[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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