[time-nuts] Best Rubidium Frequency Standard

EWKehren at aol.com EWKehren at aol.com
Sat Mar 12 11:59:54 EST 2016


Having used FRK for over 35 years I am partial to FRK/M100. More  later.
We have had some bad experience with PRS-10 failing lamp module and others  
have shared the same observation. Clear sign of oxidation and we know the 
unit  has never been exposed to water!
Back to FRK. Previously mentioned bigger is better also heatsink on all  
Rb's are a must Fan control is better. The biggest drawback of FRK and M100 is 
 availability of lamps. At one time you could buy them for $ 300. I have 
spares  for our team. If you buy one make sure lamp voltage is at least 8 
Volt. Many of  the M 100's have not seen continuous duty.
The question is what do you want. We are frequency nuts and use FRK and  
M100 with active Fan control and keep the backplate to 0.01 C. Typical aging 
is  below 5 E-14 per day over a 600 day period. An other plus is to the best 
of my  knowledge M 100 have the only measured pressure sensitivity test 
data. Data  would also apply to FRK's.
Quite a few time-nuts have controlled these Rb's with a Shera contoller I  
included. The weakness of Shera is the AD1861 audio DAC. At one time we did 
a  detailed analysis of available DAC's, went as far as designing and 
building  a test board capable of auto testing multiple DAC's using the LTC2400 
and  decided for Rb's the best  DAC is the 16 bit LTC1655.
If not M100/FRK with what is out there I would go with Skip's RDR   Fe5650. 
(no commercial interest) We have a couple of them. From what I can tell  
there is a high degree of similarity with the 5680A different packaging. There 
 is a lot of data available, there was at one time a FE5680A frenzy after I 
did  my first post based on some recommendation from Germany where they 
enjoyed  popularity at least a year before us. What happened to our German time 
nuts?  What comes now out of China I would not touch, my second order was 
so bad I had  to return it. I doubt that Skip's units ever saw China, he may 
want to comment  on it. As I mentioned in my first post and confirmed 
subsequently there are  frequency spikes on the output and a cleanup is mandatory, 
I have a plot it  was done with a HP5065A and time pod, maybe  byTom? 
Cooling is low cost  with a Laptop heatpipe/fan. Frequency control can be done 
with RS232 or a GPSDO.  Cash Olsen is ready to ship first set of units for $65 
plus shipping.
Bert Kehren
 
 
In a message dated 3/12/2016 11:02:12 A.M. Eastern Standard Time,  
kb8tq at n1k.org writes:

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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