurements the TICC input clock does not need to be as good because it is basically being used as a short-term time-transfer reference.Both Heather and Timelab support the TICC.

author: Miti
author_rank: Super Contributor
timestamp: December 18, 2018, 01:18:45 am
content: Quote from: texaspyro on December 17, 2018, 02:57:46 amYes, I was surprised to see both OCXOs, the one in the GPSDO and the one in the frequency counter, drifting slowly up, the GPSDO adjusting the DAC lower and lower, and I having to adjust the potentiometer every few days. They seem to have slowed down but still drifting up super slow.I thought that them drifting was the reason why they were removed from the original equipment but now I understand it is normal and I can expect them to level off by now.On top of that, I had to fix the OCXO in the GPSDO, the heater transistor was disconnected from the crystal so I know at least why that one was removed.

author: metrologist
author_rank: Super Contributor
timestamp: December 18, 2018, 07:12:58 pm
content: Quote from: Miti on December 16, 2018, 11:54:25 pmThat is just within spec. It will probably get better as it runs. My Wenzel timekeeper has increased 0.593mHz since September. Not as impressive as texaspyro's...

author: mikepi
author_rank: Newbie
timestamp: April 13, 2019, 12:11:56 am
content: Hi, I'm a new member are the boards still available?

author: Miti
author_rank: Super Contributor
timestamp: April 13, 2019, 02:09:53 am
content: I've sent you a PM.

author: Miti
author_rank: Super Contributor
timestamp: October 16, 2019, 12:17:50 pm
content: I'm adding the BOM as some people are asking. It is in .csv format, just rename it.

author: ChrisJordan
author_rank: Newbie
timestamp: November 14, 2019, 03:40:59 pm
content: Hi Miti, have you got one of these OCXO boards left? How muchwould it be posted to the UK?I've got a Grundig UZ2400 counter/timer and it's OCXO has died, no circuit diagram seems to be available so I think it's easier to replace it with an OSC5A2B02 off eBay!Regards... Chris

author: aquaman8
author_rank: Newbie
timestamp: April 25, 2020, 06:12:24 pm
content: Hi Miti,Any boards left? If yes, how much for board and postage to Ontario L3X1R9?Thanks,Mitch

author: fornext
author_rank: Newbie
timestamp: May 24, 2020, 11:00:24 pm
content: Sorry to be late to the party... I would buy a board if you have any left. I'm new here, how would I go about it?Thanks for the post.

author: pizzigri
author_rank: Regular Contributor
timestamp: October 15, 2020, 01:30:07 pm
content: Updating this thread as I am building the timebase! Therefore, I have85boards just in from JLCPCB (keeping a spare just in case) that I have very little use for.So for 5 Euro each, plus postage (your choice of delivery... i.e. registered mail in EU with certified delivery is going to be around 2.65 Euro for a parcel up to 50g), you can have one of the boards!I asked Miti for permission, and this is obviously not done for commercial reasons whatsoever.Anyone interested, just PM me.Best,FrancoETA: the scratches are in the plastic envelope, not on the boards. Just FYI.

author: Miti
author_rank: Super Contributor
timestamp: October 15, 2020, 05:33:43 pm
content: Sorry I missed all these requests for boards. I don’t have any board left.

author: pizzigri
author_rank: Regular Contributor
timestamp: October 24, 2020, 11:07:40 am
content: Hello Miti,I am building the board, however there are a few things that are unclear to me in actually mounting the OCXO on the meter.First off, the jumper you refer to are W2 and W3, correct? Meaning I remove the 0R part from W2 and solder it to W3 to switch to oven XO.Plus, I removed the original TCXO, added the ferrite inductor and I have a 70nf ceramic disc capacitor salvaged from old equipment (forgot to order it in the Mouser BOM... crap), would that be OK?Do I need to do other things to make the transition?Also, I can not find replacements for the three big caps in the power section, especially the big ones as they have three leads.... any suggestions? It’s not that they don’t work, but the smaller one is suspicious and since the meter is open on the bench I thought to recap it.

author: Miti
author_rank: Super Contributor
timestamp: October 31, 2020, 02:20:42 am
content: That sounds right to me. I did not recap my counter, it may not be necessary.

author: pizzigri
author_rank: Regular Contributor
timestamp: November 18, 2020, 05:53:47 pm
content: Ok, so to update this thread with a happy ending....I built the board and installed it. The OCXO I bought from Ebay continued drifting for almost two weeks, I actually thought it was defective. However, in the end it settled and I managed to calibrate it against the GPSDO to a couple millihertz. Extremely difficult to since the freaking OCXO can feel the heat coming off my hand when I get near to it. The Morion MV85 I have is not so critical. Mah? In any case, once done it’s over a week Miti’s board is stable and not drifts at all. I am enclosing a couple pictures, the first one is at turn on of the meter, the second one is after 20 minutes and is spot on. I am grateful for Miti for the project and help in building it and also to every one of the EEV Blog members that also helped and posted in this thread. The HP 5385A is a fantastic counter, no fancy stuff but a basic solid meter that just works and has great resolution, I mean there aren’t all that many 11 digit counters around at less than 200$, granted not on all ranges....

author: pizzigri
author_rank: Regular Contributor
timestamp: November 20, 2020, 10:34:19 am
content: So, since people have asked...Miti's OCXO board is a direct replacement for Option 004 Oven Timebase, mfr 28480, code 0960-0636.And, is therefore compatible with the following HP meters:5384A5385A5386A

author: Miti
author_rank: Super Contributor
timestamp: March 28, 2021, 01:39:01 pm
content: I attached the Gerber file, schematic and BOM. Some components in the BOM must be selected for your OCXO specs.

author: wkb
author_rank: Super Contributor
timestamp: November 07, 2021, 11:07:57 am
content: Having just acquired an OCXO-deprived HP5385A I stumbled onto this thread.i happen to have 5 of these CTI OCXO's on hand so..And, maybe useful, I have a sort-of datasheet for them. See attached.From that datasheet I conclude that the 4.095V reference is what is needed for Miti's PCB?Wilko

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: November 07, 2021, 03:20:32 pm
content: How does the CTI you mention stack up, compared to Oscilloquartz 8663XS ?

author: wkb
author_rank: Super Contributor
timestamp: November 07, 2021, 03:25:59 pm
content: No idea, you would have to compare the specs of the Oscilloquartz against the CTI specs.I plan to fit a CTI for those cases the Hp5385A needs to be used outside of my ham shack. While in the shack it will be fed a proper reference either from my Efratom Rb or a Samsung UCCM GPSDOWilko

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: November 07, 2021, 03:39:21 pm
content: Right. Agree completely with your plan.

author: Miti
author_rank: Super Contributor
timestamp: November 08, 2021, 11:43:45 am
content: Quote from: wkb on November 07, 2021, 11:07:57 amI can’t see how you concluded that based on the data sheet, but I may have missed something.The idea is to have the tightest possible adjustment range around the VC that would give you a 10MHz output. You can’t know what that VC value is until you measure it. So power on your OCXO, let it stabilize for couple of weeks, then measure its frequency with your frequency counter using GPSDO as reference. Adjust the VC until you get 10MHz. See what that VC is and calculate the components to generate that voltage +/- few tens to a hundred mV so you can have fine adjustment, and that should be around 2V.

author: wkb
author_rank: Super Contributor
timestamp: November 08, 2021, 12:04:54 pm
content: Well, the adjustment voltage range the datasheet gives brings me to that conclusion.In industrial production they cannot run the OCXO for a couple of weeks to see what voltage reference might match best. So I assume they go for a ref that allows full range adjustments. One could use a coarse/fine pair of adjustments if need be?Wilko

author: PerArdua
author_rank: Regular Contributor
timestamp: September 08, 2022, 08:17:12 pm
content: Thank you for sharing your design Miti.Would you be able to confirm the dimensions between pins of the OSC5A2B02 please? I've not been able to find a datasheet with this information online.

author: Miti
author_rank: Super Contributor
timestamp: September 09, 2022, 05:47:59 pm
content: Quote from: PerArdua on September 08, 2022, 08:17:12 pmYou can measure it in the Gerbers, my measurement shows 19.05mm between corner pins and pin 2 equal distance to 1 and 3.I can't remember if I found the datasheet or I measured but I created the Eagle library. It seems to fit well.