amplitude with no more than 3 dB dip in the center,
able attenuator output, to an RF INPUT connector
Set the RESOLUTION control fully clockwise. Adjust
of the Type 491. Check the accuracy of each IF
the 100 kHz Resolution Cal R543, for a resolution
ATTENUATOR dB selector against the calibrated
bandwidth between 100 kHz and 120 kHz at the 6
attenuator on the Signal Generator. Accuracy must
dB point. Check that the bandpass decreases to less
equal or exceed 0.1 dB/dB of attenuation.
than 1 kHz with the RESOLUTION control in the fully
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31. Check Attenuation Range of IF Gain Control.
counterclockwise position.
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Check the range of the IF GAIN control. Must equa
24. Adjust the kHz/DIV DISPERSION Calibration.
exceed 50 dB.
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Apply 10 ns and 1 s markers to the RF INPUT. Set
32. Check INTENSIFIER Control Range.
the DISPERSION to 500 kHz/div. Preset the DISPER-
Set the DISPERSION to 100 kHz/div, and the RESOLU-
SION BAL to midrange position. Adjust C384 and
TION control to maximum. Set the VERTICAL DIS-
C385 for 1 marker per two divisions. Adjust these
PLAY switch to LOG position and adjust the GAIN
capacitors simultaneously in opposite directions to
control for an 8 division display. Intensified portion of
keep the 200 MHz signal centered on screen. Adjust
the display with the INTENSIFIER control fully clock-
kHz/Div Cal R368, for optimum dispersion linearity.
wise should measure between 3.5 and 4.5 divisions.
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25. Check Dispersion Accuracy of the kHz/DIV Ranges.
33. Check Signal Amplitude to RECORDER Connector.
Apply time markers from the Time-Mark Generator
With VERTICAL DISPLAY in LIN position, the signal
to the RF INPUT as listed in Table 6-4 and check the
output to the RECORDER connector when terminated
kHz/div dispersion accuracy through + and 2.5
into 600 Ω load should equal or exceed 4 mV/ divi-
MHz change in the IF center frequency. Dispersion
sion of displayed signal.
accuracy must not exceed 3% over the center
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34. Check Video Filter Operation.
8 divisions of the graticule sweep length.
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35. Check Incidental Frequency Modulation. Page 6-32
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26. Adjust Avalanche Voltage.
Incidental FM for a 200 MHz IF signal should not
Connect the test oscilloscope to the 1 MHz MARKERS
exceed 200 Hz. Incidental FM for a tunable signal
OUT, turn on the tNT REF FREQ control. Adjust the
(IF + Local Oscillator) in phase lock condition should
Avalanche Volts R1131, from a counterclockwise posi-
not exceed 300 Hz.
tion, clockwise until the avalanche transistor is just
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below the point of free running avalanche. Set the
36. Adjust the Narrow Band IF Amplifier Peaking.
band selector to C. Push the LOCK CHECK button
and tune the RF CENTER FREQUENCY control. Check
Apply a 200 MHz signal to J100 on the honeycomb
for beat signals through band C.
assembly. Adjust T464, T454, C435 and C425, in the
order listed, for optimum signal amplitude and sym-
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27. Adjust 1 MHz Reference Frequency Range. Page 6-29
metry. Adjust L444 for optimum amplitude and stable
Apply the output from the 1 MHz MARKERS OUT
70 MHz oscillator operation.
connector, through a 20 dB attenuator, to J100 on the
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37. Adjust Wide Band Amplifier Response and Check
honeycomb assembly. Adjust L1108 for positive oscil-
System Flatness.
lator start as the INT REF FREQ control is turned from
OFF to on position. Adjust L1104 for a frequency shift
Apply a calibrated 75 MHz signal to J120. Connect a
of 1.2 kHz in the 1 MHz oscillator, as the INT REF
test oscilloscope to J188. Turn the 20 dB ATTENU-
FREQ control is rotated through its range.
ATOR switch on.
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Adjust L144 for maximum response to 75 MHz signal.
28. Adjust Band C Balance then Band A and B Balance.
Apply 65 MHz and adjust L147 for minimum response
to 65 MHz. Remove the Signal Generator signal and
Center the FINE RF CENTER FREQ control. Set the
test oscilloscope; reconnect honeycomb cables to J120
band selector to C. Push the LOCK CHECK button
and J188.
and adjust Band C Bal R1140, for a centered trace.
Switch the band selector to B or A. Push the LOCK
Apply a frequency and amplitude calibrated signal
CHECK button and adjust band A and B Bal R1150
to an RF INPUT connector and check the response
for a centered trace.
flatness of the Type 491. Response flatness should
vary over 1.5 dB over 50 MHz dispersion for
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29. Check Dynamic Range of Vertical Display Modes,
band A, 1.5 dB over 100 MHz dispersion for bands
B and C.
Dynamic range of the 8 division screen is as follows:
Adjust C137 and L134 for optimum sensitivity and re-
LIN ≥26 dB, LOG ≥40 dB and SQ LAW ≥13 d B .
sponse flatness. Adjust C68 on band B RF Mixer, for
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optimum sensitivity and bandpass flatness at the high
30. Check Accuracy of IF ATTENUATOR selectors.
frequency end (800 MHz) of band B.
Apply a signal within the frequency range of one
Check system flatness as per Table 6-4, 6-5, and instru-
band, from a Signal Generator with a calibrated vari-
ctions to check band C. System flatness within 1.5
6-6
