29. Check Dynamic Range of Vertical Display
Limit (.1 dB/dB)
b. Apply a 200 MHz signal from an RF Signal Generator
5.93 to 6.07 div
with a calibrated variable output attenuator to band A RF
5.86 to 6.14 div
INPUT connector. Signal amplitude should be less than
5.7 to 6.3 div
5.5 to 6.6 div
c. Adjust the GAIN control and the Variable Output
5.0 to 7.2 div
Attenuator for a display amplitude on the Type 491 of 8
4.8 to 7.5 div
The 1 and 2 dB measurements are very difficult because of
signal stability and the noise level. Over these small levels
until the signal is just visible (about 0.5 minor divisions).
the square law mode may be used. This expands the screen
Note the difference in attenuator reading between the full
changes for the same level change by the square power as
screen display and the 0.5 minor division display.
listed in Table 6-6b. Use reference signal amplitude of 5 divi-
e. Check the dynamic range af each VERTICAL DISPLAY
sions to avoid going outside the graticule area.
switch mode to the following specifications:
LIN; ≥ 2 6 d B
LOG; ≥40 d B
SQ LAW; ≥13 d B
An alternate method which is not as accurate but is suf-
30. Check Accuracy of IF ATTENUATOR dB
ficient for most applications is as follows:
1. Apply a -60 dBm, 200 MHz signal from the signal
Accuracy of the IF ATTENUATOR dB selectors is checked
generator to the RF INPUT connector. Adjust the Spectrum
at the factory to insure they are within the 0.1 dB/dB spec-
Analyzer GAIN control for a signal amplitude of 5 divisions.
ification. Any change in this tolerance should be a large
one and due to component failure. Step attenuators with
2. Switch the 1 dB ATTENUATOR switch on and adjust the
rigid specifications are, therefore, not recommended. How-
signal generator Attenuator control to return the signal ampli-
ever, if the user desires to precisely measure the error of
tude to 5 divisions.
the dB selectors, he must accurately calibrate the recom-
mended equipment or use an attenuator with more rigid
3. Check the new reading of the Attenuator dial. Should
read -50 dBm 0.1 dBm.
4. Turn the 1 dB ATTENUATOR switch to OFF. Check the
remainder of the IF ATTENUATOR selector steps as directed
b. Apply a 200 MHz signal, that is 10 dB below 1 mW,
from the signal generator through a 2 Attenuator (6 dB), a
Tens and Units Step Attenuator and a 10 Attenuator (20 dB)
to the Type 491 RF INPUT connector.
c. Set the Tens Step Attenuator for 20 dB and the Units
RF Generator Attenuator
Step Attenuator for 12 dB attenuation.
IF ATTEN switch ON
-58 dBm .2 dBm
d. Adjust the GAIN control for a signal amplitude of 6
-56 dBm .4 dBm
divisions on the analyzer.
-52 dBm .8 dBm
e. Check the accuracy of the IF ATTENUATOR dB se-
-44 dBm 1.6 dBm
lectors as follows:
-40 dBm 2.0 dBm
1. Switch the 1 dB ATTENUATOR switch to on and switch
out 1 dB attenuation through the Units Step Attenuator.
31. Check Attenuation Range of IF GAIN
2. Check the display amplitude. Must equal 6 divisions
0.7 minor divisions.
a. Equipment setup is given in step 30.
3. Switch the 1 dB ATTENUATOR switch to the OFF posi-
b. Turn the GAIN control fully counterclockwise. Adjust
tion, then check the remaining IF ATTENUATOR dB steps as
the Signal Generator variable output attenuator for an 8