LIN; ≥ 2 6 δ Β .
5-4a
LOG; ≥40 d B .
Signal Amplitude
Spectrum
Step
SQ LAW; ≥ 1 3 δ Β
Limits (.1 dB/dB)
Analyer
Attenuators
Units
Tens
b. Apply 200 MHz signal that has an amplitude less than
1 dB
5.93 to 6.07 div
11
20
-40 dBm, from a VHF Signal Generator that has a cali-
2 dB
5.86 to 6.14 div
10
20
brated variable output attenuator, to band B RF INPUT con-
nector.
4 dB
20
5.6 to 6.3 div
8
8 dB-
4
20
5.5 to 6.6 div
c. Adjust the GAIN control and the variable attenuator
16 dB
10
5.0 to 7.2 div
6
of the Signal Generator for a display amplitude of 8 divi-
20 dB
4.7 to 7.6 div
2
10
sions (full screen).
The 1 and 2 dB measurements are very difficult, because
d. Increase the output attenuation of the VHF Signal Gen-
of signal stability and the noise level. For these small signal
erator until the signal is just visible (about 0.5 minor divi-
sion) on the display. Note the difference in the attenuator
levels, the square law mode may be used to expand the
screen changes, for the some level change by the square
readings.
power as listed in Table 5-4b.
e. Check the dynamic range of each VERTICAL DISPLAY
switch position. Must equal or exceed the range listed in
TABLE
5-4b
step a.
f. Return the VERTICAL DISPLAY switch to the LIN posi-
tion.
An alternate method which is not as accurate but is suf-
ficient for most applications is as follows:
18. Check Accuracy of IF ATTENUATOR
dB Selectors
1. Apply a 200 MHz signal (at 60 dB below 1 mW, as
shown an the Attenuator dial) from the signal generatar
Accuracy of the IF ATTENUATOR dB selectors is checked
to the RF INPUT connector. Adjust the Spectrum Analyzer
at the factory to insure that they are within 0.1 dB/dB specifi-
GAIN control for a signal amplitude of 5 divisions.
cation. Any change in this tolerance should be a large one and
2. Switch the 1 dB IF ATTENUATOR switch on and adjust
due to component failure. Step attenuators with rigid
the signal generator output attenuator control to return the
specifications are, therefore, not recommended. However, if
signal amplitude to 5 divisions.
the user desires a precise check of the attenuator error, he
must either accurately calibrate the recommended equipment
3. Check the new reading of the attenuator dial. Should
or use step attenuators with more rigid specification.
read -59 dBm.
4. Turn the 1 dB IF ATTENUATOR switch to OFF. Check
a. Requirement-IF
ATTENUATOR
selections
must
remain
the remainder of the IF ATTENUATOR selector steps as
within 0.1dB/dB.
directed in Table 5-4c.
b. Apply a 200 MHz signal from the signal generator that
TABLE 5-4c
is 10 dB below 1 mW, through a 2X attenuator (6 dB), a Tens
and Units step attenuator and a 10X attenuator (20 dB) to the
Type 491 RF INPUT connector. (Fig. 5-5).
c. Set the Tens attenuator far 20 dB attenuation and the
Units attenuator for 12 dB attenuation.
d. Adjust the GAIN control far a signal amplitude of 6
divisions on the analyzer screen.
e. Check the accuracy of the IF ATTENUTOR dB selectors
as follows:
19. Check Attenuation Range of IF GAIN
Control
1. Switch the Type 491 1 dB attenuator siwtch to ON and
switch out 1 dB of attenuation through the units step attenua-
a. Requirement-The IF GAIN control range should equal
tor.
or exceed 50 dB.
2. Check the display amplitude. Must equal 6 div. 0.7
b. Turn the GAIN control fully counterclockwise. Adjust
minor division (.1 dB/dB).
the VHF Signal Generator output for an 8 division signal
amplitude. Note the variable attenuator dial reading.
3. Switch the IF ATTENUATOR switch to OFF position,
c. Increase the output attenuation 50 dB from the noted
then check the remaining IF ATTENUATOR switch steps
position.
as directed in Table 5-4a.
5-8
