[time-nuts] Best Rubidium Frequency Standard

timenut at metachaos.net timenut at metachaos.net
Fri Mar 11 20:50:22 EST 2016


Bob,

After all of the excellent feedback here, my current thinking is that I can
get a parts / repair PRS-10 for somewhere near $150. There are several reasons
that this might be the best option...

   1. It appears to be about the best that I can afford from what I have seen
      of the testing that others have done. The HP 4065A is completely out of
      the question. The only one I see available is $1340, plus shipping. A
      brand new PRS-10 is $1495. So the choice there would be a very old unit
      that might work for a few months or even a few years, but probably not
      very long - with no parts available without using a parts unit. Or, a
      unit nearly as good that has an expected life span of 20+ years and
      which is still in production and would be under warranty for the first
      year or so.

   2. There are complete schematics available for the PRS-10 which gives me a
      leg up on attempting a repair. There are also detailed circuit operational
      descriptions in the service manual. That helps too.

   3. Worst case, SRS has a repair service available at, at least in the past,
      a reasonable cost (reportedly a fixed price of $200). Now you need an
      RMA quote, but the price probably hasn't changed that much. If the
      repair is something that I can't handle - e.g. the rubidium tube is bad,
      then it can still be repaired for a total cost of around $350 to $400.

      In that case the total cost might be a bit higher than a working unit.
      Or, perhaps not. The two working TSD12s that I see on eBay (apparently
      the same as the PRS-10 except the lock flag is set to 3 instead of 1 and
      which can be reset) are $285 and $512. And I don't see any working
      PRS-10s at all. If this option is necessary then the cost would be
      split, making it easier to swallow. And, SRS calibrates the unit when
      they fix it at no extra cost (as long as it is requested before shipping).

   4. The PRS-10 can handle the GPS synchronization simply by feeding the GPS
      1 pps signal to it. That eliminates a lot of secondary effort needed to
      get the disciplining up and running. That would minimize both the cost
      and effort. Control of both the PRS-10 and an LEA U-Blox can be done via
      an USB to RS-232 adapter (or two). This feature is something that none
      of the alternative rubidiums appear to have.

   5. The PRS-10 has free windows software to assist in programming and
      controlling it.

The main negative is that I have never repaired an SMD product before. I don't
know if my skills are up to it. However, I can practice on junk before I
actually attempt to make a repair. And that is certainly a skill that will be
needed in the future!


Mike

> HI

> None of this is a simple slam dunk.

> The 5065 has great ADEV numbers. In “as delivered” condition It has horrid
> TC and pressure sensitivity. It also is > 10X more expensive than a lot of the other devices.

> The units that *can* be disciplined are rarely set up to do so properly off
> of a GPS source. If you want to run one as a 24/7 GPSDO, that may be a significant issue.

> All of the “modular” Rb’s require heat sinking. For a reasonable lifespan,
> either a fairly healthy heatsink or  something smaller plus a fan is called
> for. The impact on lifespan can easily be 10:1. 

> If your target is something like a microwave radio, many Rb’s are
> “challenged” in terms of phase noise and/or spurs. Some sort of cleanup will be needed for almost all of them.

> The salvage process that some parts have been through is a bit brutal.
> That’s both good news and bad news. It lets you buy a “kit of 5” Rb’s to
> repair yourself for very little money. With luck you will get two or three
> working and still not have spent $200 on the batch (delivered). On the other
> hand, if you expect a really good unit when spending a lot more money …. you
> may not like the water damage (or whatever). 

> Lots to think about.

> Bob





>> On Mar 11, 2016, at 4:45 PM, Mark Sims <holrum at hotmail.com> wrote:
>> 
>> Mark's Law of Rubidium Goodness... the bigger the box, the better it is.  The HP5065A is one of the best units ever made.  It can rival a cesium beam unit.  The X72 is a horrid little creature.
>> 
>> 
>> I would also go with the M100 / FRK units.   The LPRO an FE56xx units were designed for telecom use and meet the specs required of them and low cost.   The M100 and FRKs saw a lot of use in military systems.
>> 
>> Which one you choose is best determined by your budget,  applications, and requirements.  A noisy little X72 could be just fine,  or you may need the beastly HP5065.
>> 
>> 
>> 
>> 
>> 
>>                                                                                 
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-- 
Best regards,
 Timenut                            mailto:timenut at metachaos.net



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