Calibrationโ492/492P Service Vol. 1 (SN B030000 & up)
Performance Check
e. Check the accuracy of the 50 ms to 2 ms TIME/DIV
settings by applying appropriate markers for each setting
and note the displacement as described in part d of this
step.
f. If the instrument has Digital Storage, deactivate the
Digital Storage. Change the RESOLUTION BANDWIDTH to
1 MHz and adjust FREQUENCY for a satisfactory display of
the time markers. Check the accuracy of the 1 ms and 20 ms
TIME/DIV selections.
g. Remove the time mark generator output to the RF
INPUT and EXT TRIG input of the 492/492P. Connect the
comb generator 500 MHz signal to the RF INPUT and mod๎
ulate the comb generator with .1 s markers by applying the
marker output from the time mark generator to the Pulse
input of the comb generator.
h. Set the TIME/DIV to .1 s and activate INT Triggering.
Change the FREQ SPAN/DIV to 50 MHz and adjust the
FREQUENCY to center the 500 MHz comb signal. If the
instrument has Digital Storage, activate VIEW A, VIEW B.
13. Check Resolution Bandwidth and Shape Factor
(bandwidth within 20% of that selected, shape factor
7.5:1 or less)
a. Apply the CAL OUT signal to the RF INPUT. Set the
front-panel controls as follows:
FREQUENCY RANGE 0โ4.2 GHz (0โ1.8 GHz,
Option 01)
100 MHz
โ 20 dBm
2 dB/DIV
500 kHz
FREQUENCY
REF LEVEL
Vertical Display
FREQ SPAN/DIV
RESOLUTION
BANDWIDTH 1 MHz
PEAK/AVERAGE Fully cw
Digital Storage (Option 02) VIEW A/VIEW B
TIME/DIV AUTO
MIN NOISE On
b. Adjust the FREQUENCY to center the calibrator sig๎
nal on screen and measure the โ 6 dB bandwidth (see Fig.
3-10A). Bandwidth must equal 1 MHz ยฑ200 kHz.
i. Change the REF LEVEL to -30 dBm, then reduce the
RESOLUTION BANDWIDTH to 1 kHz and the FREQ
SPAN/DIV to 100 kHz while adjusting the FREQUENCY to
optimize time markers on the display. Reduce the FREQ
SPAN/DIV to zero.
j. Check the accuracy of the .1 s to 5 s sweep rates by
applying appropriate markers to modulate the comb gener๎
ator signal as the TIME/DIV selector is changed over this
range.
c. Change the Vertical Display mode to 10 dB/DIV.
d. Estimate the -60 dB bandwidth (see Fig. 3-10B).
Calculate the shape factor (60/6 dB bandwidth ratio). Shape
factor should equal 7.5:1 or less.
e. Switch the RESOLUTION BANDWIDTH to 100 kHz
and the FREQ SPAN/DIV to 100 kHz. Check the bandwidth
and shape factor of the 100 kHz filter by repeating the fore๎
going procedure.
12. Check Pulse Stretcher
a. Apply 1 ms time marks from the time mark generator
to the RF INPUT of the 492/492P. Set the TIME/DIV to
500 ms, RESOLUTION BANDWIDTH to 1 MHz, Vertical
Display to 2 dB/DIV, and REFERENCE LEVEL to
-10 dBm.
b. Tune the FREQUENCY to approximately 0 MHz so
the amplitude of the markers is near full screen. If neces๎
sary, change REF LEVEL. Set Digital Storage off, and
SPAN/DIV to ZERO.
c. Activate PULSE STRETCHER and check that it ex๎
tends the fall time of the markers.
f. Check the resolution bandwidth and shape factor for
the remaining RESOLUTION BANDWIDTH selections. De๎
crease the FREQ SPAN/DIV as necessary to check each
selection. Bandwidth must be within 20% of the bandwidth
selected and the shape factor 7.5:1 or less.
g. Deactivate MIN NOISE.
Alternate Procedure for Checking 100 Hz
Bandwidth
The 2nd LO drift characteristics of some instruments
may make the above procedure impractical for measuring
REV AUG 1981
3-23
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