SECTION 6
CALIBRATION
Introduction
This spectrum analyzer is a stable laboratory instrument
which should not require frequent recalibration. Perform-
ance however, should be checked os directed in Section
5, approximately every 1000 hours of operation or every six
months if used intermittently. This assures proper apera-
tion or indicates the section of the instrument that needs
calibration.
This calibration procedure is arranged so the instrument
can be checked and calibrated with the least interaction of
adjustments and reconnecting of test equipment. A single step
can usually be performed, provided interaction between
steps and adjustments is considered.
CAUTION
Removing or replacing the dust cover for the
instrument may be hazardous. Remove or replace
the cover as follows: Place the accessory cover
(front) on the instrument. Set the instrument on
the front-panel cover (do not set the instrument
on the front-panel controls). The dust cover may
now be removed or replaced with safety and ease.
Recommended Equipment
The equipment required to calibrate the Type 491 is listed
in three groups: 1. Basic equipment: Check and calibrates
the Type 491 except for the following; sensitivity, system
flatness, front-end calibration, and the honeycomb assemblies.
2. Equipment required for checking the honeycomb assembly.
3. Equipment required to check the system sensitivity and
calibrate the local oscillator and mixer sections.
The calibration of the honeycomb, local oscillator and
mixer sections is complex and requires special skills and
equipment. We recommend returning these assemblies to
Tektronix for recalibration. See the Maintenance section
for instructions concerning removal of these assemblies.
Minimum test equipment specifications are listed. If sub-
stitute equipment is used, it must meet or exceed specifica-
tions of the recommended equipment. Proper dial and equip-
ment setups of the substitute equipment must be determined
by the user. Signal generators should be relatively free of
harmonic content to provide a clean display.
Group 1
1. Test Oscilloscope and Vertical Plug-In Unit with
1×
and 10× probes. Minimum sensitivity .005 V/cm, frequency
response DC to 30 MHz. Tektronix Type 540 Series oscillo-
scope with Type 1A1 Plug-In Unit and Tektronix P6010
(10×)
and P6011 (1×) test probes.
2. Time-Mark Generator. Marker outputs, .5 s to .1 µs and
frequency outputs of 20 MHz
{
50 MHz, 100 MHz and 200 MHz;
accuracy 0.001%. Tektronix Type 184 Time-Mark Generator.
3. Audio Signal Generator. Frequency range 10 Hz to
1 MHz, variable output amplitude to at least 10 volts peak
to peak, accuracy ±3%. General Radio Model 1310A or
Hewlett-Packard Model 241A.
4. VHF Signal Generator. Frequency range 10 MHz to
400 MHz, accuracy ±1%, calibrated 0 to -120 dBm, vari-
able output.
Hewlett-Packard Model 608D.
5. Constant Amplitude Signal Generator. 1 MHz to 10
MHz amplitude 1 V to 5 V peak to peak. Tektronix Type
191 Constant Amplitude Signal Generator.
6. Variable Autotransformer. Voltage range 96 to 137
(192 to 274) volts nominal line. Monitor output voltage with
an AC
(RMS) voltmeter. General Radio Model W10-MT3W
Metered Variac.
7. Multimeter. Minimum sensitivity 20,000
Ω /volt, accuracy
within 1% at 10V, 12V, 125V and 3750V; ammeter range
to 1 ampere, Simpson Model 262 or Triplet Model 630-PL.
8, Step Attenuators. 1 dB and 10 dB steps, accuracy ±1.5
db to 90 dB (below 1 GHz)
1
. Hewlett-Packard Type 355C
and 355D Step Attenuators.
9. Harmonic Generator. Tektronix Calibration Fixture 067-
0594-00.
10. 200
MHz Trap. Tektronix Calibration Fixture 067-0595-
00.
11. Adapter Cable. BNC female to subminiature female,
4½ inches. Tektronix Part No. 175-0321-00. Subminiature
to BNC male, P6041 probe cable, Part No. 010-0164-00.
12. Two (2) GR to BNC male adapters. Tektranix Part No.
017-0064-00.
13. Clip lead adapter, BNC. Tektronix Part No. 013-0076-
00.
14. Termination, 50 Ω, BNC. Tektronix Part No. 017-0083-
01.
15. BNC T connector. Tektronix Part No. 103-0030-00.
16. Two (2) BNC coaxial cables, 50
Ω. Tektronix Part No.
012-0057-00.
17. 10 dB attenuator pad
2
, type N fitting. Tektronix Part
No. 011-0085-00.
18. 20 dB attenuator pad
2
, type N fitting. Tektronix Part
No. 011-0086-00.
19. 40 dB attenuator pad
2
, type N fitting. Tektronix Part
No. 011-0087-00.
1
Accuracy of the IF ATTEN dB selectors is checked at the factory to
insure they are within the 0.1 dB/dB specification. Change in this
tolerance should be large and due to component failure. Step at-
tenuators with rigid specifications are therefore not recommended,
however, if the user desires to precisely check the attenuator error,
he must either accurately calibrate the recommended equipment or
use attenuators with more rigid specifications.
2
Supplied with accessories kit.
Note.
Calibration will be performed in the AN/TSM-35V5 maintenance shelter.
6-1
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