Re: PTB 100 Ball Efratom


Chuck Harris
 

I did one in a HP5065A.

I had a bad oven, and a black Rb lamp, and fixed both.
The oven had an internal short between its formvar covered
nichrome wire wound heater, and the outer mumetal shield...
This put the oven on full heat, and melted all of the solder
on the lamp's board... parts fell out of their holes.

But, curiously didn't clean the glass on the bulb. I used
a propane torch, as I recall. The glass is quartz, so heating
it is not all that risky.

Corby Dawson is where I first got the idea.

Corby has made some optical modifications to the 5065A
standards that eeek out another order of magnitude of S/N
performance.

-Chuck Harris



stevenhorii wrote:

Chuck,

I got my information from this article:

http://www.wriley.com/A%20History%20of%20the%20Rubidium%20Frequency%20Standard.pdf


However, I think we are both right - see page 5 of the article. It notes
the problem is a tradeoff between too much Rb (noise) and depletion from
the Rb diffusing into the glass.

There was a guy (Corby Dawson?) who was able to restore Rb frequency
standards - maybe by doing what you suggested. Have you tried this? I've
got a non-working Efratom standard I should try it on.

Thanks for improving the answer and suggesting a fix.

Steve H.

On Mon, Jul 13, 2020 at 1:35 PM Chuck Harris <cfharris@...> wrote:

I don't think Rb depletion is quite correct.

What I, and others, have found on units that just
ran out of steam, is generally that the RF excited
Rb vapor lamp has plated out its Rb metal on the
envelope of the lamp, seriously reducing the intensity
of the emitted light.

The cure is to re-vaporize the Rb metal off of the
lamp's glass bulb.

To do this, take the Rb lamp assembly apart, and you
will generally see the lamp's envelope is black in
appearance. Heat it with a hot air gun and at a
certain temperature, you will see the black coating
simply disappear.

The Rb lamp is ready to go another decade or so.

-Chuck Harris

stevenhorii wrote:
I can’t tell you about phase noise, but a key feature of rubidium
standards
is their operating life. The life is limited by depletion of the rubidium
in the discharge lamp. Because studies by manufacturers of the
performance
of the standards they make, they can provide estimated lifetimes based on
rubidium depletion. Because of the reliability requirements of frequency
and time standards (for example in cell phone tower electronics) they are
often swapped out for new oscillators as they get within the range of the
expected end-of-life. The large number of rubidium standards that turn up
on eBay is at least partly a result of this preventive maintenance
program.
Most of the used standards likely will have limited life. However, their
low cost means you might be able to afford to buy more than one so you
can
swap in one that works for one that has failed.

The standard I know that was designed with longer life in mind is the
Stanford Research Systems (SRS) line, Their PRS-10 model, for example,
has
a design life of 20 years. Just look up the model for a description of
the
long-term stability and low phase noise. The standard can monitor the
lamp
start voltage as it rises as the rubidium depletes. These standards sell
for more on eBay because of the longer life and likelihood that they will
work for you even as used units. Some honest and knowledgable sellers can
tell you the lamp voltage. Disclosure: no financial connection with
either
Ball-Efratom or PRS. I do own standards from both and I bought used ones
on
eBay and they work (and are working after a couple of years) despite
being
used units. On the other hand, I have some HP and Tracor/Sulzer quartz
frequency standards that are more than 20 (the HP) and 50 years old,
respectively. I’ve had to repair a couple of the Tracor units, but the
problem was almost always a transistor in the divider/amplifier stage
that
failed. I also have a couple of Frequency Electronics quartz standards -
these are mil-spec units (URQ-10 and URQ-23) and work fine, but I’ve no
idea how long they were in service. They all have built-in battery packs
that are built up from “D” size nicad cells (I think - the packs are
sealed) and all have failed. They run fine without the batteries - the
power supply does not use the battery pack as a filter.

Anyone interested in time and frequency should have a look at the Time
Nuts
site:

http://leapsecond.com/time-nuts.htm

SteveH




On Mon, Jul 13, 2020 at 11:36 garp66 <@green> wrote:

Does anyone know how the PTB-100 Ball Efratom Rubidium standard
performs &
compares
technically (data & experience), with any of the other available
frequency standards ?

(phase noise, etc...)

-- and how it ages ?

Is the PTB-100 still a useful, viable kit ?

thank you,
rick









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