[time-nuts] Best Rubidium Frequency Standard

Bob Camp kb8tq at n1k.org
Sat Mar 12 18:52:07 EST 2016


Hi

If you dig into the modern GPS Rb’s they put the 5065 to shame. They are also don’t seem to show up on eBay ….

Bob

> On Mar 12, 2016, at 4:50 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
> 
> 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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