HP 5065A questions
Hello time-nuts,
I have recently had the opportunity to play with an HP 5065A rubidium
standard and have some questions. This unit has been powered down for
quite a long time, it appears to be almost working. I can see both the
137Hz and second harmonic signals but they seem very low.
In the manual (the one from KO4BB.com) in section 3.9 (pg 3-1) there is a
procedure to apply a 1A current through the TEC until the 2nd harmonic
comes back (due to cell flooding).
-
What the heck is rubidium cell flooding, and how does the TEC in the
5065A fix this problem? None of the -many- rubidium oscillators that I
have been inside before has a TEC, and I have never seen the subject
addressed.
The manual suggests that it may take several weeks at the 1A current to fix
the problem (normal operation of the 5065A applies .7V across the TEC). -
When the coarse oscillator control is swept across 5Mhz (open loop) the
137Hz ERROR signal swings about +/-8 on the meter. This seems low (and may
be related to this flooding issue). Just wondering what others have seen
on their units? -
On page 5-15 of the manual it says to adjust A7R29 for a 2nd harmonic
voltage of 4V at A14(1). In the section on A14 on page 8-61 the table
states that the normal A14(1) voltage is 8V. So which is it? Granted the
2nd harmonic won't extinguish the CONTINUOUS light until it falls to less
than about 1.1V.
I'm also curious about the level of the 60MHz signal feeding the Rb cell.
This unit has several volts of RF, which appears to be plenty, but just
wondering if anyone has any baseline information.
Also, any hints about the care and feeding of the HP 5065A would be
welcome. Thanks in advance.
Regards,
Skip Withrow
On 9/25/2016 6:42 PM, Skip Withrow wrote:
- What the heck is rubidium cell flooding, and how does the TEC in the
5065A fix this problem? None of the -many- rubidium oscillators that I
have been inside before has a TEC, and I have never seen the subject
addressed.
The manual suggests that it may take several weeks at the 1A current to fix
the problem (normal operation of the 5065A applies .7V across the TEC).
Cell flooding is one of the dirty little secrets of Rb standards.
I worked on the 10816 mini rubidium. There is supposed to be liquid
rubidium in a reservoir somewhere. We used the tip off as the
reservoir. The oven design (optimistically IMHO) attempted to have
a heat leak on the tip off that kept it cooler than the rest of
the cell, yet the oven was still supposed to isolate the cell
temperature from the environment. Capillary action was supposed
to keep the liquid rubidium in the tip off. However, it might
come out of the unit was jiggled or turned over or stored, powered
down, in a hot place. Then, Rb might get on the optical window,
and then you have a serious error in frequency. The (again optimistic)
concept was that you would just run the unit for a long time until
the rubidium on the window hopefully evaporated and ended up in the
tip off. Yeah, right.
The 5065 (a VASTLY superior design compared to the 10816) was much
less likely to be jiggled or turned over, and at least had a
TEC to cool the Rb reservoir in case it got flooded.
Rick
Hi,
On 09/26/2016 04:04 AM, Richard (Rick) Karlquist wrote:
On 9/25/2016 6:42 PM, Skip Withrow wrote:
- What the heck is rubidium cell flooding, and how does the TEC in the
5065A fix this problem? None of the -many- rubidium oscillators that I
have been inside before has a TEC, and I have never seen the subject
addressed.
The manual suggests that it may take several weeks at the 1A current
to fix
the problem (normal operation of the 5065A applies .7V across the TEC).
Cell flooding is one of the dirty little secrets of Rb standards.
I worked on the 10816 mini rubidium. There is supposed to be liquid
rubidium in a reservoir somewhere. We used the tip off as the
reservoir. The oven design (optimistically IMHO) attempted to have
a heat leak on the tip off that kept it cooler than the rest of
the cell, yet the oven was still supposed to isolate the cell
temperature from the environment. Capillary action was supposed
to keep the liquid rubidium in the tip off. However, it might
come out of the unit was jiggled or turned over or stored, powered
down, in a hot place. Then, Rb might get on the optical window,
and then you have a serious error in frequency. The (again optimistic)
concept was that you would just run the unit for a long time until
the rubidium on the window hopefully evaporated and ended up in the
tip off. Yeah, right.
The 5065 (a VASTLY superior design compared to the 10816) was much
less likely to be jiggled or turned over, and at least had a
TEC to cool the Rb reservoir in case it got flooded.
You might also develop a thin film of rubidum on the window, which
filters out the D-lines and less optical pumping is achieved. Heating
and collecting it back at the tip-off does help. The 5065A is the only
one I know that has a TEC to support this action.
Cheers,
Magnus