[time-nuts] Best Rubidium Frequency Standard

Bob Camp kb8tq at n1k.org
Sat Mar 12 08:54:04 EST 2016


Hi

The PRS-10 generally shows up in versions that do not have 
the external pps input working. Even on the ones that *do* have 
a pps, it is not one that works well with the pps from a GPS. Simply
put, that option is not worth spending money on. 

Manually adjusting an Rb against a GPS is a bit time consuming, but 
fairly easy to do.You need observations spread over days and you need
to keep track of what you have done. Once adjusted it should run quite 
well for a long time. Weekly / monthly / quarterly checks should be all it needs.

All modern Rb’s are based on firmware. different versions have different 
code in them. Swapping those files around is *not* often successful. Repair
can easily involve parts that no longer are made. A lot of PRS-10’s simply 
get scrapped…

====

For $129 you can get a batch of 5 Temex Rb’s. They probably will need two
dollars worth of caps replaced. You likely will find that one or two of them work
“as is”. 

Bob


> On Mar 11, 2016, at 8:50 PM, timenut at metachaos.net wrote:
> 
> 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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