i
i
i
I
o
a. Test equipment setup is shown in Fig. 3-3. Apply a
-20 dBm, 100 MHz signal, from the signal generator
through 10 dB and 1 dB step attenuators (set at 0 dB), to
the RF INPUT; or directly to the RF INPUT of the 492/492P
if individual fixed attenuators are to be used as the stan
dard. Set the front-panel controls as follows:
FREQ SPAN/DIV
20 MHz
AUTO RESOLUTION On
Vertical Display
10 dB/DIV
Video Filter
WIDE
REF LEVEL
— 10 dBm
MIN RF ATTEN
OdB
b. Tune the signal to center screen, then decrease the
FREQ SPAN/DIV to 10 kHz. Now change the RESOLU
TION BANDWIDTH to 10 kHz and again center the signal
on screen.
c. Change the Vertical Display to 2 dB/DIV. Adjust the
signal generator output so the signal amplitude is six divi
sions with the top of the signal positioned on the 6 th
graticule line.
g. Deactivate MIN NOISE. Return the 1 dB step
attenuator to 0 dB, decrease the signal generator output to
10 dB or add 10 dB of external attenuation with the 10 dB
step attenuator. Readjust the generator output so the signal
level is again at the reference line (6 division amplitude).
Calibration—492/492P Service Vol. 1 (SN B030000 & up)
Performance Check
h. Change the REF LEVEL in 1 dB increments from
—20 dBm to -3 0 dBm adding 1 dB increments of external
attenuation with the 1 dB step attenuator and note incre
mental and 10 dB step accuracies.
i. Return the 1 dB step attenuator to 0 dB, decrease sig
nal level 10 dB by adding 10dB more of external attenu
ation or decreasing the signal generator output level then re
establish the signal reference amplitude.
j. Check the —30 dBm to —40 dBm gain accuracies as
previously described.
k. Repeat the procedure checking gain accuracies to
-7 0 dBm.
d. Activate MIN NOISE and note signal level shift. Shift
must not exceed ±0.8 dB, or 2 minor divisions (attenuator
) plus gain accuracies).
e. Re-position the signal level to the graticule reference
line by adjusting the output of the signal generator.
f. Switch the REF LEVEL from -10 dBm to —20 dBm
in 1 dB steps, adding 1 dB of external attenuation at each
step and note incremental accuracy and the 10 dB gain ac
curacy. Incremental accuracy must be within 0.2 dB/dB (0.5
minor division). Maximum cumulative error must not exceed
0.5 dB (1.5 minor divisions) except when stepping from the
9 dB to 10 dB increment, where the error could be an addi
tional 0.5 dB.
I. Establish a signal reference at -7 0 dBm, activate
NARROW VIDEO FILTER, then check gain accuracy to
—80 dBm.
m. Limitation to gain variation measurements over the
remaining range is imposed by noise and residual FM’ing.
Without Option 03 (phaselock stabilization) oscillator FM'ing
limits practical gain variation measurements to the 10 kHz
resolution bandwidth position which further compounds the
measurement problem with a 10 dB higher noise floor than
the 1 kHz resolution bandwidth. The gain variation accuracy
of the -8 0 dBm to —100 dBm REF LEVEL positions are
closely related to the accuracy of the previous checks;
therefore, they are not validated in an instrument without
Option 03.
Table 3-3
CORRECTION FACTOR TO DETERMINE TRUE SIGNAL LEVEL
Ratio in dB of signal plus
noise—noise
3.01
4.0 5.0 6 .0 7.0 8 .0 9.0
1 0 .0 1 2 .0 14.0
Subtract this correction factor
for true signal level
3.01
2 .2 0 1.65 1.26
0.97
0.75 0.58
0.46
0.28
0.18
REV SEP 1983
3-13
To Next Page
Loading...
