Performance Evaluation
60
CG635 Synthesized Clock Generator
2.
Press ‘SEL’ in the CONFIG section until “CAL” is flashing
3.
Press ‘SET’ in the CONFIG section until “cloc Source” is displayed
4.
Press SCALE
Ÿ
in the SCOPE AND CHART section until “cloc Source rear” is
displayed
5.
Press MODE
ź
button until the selected mode is FREQ.
6.
Press ‘SEL’ in the CONFIG section until “OUT” is flashing
7.
Press ‘SET’ in the CONFIG section until “Gate Scale” is displayed
8.
Press SCALE
Ÿ
in the SCOPE AND CHART section until 100 is displayed.
9.
Press the DISPLAY
Ÿ
to return to the normal display
10. Press the GATE/ARM
Ÿ
button once to set the gate to 10 s
11. If a rubidium timebase is installed in the CG635, press the GATE/ARM
Ÿ
button once more to set the gate to 100 s
12. Press the SAMPLE SIZE
ź
button three times to set the sample size to 1.
13. Turn the trigger level knob above the channel A input counter clockwise until
AUTO is highlighted.
14. Press the channel A ‘INPUT’ button once to switch to 50
termination.
Timebase Calibration Test
It is critical that the timebase be fully warmed up before measurements are taken. Allow
at least 1 hour of warm-up for an OCXO or Rubidium timebase. Allow at least 30
minutes of warm-up for a standard timebase.
Record the timebase frequency reported by the SR620 and compare it to the stated one-
year accuracy shown in Table X for the installed timebase.
Table 33: Timebase calibration test
Timebase
Min Freq. (Hz)
Measured Freq. (Hz)
Max Freq (Hz)
Standard 9,999,950.000,000
10,000,050.000,000
Opt 2: OCXO
9,999,998.000,000
10,000,002.000,000
Opt 3: Rubidium
9,999,999.995,000
10,000,000.005,000
Calibration
The CG635’s internal timebase may be calibrated using the measurements taken above if
communication over a remote interface is enabled. The process is iterative. Send the
query
TCAL?
to get the current value of the cal byte. If the measured frequency is low,
this number should be increased, otherwise it should be decreased. Send a new value by
sending the command
TCAL dddd
, where dddd is the new 4 digit cal byte. After sending
the new cal byte, measure the frequency again and continue iterating until calibration is
achieved to the desired accuracy.
