[time-nuts] Best Rubidium Frequency Standard

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Mar 12 16:50:52 EST 2016


The ultimate solution to this conundrum is to roll ones own Rubidium standard 
to achieve performance beyond the HP5065A e.g.:
https://doc.rero.ch/record/32317/files/00002318.pdf

Bruce

On Saturday, March 12, 2016 01:46:29 PM Bob Camp wrote:
> Hi
> 
> Another example of the “stored in magic memory” issues on some modern Rb’s:
> 
> To improve the yield of Rb’s cells, a DDS can be used to tune a bit one way
> or the other off of the normal resonance frequency. The reasons why they
> are off are a bit involved, the fact is they do get manufactured that way.
> To line things up with these cells, some sort of coarse tune word is dumped
> into the flash / eprom / whatever. That DDS now knows where to find the
> resonance of the cell and it has. This all works fine until you swap a cell
> between boards. The new cell may (or may not) line up with the old cell.
> Things may (or may not) lock up properly.
> 
> Once you get past the “blown capacitor”, “no output on the regulator” or
> “dead power transistor” sort of fixes …. the newer Rb’s are not
> particularly easy to care for and feed. Indeed, the Temex units I mentioned
> earlier probably all could be fixed with detailed work and access to the
> code. I stop when the simple “replace these 4 caps” stuff does not bring
> them to life. As long as that gets more than 60% running, I’m happy.
> 
> Bob
> 
> > On Mar 12, 2016, at 12:14 PM, cdelect at juno.com wrote:
> > 
> > Mike,
> > 
> > If you are planning to buy "suspect units" with the intent to repair I
> > would steer clear of the PRS10.
> > 
> > It is true you can pay for a factory repair but having the schematics and
> > theory of operation only helps for particular repairs.
> > 
> > This is because a lot of the alignment parameters are stored in memory
> > and there are no instructions on these alignments and how to store them.
> > 
> > An example: I had a unit come in for repair. It had no output. The
> > customer, a professor, said a student applied a large DC to the output.
> > The output is direct from an RF transformer. It burnt open the winding.
> > 
> > I thought, how hard can it be?
> > 
> > I popped off a good output board from a junker and installed it. I now
> > had an output but the unit would not operate properly. Part of the output
> > go to other circuitry that would need to be aligned to match. No way to
> > do that or store the alignment! Bummer.
> > 
> > Luckily the transformer was a metal can type. I opened it up and rewound
> > the tiny wire output coil and that restored the unit to operation.
> > 
> > After that I sold my pile of defunct PRS10 units and don't plan to
> > purchase any more.
> > 
> > For ease of repair the HP 5065A is first, then the FRKL and H, these have
> > bog standard thru hole circuitry and the manuals are excellent. Another
> > of the worst is the M100 as its cards are conformal coated and the lamp
> > oven assy. is potted! As you mentioned most of the later telecomm units
> > are surface mount and most have some sort of microprocessor involved.
> > 
> > Cheers,
> > 
> > Corby
> > 
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