Tektronix 491 User manual

TM 9-6625-2467-15
DEPARTMENT OF THE ARMY TECHNICAL MANUAL
OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, GENERAL SUPPORT,
AND DEPOT MAINTENANCE MANUAL
(INCLUDING REPAIR PARTS)
SPECTRUM ANALYZER
(TEKTRONIX, INC. MODEL 491)
(6625-494-2937)
HEADQUARTERS,DEPARTMENT OF THE ARMY
DECEMBER 1969

WARNING
HIGH VOLTAGE
is used in the operation of this equipment.
DEATH ON CONTACT
may result if personnel fail to observe safety precautions.
Learn the areas containing high voltage
in each piece of equipment.
Be careful not to contact high-voltage or 115-volt ac input connections
when installing or operating this equipment.
Before working inside the equipment, turn power off and ground points of
high potential before touching them.

This manual
reproduced by
TECHNICAL MANUAL
)
)
No. 9-6625-2467-15 )
contains copyright material
permission of TEKTRONIX, Inc.
TM 9-6625-2467-15
HEADQUARTERS
DEPARTMENT OF THE ARMY
Washington, D.C., 15 December 1969
SPECTRUM ANALYZER (TEKTRONIX, INC. MODEL 491)
Section 1
Section 2
Section 3
Section 4
Section 5
Section 6
Section 7
Section 8
Section 9
APPENDIX A.
B.
C.
(6625-494-2937)
CONTENTS
Characteristics
Operating Instructions
Circuit Description
Maintenance
Performance Check
Calibration
Abbreviations and Symbols
Electrical Parts List
Mechanical Parts List Information
Mechanical Parts List
Diagrams
Mechanical Parts List Illustrations
Accessories
BASIC ISSUE ITEMS LIST
MAINTENANCE ALLOCATION CHART
REPAIR PARTS LIST
Abbreviations and symbols used in this manual
are based on or taken directly from IEEE Stand-
ard 260 “Standard Symbols for Units”, MIL-
STD-12B and other standards of the electronics
industry.
i

ii
Fig. 1-1. The Type 491 Spectrum Analyzer.

SECTION 1
CHARACTERISTICS
The Type 491 Spectrum Analyzer is a wide band,
general purpose portable spectrum analyzer with an RF
center frequency range from 10 MHz to 40 GHz. The ana-
lyzer displays signal amplitude as a function of frequency
for a selected portion of the
played along the horizontal
amplitude on the vertical axis
spectrum, Frequency iS dis-
axis
of a (dispersion) and signal
self-contained system.
The following electrical characteristics apply at an ambient
temperature of 25° C (±5°C) after an initial warmup period
of approximately 20 minutes.
ELECTRICAL CHARACTERISTICS
Characteristic Performance Requirement Supplemental Information
RF Center
Frequency Range
10 MHz to 40 GHz—See Table 1-1
CW Sensitivity See Table 1-1
I
(S + N=2N)
Dial Accuracy Within ± (2 MHz +1% of dial reading) IF CENTER FREQ central at 000, FINE IF
ICENTER FREQ control and FINE RF CENTER
FREQ controls centered.
TABLE 1-1
Minimum CW
Sensitivity (S + N = 2N)
Band and Supplemental
Scale RF CENTER FREQUENCY 1 kHz RESOLUTION 100 kHz RESOLUTION Information
A-1
10-275 MHz –100 dBm –80 dBm
B-2 275-900 MHz –110 dBm –90 dBm
3 800-2000 MHz –105 dBm –85 dBm
C-4
1.5-4.0 GHz –110 dBm –90 dBm
5 3.8-8.2 GHz –100 dBm -80 dBm
6 8.0-2.4 Ghz –95 dBm –75 dBm
712.4-18.0 GHz –90 dBm –70 dBm
8 18.0 -26,5 GHz
–80 dBm -60 dBm
!
26.5-40.0 GHz –70 dBm -50 dBm
50 Ω source impedance.
All voltages are RMS.
TABLE 1-2
DISPERSION/DIV
Setting
Accuracy
Remarks
10MHz —
±3% (±0.3 MHz/Div) Over the ±25 MHz of the IF Center FREQ control ex-
5 MHz ±3% (±0.15 MHz/Div) cept the 10 MHz/DIV position (± 10 MHz). The DIS-
2 MHz PERSION CAL adjust can be reset to improve the ac- ±5% (±0.1 MHz/Div) curacy at a specific IF CENTER FREQ control setting
1 MHz ±7% (±70 kHz/Div) by using the front panel 1 MHz CAL MARKERS OUT as
.5 MHz ±10% (±50 kHz/Div) a calibrated signal.
.2 MHz ±15% (±30 kHz/Div) Measured over the center 8 divisions of the graticule.
1-1

ELECTRICAL CHARACTERISTICS (cont)
Characteristic Performance Requirement Supplemental Information
Dispersion
MHz/DIV RANGE
Range .2 MHz/Div to 10 MHz/Div In a 1-2-5 seauence
Accuracy See Table 1-2
Linearity ±3% (over an 8 division display)
kHz/DIV RANGE
Range
1 kHz/Div to 500 kHz/Div in a 1-2-5 se-
quence and zero dispersion.
Accuracy ±3% of each setting Over the ±2.5 MHz range of the IF
CENTER FREQ control. Measured over the
center 8 divisions of the graticule.
Linearity ±3% (over an 8 divisions display)
Resolution ≤1 kHz to ≥100 kHz; in 11 uncalibrated May be coupled with the DISPERSION con-
steps. trol or switched separately.
IF Center Frequency
Control Range” IF CENTER FREQ FINE
1 kHz/DIV to 500 kHz/DIV
Dispersion ≥(+ and – 2.5 MHz) ≥(+ and – 50 kHz)
0.2 MHz/DIV to 5 MHz/DIV ≥(+ and – 25 MHz) ≥(+ and – 1 MHz)
10 MHz/DIV ≥(+ and – 10 MHz) ≥(+ and – 1 MHz)
IF Attenuation
Range 0 to 51 dB In combinations of 1, 2, 4, 8, 16 and 20 dB.
Accuracy ±0.1 dB/dB
IF GAIN Control
Range ≥50 dB
Display Flatness with IF CENTER 3 dB maximum amplitude variations from Band 1 (10 MHz to 275 MHz) 50 MHz dis-
FREQ at 000 10 MHz to 12.4 GHz. persion.
6 dB maximum amplitude variations from Bands 2 through 8 (275 MHz to 40 GHz]
12.4 GHz to 40 GHz 100 MHz dispersion.
Incidental FM
IF ≤200 Hz Typically 100 Hz. Up to 400 Hz if power
line frequency drops to 48 Hz.
IF + LO ≤300 Hz (at LO fundamental and with
phase lock operation)
Phase Lock
Internal Markers 1 MHz ±0.1% (Control next to OFF posi-
tion.)
INT REF FREQ Range At least 1 kHz but not more than 1.3 kHz
above measured frequency with the INT
REF FREQ control counterclockwise (next to
OFF position.)
Stability; Ref. Osc. ≤1 port in 107.
(Short term FM)
External Phase Lock
Reference Input
Frequency 1 MHz to 5 MHz
Voltage 1 to 5 volts peak to peak.
Display Functions
Dynamic Range
LOG
LIN
SQ LAW
Maximum Input Power
≥40 dB with 8 division display
≥26 dB with 8 division display
Instrument must be inside the dust cover.
≥13 db with 8 division display
-30 dBm for linear operation See Fig. 2-8
+15 dBm diode mixer, power limit
1-2

Characteristic
Tube Type
Phosphor
Accelerating Potential
Graticule Type
Area
Illumination
Unblinking
TIME BASE
Characteristic Performance Requirement Supplemental Information
,
RECORDER Output ≥4 mV per displayed division amplitude of Rear panel connector
signal in LIN made.
Sweep Range 10 µs/div to 0.5 s/div In a 1, 2, 5 sequence
Sweep Accuracy ±3%Measured within the center 8 divisions
VARIABLE Time/Div ≥2.5:1 An uncalibrated control provides continu-
ously variable sweep rates from 10 µs/div
to approximately 1.25 s/div.
Sweep Length 10.5 divisions ±0.2 div.
Sawtooth Output 70 mV to 90 mV (P-P) Rear panel connector
TRIGGERING
Trigger Sensitivity
Internal ≤0.2 division, 20 Hz to 100 kHz
External ≤0.2 volt, 20 Hz to 100 kHz
Maximum Input Voltage 100 volts (DC + peak AC)
POWER REQUIREMENTS
Input Voltage
115-volt range LOW- 90 to 110 VAC
MED- 104 to 126 VAC
HIGH- 112 to 136 VACLine voltage ranges provide regulated DC
230-volt range LOW- 180 to 220 VAC voltages, when line contains less than 2%
MED- 208 to 252 VAC total harmonic distortion.
HIGH- 224 to 272 VAC
Line Frequency 48 to 440 Hz
Input Power 55 watts maximum
CATHODE RAY TUBE
Information
T4910-7-1
P7
Approximately 3.75 kV
internal
8 divisions vertical by 10 divisions horizontal
Construction
Finish
Overall Dimensions [measured
at maximum points]
Each division equals 0.8 cm.
Variable edge lighting
Deflection type, DC coupled
MECHANICAL CHARACTERISTICS
Alluminum-alloy chassis, panel and cabinet
Glass laminate etched-circuit boards
Anodized panel, blue vinyl-coated cabinet
7¼” high, 12½" wide, 23½” long (includes
ENVIRONMENTAL
The following environmental test limits apply when tested
in accordance with the recommended test procedure. This
instrument will meet the electrical performance requirements
given in this section, following an environmental test.
panel cover and carrying handle)
CHARACTERISTICS
1-3

Characteristic
Temperature
Operating
Non-operating
Altitude
Operating
Non-operating
Humidity
Non-operating
Electromagnetic Interference (EMI)
Radiated Interference
Conducted Interference
Vibration
Operating
Shock
Operating and non-operating
Transportation
Package vibration
Package drop
Performance Requirement
–15° C to +55° C
–55° C to +75° C
15,000 feet maximum
Five cycles (120 hours) of
Method 106B
150 kHz to 1000 MHz
150 kHz to 25 MHz
Mil-Std-202C,
Resonant searches along all 3 axes at 0.025
inches, frequency varied fram 10-55 c/s. All
major resonances must be above 55 c/s.
One shock of 30 G, one-half sine, 11 milli-
second duration each direction along each
major axis.
Meets National Safe Transient type of test
when correctly packaged. One hour vibra-
tion slightly in excess of 1 G.
30 inch (18-inches for R491) drop on any
corner, edge or flat surface.
Supplemental Information
Automatic resetting thermal cutout protects
instrument from overheating.
Altitude referred to sea level. Operating
temperature capabilities decline 10 C per
1000 feet altitude above sea level.
May be tested during non-operating tem-
perature test.
Exclude freezing and vibration.
Tested within an electrically shielded enclo-
sure with the CRT mesh filter installed.
Within the limits described in MIL-I-6181D,
Figs. 7, 8, 14 and 16.
Conducted interference through the power
cord.
Instrument secured to vibration platform
during test. Total vibration time, about 55
minutes.
Guillotine-type shocks. Total of 12 shocks.
Package should just leave vibration surface
1-4

SECTION 2
OPERATING INSTRUCTIONS
Introduction
A Spectrum Analyzer is an instrument that graphically
presents a plot of signal amplitude as a function of frequency
for a selected portion of the spectrum. The Type 491 is
designed to provide a spectral display of the frequency
distribution of electromagnetic energy within the frequency
range of 10 MHz to 40 GHz. Signals are displayed as a
spectrum on a CRT screen with signal energy plotted on the
vertical axis against frequency on the horizontal axis.
The Type 491 can be operated from either 115 or 230-volt
nominal line voltage with a range from 90 to 136 VAC or
180 to 272 VAC. Two selector-type connectors on the power
input panel may be positioned to accommodate these volt-
age ranges. The selection assembly also includes two line
fuses which are positioned correctly when the correct selec-
tion is made for either 115 or 230-volt nominal operation.
Fig. 2-3 shows the power input panel on the rear of the
instrument and the voltage range and nominal line voltage
selectors.
This type of display provides the following information;
The presence or absence of signals, their frequencies, fre-
quency drift, relative amplitude of the signals and the nature
of modulation if any, plus many other characteristics.
This section of the manual describes the function of the
front and rear panel controls and connectors, power supply
connection, and a procedure for first time operation, to intro-
duce the operator to the operational functions of the controls.
The remainder af the section then describes operation tech-
nique with some measurement applications and signal
interpretations.
Front Cover and Handle
The front cover furnished with the Type 491 provides a
dust tight seal around the front panel. Use the cover to
protect the front panel when storing or transporting the
instrument, The cover also provides storage for the external
waveguide mixers and other accessories. See Fig. 2-1.
CAUTION
Removing or replacing the dust cover on the instru-
ment may be hazardous, if the” instrument is lifted
out of, or slid into, the dust cover. To remove or
replace the dust cover, set the instrument on a
bench or table, then slide the cover off or on the
instrument. The instrument may also be set on the
front panel cover and the dust cover slipped on or
off the instrument. Do not set the instrument on
the front panel controls.
The handle of the Type 491 can be positioned to carry
the instrument or it can be positioned at several angles to
serve as a tilt-stand. To position the handle, press in at both
pivot points (see Fig. 2-2) and adjust the handle to the
desired position. The instrument may also be set upright
on the rear panel feet for operation or storage.
Voltage Considerations
Fig. 2-1. Accessory storage provided in the front cover of the Type
491
2-1

Fig. 2-2. Handle positioned to provide a stand for the instrument.
CAUTION
The Type 491 should not be operated with these
voltage selector switches in improper positions.
Operation of the instrument with incorrect voltages
will either blow the protective fuses or the instru-
ment will not operate properly.
The Voltage Range Selector located on the rear panel
permits the instrument to operate on line voltages above and
below the nominal 115 or 230 volts. Each selection provides
correct regulation through an overlap voltage range into the
next higher or lower range. It is best to select a range with
its center voltage near your nominal line voltage, thus pro-
viding adequate regulation over a plus and minus devia-
tion of the input line voltage.
The following procedure will prepare the instrument for
operation at your average input line voltage:
1. Remove the cover assembly over the selectors by
unscrewing the two cap screws, then pull the cover with the
attached fuses away from the panel.
2. Pull the Line Voltage Selector out and turn the connector
around to plug it back into the correct position.
3. To change the regulating range, pull out the Range
Selector bar, slide it to the desired range and plug it into
the correct position. Select a range which is centered about
the average line voltage to be applied to the instrument.
See Fig. 2-3.
4. Re-install the cover. Make certain the cover fits firmly
against the rear panel, so the line fuses are seated in their
sockets, and tighten the two cap screws.
5. Before applying power to the instrument, check that the
indicating tabs on the switch bars are protruding through
the correct holes for the desired voltage setup.
2-2
Fig. 2-3. Power panel and selectors.
Spectrum Analyzer Terms
The following glossary of spectrum analyzer terms is pre-
sented as an aid to understanding the terms as they are used
in this manual.
Spectrum Analyzer-A device that displays a graph of the
relative power distribution as a function of frequency, typi-
cally on a cathode-ray tube or chart recorder.
Types: Real-time and non real-time.
A real-time spectrum analyzer performs a continuous
analysis of the incoming signal, with the time sequence of
events preserved between input and output.
A non-real-time spectrum analyzer performs an analysis
of repetitive events by a sampling process.
Methods: Swept front end and swept intermediate fre-
quency.
A swept front end spectrum analyzer is a superheterodyne
spectrum analyzer in which the first local oscillator is swept.
A swept IF spectrum analyzer is a superheterodyne spec-
trum analyzer in which a local oscillator other than the first
is swept.