HP 53131A/53132A/53181A High Stability Timebase - Page 1
Forum section: electronics / testgear

author: gerrysweeney
author_rank: Regular Contributor
timestamp: May 28, 2013, 10:11:37 am
content: Hi, does anyone have a readable schematic for any of the timebase option for the HP 531xxA counters? I can see that there is an SPI bus going to the module but the schematic in the manual published from the Agilent site for the timebase module is not readable because its a low-res scan of the schematic. The document I am talking about is here:http://cp.literature.agilent.com/litweb/pdf/5989-6308EN.pdfI am guessing that the SPI bus is used to provide the voltage control so that the OCXO can be calibrated from the front panel or GPIB bus, it might also be used to sent ready status information from the OCXO to the counter - not sure, I am guessing. Seeing the schematic and the components on it would help figure it out.If anyone can help out I would appreciate it.Thanks,Gerry

author: gerrysweeney
author_rank: Regular Contributor
timestamp: May 28, 2013, 10:19:10 am
content: I just checked the component list and found that the SPI bus is driving an AD7243 (http://www.analog.com/static/imported-files/data_sheets/AD7243.pdf) 12-bit DAC which I guess is what is used to trim the OCXO. The rest of the schematic would appear to be output buffers and local PSU's. It would still be useful to see a detailed schematic though....Gerry

author: free_electron
author_rank: Super Contributor
timestamp: May 28, 2013, 01:50:35 pm
content: Search for the clip. That one has readable schematics in it.

author: gerrysweeney
author_rank: Regular Contributor
timestamp: May 28, 2013, 02:39:32 pm
content: Hi @free_electron I did try to search, I found a couple of documents directly from the Agilent site (link in the previous post) and the schematics are very readable apart form the one page that has the frequency reference option which is scanned in and very low res - this is why I posted the question - I was hoping someone might have a printed version they could scan in at a more workable res.Gerry

author: free_electron
author_rank: Super Contributor
timestamp: May 28, 2013, 03:09:55 pm
content: Get the clip for the 131, not the 132. The schematics are much more readable.

author: gerrysweeney
author_rank: Regular Contributor
timestamp: May 28, 2013, 03:31:19 pm
content: @FreeElectron I tried that, I have both documents. Problem is, the 53131A manual (http://cp.literature.agilent.com/litweb/pdf/5989-6307EN.pdf) does not include the schematic for the optional timebase module, the manual for the 53132A (http://cp.literature.agilent.com/litweb/pdf/5989-6308EN.pdf) does....but the OCXO module schematic page is unreadable, thats why I asked the question in the first place...Gerry

author: gerrysweeney
author_rank: Regular Contributor
timestamp: May 29, 2013, 06:28:14 pm
content: Bump...anyone? please....

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 12:39:11 am
content: I built my own timebase now:http://gerrysweeney.com/diy-hpagilent-53131a-010-high-stability-timebase-option/Gerry

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 12:41:30 am
content: I am going to get some PCB's made and possibly make some of these timebases up, if anyone is interested please post a comment on blog page so I can get a sense of the number of people interested either in a blank board or a ready made and ready to install 010 High Stability Timebase optionhttp://gerrysweeney.com/diy-hpagilent-53131a-010-high-stability-timebase-option/Thanks,Gerry

author: free_electron
author_rank: Super Contributor
timestamp: September 02, 2013, 03:22:21 pm
content: Meeee ! Two boards please...

author: free_electron
author_rank: Super Contributor
timestamp: September 02, 2013, 03:23:21 pm
content: I have cloned the third channel ... Got the special amplifiers and the divider. I just need to send the board to itead to have it made.

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 04:02:31 pm
content: Quote from: free_electron on September 02, 2013, 03:23:21 pmI (correction Andy but I am re-laying out in Dip trace and am probably going to make a few) have also cloned the 3rd Channel, see here:http://gerrysweeney.com/diy-hpagilent-53131a-030-3ghz-channel-3-option-board/Gerry

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 04:04:42 pm
content: Quote from: free_electron on September 02, 2013, 03:22:21 pmWould you mind posting a comment on the blog page link above, that way I have all interested folk in one place for counting.ThanksGErry

author: bingo600
author_rank: Super Contributor
timestamp: September 02, 2013, 08:30:55 pm
content: Quote from: gerrysweeney on September 02, 2013, 12:41:30 amGerry ...Any idea about the approx. price for a kit or a pcb ?/Bingo

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 08:36:03 pm
content: Quote from: bingo600 on September 02, 2013, 08:30:55 pmHi Bingo,It depends on volume, until I know how many its hard to know price-wise. This is not my living, its just a means to help fund the blog activity so they should not be too expensive.Gerry

author: free_electron
author_rank: Super Contributor
timestamp: September 02, 2013, 09:32:15 pm
content: Quote from: gerrysweeney on September 02, 2013, 04:02:31 pmandy's design is not a clone. it is modified. i have the real parts ( most of the real parts are obsolete but i managed to track em down. )

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 09:57:00 pm
content: Quote from: free_electron on September 02, 2013, 09:32:15 pmThats correct, its not a direct "copy" of the HP one, its an implementation - as is my OCXO board. I see no issue with building a variation of a design and calling it a "clone" though, my first computer was an IBM AT Clone but it was not a chip-for-chip copy of an original IBM AT so I guess we are talking semantics, while its not a "clone" in the dictionary sense of the word, its an "alternative" equivalent functional option.Gerry

author: free_electron
author_rank: Super Contributor
timestamp: September 02, 2013, 10:14:31 pm
content: Oh.. Hmm i will need to look at your schematic then to see what you altered. I have the real hp oscillator module 11801. I thought you made aboard replicating the entire circuit.For the rf front end , andy's board doesnt fit the machine properly. It doesnt have the holes in the right spot to mount it, the flatcable is 'messy'. Has a test been done if it is just as sensitive and works over the same range as the original ? Can it handle the same overload as the original ?I don't mind that the circuit is not 100% identical, as long as it performs the same, or better..

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 10:39:10 pm
content: Quote from: free_electron on September 02, 2013, 10:14:31 pmHi,I am not sure about the performance exactly to be honest - I made a test (you can see in my video) to 1GHz and the board worked down to about 25Mhz and down to -26dbm so I am not sure how that compares to the original, the performance seems reasonable to me but I am no RF expert. Does that sound far off?Fair point about the mounting holes, thats one of the reasons why I wanted to re-lay the board agin with all the right mounting holes.As for the OCXO board, I did not re-create the HP board with e edge connector - I laid the board out to work with the OCXO's I had to hand. If I had an original I would have tried to accommodate it but I am not sure the edge connector is common and available now days.The flat cable was a problem in Andy's board layout because he followed the pin numbering convention for IDC pin headers but HP did not! the ensuing messy wiring was the work-around for that. Again, another reason to re-lay the board.Gerry

author: dr.diesel
author_rank: Super Contributor
timestamp: September 02, 2013, 10:48:13 pm
content: Gerry/Andy,If you guys decide to run a batch of 3Ghz option boards, count me in for one of those also!ThanksAndy (lots of Andy's around here)

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 10:50:35 pm
content: Quote from: dr.diesel on September 02, 2013, 10:48:13 pmSure thing, I will post here if we do. I will make the OCXO boards first though.Gerry

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: September 02, 2013, 10:52:31 pm
content: Gerry,Not sure if this has already been addressed, but the schematic for the option 030 RF boards on your homepage has a serious drawing error: The MMICs needs to have a current limiting resistor in series with the RF choke. I suspect you must already be doing this, as running them directly from 12V will make them go *Poof* rather immediately.Trying to decide whether to sign up for this project.Edit: There may be another nitpick on that schematic: The DC blocking cap at the RF input ought to be between the protection diodes and the MMIC input. Otherwise one of the diodes are likely to be forward biased by the resistors inside the first MMIC, offsetting the DC bias point.

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 10:57:07 pm
content: Quote from: ElectroIrradiator on September 02, 2013, 10:52:31 pmHi there, yes I knew about that, I was drawing it more block diagram style to explain the basic operating principle, I did not include the resistors although I was aware they should be there. I did not update the hand-drawn schematic because thats what I used in the explanation in the video. I will put a note on the blog page to avoid any confusion.ThanksGerry

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 02, 2013, 11:00:53 pm
content: Quote from: ElectroIrradiator on September 02, 2013, 10:52:31 pmBlog page updated...

author: max-bit
author_rank: Frequent Contributor
timestamp: September 29, 2013, 07:39:54 am
content: HiDoes anyone have schematics options 050, 124?The challenge is particularly option 124Auctions are not available.At the dealer is better not to ask (probably cost well over $ 1,000).Maybe someone has pictures? these options?Marcin

author: gerrysweeney
author_rank: Regular Contributor
timestamp: September 29, 2013, 08:13:30 am
content: Quote from: max-bit on September 29, 2013, 07:39:54 amThose would be interesting to see, I suspect they are much the same, just higher rated MMC's and a different pre-scaller, or perhaps even two pre-scalers.Gerry

author: max-bit
author_rank: Frequent Contributor
timestamp: September 29, 2013, 01:24:56 pm
content: I think so tooIf I get guidance - specifications J2 connector, I just can undertake the design of such a module.It will not be easy (availability of items) but you can take a chance?

author: EV
author_rank: Frequent Contributor
timestamp: October 02, 2013, 11:35:39 am
content: Gerry,I have sent a PM to you!EV

author: pmcouto
author_rank: Unknown
timestamp: October 02, 2013, 06:05:47 pm
content: Hi,The document “Agilent 53132A Component Level Information” (5989-6308EN.pdf) contains partial information about the 12,4 GHz Prescaler (page 38-42).This module consists of two subassemblies:-Subassembly with front panel N connector, protection, input amplifier and 1st prescaler-Base board with power supply + filtering for input amplifier/1st prescaler and 2nd prescalerUnfortunately, only the second subassembly is documented…I have never seen this option and I couldn’t find any decent picture of it, so I have no idea about what components were used in the first subassembly.Based on the 2nd prescaler specs and configuration, it’s easy to figure out the divide ratio of the 1st prescaler. It’s also not that hard to design a suitable amplifier and input protection, so it should be possible to design a “clone” 12 GHz prescaler for this family of HP/Agilent counters.Some time ago, facing the need to accurately measure a 5 GHz signal, I thought about building a prescaler for my 53131A, so I searched the web for some useful information – All I could find was a couple of posts (time-nuts IIRC) about a non-successful attempt to build a working clone of 12 GHz prescaler…The problem seems to be the recognition of the prescaler – apparently, in addition to the physical installation of the module, some kind of “SW activation” or HW modification is needed.Analyzing the schematics, prescaler option connector at the main board contains 2 signals apparently used to identify the connected module (CH3CODE0 and CH3CODE1). I don’t know if the person who tried to clone the prescaler “played” with these ID bits.It also seems that a 0 ohm resistor will have to be installed in the main board to have +5V present on the connector.In summary:Too many open questions and few answers + missing information.I’ve just ditched the idea of building a clone and ended up building an external “divide by 1000” 12 GHz prescaler that works perfectly.This prescaler is based on Hittite’s HMC363S8G and is very cheap to build.I have no idea about the sensitivity of this prescaler, but it should be close to HMC363S8G specs, degraded only by the connector + PCB attenuation.This is my “home made” 12 GHz Prescaler:

author: gerrysweeney
author_rank: Regular Contributor
timestamp: October 02, 2013, 08:11:33 pm
content: Quote from: EV on October 02, 2013, 11:35:39 amJust replied

author: gerrysweeney
author_rank: Regular Contributor
timestamp: October 02, 2013, 08:14:01 pm
content: Quote from: pmcouto on October 02, 2013, 06:05:47 pmThanks useful info, thank you. I am pretty sure that the ID bits should define the pre-scaller ratio, with four bits I will guess its 1.3Ghz, 3Ghz, 5Ghz and 12Ghz. Next time I have a counter apart I will have a play around and find out.As for building a 12Ghz prescaller, even if I wanted to I have nothing that can generate 12Ghz so I could not verify it - I am not an RF guyGerry

author: mamalala
author_rank: Unknown
timestamp: October 02, 2013, 10:05:11 pm
content: Quote from: gerrysweeney on October 02, 2013, 08:14:01 pmMaybe one of these used rubidium standards from eBay can help you there? There is a microvave signal, applied to the resonance cell. If the RB oscillator is locked, that frequency should be about 6.834... GHz.The FE-5680A are on eBay for cheap sometimes, i paid around 60 Euros for mine about 2 years or so ago.Greetings,Chris

author: max-bit
author_rank: Frequent Contributor
timestamp: October 14, 2013, 07:47:09 am
content: I am also trying to build a divider up to 12 GHzThe information in this case is described on page Gerry.http://gerrysweeney.com/diy-hpagilent-53131a-010-high-stability-timebase-option/ # commentsThe description is also on my websitehttp://www.rflab.pl/projekty/DIVIDER12GHZ/DIV12GHZ.htmIf anyone has suggestions, please write themI'm open to any comments.Assumptions:Work for 12-13 GHzThe divider /128Sensitivity -35 dBm

author: andyb
author_rank: Regular Contributor
timestamp: October 14, 2013, 12:30:22 pm
content: There's a 3GHz prescaler on ebayhttp://www.ebay.com/itm/3GHz-Prescaler-for-Agilent-53131A-53132A-Counters-/111185036171?pt=LH_DefaultDomain_0&hash=item19e325038bNot sure if it's original..

author: andy_silicon
author_rank: Regular Contributor
timestamp: October 14, 2013, 03:27:23 pm
content: Doesn't look original - no HP / Agilent logo. Seems to use a linear regulator instead of zener. Also doesn't use a pcb connector for the RF.So if I was bidding on that - I'd like to know the details of the components , mmic , clamp diodes , prescaler. I'd also like to know the performance specs.

author: max-bit
author_rank: Frequent Contributor
timestamp: October 14, 2013, 05:43:27 pm
content: for $ 100 like the original? HP Agilent?without exaggeration

author: max-bit
author_rank: Frequent Contributor
timestamp: October 14, 2013, 06:00:04 pm
content: Does anyone can give me a PCB dimensions and spacing of holes? (sized PCB)Please

author: max-bit
author_rank: Frequent Contributor
timestamp: October 29, 2013, 06:32:00 am
content: HiUpdated the diagramThere is also a PCB designhttp://www.rflab.pl/projekty/DIVIDER12GHZ/DIV12GHZ.htm

author: max-bit
author_rank: Frequent Contributor
timestamp: October 30, 2013, 04:47:22 am
content: Correction of ideas ...One.Service manual HP (Agilent) is a joke.On each side of something else....See pages 8, 20, 39, numbering pin connector J2 on each side of the other...Two.The divisor to 3 GHz by 128But it's 12 GHz should be 512, the meter detects this by J2-9 J2-10 (I think)and ...Apply so different divider instead HMC394 will use uPB1505. This is a divide by 64So the divider (I assume input frequency 12 GHz) HMC363 (/will be 1.5 GHz, then the divider uPB1505 (/ 64) is the frequency of 23 .. MHz

author: max-bit
author_rank: Frequent Contributor
timestamp: November 02, 2013, 03:57:37 pm
content: The site is the Latest Version PCB, if anyone has any comments on this?At the moment there are no?http://www.rflab.pl/projekty/DIVIDER12GHZ/DIV12GHZ.htmNow I took care of the execution of the PCB.I have a little problem with getting laminate or RO4003C Rogers RO4350.But somehow it'll getIf it would work,(all materials will be made ??available for free of course), if anyone is interested ?

author: max-bit
author_rank: Frequent Contributor
timestamp: November 09, 2013, 02:26:22 pm
content: HiDoes anyone know how to force the division by 512 meter HP 53131 (2)?

author: mimmus78
author_rank: Unknown
timestamp: December 09, 2013, 04:23:35 pm
content: Does anyone is going to build this in Italy?A made a check with it.rs-offline.com and the list (with all minimal order quantity) is something like 70€ shipped (with no connectors and flat cable).Any advice to get "all" those parts cheaper here?D.

author: max-bit
author_rank: Frequent Contributor
timestamp: December 22, 2013, 09:23:02 am
content: Last update operation dividerhttp://www.rflab.pl/projekty/DIVIDER12GHZ/DIV12GHZ.htmAnd a new project divider to 26 GHzhttp://www.rflab.pl/projekty/DIVIDER26GHZ/divder%20up%20to%2026%20GHz.htm

author: neopticus
author_rank: Contributor
timestamp: September 06, 2015, 08:18:28 pm
content: What is the current status of these 030 option clones?I can see there are two guys selling these on eBay:http://www.ebay.com/itm/HP-Agilent-53131A-52181A-53132A-Clone-Option-030-3GHz-Frequency-Counter-/171761138421andhttp://www.ebay.com/itm/3GHz-Prescaler-for-HP-Agilent-53131A-53132A-53181A-Counters-/111756351935The first seems little bit more professionally done (soldering and the SMA connector). Also somewhat more sensitive according to "specs" there..Has anybody bought these?

author: smgvbest
author_rank: Unknown
timestamp: October 12, 2015, 11:25:07 pm
content: HiI was wondering if anyone here has a 53132A that could provide a good Hi-Res Photo of the main board.?Or if anyone happened to have a totally trashed board I could get from them that would also work.I've got one photo but not very good. Just been trying to compare and see what would be required to hack a 53131A board to a 53132ANow if anyones knows if it's possible or not and could save me time investigating that would be helpful as wellI know 2xAD7580JP, 1xXC3042A-7PC84C are the main differences but I'm sure there are others.

author: jhenderson0107
author_rank: Regular Contributor
timestamp: October 13, 2015, 01:23:45 am
content: Quote from: neopticus on September 06, 2015, 08:18:28 pmI purchased three of the clone 030 boards from the first link - two for work and one for home. All worked perfectly.

author: neopticus
author_rank: Contributor
timestamp: October 13, 2015, 04:26:50 am
content: Quote from: jhenderson0107 on October 13, 2015, 01:23:45 amThanks for the heads-up! I noticed that Signal Path vlog had reviewed the 030 option board from the second link and he was happy with it, so I guess they both are ok.

author: smgvbest
author_rank: Unknown
timestamp: October 13, 2015, 02:09:59 pm
content: On another note, I purchased Gerry's OXCO option and it works great. Very easy to install and get going and Gerry was very helpfully and replied very quickly to messagesI highly recommend getting the OXCO from Gerry.

author: Zucca
author_rank: Unknown
timestamp: October 13, 2015, 02:29:09 pm
content: Yeah Gerry is great... another happy customer here (not for the OXCO thow). Anyway I am planning just for fun to put a Rubidium 10Mhz OXCO in the 53132A... it is just a nice idea in my head... I didn´t designed nothing yet... so it could be a jump in nothing.

author: gfiber
author_rank: Contributor
timestamp: October 13, 2015, 04:01:00 pm
content: I purchased Gerry's High Stability Oscillator and it works very good. Also purchased the 030 prescaler option for Poland and it also seems to work fine up to as high as my sig gen can operate.Gary K8IZ

author: dadler
author_rank: Unknown
timestamp: October 27, 2015, 06:39:11 am
content: Quote from: smgvbest on October 12, 2015, 11:25:07 pmI had my 53132A open to replace the timebase (again), and took some pictures. Sorry, the quality isn't great.https://www.dropbox.com/sh/5y8psm4keqcvqlr/AAA82ApH-6AeUKMqwPnYpKOPa?dl=0

author: smgvbest
author_rank: Unknown
timestamp: April 22, 2017, 04:33:35 pm
content: @max-bitwhat happened with your 12 and 26 ghz boards.I've checked your site and last update was in 2013, did you ever produce the boards? I'd love to try the 12ghz board out though I can't get that high. I've got a R&S SMIQ for 6ghz but currently can test to 3 ghz (actually about 3.1 works)

author: snickers
author_rank: Contributor
timestamp: February 08, 2025, 05:51:30 am
content: Hello everybodyIf someone is interested, I'm the designer and manufacturer of this timebase unithttps://www.ebay.com/itm/126384459263

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 03, 2025, 07:33:05 pm
content: Has anybody tried the circuit valley project for this?https://www.circuitvalley.com/2018/07/agilent-53132a-53131a-ocxo-ultra-high-stability-oven-time-base-upgrade-option-open-source.htmlThey have a ready made OCXO and the PCB both available on eBay:https://www.ebay.com/itm/154252979327Thanks,Josh

author: Rubo
author_rank: Regular Contributor
timestamp: July 03, 2025, 09:25:10 pm
content: Quote from: snickers on February 08, 2025, 05:51:30 amLooks interesting. If I didn't already have a different OCXO, I would be buying one.

author: Rubo
author_rank: Regular Contributor
timestamp: July 03, 2025, 09:29:57 pm
content: Quote from: KungFuJosh on July 03, 2025, 07:33:05 pmI have one in my 53132A. It's pretty much dead on with a BG7TBL GPSDO-OCXODon't have anything more stable to compare it to, right now.

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 04, 2025, 12:17:19 am
content: Quote from: Rubo on July 03, 2025, 09:29:57 pmWell?? Get on it!

author: Rubo
author_rank: Regular Contributor
timestamp: July 04, 2025, 05:52:09 am
content: Don't pour oil in the fire, pretty pleaseI've been on the hunt for something radioactive for a while now

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 04, 2025, 02:51:05 pm
content: Not oil; straight gasoliiiine!! 🤣

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 14, 2025, 01:47:36 pm
content: I enjoy exploring my new Agilent 53132A meter. I made a video, which I posted a bit over a week ago (see below) focusing on how to get digital 13-15 from the instrument - especially when comparing two time sources - and whether that makes sense in terms of accuracy.But, as I discuss in my video, I am puzzled by one aspect of the 53132A: why does a measurement in the Digit Arm mode take so much more time than one in the Gate Time Arm mode, for the same number of produced digits?As I understand from the documentation, these modes are similar in terms of accuracy and other aspects (unlike the automatic arm mode, which is a different mode in several respects).The measurement speed difference is huge - in the below graph, I show my observations for the Digits Arm mode, while for Gate Tim Arm mode, it is up to 10x or 100x faster!Does anyone know why these modes are so different in measurement time, and whether there are other differences between these modes?Best, Rudi<a href="">Video REL #58 Agilent 53132A - Recovering the lost 13-15 digits

author: EvgenyG
author_rank: Regular Contributor
timestamp: July 15, 2025, 01:37:20 am
content: Thanks Rudi, that's a great comparison video! In Digits arming mode, it auto adjust gate time to produce desired accuracy. That depends on frequency, the higher the frequency, the sooner you get the desired amount of digits. How exactly it does that? That's a good question, perhaps the answer is somewhere deep in those formulas in the manuals.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 15, 2025, 06:11:40 am
content: Thanks EvgenyG But while a gate time of 1 second easily gives idle a 12 digit result (with input frequency of 10MHz), the Digit Arm mode wants sone 40 seconds for that! I reviewed the manual and all other documents available to me in quite some detail but cannot find any explanation or hint..

author: EvgenyG
author_rank: Regular Contributor
timestamp: July 15, 2025, 06:28:38 am
content: I found this formula is in the spec sheet and had a bit of a thought:If you're using gate time, put the gate time in there, solve for LSD.If you using digit arming, put number of digits, solve for gate time.When you put gate time in there, it might give you something like 11.2 digits, hence why you will see 12 digits but the last digit will be like 0.2 accuracy, i.e. taking values like 0 and 5 or 2 and 7.If you put digits in there, you will get EXACTLY that number of digits, and gate time will be adjusted.Makes sense?

author: EvgenyG
author_rank: Regular Contributor
timestamp: July 15, 2025, 06:36:48 am
content: Quote from: RBBVNL9 on July 15, 2025, 06:11:40 amConsider this experiment: Set 1 second gate time, 10MHz signal. Try to increase last 12th digit by 1 (increasing your it on your signal generator). If you can get it to cycle through all 10 digits, then it is exactly 12 digits precision.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 27, 2025, 08:44:16 am
content: Dear EvgenyG, thanks for the reply, and sorry for the delay in answering (I was travelling in Japan...)I have indeed been looking into the formula you referred to:This formula seems to confirm that both “Time Arming” and “Digit Arming” are the same in terms of the shown digits in relation to gate time. But I do have things I do not understand when I use this formula.Firstly, the values I get for different frequencies do not seem to make any sense to me. Let me show my calculation:UPDATE: SEE CORRECTED VERSION OF THESE CALCULATIONS IN A POST BELOW...And for a range of different frequencies:UPDATE: SEE CORRECTED VERSION OF THESE CALCULATIONS IN A POST BELOW...These results for LSD shown do not make any sense to me. And, of course, when the formula ends with something like "* freq" then you get such a wide set of results...Secondly, it is rather ambiguous that the last term is frequency OR periods, these are different things, and the outcome of the formula is widely different (still, both outcomes do not make sense to me).At the same time, the condition for 200 kHz in the formula does seem to be visible in my own measurement, posted before:Perhaps you or anyone else can help me, or perhaps point out any error I may have made?Thanks, best RudiPS. Am I the only one struggling so much with adding attachments to a post on this forum? I only seem to manage if I add only one, then post, then modify, add another one, then save, and so on...

author: EvgenyG
author_rank: Regular Contributor
timestamp: July 28, 2025, 12:20:57 am
content: Hi Rudi,I've spent a good few hours with wolfram alpha myself, and tried everything and the formula does not seem to work. I tried changing units, etc but the numbers just won't make sense. Perhaps someone with better HPAK frequency counter knowledge and their maths could help. I will try to play with that formula again some time later.Could you please try least significant digit experiment as described above? I want to see if you could get the last digit to cycle through all 10 values when in time arming mode.

author: EvgenyG
author_rank: Regular Contributor
timestamp: July 28, 2025, 12:36:55 am
content: The upper nominator is actually 2 * sqrt(2) * 225ps, and not 2 * sqrt(2 * 225ps). With 1second gt / 10MHz I get 0.000044. Is that 0.000044 Hz precision?

author: EvgenyG
author_rank: Regular Contributor
timestamp: July 28, 2025, 05:12:37 am
content: Answering my own question, yes it is. All of units in braces cancel out and become a number. The Hz unit stays on, which means final answer is in Hz.

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2025, 01:52:03 pm
content: Coming from the signal processing side of things and not precision counters and timing. Nyquest tells us we need at lease 2 samples to resolve the signal, so if doing an FFT we need a data collection "gate" of at least the reciprocal of the lowest frequency of interest and a "sample rate" at least twice this lowest frequency. Example if we are collecting data over a 1 second period then the lowest resolvable frequency is 1Hz and the minimum sample rate is 2Sa/s, while the highest resolvable frequency is 1/2 the sample rate.With a precision counter, which we understand counts the number of full cycles over a given gate period, it seems the frequency resolution is the reciprocal of the gate period, so how does one resolve anything lower than the reciprocal of the gate period? Example with a gate period of 1 second the lowest resolvable frequency count is 1Hz. This makes sense to us and the only way we can "see" getting a higher resolution than the gate period dictates is to "sample" the input at a higher rate and create "fractional cycles" which are then added to the full cycle counts within the gate period which somewhat seems "guessing" if the input isn't uniform in width and/or jittery (same for counting both waveform input "edges" which seems could resolve to fractional half cycles, but still subject to non-uniform width/jitter effects).As an example, we have a 1000Hz signal and a counter gate of 1 second. So we should get 1000 counts over than gate period. If the input is 1000.2 Hz, we still get the same 1000 count over the gate 1 second period unless we extend the gate period to 10 second which will yield 10002 counts.Anyway, this is way we understand things, any enlightenment from the counter experts is greatly appreciated.Best

author: ch_scr
author_rank: Frequent Contributor
timestamp: July 28, 2025, 02:17:23 pm
content: I found this article which explains the methods:MW&RF "Measure Frequency With Time-Stamping Counters"But basically there is the "straight-forward" and the "reciprocal" counting method, the use of interplolators to increase resolution (resolve "half-counted" cycles)and the "time-stamping method" to get around dead-time and to acquire many measurements which then yield the precise measurement by averaging.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 28, 2025, 02:54:34 pm
content: @ EvgenyG,Thanks so much, you are right! The tresshould indeed not be in the root term, and by doing so, the two divisions are dimensionless (as they should), and then multiplied by frequency, result in the dimension Hz, meaning that the result is not shown as # of digits (what we all first thought, I guess), but as a frequency.For the sake of completeness, I corrected my earlier calculations for different frequencies.And yes, I still plan to do the least significant digit experiment as you described - need to find some time for it@ mawyattThanks for your thoughts. They align in great degree with what I describe in my video, in terms of # of pulses that can be observed in a given gate time.@ ch_scrThat is a great article. The earlier observations already suggested that at 200kHz, the meter changes from reciprocal to conventional mode. The interpolating technology is fascinating, going to dig into that. Have you by any means been able to see the figures and tables in the article? They seem to be no longer available, and also the wayback machine did not seem to have caught them (it archived the URLs with the pics and the tables, but these already had a 404 code) And there is also an 'continue reading' at the bottom of the page that does not seem to work for me...@ allI'm learning a lot from you, but I still was not able to find an answer to my main question, which was why it takes much more time in the Digit Arm mode than in the Gate Time Arm mode to get to a given number of digits. The manual (and also the formula discussed) suggests these modes are equivalent in accuracy and resolving time, but in practice, the measurement time difference is enormous, like a. factor of 10 or 100. Mmm. There must be a reason for that...

author: EvgenyG
author_rank: Regular Contributor
timestamp: July 28, 2025, 03:31:46 pm
content: Rudi, I've just found this in the manual. Perhaps the counter sets the gate time more than necessary to adjust for this condition in the screenshot. There are also frequency error which is 0.001Hz at 10Mhz / 1 sec gate time and the unit could be taking that into consideration as well to achieve required digits precision in digits arm mode. See pages 3-5, 3-6 of the manual, they actually add frequency error to that formula to determine the upper boundary.I think what happens is, when in digits arm mode, the unit 100% guarantees N digits precision, where as in time arming, there may be certain conditions, when precision won't be met, because of the measurement error and the unit adjusts for those conitions. There is an example on page 3-8, where they do they actually showcase that for 15Mhz/1sec gate time, precision won't be 10 digits:====================Given an HP 53132A with a High Stability Oven that was calibrated 3 days ago, measure a 15 MHz square wave signal (which has negligibletrigger error) with a 1 second gate time. Compute the measurement error to within 2-sigma confidence.[math skipped]Which is to say that the HP 53132A would display results in the range 15 MHz ±60.2 mHz. Note however that the dominant error is the TimeBase Error. If an even higher stability time base is available or if the instrument can be source locked to the 15 MHz signal, then this error termcan be substantially reduced. The measurement resolution under these conditions is ±75 μHz (1 sigma) which determines the number of digitsdisplayed.====================

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 28, 2025, 06:36:28 pm
content: QuoteWhile the figures and tables in that article seem to be missing, I found another article that might be the 'source' of this one, and has the picturesIt'shere.

author: Cyclotron
author_rank: Unknown
timestamp: July 29, 2025, 01:46:12 am
content: Quote from: KungFuJosh on July 03, 2025, 07:33:05 pmI have built the prescaler and high stability timebase design from Circuit Valley's designs and they both work fantastic in my HP 53131A and HP 53132A.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 29, 2025, 06:09:14 am
content: QuoteDear EvgenyG, that does make sense, and I have been thinking a bit along the same lines. Still, the difference in gate time is much bigger that I would expect it to be, but maybe that is just me...Concerning the specific text you referred to in the manual:This has to do with the special case in which in measured frequency is very close to its 10MHz reference frequency (or very close to any rational fraction or multiple of that's within about 7 digits of 10 MHz). There is an enlightening post in the time-nuts forum, which explains why:“The 53132A is a "12 digit/s" counter. Unless the frequency is really close to 10 MHz. Then it becomes a 11 digit/s counter. This is because it uses oversampling (IIRC, 200k samples/s) and it relies to some extent on statistics for its 12 digit resolution.”This post, and more details, can be foundhere.Thanks for your efforts!Best, Rudi

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: July 31, 2025, 03:25:50 pm
content: Dear EvgenyV,QuoteI agree that the taste of the pudding is in the eating. Doing your experiment, we can test whether the 12th, 13th, maybe even 14th or 15th digit, represent accurate measurements. Today I found a bit of time to do this experiment, but also ran into several challenges in how to do this - especially the lack of sufficiently small increment steps of my frequency generators. But I found a solution...Eventually, I documented it all in a new video - see below. And a teaser: The Agilent 53132A did much better than I expectedBest, Rudi