HP 5328A universal frequency counter teardown

in Teardowns by DP | 10 comments

Kenneth scored two HP universal frequency counters and popped them open. One generates the timebase from an uncompensated oscillator in a TO-5 package, while the other uses a large temperature controlled oven oscillator:

here is both of my counters measuring the same 1pps  taken from my AdaFruit GPS receiver.  The lower one with the  oven-compensated oscillator (which is marked as being calibrated in 1999) is spot on, while the top counter using an unprotected crystal oscillator drifts up and down 0.1-0.2ppm, and is almost 5ppm slow…The standard time base is rated for 2.5ppm drift between 0 and 50 degrees Celsius, where the [oven oscillator] time base has the much tighter 0.007ppm.  Since these counters display eight (or nine) digits, 2.5ppm is very visible, where 0.007ppm will at worst only effect the least significant digit.

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Comments

  1. Bruce says:

    Hmm, interesting. Is there such a thing as a GPS-based universal frequency counter? Might this be a project one could do at the “competent hobbyist” level?

    • It’s not unusual to use GPS in a control loop to discipline a Rb reference, which then generates 10MHz as the time base for a counter, so yeah, you can build a GPS-based counter. With the GPS 1pps, the challenge is that you need a really stable oscillator to multiply 1pps up to the needed 10MHz, and you need to be able to measure very small phase changes.

      • Bruce says:

        Interesting, thanks. Apparently I can’t post links here, but I’ve found references to a Rockwell Jupiter GPS unit (that I’ve found on eBay for $65) that has a 10kHz timebase. Presumably that’s going to be cheaper than an Rubidium reference, since I can’t find an online mention of what one would cost (read: more than you want to spend, dirty hobbyist!)

      • Used FE-5680 Rb references are $75 on eBay, and (supposedly) 300Hz agile. 10kHz puts a cruel upper limit on frequency range or period resolution.

      • Bruce says:

        Woah, cool. New toy for the wish list!

  2. JBeale says:

    Wow, it’s $75 now? Price has been going up. If you’re interested in the FE-5680A, here is a FAQ regarding that unit: http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq

  3. arhi says:

    I fairly recently purchased few 5680A and they were 40$ (few weeks ago) .. the shipment was “a lot more” but the devices themselves were only $40.

    Anyhow, disciplining 5680A with GPS is going to be huge pain in the but, IMO it’s way simpler to make yourself ovenized 10MHz reference and then discipline that reference with GPS. Properly made ovenized oscillator will work incredibly stable (better then your average high end 9-10 digit counter), you just need to use GPS to get it to lock on exactly 10MHz (and not by using direct feedback every second but by fixing the cumulative error every 48 hours or so)

    As for the counters, I recently took pictures of mine AGILENT 53181A counter. This is one interesting device. VERY INTERESTING device. I suggest anyone interested check out the schematic (available on HP site) … it’s super cool, it has bunch of ADC and DAC devices inside, separate interpolator .. very cool thing… schematic is a very interesting read. If you want pic’s they are available here

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