Fluke/Philips PM66xx frequency counter OCXO upgrade


Dan Watson documented on his blog an OCXO upgrade board he designed for the Fluke/Philips PM66xx line of frequency counters:

My counter came with the standard XO timebase option, which has fairly poor specs for stability and drift. It is difficult to trim precisely with the single-turn trimmer capacitor on the board. For most testing in my lab I use an external reference from a GPSDO, but it is still nice to have an accurate timebase available in the counter if I need to take it somewhere and do testing away from the bench.
Previously I posted about an OCXO upgrade I made for my Racal-Dana 1992. The fun of designing a similar upgrade for the Philips counter was one of my motivations for purchasing it. My upgrade board is roughly equivalent to the original PM9691 OCXO module, and it should be compatible with any Fluke/Philips counter that is capable of using that option.

More details at The Sync Channel blog.  Project files available at Github.

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  1. I looked at the Fluke/Philips PM6662 frequency counter, which is a member of the PM66xx counter family, but did not recognize the card size of the decribed OCXO as fitting the counter. The XO former replacement board (MTCXO PM9607) is oriented sideways, has its connector right hand side on that option board and is a higher stability option on many of those PM 666X counters. The basic XO which is supplied, if the PM666X is ordered without an additional timebase option, is rather simple, consisting of an XO and a rather cheap looking (open air) trim capacitor of questionable quality. My unit displays – with a GPSDO based 10 MHz reference signal – a frequency deviation between -0.28 ppm (cold) to +12,0 ppm (operating temperature), which is for a 9-digit counter (max 1.3 GHz) rather “bad”, but quite common for a basic XO timebase.

    Does anyone know, if this OCXO board does fit the PM6662/PM6669 etc ?

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