The HP 5328 Universal Counter is all the counter you’ll ever need. It’s rugged, does its job well, and like all old HP gear, keeps on going. When it breaks, though, that’s a problem.
[Tom] had an 5328 Universal Counter with a broken Oven Controlled Crystal Oscillator. This is the HP 10544 OCXO and replacements are pretty spendy. Instead of buying a vintage unit, [Tom] decided to make a replacement.
The OXCO in the HP 5328 is just an option. If the frequency counter has this option installed, a 30-pin edge connector in the counter is stuffed with a little PCB. Like all HP gear, the schematics are readily available, and the original OXCO can be quickly reverse engineered.
The design of the replacement is fairly straightforward. A 10MHz OXCO from Oscilloquartz is used, powered from the 28V rail in the 5328 with a simple switching regulator. Apart from that, it’s just an inverter to get the logic levels correct, and a small, multi-turn pot to calibrate the new OXCO. The completed unit is much smaller than the original OXCO option, so it can be plugged directly into the 30-pin card edge slot, leaving the gigantic standoff inside the frequency counter as a reminder of days gone by.
Never knew there was any such thing. Makes sense. You control the temp, you control the frequency. The “oven” is in that metal enclosure?
Yep, there are several kinds of devices available in temp controlled ovens for stable output.
Wasn’t this already featured on HaD a while ago? ISTR some kind of custom built replacement for an unobtainable part for some HP equipment.
I know what you’re thinking (I had to search my brain for the answer) – but we covered a similar hack but for a Racal-Dana 199x frequency counter. http://hackaday.com/2013/09/23/diy-high-stability-timebase-hack-for-25-why-frequency-stability-matters/ kinda of the same thing. Of you may be thinking of the time we covered adding a 10MHz Rubidium Frequency Standard (salvaged from a cell phone tower) to the external time input of a counter – you can see that here: https://www.youtube.com/watch?v=g862Xy_VXcY . I think Dave Jones did a video as well,
Even more related, Gerry Sweeney of the Racal-Dana hack has also made an OCXO option board for his HP counter: http://hackaday.com/2013/08/26/making-a-hp-frequency-counter-more-accurate/
I believe Galane is refering to this;
http://hackaday.com/2014/04/21/rebuilding-a-custom-ic-saves-hp-pulse-generator/
Rebuilding with discrete components an ECL-logic piece of purified unobtainium to fix a pulse generator.
OCXO or OXCO?