Embedded Engineering : DIY Fluke Philips PM66xx OCXO 10MHz Oven Oscillator option board for PM6680B PM6681

Wednesday, May 18, 2022

DIY Fluke Philips PM66xx OCXO 10MHz Oven Oscillator option board for PM6680B PM6681

Quite a while ago I had written about how I upgraded oscillator of my Agilent/HP 53132A. I have recently bought a broken Fluke/Philips PM6680B Frequency counter. Though i was able to quickly fixed issues with the unit by replacing power supply capacitors, the unit still has really crappy original reference oscillator. So I decided to make my own PM9692 Ultra High Stability Oven Time Base with CTS 196 OCXO.

Schematic

Module is relatively simple compared to Agilent 53132A OCXO, Board only has a switching regulator to step down from 12V/24V input to Oven Oscillator Operating Voltage which is 5V. Board also has a 20 Turn Trimpot to fine adjust oscillator frequency for calibration. High resolution PDF Schematic can be found on Projects github https://github.com/circuitvalley/PM6680_PM6681_OCXO_time_base_option

CTS 196 oscillator has specifications for Temp 5PPB while 1ppb/day and 100ppb/year aging

Option board is installed on BU105 Header which is 10 pin single line header. This part of PM6680B schematic shows BU105.

PCB

Its a 2 Layer board with pretty basic requirements, can be ordered from almost anywhere.

For standoff I use WÜRTH 9774080360R Stainless steel standoff. and used relatively easily available 2x10 dual pin header rather than expensive threw board connector. Though only single line is needed as but dual line header provide some rigidity to the connectors at really low cost against going for some other connector solution.