The HP 115BR is not one of the most well-known products from Hewlett-Packard. And yet, it was remarkably important nonetheless. This hardware once synced time around the world. Now, for our 2025 One-Hertz Challenge, [curiousmarc] has taken on the job of restoring it.
The HP 115BR itself was not used alone, but in concert with the HP5060A atomic clock. The latter would output a 100 KHz reference output. It was the job of the HP 115BR to divide this frequency down to provide a superbly accurate 1-second tick.
The example on [curiousmarc]’s bench showed up in poor shape. It was “very broken,” and he reported that it had also previously been hacked to some degree. However, he has been able to restore it to proper functionality, including the special modification for continuous tick adjustment, as used in the 1964 flying atomic clock experiment. He was even able to sync it to NIST’s current atomic clock signal from Fort Collins using the WWW radio signal.
We’ve seen plenty of old HP metal restored over the years; it’s always pleasant to see how well things were built back in the day. Video after the break.
Of interest, when I went to NIST ‘time school in the 1980’s in Boulder, Co, the ‘father’ of the HP 5060A Atomic clock, Leonard Cutler, told me that his boss had him place a 12 hr clock in the unit, because without a clock, it wasn’t an atomic clock! Of course, it was not a clock at all, but a frequency reference. Management…
Austin Lesea
I have a mint condition HP 115BR sitting in my office – anyone know if it’s worth much?
I donated this one to Curious Marc.
It was worth the cost of shipping to see all the fun and use he’s getting out of it.
Maybe see if he needs a second one for his upcoming atomic clock relativity experiment.
WWW Radio station? Do you mean WWV? Although great typo :D