Tektronix 1L40 User manual

IVIA IN I U A L
Serial Numhef/^ *- ‘
TYPE 1L40
Le^hi
SPECTRUM
ANALYZER
Tektronix, Inc.
S.W. Millikan Way • P. O. Box 5 • Beaverton, Oregon 97 5 • Phone 644- 161 • Cables: Tektronix
7 - 9 4- 1 68

WARRANTY
All Tektronix instruments are warranted
against defective materials and workman
ship for one year. Tektronix transformers,
manufactured in our plant, are warranted
for the life of the instrument.
«-r
Any questions with respect to the war
ranty mentioned above should be taken
up with your Tektronix Field Engineer.
Tektronix repair and replacement-part^
service is geared directly to the field,
therefore all requests for repairs and re
placement parts should be directed to the
Tektronix Field Office or representative
in your area. This procedure will assure
you the fastest possible service. Please
include the instrument Type and Serial or
Model Number with all requests for parts
or service.
Specifications and price change privi
leges reserved.
Copyright © 1968 by Tektronix, Inc.,
Beaverton, Oregon. Printed in the United
States of America. All rights reserved.
Contents of this publication may not be
reproduced in any form without permis
sion of the copyright owner.
®
Type 1L40

Dl«*\.»Y TIME MVtTi V lM -M O * ----------- *■)
«V<L*Y
CONTENTS
Section 1 Specification
Section 2 Operating Instructions
Section 3 Circuit Description
Section 4Maintenance
Section 5 Performance Check and Calibration
Abbreviations and Symbols
Parts Ordering Information
Section 6 Electrical Parts List
Mechanical Parts List 1Information
Section 7 Mechanical Parts List
Section 8 Diagrams
Mechanical Parts List Illustrations
Accessories
ro f- '.1 ,6 , r
( COUMTBp.%
Abbreviations and symbols used in this manual
are based on or taken directly from IEEE Stand
ard 26 ‘‘Standard Symbols for Units", MIL-
STD-12B and other standards of the electronics
industry. Change information, if any, is located
at the rear of this manual.
Type 1L40

OISPERSI'
.2 e
2 5
10 no
RF CENTER I NT REF 1 MH: CAL
FREQ LOCK FREO MARKERS
CHECK > £ $ *5 7 ^
. - . RF INPUT
TEKTRONIX. INC
SERIAL
PORTLAND. OREGON U S-A
. SWEEP INPUT
V MWI OTN K1ICTW
| 4 > ON «»B MATE
f
Type 1L40 ®
Fig. 1-1. Type 114 Spectrum Analyzer

Type 1L40
SECTION 1
TYPE JL40 SPECIFICATION
Change information, if any, affecting this section will be found at the
rear of the manual.
The Type 1L4 Spectrum Analyzer is designed as a plug
in unit for use in Tektronix Type 53 -, 54 -, 55 - and 58 -1
Series Oscilloscopes. It can also be used in a Plug-In Unit
Power Supply (such as the Type 132 or Type 133 Power
Supplies) when the analyzer is provided with either a 1 V
or 15 V sawtooth signal whose base is within ± 2 V of
ground.
When used in the above listed oscilloscopes, the analyzer
displays the relative power distribution of applied signals
on the CRT vertical axis as a function of frequency on the
horizontal axis.
Frequency coverage within the 1.5 GHz to 4 GHz range
is provided by the selection of mixers2 and adapters which
are listed in the accessories section of the manual. These
mixers and accessories must be ordered separately as re
quired.
The electrical characteristics apply over an ambient
temperature range of ° C to 5 ° C provided the environ
mental ambient temperature has been stable for 4 hours
and an initial warmup period of 2 minutes with power
applied is provided for the instrument to stabilize. The
performance check procedure in Section 5 provides a con
venient method to check the operating requirements listed
in this section.
ELECTRICAL CHARACTERISTICS
Characteristic Performance Requirement
RF Center
Frequency Range 1.5 GHz to 4 GHz—See Table 1-1
CW Sensitivity
(S + N = 2N) See Table 1-1
Dial Accuracy Within ± (2 MHz + 1 % of dial read
ing) IF CENTER FREQ control at ,
FINE (IF) control centered and FINE RF
CENTER FREQ control centered.
Local Oscillator
Frequency Range 1.7 GHz to 4.2 GHz
Dispersion
MHz/CM Range .2MHz/cm to lOMHz/cm in a 1-2-5
sequence
Accuracy See Table 1-2
Linearity Within 3% over a 1 centimeter
display
'A Tektronix Type 81A Plug-In Adopter must be used with 58
Series Oscilloscopes.
JThe Type 1L4 is normally supplied with a coaxial mixer, Tektronix
Part No. 119- 96- , which provides a frequency coverage range
from 1.5 GHz to 12.4 GHz.
kHz/CM Range 1 kHz/cm to 5 kHz/cm in a 1-2-5
sequence and zero dispersion
Accuracy Within 3% (with ±2.5 MHz change
in IF center frequency)
Linearity Within 3% over a 1 centimeter
display
Resolution Band
width <1 kHz to >1 kHz; in 11 uncali
brated steps. May be coupled with
DISPERSION control or switched sep
arately.
Spurious Signals
Internal Sources <2X noise amplitude. RF INPUT ter
minated into 5 Q
With Main
Response At least —4 dB at 1 kHz resolution.
DISPERSION Range at kHz/CM posi
tion. RF INPUT terminated into 5 Cl
IF Center Frequency
Control Range
1 kHz/cm to
5 kHz/cm
Dispersion
IF CENTER FREQ FINE
> (+ and -2 .5
MHz) > (+ and —5
kHz)
.2MHz/cm to
5 MHz/cm
Dispersion
> ( + and -2 5
MHz) > (+ and —1
MHz)
1 MHz/cm
Dispersion > ( + and —1
MHz) > (+ and —1 MHz)
IF Attenuation
Range to 51 dB. In 1, 2, 4, 8, 16 and 2 dB
steps.
Accuracy Within ± .1 dB/dB
IF GAIN Control
Range 5 dB or greater
Display Flatness
with IF CENTER
FREQ at
Within 3dB from 1.5 GHz to 12.4
GHz. Within 6 dB from 12.4 GHz to
4 . GHz. Within 5 MHz of RF
Center Frequency.
Incidental FM
IF kHz/CM
Dispersion <2 Hz
LO + IF
Without Phase
Lock < 2 kHz at local oscillator fundamen
tal.
Wih Phase
Lock <3 Hz at local oscillator fundamen tal.
Internal Phase Lock
Internal Markers 1 MHz + .1% (INT REF FREQ control
next to the OFF position.)
l - l

Specifica ion— Type 1L40
ELECTRICAL CHARACTERISTICS (confj
Characteristic Performance Requirement
Pulling Range
of INT REF
FREQ Control
>1 kHz to <1.3 kHz. Measured from
a frequency reference established with
the INT REF FREQ control fully coun
terclockwise next to OFF position.
Stability;
Ref. Osc <1 part in 1 7
External Phase Lock
Reference Input
Frequency Range 1 MHz to 5 MHz
Voltage Required 1 to 5 volts peak to peak
TABLE 1-1
Dynamic Range of
Display Functions
(6 cm display)
LOG >4 dB
LIN >26 dB
SQ LAW >13dB
Video Input
Response <16 Hz to >1 MHz at - 3 dB points
Maximum Input
Power —3 dBm for linear operation -)-15dBm (25 mW) power limit for
diode mixer
TO RECORDER
Output LIN mode: >2m V/cm of displayed
signal amplitude when connected to
6 ohm load.
TABLE 1-2
Frequency Range of Mixers Dispersion/CM
and Minimum CW Sensitivity3 (S -fN = 2N)
Setting Accuracy
1 MHz Within 3%
5 MHz Within 3%
2 MHz Within 5%
1 MHz Within 7%
.5 MHz Within 1 %
.2 MHz Within 15%
Scale Type and Tektronix
Part Number of Mixer RF CENTER
FREQUENCY 1 kHz
RESOLUTION 1 kHz
RESOLUTION
1Coaxial — 119- 96- 1.5-4. GHz —11 dBm -9 dBm
2Coaxial — 119- 96- 3.8-8.2 GHz —1 dBm —8 dBm
3Coaxial — 119- 96- 8. -12.4 GHz -9 5 dBm -7 5 dBm
4 Waveguide4 119- 97- 12.4-18. GHz —9 dBm -7 dBm
5Waveguide1 119- 98- 18. -26.5 GHz —8 dBm —6 dBm
5Waveguide4 119- 99- 26.5-4 . GHz —7 dBm —5 dBm
ENVIRONMENTAL CHARACTERISTICS
The following environment test limits apply when tested in
accordance with the recommended test procedure. Details on
environmental test procedures, including failure criteria, etc.,
may be obtained from Tektronix, Inc. Contact your local
Tektronix Field Office or representative.
Characteristic Operating Requirements
Temperature
Non-operating -4 ° C to +65° C
Operating °C to +5 °C
To meet operating specifications the
instrument must stabilize at an ambient
temperature within this range for 4
hours before operation.
Altitude
Non-operating To 5 , feet
Operating To 15, feet
Shock
Non-operating 3 g's, ’/2 sine, 11 ms duration, 1 shock
per axis. Guillotine-type shocks.
Vibration
Operating 15 minutes each axis at . 15 inches;
frequency varied from 1 -5 -1 Oc/s in
1 minute cycles. Three minutes each
axis at any resonant point. Tested
with instrument secured to vibration
platform.
Transportation
Package Vibration 1 hour at 1 g
Package Drop 3 inches on 1 corner, all edges radia
ting from that corner and all flat sur
faces.
MECHANICAL CHARACTERISTICS
Characteristic Information
Construction
Chassis Aluminum
Front-Panel Aluminum alloy with anodized finish
Circuit Boards Glass-epoxy laminate
1-2
'5 It source impedance. MIXER PEAKING adjusting for optimum signal amplitude.
‘To be used with Waveguide Mixer Adapter Tektronix Part No. 119- 1 4- and cable TNC, coaxial,
Tektronix Part No. 12- 115- .

SECTION 2
OPERATING INSTRUCTIONS
Type 1L40
Change information, if any, affecting this section will be found at the
rear of the manual.
In roduc ion
This section of the manual presents installation instruc
tions, a glossary of Spectrum Analyzer terms, a description
and function of the Type 1L4 front panel controls and con
nectors, a first time operation procedure, and some basic
applications for the analyzer.
Ins alla ion
The Type 1L4 is designed to operate in all Tektronix
Oscilloscopes that accept the letter or 1-series plug-in units.
It may also be used with Tektronix Type 132 or Type 133
Plug-In Power Supply units, with the output displayed on
the CRT of any oscilloscope that has a 1 V or 15 V
sweep output available.
Set the Sweep Voltage selector at the rear panel (see
Fig. 2-4) to the required position for the oscilloscope the
analyzer is to be operated with. If the oscilloscope saw
tooth voltage output is not given on the chart, refer to the
oscilloscope instruction manual.
Insert the Type 1L4 into the plug-in compartment and
fasten the securing latch. Connect a cable or patch cord
between the oscilloscope sweep output and the Type 1L4
L
f.
1 »
> •
if
/
(A) Normal response to a cw signal
J
j
/
f
(B) Effeet of distortion cn a cw signal.
Fig. 2-1. (A) Normal response to a cw signal. (B) Effect of
distortion on a CW signal.
SWEEP INPUT connector. Turn on the oscilloscope power
and allow approximately 2 minutes wgmum—pfilipd for
the instrument to stabilize.
Oscilloscope Modifica ion
If the Type 1L4 is used with early Tektronix Type 541,
541 A, 543, 543A, 545 and 545A oscilloscopes, an undesir
able display distortion and dispersion non-linearity may
be present. This distortion is caused by a portion of the
vertical output signal from the Vertical Signal Out C. F.
V1223A (V1 5 B Type 545), feeding into the Spectrum Ana
lyzer on the +225 V supply. The distortion appears as a
change of dispersion linearity with a change of the analyzer
GAIN control setting and is most noticeable in the narrow
dispersion setting such as 1 kHz/cm. It also appears as
a non-symmetrical response to a CW signal in which the
slope of one side of the signal drops abruptly to the base
line. See Fig. 2-1.
This condition is corrected by changing the +225 volt
supply for the Vertical Signal Out C. F. from the junction
of R1 8 and R1 7 (R1153 and R1152, Type 545) to the
other side of R1 8 (R1153) which is the + 225 V supply.
Fig. 2-2 is a diagram of the circuit involved.
Spec rum 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.
Spec rum Analyzer—A device that displays a graph of
the relative power distribution as a function of frequency,
typically on a cathode-ray tube or chart recorder.
Types: Real-time and non real-time.
A real-time spectrum analyzer performs a continous
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 a repetitive event 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.
Cen er frequency (radio frequency or intermediate fre
quency)—That frequency which corresponds to the center of
the reference coordinate.
2-1

Opera ing Ins ruc ions— Type 1L40
Fig. 2-2. Change as indicated on this partial schematic of the Vertical Amplifier.
Cen er frequency range (radio frequency)—That range
of frequencies which can be displayed at the center of
the reference coordinate. When referred to a control
(e.g., Intermediate Frequency Center Frequency Range) the
term indicates the amount of frequency change available
with the control.
Dispersion (sweep width)—The frequency sweep excur
sion over the frequency axis of the display. Can be express
ed as frequency/full frequency axis, or frequency (Hz)
division in a linear display.
Display fla ness—Uniformity of amplitudes response
over the rated maximum dispersion (usually in units of dB).
Drif (Frequency drift)—Long term frequency changes or
instabilities caused by a frequency change in the spectrum
analyzer local oscillators. Drift limits the time interval that
a spectrum analyzer can be used without retuning or reset
ting the front panel controls (units may be Hz/s, Hz/1° C,
etc).
Dynamic range (on screen)— The maximum ratio of
signal amplitudes that can be simultaneously observed with
in the graticule (usually in units of dB).
Dynamic range (maximum useful)—The ratio between
the maximum input power and the spectrum analyzer sensi
tivity (usually expressed in dB).
Frequency band—The range of frequencies that can
be covered without switching.
Frequency scale—The range of frequencies that can
be read on one line of the frequency indicating dial.
Inciden al frequency modula ion (residual frequency
modulation)—Short term frequency jitter or undesired
frequency deviation caused by instabilities in the spectrum
analyzer local oscillators. Incidental frequency modulation
limits the usable resolution and dispersion (in units of Hz).
Incremen al lineari y—A term used to describe local
aberrations seen as non-linearities for narrow dispersions.
Linear display—A display in which the vertical deflec
tion is a linear function of the input signal voltage.
Lineari y (dispersion linearity)—Measure of the compari
son of frequency across the dispersion to a straight line
frequency change. Measured by displaying a quantity of
equally spaced (in frequency) frequency markers across the
dispersion and observing the positional deviation of the
markers from an idealized sweep as measured against a
linear graticule. Linearity accuracy, expressed as a percenf-
AW
age is within —^ — X 1 %, where AW is maximum po
sitional deviation and W is the full graticule width.
Maximum inpu power—The upper level of input
power that the spectrum analyzer can accommodate with
out degration in performance (spurious responses and signal
compression). Usually in units of dBm.
2-2

Opera ing Ins ruc ions— Type 1L40
Minimum usable dispersion—The narrowest dispersion
obtainable for meaningful analysis. Defined as ten times
the incidental frequency modulation when limited by “ inci
dental frequency modulation" (in units of Hz).
Phase lock—The frequency synchronization of the local
oscillator with a stable reference frequency.
Resolu ion—The ability of the spectrum analyzer to
resolve and display adjacent signal frequencies. The meas
ure of resolution is the frequency separation (in Hz) of two
equal amplitude signals, the displays of which merge at
the 3 dB-down point. The resolution of a given display
depends on three factors; sweep speed, dispersion and the
bandwidth of the most selective (usually last IF) amplifier.
Resolu ion bandwid h—The —6dB bandwidth with
Gaussian response of the analyzer, with the dispersion and
sweep time adjusted for the minimum displayed bandwidth
of a CW signal. Resolution and resolution bandwidth be
come synonymous at very long sweep times.
Op imum resolu ion—the best resolution obtainable
for a given dispersion and a given sweep time. Theoreti
cally or mathematically:
_ . , . dispersion (in Hz)
Optimum resolution = ------------ ; ------ - ------------ r-r
sweep time (in seconds)
Op imum resolu ion bandwid h—The bandwidth at
which best resolution is obtained for a given dispersion
and sweep time.
Theoretically and mathematically:
_ . . ,, Dispersion (in Hz)
Optimum resolution bandwith = .66 — ---------- ; ----- - ----------- r-.
Sweep time (in seconds)
Safe power level—The upper level of input power
that the spectrum analyzer can accommodate without physi
cal damage (usually in units of dBm).
Scanning veloci y—Product of dispersion and sweep
repetition rate units of Hz/unit time.
Sensi ivi y— Rating factor of spectrum analyzers ability
to display signals.
1. Signal equals noise: That input signal level (usually
in dBm) required to produce a display in which the signal
level above the residual noise is equal to the residual
noise level above the baseline. Expressed as: Signal -f
noise = twice noise.
2. Minimum discernible signal: That input signal level
(usually in dBm) required to produce a display in which
the signal is just visible within the noise.
Skir selec ivi y—A measure of the resolution cap-
bility of the spectrum analyzer when displaying signals of
unequal amplitude. A unit of measure (usually in Hz) is the
bandwidth at some level below the 6dB down points.
For example lOdB, 2 dB or 4 dB down.
Spurious response (spurii, spur)—an erroneous display
or signal which does not conform to the indicated frequency
or dial reading. Spurii and spur are the colloquialisms used
to mean spurious response (plural) or spurious response
(singular) respectively. Spurious responses are of the follow
ing type:
1. IF feedthrough—Signal frequencies within the IF pass-
band of the spectrum analyzer that are not converted in
the first mixer but pass through the IF amplifier and produce
displays on the CRT that are not tunable with the RF center
frequency controls.
2. Image response— The superheterodyne process results in
two major IF responses, separated from each other by twice
the IF. The spectrum analyzer is usually calibrated to only
one of these two responses. The other is called the image.
3. Harmonic conversion—The spectrum analyzer will re
spond to signals that mix with harmonics of the local os
cillator and produce the intermediate frequency. Most
spectrum analyzers have dials calibrated for some of these
higher order conversions. The uncalibrated conversions are
spurious responses.
4. Intermodulation— In the case of more than one input
signal, the myriad of combinations of the sums and differ
ences of these signals between themselves and their multi
ples, creates extraneous responses known as intermodu
lation. The most harmful intermodulation is third order,
caused by the second harmonic of one signal combining
with the fundamental of another.
5. Video detection—The first mixer will act as a video
detector if sufficient input signal is applied. A narrow pulse
may have sufficient energy at the intermediate frequency
to show up as intermediate frequency feedthrough.
6. Internal—A spurious response on the display caused by
a signal generated within the spectrum analyzer that is in
no way connected with an external signal.
7. Anomalous IF responses—The filter characteristic of the
resolution-determining amplifier may exhibit extraneous
pass-bands. This results in extraneous spectrum analyzer
responses when a signal is being analyzed.
8. Zero frequency feedthrough-—(zero pip)—The response
produced when the first local oscillator frequency is within
the IF passband. This corresponds to zero input frequency
and is sometimes not suppressed so as to act as a zero
frequency marker.
Sweep repe i ion ra e— The number of sweep excursions
per unit of time. Approximately the inverse of sweep time
for a free-running sweep.
Sweep ime— The time required for the spot in the refer
ence coordinate (frequency in spectrum analyzer) to move
across the graticule. (In a linear spectrum system, sweep
time is Time/Division multiplied by total divisions.)
CONTROLS AND CONNECTORS
The following is a brief description of the operation or
function of these controls and connectors on the front panel.
See Fig. 2-3. A more detailed description is provided later
in this section under general operating information.
DISPERSION Selects the range of the DISPERSION
RANGE control; MHz/CM position provides a
frequency dispersion range from 1
MHz to .2MHz/cm. kHz/CM position
provides frequency dispersion range
from 5 kHz/cm to dispersion.
2-3

Opera ing Ins ruc ions— Type 1L40
OISP CAL— Adjustment
to match the oscilloscope
sweep amplitude to
analyzer dispersion.
OISP BAL— Adjusted to
balance the dispersion
center of the MHz/CM
and the kHz/CM posi
tions of the DISPERSION
RANGE switch.
DISPERSION RANGE—
Selects the MHz or kHz
range of the
SION control.
DISPERSION —
the frequency width or
display window.
COUPLED
— Selects the resolution
bandwidth of the analy
zer. Pull the knob and
turn to uncouple from
the DISPERSION.
VIDEO FILTER— Restricts
the video bandwidth to
reduce high frequency
response and filter out
noise.
GAIN— Varies the ver
tical gain of the Spec
trum Analyzer.
INPUT
SWEEP INPUT
BAWTBOs* micro*
M KM PUT!
TO RECORDER— J a c k
provides an output for
recorders, etc.
VIDEO INPUT— BNC con
nector to apply video
input signals to be dis
played as a convention
al (time domain) dis
play.
VERTICAL D IS PL A Y—
Selects display mode.
LOGarithmic, LINear,
SQuare LAW (power)
or VIDEO.
LOCK CHECK— Push the
button to check and set
phase lock operation.
I NT REF FREQ— Varies
internal reference fre
quency over a range of
approximately 1 kHz
and selects the reference
frequency source (inter
nal or external).
Phase Lock Connector—
Used to apply an exter
nal reference frequency
to the phase lock circuits
or to provide an outlet
Tor the internal 1 MHz
reference fre q u e n c y
markers which may be
used to calibrate the dis
persion.
MIXER PEAKING— Opti
mizes the conversion ac
tion of the mixer.
RF INPUT— Coaxial re
ceptacle which accepts
various mixers. Input
signals < — 3 dBm re
commended, — 15 dBm
maximum for all mixers.
SWEEP IN PU T— BNC
connector for applying
the sawtooth waveform
(1 V or 15 V) from
the associate oscillo
scope.
RF CENTER FREQ— Con
trol tunes the local os
cillator and the dial.
Dial indicates the center
frequency of the display
when the IF CENTER
controls are cen-
POS— Controls the ver
tical position of the dis-
play.
CAL— A d j u 11 m e n t »o
calibrate the midrange
position of the IF CEN
TER FREQ.
FINE— 1 turn control for
fine adjustment of tho
IF center frequency.
IF CENTER FREQ— 1
turn control that varies
the IF center frequency
of the display.
IF ATTEN dB— Series of
calibrated attenuation
steps.
/ FINE RF FREQ— Fine tun-
/ ing adjustment of the
/ local oscillator to set
j phase lock
rm uM Aa iv z ii
.LUo-iiyuNrr
IF
ATTEN dB
2-4
Fig. 2-3. Function of front panel controls and connectors.

Opera ing Ins ruc ions— Type 1L40
DISPERSION
COUPLED
RESOLUTION
DISP CAL
DISP BAL
IF ATTEN dB
GAIN
IF CENTER
FREQ
FINE
CAL
VIDEO FILTER
Selects the dispersion (frequency width)
of the display in conjunction with the
DISPERSION RANGE switch. Dispersion
ranges from lOMHz/cm to 1 kHz/cm
in a 1-2-5 sequence, plus an additional
position of approximately zero disper
sions are provided. When the DISPER
SION selector is in the position, the
analyzer functions as a fixed tuned re
ceiver. This provides a display that
shows the time domain characteristics
of modulation within the resolution
bandwidth capabilities of the analy
zer.
Selects the analyzer resolution band
width. Eleven selectable ranges, from
more than 1 kHz to less than 1 kHz are
provided. The normal resolution for a
given dispersion is generally obtained
with the RESOLUTION control coupled
to the DISPERSION selector.
A screwdriver adjustment to calibrate
the MHz/cm dispersion.
Adjusted to balance the dispersion cen
ter (center frequency point) of the
MHz/CM and kHz/CM position of the
DISPERSION RANGE switch.
Series of six toggle switches to provide
calibrated IF attentuation in 1 dB steps
from 1 dB to 51 dB.
A variable control of the analyzei IF
gain, plus a variable control over the
video INPUT signal amplitude.
A 1 turn control that shifts the IF center
frequency. Provides a ±1 MHz adjust
ment in the 1 MHz/cm dispersion posi
tions, a ± 2 5 MHz adjustment of the
center frequency, through the 5 MHz/cm
to .2 MHz/cm positions, and a ±2.5
MHz adjustment through the 5
kHz/cm to 1 kHz/cm DISPERSION posi
tions.
A one turn control, that operates in
conjunction with the IF CENTER FREQ
control, to provide a fine adjustment
of the IF center frequency. Provides ±1
MHz adjustment for the .2 MHz/cm
through the 1 MHz/cm dispersion posi
tions and ±5 kHz for the 1 kHz/cm
through the 5 kHz/cm DISPERSION
positions.
With the IF CENTER FREQ control
centered, it calibrates the IF center fre
quency to 2 MHz.
With the switch in the up position the
video bandwidth is restricted to reduce
high frequency video components, such
as noise, from distorting the display
and enables easier evaluation of sig
nal modulation when viewing signals
near minimum resolution.
VERTICAL
DISPLAY
RF CENTER
FREQ
FINE RF CEN
TER FREQ
MIXER
PEAKING
LOCK CHECK
INT REF FREQ
1 MHz MARKERS
OUT-EXT REF
FREQ IN
TO RECORDER
Selects logarithmic, linear or square
law display for the frequency domain
displays, and VIDEO for a time domain
display. In the LOG position,
signal display amplitude is logarith
mic, with a dynamic range >4 dB. In
the LIN position, a signal display
amplitude is linear with a dynamic
range >26 dB. In the SQ LAW position
signal amplitude is a square law func
tion or the display amplitude is a func
tion of signal power. The SQ LAW
dynamic range is >13dB.
The VIDEO position connects the INPUT
connector to the vertical amplifier of
the plug-in oscilloscope.
Tunes the RF center frequency from 1.5
GHz to 4 GHz. With the IF CENTER
FREQ control in the position, the RF
CENTER FREQ dial indicates the center
frequency of the display.
A fine adjustment of the RF local oscil
lator frequency. Especially useful in
tuning the oscillator to a phase lock
condition with the reference frequency.
A control used to optimize the conver
sion action of the first mixer. The con
trol is adjusted to optimize mixer
conversion for any fixed center fre
quency setting. This must be done for
each dispersion window.
A pushbutton switch that applies the
output of the phase lock amplifier to
the vertical display system, providing
a visual indication to the operator.
The operator can then check a particu
lar lock point or establish a phase lock
of the 1st local oscillator to the stable
reference frequency.
Phase Lock Operation on page 2-1 ,
describes the procedure.
A switch and control. The control varies
the internal 1 MHz reference frequency
over a range of approximately 1 kHz.
With the control in the OFF position, the
internal reference frequency is turned
off, and an externally applied signal to
the EXT REF FREQ IN (1 MHz MARKERS
OUT) connector becomes the reference
frequency.
A BNC connector that provides 1 MHz
marker output signals to calibrate the
dispersion. With the INT REF FREQ con
trol in the OFF position, an external sig
nal between 1 MHz and 5 MHz (1 to 5 V
peak to peak) applied to the connector
becomes the reference frequency for
phase lock operation.
Signals on the display may be record
ed by plugging into the TO RECORDER
output. The output is linear and equals
2 mV or more per centimeter of
displayed signal amplitude (in the LIN
mode) into a 6 ohm load.
2-5

Opera ing ins ruc ions— Type 1L40
RF INPUT—Coaxial receptacle which connects through
either a Coaxial Mixer and low loss coaxial cable to the
signal source or (if above 12.4 GHz), through a Waveguide
Mixer Adapter and a two-foot coaxial cable to one of
three Waveguide Mixers which connect to the signal source.
See Signal Applications.
Signal Applica ion
The frequency of an RF signal determines how it will be
applied to the RF INPUT. Signals in the frequency range of
1.5 GHz to 12.4 GHz are applied through a low loss coax
ial cable, such as RG-9B/U, to a Coaxial Mixer Assembly
which is installed into the input receptacle. Signals in the
12.4 GHz to 4 GHz range are applied to an external
Waveguide Mixer which connects through a two-foot coax
ial cable and a Waveguide Mixer Adapter to the input
receptacle. The Waveguide Mixer Adapter replaces the
Coaxial Mixer Assembly in the input receptacle.
Mixers and accessories may be ordered separately as
required. The selection of mixers and adapters for the fre
quency coverage is as follows:
1.5 GHz to 12.4 GHz — Plug-In Coaxial Mixer, Tektronix
Part No. 119- 96- .
12.4 GHz to 4 GHz—Waveguide Mixer Adapter, Tek
tronix Part No. 119- 1 4- ; Coaxial Cable, Tektronix Part
No. 12- 115- and one of the following Waveguide.
Mixers.
Band Wave
guide
(El A
designa
tion )
Frequency
Range Flange
Type Tektronix
Part
Number
Ku WR62 12.4 GHz to
18. GHz UG-419/U 119- 97-
KWR42 18. GHz to
26.5 GHz UG-595/U 119- 98-
Ka WR28 26.5 GHz to
4 . GHz UG-599/U 119- 99-
The Mixer Adapter or Coaxal Mixer may be removed
from the input receptacle by turning the retainer ring in
either direction. To replace either assembly, push the
adapter or coaxial mixer against the spring until the flange
bottoms, then turn until the latch snaps to hold the unit in
place.
Signal input power to the analyzer should not exceed
—3 dBm. Signals above this level overload the 1st mixer
and/or the 1st IF stage and generate spurious' signals on
the display. Add at least 1 dB of attenuation to the input
when the signal begins to compress (no increase of signal
amplitude wth an increase of signal level). A conversion
chart (Fig. 2-5) may be used to calculate input signal level.
CAUTION
Signals stronger than + 1 5 dBm applied to the
input or mixer will damage or burn out the mixer
diodes.
Mismatches between the signal source and the RF INPUT
connectors may be caused by signal source output imped
ance, long coaxal cables, etc. These mismatches will ad
versely affect display flatness. When optimum flatness is
desired and signal strength is adequate, a 5 Q attenuator
pad of approximately 6 to 1 dB should be added between
the signal source and the input to the mixer. The addition
of the attenuator will minimize reflections and optimize
display flatness. '
NOTE
Quality of attenuator used is of vital importance.
It is suggested that attenuators such as Tektronix
Part Numbers 11- 85- (1 dB), 11- 86-
(2 dB) and 11- 87- (4 dB) or equivalent
be used.
FIRST TIME OPERATION
Preliminary
If the instrument has not been installed into the plug-in
compartment of the oscilloscope as directed under Installa
tion, proceed as follows:
a. Set the Sweep Voltage selector at the rear panel (see
Fig. 2-4) to the correct position (1 V or 15 V) for the
oscilloscope being used. Some Tektronix Oscilloscopes and
their sweep voltage output are listed on the back panel of
the instrument. If your oscilloscope is not listed, check the
specifications given in the oscilloscope instruction manual
for the voltage swing of the sawtooth out signal.
Fig. 2-4. Rear panel of the Type 1L4 showing sawtooth selector.
b. Insert the Type 1L4 into the plug-in compartment and
fasten the securing latch.
c. Turn on the oscilloscope power, connect a patch cord
between the Oscilloscope Sweep output and the Type 1L4
SWEEP INPUT connector. Allow approximately 2 minutes
warmup period for the instrument operation to stabilize.
d. Set the Type 1L4 and plug-in oscilloscope front panel
controls as follows:
DISPERSION RANGE MHz/CM
DISPERSION—COUPLED Controls coupled together
RESOLUTION and in the lOMHz/cm
position
2-6

Opera ing Ins ruc ions— Type 1L40
IF ATTEN dB
IF CENTER FREQ
FINE
POS
VIDEO FILTER
VERTICAL DISPLAY
GAIN
FINE RF CENTER FREQ
INT REF FREQ
MIXER PEAKING
All switches in OFF position
Centered ( )
Midrange
Centered
OFF
LIN
CCW
Centered
OFF OR EXT REF FREQ IN
CCW
Plug-in Oscilloscope
Time/Cm 5 ms
Triggering Adjusted for a free
running sweep
1. Turn the Intensity control clockwise until a trace is
visible, then adjust the Focus and Astigmatism controls for
optimum trace definition.
2. Position the trace to the horizontal center and to the
bottom line of the graticule with the Position controls.
3. Adjust the Scale Ilium control for the desired graticule
illumination.
4. Using a signal generator, apply a low amplitude
signal (between —6 and—3 dBm) within the frequency
range of the instrument to the Coaxial or Waveguide Mixer.
5. Adjust the GAIN control for a moderate noise level
( .5 cm) on the display, then rotate the RF CENTER FREQ
control through the dial range. Note the rate and direction
of movement (left to right or right to left) of the signals
across the screen.
6. Tune the dial to the frequency of the applied input
RF signal.
7. Adjust the MIXER PEAKING control for optimum signal
amplitudes.
8. Adjust the GAIN and/or IF ATTEN dB switches for a
signal amplitude on the display of approximately 4 centi
meters.
9. Tune the signal to the extreme left graticule line with
the RF CENTER FREQ control. Note the dial reading. Tune
the signal to the extreme right graticule line and note the
dial reading. The difference between dial readings is the
total dispersion window for this 1 centimeter display. Tune
the signal to the center of the screen and switch th DISPER
SION-COUPLED RESOLUTION selector to the 5MHz/cm
position. It should decrease to ’/2 the total dispersion
noted with the DISPERSION selector in the lOMHz/cm posi
tion. Tune the signal to the center of the screen.
1 . Tune the IF CENTER FREQ control through its range.
Note that all signals move across the screen in the same
direction and the same amount. This control will shift the
IF center frequency approximately and —25 MHz with
the DISPERSION controls set to 5MHz/cm. Tune the IF
CENTER FREQ control to its centered ( ) position.
11. Change the DISPERSION selector to .5MHz/cm posi
tion. Adjust the FINE IF CENTER FREQ control. Note the
frequency range of this control. This control will shift the
IF center frequency approximately -f- or — 1 MHz with the
DISPERSION selector set to ,5MHz/cm position.
12. Switch the plug-in oscilloscope Time/Cm switch
between the .1 s and .1 ms positions. Note the change in
signal amplitude and the resolution. Return the Time/Cm
selector to the 5 ms position
2-7

Opera ing Ins ruc ions— Type 1L40
(A) Large and small beat signal displays. LOCK CHECK
button is depressed while the RF CENTER FREQUENCY con
trol is slowly tuned.
(B) LOCK CHECK button depressed while RF FINE FREQ
control is adjusted. Display DC level w ill shift as control is
adjusted. Select a beat mode near the screen center for best
operation.
Signal feet
?/
1 thro jgh
[
(C) Null point. Oscillator will now lock in phase with the ID) LOCK CHECK button released. Normal display of a phase
reference frequency. Release LOCK CHECK button. locked condition. Center desired signal on screen with the IF
CENTER FREQ controls.
Fig. 2-6. Lock check displays
13. Set the DISPERSION selector to 5 kHz, switch the
DISPERSION RANGE switch to the kHz/CM position, then
decrease the DISPERSION to kHz/cm keeping the signal
centered on screen with the IF CENTER FREQ control. Un
couple the RESOLUTION control and turn clockwise. Note
that the displayed bandwidth increases as the resolution
bandwidth is increased. The resolution bandwidth may be
varied from approximately 1 kHz to 1 kHz. Return the
RESOLUTION control to the coupled position with the DIS
PERSION selector.
14. Turn the INT REF FREQ switch to the INT position.
15. Push the LOCK CHECK button and turn the RF CENTER
FREQ control slowly through the signal frequency. Note
the phase lock beat signals between the tunable local oscil
lator and the Internal Reference Frequency oscillator as
the display blooms then snaps into the phase lock opera
tion (Fig. 2-6). See Phase Lock Operation on page 2.
16. With the LOCK CHECK button depressed, adjust the
FINE RF CENTER FREQ control. Note the beat frequency
display, as the control is varied, and the vertical displace
ment of the display baseline. This baseline vertical shift
is the change in the output DC level of the phase lock ampli
fier. Note the zero beat signal compression at the extreme
position of this control compared to the amplitude near
the center. Phase lock condition should be set with the DC
level midrange between the two extreme positions noted
above on the CRT as the FINE IF CENTER FREQ control was
rotated. Adjust for phase lock operation and release the
LOCK CHECK button.
17. Set the DISPERSION selector to 5 kHz, switch the
DISPERSION RANGE switch to the kHz/CM position, then de
crease the DISPERSION to 5 kHz/cm, keeping the signal
centered on screen with the IF CENTER FREQ control. If the
signal should suddenly shift off screen, phase lock operation
has probably been lost. A slight adjustment of the FINE RF
CENTER FREQ control will usually restore the phase lock con
dition and return the signal on screen.
2-8

Opera ing Ins ruc ions— Type 1L40
18. Uncouple the RESOLUTION control and turn the con
trol clockwise. Note the bandwidth increase as the resolution
bandwidth is increased. The resolution bandwidth may be
varied from approximately 1 kHz to 1 kHz. Return the
RESOLUTION control to the coupled position with the DIS
PERSION selector.
e. Set the DISPERSION control to the 5MHz/cm position.
Position the signal to the graticule center with the Oscillo
scope Horizontal Position control. If the signal is more
than 1 centimeter from the sweep center, it should be center
ed with the internal Sweep Center adjustment R2 4. See
Calibration section.
Fron Panel Calibra ion Adjus men s
Three screwdriver adjustments provide calibration adjust
ments for the DISPERSION, IF CENTER FREQ and the DIS
PERSION RANGE balance. These front panel adjustments
must be recalibrated, if the Type 1L4 is shifted to another
oscilloscope, to compensate for differences in sawtooth
amplitudes. It is also advisable to check the adjustments
periodically during regular use. Adjustment and a calibra
tion check may be performed as follows:
3. DISP-BAL Adjus men
a. Tune the RF signal to the screen center as described in
step 2.
b. Adjust the DISP BAL for minimum signal shift as the
DISPERSION RANGE selector is switched between the MHz/
CM and kHz/CM positions. (Start the balance adjustment
with the DISPERSION RANGE switch in the kHz/CM position
and the DISPERSION in the 5 MHz - 5 kHz position, then
decrease the DISPERSION to the .2 MHz - 2 kHz position.)
1. Balance and Calibra ion Check
a. Set the INT REF FREQ control to OFF position.
b. Tune a signal on screen with the RF CENTER FREQ con
trol.
c. Tune for minimum signal shift as the DISPERSION
RANGE is switched from MHz/CM to kHz/CM positions.
d. With the DISPERSION RANGE selector at the MHz/CM
position, adjust the IF CENTER FREQ control for minimum
signal shift as the DISPERSION selector is switched through
the 1 MHz to .2 MHz positions.
e. Set the DISPERSION RANGE selector to kHz/CM posi
tion and the DISPERSION to 5 kHz/cm.
f. Center the signal in the graticule area with the Horizon
tal Position control. Check the signal position on the sweep.
The signal should locate within ±1 cm of the sweep center
with the sweep extending over the 1 centimeter width of
the graticule. Front panel calibration is required if this
requirement is not met. Perform the following adjustments
if front panel calibration is required.
NOTE
These adjustments interact, and must be performed
in sequence.
Final adjustment is made with the DISPERSION RANGE
selector in the kHz/cm position and the DISPERSION in the
1kHz position. Fine adjustment of the DISP BAL (with the
IF CENTER FREQ set to ) permits dispersion changes
from lOMHz/cm to 1 kHz/cm with minimum shift in signal
position on the screen.
NOTE
If dispersion balance cannot be achieved by the
above procedure, the instrument requires internal
adjustment. Refer to the Calibration section of the
manual.
4. DISP-CAL Adjus men
a. Set the Analyzer front-panel controls as follows:
IF ATTEN dB
IF CENTER FREQ
DISPERSION RANGE
DISPERSION-COUPLED
RESOLUTION
VERTICAL DISPLAY
INT REF FREQ
All OFF
(centered)
kHz/CM
5 (inner ring)
SQ LAW
CCW (next to OFF posi
tion, but not switched
to OFF OR EXT REF
FREQ IN position)
2. IF CENTER FREQ CAL Adjus men
a. Set the IF CENTER FREQ control to and center the
FINE control. Center DISP BAL and the IF CENTER FREQ-
CAL adjustments. Set the DISPERSION RANGE switch to
the MHz/CM position and the DISPERSION control to 5 MHz/
cm position.
b. Apply a stable RF signal to the RF INPUT connector.
Adjust the GAIN control to obtain a usable signal ampli
tude.
c. Adjust the RF CENTER FREQ and the FINE RF CENTER
FREQ controls for minimum signal shift as the DISPERSION
RANGE is switched between the MHz/CM and the kHz/CM
positions.
d. With the DISPERSION RANGE in the MHz/CM position,
adjust the IF CENTER FREQ-CAL for minimum signal shift
as the DISPERSION control is switched through the MHz
(1 MHz - .2 MHz) positions.
b. Connect the 1 MHz CAL MARKERS OUT signal through
a coaxial cable to the RF INPUT connector.
c. The display will probably have one set of calibration
markers superimposed with another set of markers. (One
set of markers only when Waveguide Mixer Adapter is
used.) If this is the case, adjust the RF CENTER FREQ controls
to bring the tunable markers into horizontal alignment with
the feed-through or fixed markers.
d. Adjust the DISP-CAL for 1 marker/centimeter. See Fig.
2-7. Use the Horizontal Position control or the IF CENTER
FREQ control to align the markers to the graticule lines.
Dispersion is calibrated over the center 8 centimeters of the
display.
e. Remove the 1 MHz CAL MARKER signal from the RF
INPUT connector.
This concludes the front-panel calibration adjustments for
the Type 1L4 .
®2-9

Opera ing Ins ruc ions— Type 1L40
Fig. 2-7. 1 MHz Markers Output signal (phase lock reference)
applied to the RF INPUT connector to check dispersion calibration.
GENERAL OPERATING INFORMATION
RF Cen er Frequency Tuning
The dial and the analyzer are tuned through the frequency
range of each scale by the RF CENTER FREQ control. The
dial frequency calibration is accurate to within zb (2 MHz -f
1% of the dial reading) when the FINE RF CENTER FREQ
and the IF CENTER FREQ controls are centered. As the
dial knob is rotated clockwise, the dial tape increases in
frequency and true signals (see spurious responses) travel
across the screen from left to right.
The RF CENTER FREQ control is supplemented by a FINE
RF CENTER FREQ control that provides a fine tuning adjust
ment, through a limited frequency range, on either side of
the dial frequency. This provides a fine tuning adjustment
to establish phase lock operation.
MIXER PEAKING Con rol
The front-panel MIXER PEAKING control provides an ad
justment to improve the over-all sensitivity of the Spectrum
Analyzer. Its action is broad; therefore it can usually be
set to an optimum setting and left unless there is a large
change in the RF center signal frequency, or a change in
RF dial scale.
Phase Lock Opera ion
The 1st local oscillator can be phase locked to either
an internal 1 MHz reference oscillator or an external fre
quency source when it is applied to the EXT REF FREQ IN
connector. Locking the local oscillator to a stable fre
quency, such as the internal 1 MHz crystal controlled
oscillator, reduces the local oscillator incidental frequency
modulation and frequency drift. This allows narrow disper
sion and high resolution settings for signal analysis.
The frequency range for an external reference frequency
is 1 MHz to 5 MHz, and amplitude limitations are 1 to 5
volts peak to peak. The external signal for phase lock
operation is applied to the phase lock circuit when the
INT REF FREQ control is turned ccw to the OFF OR EXT
REF FREQ IN position.
The LOCK CHECK pushbutton applies the output of the
phase lock amplifier to the vertical display system. The
output of the phase lock amplifier contains the following:
(1) Beat frequency signals between the local oscillator and
the reference frequency when the oscillator frequency is
very close to a lock with the reference frequency. (2) A DC
reference level of the output amplifier. This DC level
changes as the FINE RF CENTER FREQ control is rotated and
shifts the local oscillator frequency a slight amount. It also
affects the vertical position of the display baseline. Thus,
by depressing the LOCK CHECK button and slowly turning
the FINE RF CENTER FREQ control, the operator will observe
the baseline of the display shift until a lock mode is
reached. The baseline will then remain stationary over a
portion of the control range as the circuit holds the local
oscillator locked to the reference frequency. Turning the
control further causes the circuit to lose its lock and the
baseline jumps from the locked position.
Beat frequency signals are usually displayed just before
aT ock point is reached. See Fig. 2-6B. However, through
part of the Type 1L4 frequency range, the phase lock
operation may be very positive and the local oscillator
will jump from one lock mode to another without displaying
the beat signals or the smooth shift of the display baseline
between lock points.
When the DC operating level of the phase lock amplifier
reaches either extreme (top or bottom of the graticule area),
the operation of the amplifier becomes non-linear and com
pression of the beat signals will be noted. Phase lock
operation becomes difficult to achieve. The displayed DC
level therefore aids in setting a phase lock condition within
the linear operating range of the phase lock amplifier.
Part of the input signal is coupled through and displayed
when the LOCK CHECK button is pushed. This permits the
operator to re-establish a particular lock point that may be
lost because of oscillator drift or other reasons. The opera
tor adjusts the FINE RF CENTER FREQ control while observ
ing the display until the signal is again at a particular lock
point (the point where the baseline or the signal position locks)
is set.
The local oscillator fundamental frequency locks in 1 MHz
steps, (from one lock mode to the next) when the internal
1 MHz reference frequency is used for phase lock operation.
This produces gaps as much as 5 MHz in the upper fre
quency scale, where the upper harmonic of the local oscilla
tor is used. Continuous tuning through these gaps is
provided by the INT REF FREQ control. Rotating the control
through its range pulls the crystal controlled reference fre
quency approximately 1 kHz. This is sufficient to shift the
local oscillator frequency through these gaps and maintain
phase lock operation.
Phase lock operation is established as follows:
1. Tune the desired signal to the center of the display with
the RF CENTER FREQ control.
2. Depress the LOCK CHECK button and adjust the FINE
RF CENTER FREQ control for a lock indication within the
center (4 cm) of the graticule. If the lock indication or beat
2-1

Opera ing Ins ruc ions— Type 1L40
signal is outside the linear operating range of the amplifier
(baseline of display at the top or bottom of the graticule),
center the display with the FINE RF CENTER FREQ control
then adjust the RF CENTER FREQ control to shift the signal
towards a beat mode (Fig. 2-6). Adjust the FINE RF CENTER
FREQ control, while observing the desired signal, for phase
lock operation then release the LOCK CHECK button.
3. Decrease the dispersion to open the screen. Keep the
signal centered on screen with the IF CENTER FREQ controls.
If the local oscillator should lose its lock condition, when
the dispersion settings are 1 kHz or less, the signal will
disappear from the screen. A slight adjustment of the FINE
RF CENTER FREQ control will usually return the signal to
the display.
4. If two or more high frequency (upper scale) signals are
to be resolved, they can be moved on the display without
losing phase lock by adjusting the INT REF FREQ con
trol.
Ver ical Display Modes
The dynamic range of the displayed signal is dependent
on the mode position of the VERTICAL DISPLAY switch. For
example: The LOG (4 dB full screen) position will accentu
ate the side lobes of a signal while the SQ LAW position
will de-emphasize the side lobes. Fig. 2-8 illustrates the
effect of each display mode or each position of the
VERTICAL DISPLAY switch.
The LOG position increases the dynamic range of the
display. Large amplitude signals are attenuated more than
small amplitude signals. This type of display approximates
a logarithmic response curve and is most effective when
there are large signal amplitude differences.
The LIN (linear) position provides linear signal amplifica
tion, so relative amplitude measurements may be performed
over the full 6 cm graticule height.
The SQ LAW (power) position provides a display that is
approximately proportional to the square of the input
2-11
Fig. 2-8. Vertical display modes showing an amplitude modulated display. Video mode show the modulation signal.

Opera ing Ins ruc ions— Type 1L40
signal amplitude and may be used to compare the power
level between signals. Small amplitude differences are
accentuated when the analyzer is operated in this mode.
In the VIDEO mode, the spectrum display is grounded.
Signals applied to the front-panel VIDEO INPUT connector
will be displayed on a conventional (time versus signal
amplitude) display. An uncalibrated GAIN control provides
variable sensitivity adjustment. Maximum sensitivity is ap
proximately .1 volt per centimeter.
The impedance of the VIDEO INPUT circuit is approxi
mately 5 ohms; therefore high-impedance probes should
not be used to couple signals to the VIDEO circuit.
Video Fil er Opera ion
The video filter restricts the video bandwidth. The filter
is useful in applications where the envelope of a pulsed RF
spectrum is desired (Fig. 2-9) or in some cases it may im
prove the display resolution, see Fig. 2-23. It does, how
ever, restrict the usable sweep rate because of the filter time
constant. The sweep rate is usually reduced to about 5 ms/
cm or slower when the filter is used.
Dispersion
Dispersion is the swept frequency width, or screen
window. The frequency excursion of the frequency axis of
the display is usually expressed as frequency per centimeter.
The dispersion for the Type 1L4 is adjustable from 1 MHz/
cm to 1 kHz/cm in a 1, 2, 5 sequence with an added zero
dispersion position for fixed frequency operation.
Dispersion accuracy is a function of the IF CENTER FREQ
control position and the DISPERSION RANGE switch setting.
See Characteristics section. The kHz/CM range is more
accurate than the MHz/CM range because of narrow swept
frequency width. When a high degree of accuracy is desired
for a particular frequency setting, the front-panel DISP-CAL
may be used to calibrate the dispersion for a specific IF
CENTER FREQ control setting. The procedure is as follows:
1. Adjust the front panel controls for the desired display.
2. Turn the INT REF FREQ control ccw but not OFF.
Apply the 1 MHz CAL MARKERS OUT signal to the RF INPUT
connector. This should provide a picket fence display. See
Fig. 2-7.
3. If a coaxial mixer is being used and two sets of
markers appear, a confusing display may be avoided by
adjusting the RF CENTER FREQ control a slight amount to
identify the feed-through or fixed markers. The tunable
markers should be turned so they coincide with the fixed
markers to eliminate confussion in the display.
4. Calibrate the display by adjusting the DISP-CAL for
the correct markers per centimeter, or read the dispersion
directly from the marker picket fence.
5. Remove the 1 MHz markers from the RF INPUT and
reconnect the signal. Perform the desired dispersion meas
urement.
6. After the measurement, recalibrate the dispersion as
described under Front Panel Adjustment.
Resolu ion and Dispersion
Resolution is the ability of the spectrum analyzer to dis
play adjacent signal frequencies discretely. The measure
of resolution is the frequency separation (in Hz) of two
equal amplitude signals when the notch or dip between
these signals is 3dB down. The resolution for a given dis
play is a function of sweep speed, dispersion and band
width of the most selective (usually the last IF) amplifier
in the signal path.
Resolution bandwidth is approximately the —6dB band
width (with Gaussian response) of the analyzer, with the
dispersion and sweep time adjusted for the minimum dis
played bandwidth to a CW signal. Resolution and resolu
tion bandwidth become synonymous at very long sweep
times.
As the analyzer sweep rate is increased, the amplitude of
a CW signal decreases and the bandwidth increases; which
2-12

Opera ing Ins ruc ions— Type 1L40
signifies that both the sensitivity and resolution of the ana
lyzer have been degraded by the increased sweep rate.
The loss of the analyzer sensitivity due to sweep rate and
the dispersion can be expressed mathematically as:
where the S/S is the ratio of the effective sensitivity to the
analyzer measured sensitivity, at very slow sweep times or
with zero dispersion.
D is the dispersion in hertz
B is the —3 dB bandwidth of the analyzer in hertz
T is the sweep time in seconds, or — — is the scan
ning velocity.
These same variables also determine the resolution of
the analyzer. The loss in resolution can be expressed as
follows:
Where R/R is the ratio of the effective resolution of the
analyzer to the analyzer measured resolution bandwidth
at very slow sweep speeds. R is somewhat arbitrary and
is taken as the displayed width of the CW signal at the
—6dB point.
The best resolution for a given dispersion and sweep
Dispersion (in Hz)
time is expressed as: Sweep Time (in s) See Spectrum
Analyzer definitions.
The resolution of the Type 1L4 Spectrum Analyzer is
optimized for most settings of the DISPERSION selector when
the RESOLUTION control is in the coupled position. Resolu
tion, however, can be varied from approximately 1 kHz
to less than 1 kHz by uncoupling the RESOLUTION control
and adjusting it as an independent function of the DISPER
SION selector.
To adequately resolve pulsed spectrum information, the
resolution bandwidth of the analyzer should be on the
order of 1/1 of the side lobe frequency width or the
reciprocal of the pulse width. The RESOLUTION control
is usually set, after the sweep rate has been adjusted, for
optimum main lobe detail. See Fig. 2-1 .
Selec ing he Sweep Ra e
The sweep rate for wide resolution coupled settings is
usually set just above the visual flicker setting; however,
as the DISPERSION is decreased the sweep rate will begin
to affect the resolution and sensitivity of the analyzer as
described under Resolution. Therefore, as the DISPERSION
settings are reduced the sweep rate should also be reduced
to maintain sensitivity and resolution.
With the DISPERSION control set to , the analyzer func
tions as a fixed tuned receiver. The analyzer then displays
time domain characteristics of the signal modulation within
the bandwidth capabilities of the analyzer. Sweep time
can now be set to examine the modulation pattern.
Timing information such as pulse repetition rate may be
obtained by triggering the sweep on the signal source (In
ternal Mode) and switching the oscilloscope Time/Cm
control to a calibrated sweep time that will permit time
measurement between the modulation pulses. See Fig. 2-11.
Triggering he Sweep
For most applications the oscilloscope triggering is set
for free run operation; however, there are applications
where it may be desirable or necessary to trigger the
1
11
| i i
1Lr_L
wm J * *
i
TIME/CM = 1 ms/CM
_ , .. . Number of CM measured ^ ... .
Pulse repetition time = ------------------------------ - ----------- XTim e/CM
Number of pulses
— X 1 ms = 2 ms, PRF — ~ ~ or 5 Hz
3 2
Fig. 2-1 . Frequency spectrum of a pulse modulated signal.
®2-13
Fig. 2-11. Measuring pulse repetition time.

Opera ing Ins ruc ions— Type 1L40
Fig. 2-12. To trigger the analyzer from the display requires .2 cm
of signal. Tune the spectrum null point away from the sweep starting
point with the RF CENTER FREQ control.
display; for example, at dispersion, or when slaving the
Type 1L4 to a recorder.
The display may be triggered internally by setting the
oscilloscope Source switch to the Int position and adjusting
the triggering controls to trigger on the display. The oscillo
scope requires approximately 2 millimeters of signal ampli
tude to trigger satisfactorily. It may therefore be necessary
to adjust the FINE RF or IF CENTER FREQ control to shift
the sweep start away from a spectrum null point. See Fig.
2-12.
If the signal is time related to the power supply line fre
quency, it is best to trigger the oscilloscope on the Line
frequency.
---------------------------FREQUENCY
Fig. 2-13. Formation of a spectrum. F is the fundamental or carrier
frequency, Fi and F: are the modulating frequencies.
(A) CENTER FREQ
DISPERSION
MODE
2 GHz
5 kHz/CM
LIN
This display shows: Carrier Frequency 2 GHz, modulating
frequency (1.8cm X 5 kHz I = 9 kHz.
% of modulation = (2 X —— X 1 ) = 5 %
4.8
(B) Same as A but resolution bandwidth increased so that
modulation is barely discernible.
(C) Over modulated signal produces extra sidebands. LOG
mode.
Fig. 2-14. Spectrum showing series of AM signals.
2-14