[time-nuts] J06 HP-59992A time interval calibrator for HP-531xx counters

Mark Sims holrum at hotmail.com
Sat Jul 8 20:15:52 EDT 2017

I think the way the fine cal works by checking the the intervals between four different edges that a lot of asymmetries in the signals are nulled out in the software.

How good are 1:2 180 degree phase shifters at exactly shifting by 180 degrees?   At what cost?   

Also coax and RF relays cost a lot.   Pretty soon your BOM cost is over what a 59992A will run... assuming you can find one.

So far my design is tending towards:  10MHz ref input -> Minicircuits doubler -> Wenzel squarer -> 74AC74 divider -> 74AC04 buffer -> level shifter.  The doubler/divider might not be needed,  but I think it will give a more symmetric output.  I might include a space for a 10 MHz TTL oscillator for non time-nut users... hopefully it might be stable enough over the short time interval for a cal measurement cycle.

For the gain cal an 5V LM4040 (or other) reference.   Routing signals to the output BNC's via 2P4T slide switches.  The slide switches might be a weak link... but they are less than 50 cents each.  Whatever, it should beat the pants off doing just the "quick TI cal"

The reason I started looking into this is that I want to upgrade the old firmware to a much newer version that allows the comma separators in the decimal digits.   Upgrading the firmware requires a new calibration.

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