Yeah, Chuck, I read that somewhere, that it's possible to rejuvenate a Rb lamp with heat. I'm hoping to get a spent Symetricomm (a more recent name of Ball Efratom, I understand) unit from Raytheon (Technologies it is now), my employer. Trouble is, it's buried inside a rack and not easy to get at. We cobbled up another Rb frequency standard of about the same age, so it may bite the dust soon, too. I'd take either or both and heat to drive the rubidium off the glass. I need a frequency standard with long term stability for holdover if my Leo Bodnar GPSDO drops out or something happens to the GPS. No, I'm not a time nut, not yet, anyway.
toggle quoted messageShow quoted text
------ Original Message ------
From: "Chuck Harris" <cfharris@...>
Sent: 7/13/2020 10:35:43 AM
Subject: Re: [TekScopes] PTB 100 Ball Efratom
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
The Rb lamp is ready to go another decade or so.
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
On Mon, Jul 13, 2020 at 11:36 garp66 <@green> wrote:
Does anyone know how the PTB-100 Ball Efratom Rubidium standard performs &
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 ?