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Model 5065A
Circuit Diagrams, Theory, and Maintenance
RVFR (RUBIDIUM VAPOR FREQUENCY REFERENCE)
ASSEMBLY A12 THEORY
The A12 RVFR Assembly is a sealed package which
should only be serviced at the factory. To remove, see
removal instructions. For a detailed discussion of the
frequency standardizing
process, see Section 4-1,
Theory.
The A12 RVFR Assembly which produces the frequency
reference is housed in a triple magnetic shield to pre
vent frequency shifts by external magnetic fields.
Isolation from ambient temperature is provided by two
separate ovens which provide regulated temperature
for; (1) the Rb
87
lamp and lamp oscillator and, (2) the
Rb
87
filter cell and the Rb
87
absorption cell. Oven cur
rents for the LAMP OVEN and CELL OVEN can be
monitored with the CIRCUIT CHECK switch.
The main components of A12 Assembly are as follows:
a. The magnetic shields.
b. The temperature ovens each with
a tem
perature sensor and heater.
c. The Rb
87
lamp and oscillator circuit which pro
duces 90 MHz to excite the lamp.
d.
The microwave cavity housing the Rb
87
absorp
tion cell, the solar cell which detects the light output of
the Rb
87
absorption cell, and the coupler which couples
the 6.834685...GHz excitation into the microwave cavity.
e. The step-recovery diode which produces the
114th harmonic of 60 MHz -5.315...MHz (6.834685...
GHz) to excite the microwave cavity.
A12 MAINTENANCE
NORMAL OPERATION
a.
Inputs:
1)
60 MHz at approximately 1 V or greater from
A3 Assembly.
Also 5.315...MHz at approxi
mately 20 mV on same cable.
2)
Approximately 18 Vdc at J15
(3 and 5) from
A11 Temperature Controller Assembly for cell
and lamp heaters.
3)
Approximately 2
1
/
2
to 6 mA at J15(6) from A15
Power Regulator Assembly.
This
current
creates the magnetic field inside the RVFR to
control its frequency.
b. Outputs:
Under normal operation with suf
ficient RF power applied, the output of A7P1 will be:
1)
At resonance, 274 Hz at a signal level of ap
proximately 3 nanoamperes.
2)
Slightly off resonance, 137 Hz at a signal level
of approximately 5 milliamperes.
3)
Completely off resonance, nothing.
4)
Dc photo induced current of approximately
_
5 0 jU a.
OPERATIONAL CHECK
a.
Because of the extremely low signal level out
puts from the RVFR and, because of the specialized
nature of the drive signals, the operational check of the
RVFR requires that the driving and amplifying circuits
—
associated with the RVFR work properly.
Thus, the
operational check for the RVFR may include operational
checks of several other assemblies.
_
b.
Procedure:
1)
Check lamp and cell ovens by placing a hand _
on the RVFR Assembly.
It should be warm to
the touch. Also check CIRCUIT CHECK meter
in the CELL OVEN and LAMP OVEN positions.
Meter should read between 15 and 35 for both —
positions.
2)
Set CIRCUIT CHECK meter to PHOTO I. Meter
should read 25 to 50. If it does, go to Step 3. __
If not proceed as described in the Circuit
Checks, Table 5-3.
3)
Magnetic field current check.
Use clip-on _ -
milliammeter
such as HP 428B and measure
output current at A15(9). It should be between
2
1
/2 and 6 mA and be controllable from the front
panel MAGNETIC FIELD control.
_
NOTE
Lack of magnetic field current will not
_
affect the signal output of the RVFR. This
current controls only the resonant fre
quency of the RVFR.
c.
RVFR signal test:
1)
Connect test setup as shown in the following
figure:
—
RVFR Test Setup
HP5065A
A 7 T P 2
A8TP2
VERTICAL
EXT
SYNC
HPI80A
OSCILLOSCOPE
r
r
T
j
8-56
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