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Model 5065A
Circuit Diagrams, Theory, and Maintenance
Table 5-2. In-Cabinet Performance Check (Cont'd)
FREQUENCY STABILITY CHECK
The
specification
for
long-term
frequency
stability of the 5065A is less than 1 x 10-" per
month.
To verify this frequency stability, the
5065A must be compared with a primary fre-
frequency
standard
to
observe
frequency
change over a 30-day period.
a.
Refer to Section 3-20, Frequency Off
set and Calibration, for instructions on making
a phase check between the 5065A and a
reference standard.
b.
Before proceeding with this check al
low a 24-hour warmup.
c. At the beginning of this check adjust
the 5065A front panel MAGNETIC FIELD con
trol to set the 5065A frequency within 1 part in
10
11
of the reference standard frequency.
d.
Run this check for 30 days or; make
two separate checks with 30 days intervening.
e. Note any change in frequency of the
5065A with respect to the reference standard
over the 30-day period. This change should be
less than 1 part in 10
11
.
With practice, the operator will be able to verify
frequency stability for most purposes by ob
serving frequency
change over
a 48-hour
period.
However, if the 5065A frequency
stability specification must be verified, a 30-day
check will be required.
5-8. INSTRUMENT TROUBLESHOOTING
5-9.
Introduction
5-10.
When operational checks indicate a frequency
change that is not within specifications for either UTC
or A1 time scales according to the setting of the TIME
SCALE thumbwheel and HI-LO switches, the following
checks should be made prior to servicing:
a.
If instrument is operating on A1 time scale, check
Synthesizer TIME SCALE thumbwheel switch and HI-LO
switch setting against the indicated A1 settings on the
A12 RVFR decal.
b.
If the instrument is operating on the UTC time
scale, check Synthesizer TIME SCALE thumbwheel
switch and HI-LO switch settings against the UTC settings
on the operating card mounted on the front panel door.
c.
Check synthesizer frequency according to the
table on foldout page which lists synthesizer output fre
quencies versus TIME SCALE settings.
NOTE
If CONTINUOUS OPERATION light goes
out after instrument has warmed up, the
CIRCUIT CHECK meter switch should be set
to the LAMP OVEN and CELL OVEN posi
tions. If either meter indication is full scale,
the instrument should be turned off imme
diately. If not, the RVFR Assembly could be
damaged by excessive heat.
5-11.
In troubleshooting the 5065A, it is helpful to con
sider the instrument as consisting of 3 sections: (1) RF
section, (2) RVFR and, (3) the low-frequency section.
These are shown in the simplified block diagram of Fig
ure 5-6.
5-12. The RF Section, by multiplication and synthesis,
generates the excitation signals for the RVFR. If the ex
citation frequencies and power levels are correct, the
RVFR Assembly should respond. This response is a 137
Hz signal if the RF excitation is slightly off frequency, and
a 274 Hz (2nd Harmonic) signal if the excitation is "on
frequency". The RVFR will not operate properly if the cell
heater circuit is not working. In the low frequency section,
the error signal is amplified and phase detected to give a
dc voltage proportional to the excitation frequency error.
This error signal is processed by the integrating amplifier
and sent to the Quartz oscillator as a control signal to hold
the Quartz oscillator at the correct frequency.
5-13. The front panel meter monitors various points in
the loop. These are indicated in Figure 8-2. Four of the five
input signals to the logic assembly (which can turn off the
CONTINUOUS OPERATION light) may be monitored on
the CIRCUIT CHECK meter. These are:
a.
The 2ND HARMONIC signal
b. The CELL OVEN signal
c.
The LAMP OVEN signal
d.
The fundamental ERROR signal
The one alarm signal that is not monitored is the "Synthe
sizer lock" signal.
5-6
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