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