[time-nuts] new here + hp 5061A

Adrian rfnuts at arcor.de
Sat Apr 12 18:19:07 EDT 2008


after reading the archives for a while I got seriously infected by the 
time-virus :)
I thought to wait posting until I have my first caesium unit. Well, just 
a few days ago I collected a somewhat scuffy hp 5061A that I acquired as 
a parts unit.

When I fired it up, it seemed to lock, but it was in the 1E-8 range off. 
Turned out to be a faulty 12.631.. MHz synthesizer. I replaced it with 
an external signal generator that is locked to the 5 MHz from the 
caesium, and now it seems to work fine. However, beside a rubidium 
oscillator, I have nothing to compare it with.

When I checked the 12.631,771,6 MHz synthesizer, I found a most likely 
bad x-tal and something weird going on with the preset divider. It 
should divide by 1366, but there was something hacked up on the board, 
so I'm unsure about the correct jumper positions of IC6. I tried to get 
it to dividing by 1366 but I had to chenge some of the apparently 
original jumper wires of the other counter stages, too. So, I'm 
suspecting there might also be problem with one or more of the N8280A 
The VCXO, when run open loop with tuning voltage from a power supply, 
lacks stability and, after tweaking it to the specified tuning range 
center, suddenly jumps by a few 100 Hz. It just doesn't show the 
stability I'd expect from an x-tal oscillator.

I'd appreciate any help, especially to find a 12.618 MHz x-tal, or a 
complete synthesizer module from a spares unit. Also, any hints for the 
correct divider jumpers would be great.


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