Oct 27

Update – DIY HP/Agilent 53131A 010 High Stability Timebase Option PCB’s Available

Following on from the project to build a DIY OCXO upgrade option for my HP/Agilent 53131A Frequency Counter I had a large number of requests for me to make the PCB’s available so others can built there own. I now have some PCB’s and are making them available for sale. I will also be making some fully assembled and tested/verified boards including an OCXO, ready-made cable and mounting stand-off’s, there will only be a limited number of these so if you are interested, let me know, first come first serve and when they are gone they are gone.

Now, someone made a comment on hackaday stating that the reason why these OCXO’s are on e-bay is because they are no good. Well I can understand why one could draw that conclusion but having now played with in access of 50 of these OCXO’s I can tell you that they all pretty much violently agree with each other and they also agree with the Rubidium Frequency Standard I have, so given they are from different sources and all free-running I am pretty comfortable they are good and usable quality devices. I read a lot on the net about “burn in time” and the general consensus seems to be, the longer you age and heat a crystal oscillator the more stable (in terms of drift) it becomes. Now I don’t know how true that is, but if it is true, then by definition, using recovered OCXO’s must actually be a good thing. Of course if you feel the need to pay a couple of hundred dollars for a new OCXO then you can of course do that – but I am pretty sure that it does NOT guarantee you any better performance, it just buys you the right to get compensated if you happen to find it does not meet the performance specifications quoted by the manufacturer and it might make you feel a little more confident. Anyway I guess the results speak for themselves and for a home lab these OCXO’s are more than good enough I think.

Here is a short video showing the various configurations built and working as well as a quick overview of the PCB its self and the configuration options.

The Schematic



This is the revision “1F” board. When I designed the board, I picked a few of the OCXO types that are available on the second-hand (salvaged) market and designed it to accommodate these. My original plan was to support four types of OCXO, the Oscilloquartz 8663-XS that I used in my own counter, a Datum 105243-002, and Isotemp OCXO-131 and a Trimble 34310-T(2). However, when I laid the board out I did not have the Trimble 34310-T(2) device to hand and made a (wrong) assumption about the footprint – which is a bad schoolboy error I know – the upshot being that while this board has a footprint and markings for the Trimble 34310-T(2) it does not fit, the pins are about 1mm out and therefore the board IS NOT suitable for that particular device. It is feasible to drill holes, the pads are just about big enough but assuming there is some demand for these boards I will order a second batch with the footprint corrected.


The following OCXO’s are known (and shown in the video) to work. Any others might work but thats up to you to verify 🙂

  • Oscilloquartz 8663-XS
  • Isotemp OCXO131-100
  • Isotemp OCXO131-191
  • Datum 105243-002

Oscilloquartz 8663-XS

This is the first OCXO I used, its more expensive than most and seems good quality and very precise. It works off of 12v and provides a nice clean sine wave output. The voltage control input works on the 0-10V range. I could not find any data on the XS version so I don’t know what its performance specifications are. I have included a download for this device but it does not cover the XS version specifically. The data sheet states that this device requires 0-10v for the frequency control, and testing seems to bear this out too. However, to get the counter to calibrate properly I selected the 0-5v range on the DAC.

Oscilloquartz  OCXO8663-pins


Datum 105243-002

This was another OCXO that I included on the board for Andy (who built the first 3Ghz pre-scaller option board), again a nice device but its specified to work on 24V and the Oven and Oscillator have separate power connections. This is the only OCXO that has a built in trim pot which allows you to set the window for the voltage control range. Although this device is specified to run at 24V, I tested its operation at 12V and it works perfectly. I did put a four-pin plug onto the board to allow you to give it a separate 24V supply but it really does not need it. I do not have any data sheet for this device but it outputs a square wave which is not as nice as having a sine wave on the output – but for this application it does not matter at all. The Frequency control input on this device is very sensitive and while it works without problem at +/-10v its centred around 2V and 0-5v works just fine.

IMG_6161  OCXO-DATUM-pins copy


Isotemp OCXO131-1xx

This is a small, compact device and comes in two variants, the OCXO131-191 which is a 12V version and the OCXO131-100 which is a 5V version, and while both share the same PCB footprint and pinouts the case for the 5v variant is taller at 18mm high where as the 12v version is a compact 11mm high. These also provide a square wave output. Both versions of the device require 0-5v on the frequency control input although to get the counter to properly calibrate I had to configure it for the +/-5V option.

Isotemp-ocxos  OCXO131-pins


Kit of Parts

Some people asked me about providing a kit of parts. I am not really geared up to do that in a time-efficient way so apart from the bare PCB, I will not be able to provide individual parts or components.

Fully Built and Tested Option

I am planning to have a limited number of these option boards fully built and tested with all the components and the OCXO pre-installed as well as a suitable cable and mounting stand-off’s, ready to install and use in your counter 531xx HP counter. I do not have an exact cost for these as I still have to source some of the components but they are likely to be be in the £75 to £95 range. I will post an update when I have these available which should be in about 2-3 weeks time.

UPDATE: I now have some fully assembled and tested boards complete with cable and mounting parts needed for a simple plug-and-play 53100 series counter upgrade. (the boards will be black, the board shown in the photo was as a result of a screw-up by the PCB supplier)



Bill of Materials

RefDes Part No Notes
C1, C2, C4, C6, C7, C8, C10, C11 100nF 0805 SMD Jellybean part
C12 1uF 0805 SMD Jellybean part – Could probably use 100nF with no problem
C3, C5, C9 47uF 16v Electrolytic. Farnell Part No: 197-3306
J2 IDC2X8M Farnell Part No: 231-0066
L1, L2, L5 100uH Farnell Part No: 935-8056
L3, L4 1uH Farnell Part No: 221-5638
R1, R2 100R 0805 SMD Jellybean part
R3, R4 220R 0805 SMD Jellybean part
R8 220R 0805 SMD Jellybean part – This is not needed unless you want to mess with the comparator bias
U1 LM361M Very fast differential comparator
U4 ADR4550 You can use a REF02 or numerous other 5V reference parts here, the pinout is pretty standard
U5 AD7243AR This is the most expensive and hard to get part

Bare PCB’s Available

UPDATE: After my first trip to the post office today I have had to amend the pricing because of the outrageous postal charges, I have been told that I cannot send something thats not made of paper as a letter! that means for my friends outside of the UK the postage is more expensive, sorry about that. The good news is, the postage does not go up with the number of boards. I hope you understand.

UK Orders

For the sake of simplicity I have opted for a flat price of £10 each, which includes postage in the UK. If you want more than two boards please contact me directly via e-mail because the weight starts to impact postage.

 1 x HP/Agilent 53131A-010/GS OCXO Option Bare PCB Rev 1F inc. Postage £10
 2 x HP/Agilent 53131A-010/GS OCXO Option Bare PCB’s Rev 1F inc. Postage £20
 HP/Agilent 53131A-010/GS Rev 1G Fully Built and Tested with Trimble 34310-T OCXO, Cable and Mounting Kit £95.00 + £10.00 P&P

Non-UK Orders

If you are outside of the UK it costs me £3.50 for a small parcel so I have opted for a flat price of £9 for each board – but postage is on top of that. If you want more than three boards please contact me directly via e-mail.

 1 x HP/Agilent 53131A-010/GS OCXO Option Bare PCB Rev 1F £12.50
 2 x HP/Agilent 53131A-010/GS OCXO Option Bare PCB’s Rev 1F £21.50
 HP/Agilent 53131A-010/GS Rev 1G Fully Built and Tested with Trimble 34310-T OCXO, Cable and Mounting Kit £95.00 + £15 shipping (tracked and signed for)
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Aug 26

DIY HP/Agilent 53131A 010 High Stability Timebase Option

Having obtained a reasonably reliable 10MHz lab reference (see here) I decided to calibrate my Frequency Counter only to find that the stock oscillator provided in the HP 53151A is absolutely terrible – a joke even! I looked around for an “010 High Stability Timebase Option” but they are rare — and if you can find one not installed in a counter they are very expensive – in the few hundred dollars range at least — and buying one from HP is, well, expensive in the extreme. There are many second-hand 10MHz OCXO modules available, these are mostly stripped from old telecommunications, satellite or cellular equipment so they are plentiful and relatively cheap to buy too. I decided to make a clone 010 option board for my counter using a second-hand OCXO bought from e-bay. I designed a PCB to get a professional finish as well as a reliable upgrade for my counter. The main goal was to make an option board that just like the original could be automatically calibrated using the internal software and front panel controls so I had to use the same DAC chip (which is now obsolete) and basic topology of the original option board to make it work.

The result speaks for its self – with the OCXO running as the timebase, the counter is able to measure the 10MHz source it was calibrated with to a precision of 100th of one cycle with no error!

The schematic is pretty simple and self-explainatory. The counter seems to need a differential square wave clock drive, this is created using a high-speed differential output comparator part LM361. The DAC is an AD7243 part from Analog Devices, this part is now obsolete and not recommended for new designs but they are still available from various sources, albeit quite expensive parts. It would have been possible to design in a newer part but for the small number of units I wanted to make, it seemed a bit pointless to go to the effort as the recommended newer part actually requires different serial signalling, and this would have required some kind of serial protocol converter micro controller. The DAC is driven by the counters microprocessor to calibrate and tune the timebase. The ADR4550 provides a high stability 5V reference for the ADC. The rest of the circuitry is basically power supply and signal filtering.

The PCB layout was designed to accommodate different OCXO footprints making it flexible. As well as supporting OCXO’s there are footprints for SMA connectors and you can even use a low-cost TCXO which cannot be automatically calibrated but is still a considerably better option than the oscillator built into the counter.

PCB’s Available : See here

The finished board fits really neatly inside the counter, and even fits around my previous Hard Power Switch Modification project.

Various Pictures


Catch you next time….

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Jul 26

DIY HP/Agilent 53131A-030 3GHz Channel 3 Option Board

As part of the process of upgrading my counter to have a DIY high stability OCXO (Oven Controlled Crystal Oscillator), someone who watched my videos had designed a DIY 3GHz Channel 3 53131A-030 option board. The original from Agilent is very expensive (obviously) and there are clones you can get on e-bay which are a quarter of the price Agilent charge which is why he decided to design his own. His name is Andy and when he saw my video’s he got in touch and offered me one of the PCB’s to which I of course said YES PLEASE 🙂

Now as it turned out, when Andy constructed his own board he had enough components left over so also constructed and tested one for me which was a really kind thing to do and very unexpected too. In exchange for this I have insisted that I can build him an OCXO board while I am doing mine to return the favour.

Anyways, I thought I would do a video to show the HP/Agilent 53131A-030 DIY 3GHz Cannel 3 Option board getting fitted to my counter. I also spend some time explaining how the pre-scaller circuit works and in basic terms what MMIC’s are and how they work too. I also make an adaption to my previous hard power switch modification to make way for the upcoming DIY OCXO board, and I measure up to get the exact board dimensions and mounting hole positions I need for the OCXO PCB layout.

The entire work and full attribution for the DIY 030 option board/PCB goes to Andy, so Andy – thank you so much for making one of these for me – I really appreciate it.

PLEASE NOTE: I will not put Andy’s Youtube/EEVblog ID here unless he asks me to, and I will not pass on his details without his express permission so please don’t ask – I respect peoples privacy. If Andy does want to share his details in connection with this project then I will gladly put them here.

PLEASE ALSO NOTE: The schematic drawing below is technically incomplete and is meant as an illustrative block diagram. In the real circuit there is also a resistor in series with each inductor at the top of each MMIC to set up the right DC conditions.

See you next time.

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Jun 24

I Need 10MHz – how hard can it be!

It all started when I wanted to calibrate my HP 53131A universal counter, which as it turns out probably has one of the crappiest and most disappointing standard oscillators ever put into a frequency counter, HP you should bow your head in shame….oh of course I forgot, a half reasonable oscillator is an “optional extra” when you by HP/Agilent – of course it is….anyway, on with the job at hand

If you have or want to play with an FE-5680A Rubidium Frequency Standard or an OSCILLOQUARTZ OCXO 8663-XS or a HP 53131A Counter or a Racal Dana 1999 counter or similar then this video will most likely be of interest 🙂 what I am trying to get is a predicable and reliable frequency and standard for my home lab.

I guess I will let the video do the talking on this one….

Here are a whole bunch of useful links that relate to this video (there are many more too if you search around the web)

Thanks to all of the authors and content creators for the above information. Thanks for watching.

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