Tektronix 7S12 User manual

Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon
070-1244-00
Product Group 42
Ibktronix-
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
7S12
TDR/SAMPLER
S/N B020000-UP
INSTRUCTION MANUAL
97077 Serial Number
First Printing NOV 1971
Revised MAR 1985

Copyright ®1971 Tektronix, Inc. All rights reserved.
Contents of this publication may not be reproduced in any
form without the written permission of Tektronix. Inc.
Products of Tektronix, Inc. and its subsidiaries are covered
by U.S. and foreign patents and/or pending patents.
TEKTRONIX, TEK, SCOPE-MOBILE, and are
registered trademarks of Tektronix, Inc. TELEQUIPMENT
is aregistered trademark of Tektronix U.K. Limited.
Printed in U.S.A. Specification and price change privileges
are reserved.
INSTRUMENT SERIAL NUMBERS
Each instrument has aserial number on apartel insert, tag,
or stamped on the chassis. The first number or letter
designates the country of manufacture. The last five digits
of the serial number are assigned sequentially and are
unique to each instrument. Those manufactured in the
United States have six unique digits. The country of
manufacture is identified as follows:
BOOOOOO Tektronix, Inc., Beaverton, Oregon, USA
100000 Tektronix Guernsey, Ltd., Channel Islands
200000 Tektronix United Kingdom, Ltd., London
300000 Sony/Tektronix, Japan
700000 Tektronix Holland, NV, Heerenveen,
The Netherlands

7S12
TABLE OF CONTENTS
SECTION 1CHARACTERISTICS Page SECTION 4MAINTENANCE (cont) Page
Description 1-1 Readout Symbol Adjustment
Electrical Characteristics 1-1 C> and <3 4-2
Physical Characteristics 1-5 Repackaging for Shipment 4-3
Environmental Characteristics 1-5
SECTION 5PERFORMANCE
SECTION 2OPERATING INSTRUCTIONS CHECK/ADJUSTMENT
General Information 2-1 Introduction 5-1
Installation 2-1 Equipment Required 5-1
Controls and Connectors 2-1 Performance Check and Adjustment
First Time Operation 2-5 Record and Index 5-2
Voltage Reflection Coefficient 2-7 7S12 Checks 5-3
Impedance Scale Overlays 2-8 S-6, S-52 and 7S12 System Checks 5-5
Time or Distance Measurements 2-8 S-5, S-54 and 7S12 System Checks 5-7
High Resolution 2-11 Adjustment Procedure 5-9
Single Sweep Operation 2-11
PRESET Calibration 2-12
Application Connections 2-12 SECTION 6ELECTRICAL PARTS LIST
Using TDR Slide Rule 2-14
SECTION 7DIAGRAMS AND CIRCUIT BOARD
ILLUSTRATIONS
SECTION 3CIRCUIT DESCRIPTION Symbols and Reference Designators
Introduction 3-1 Schematic Diagrams and Component
Vertical Circuits Block Diagram 3-1 Board Locations
Horizontal Circuits Block Diagram 3-4
Circuit Description 3-10
SECTION 8MECHANICAL PARTS LIST
SECTION 4MAINTENANCE Mechanical Parts List
Mechanical Parts List IllustraTron
Introduction 4-1 Accessories
Lubrication 4-1
Troubleshooting 4-1
Tape Dial Removal 4-2
Tape Dial Installation 4-2
Tape Dial Alignment 4-2
Revised NOV 1984 I

fIMC
DC OFFStT *1V TtMt/OIV
mVOlTS/OIV
SaSAMPLINO HEAD
Fig. 1-1. 7S12 TDR/Sampler unit,

SECTION 1
CHARACTERISTICS
Description
The 7S12 is adual-purpose plug-in unit for measurement
of recurring fast-rise signals or for time-domain
reflectometry. It occupies two compartments (one vertical
input and one horizontal input) of aTektronix 7000-series
oscilloscope.
The 7S12 has two compartments for plug-in heads. The
left-hand compartment (labeled SAMPLING on the 7S12
front panel) accepts Tektronix S-series Sampling Heads.
The type of sampling head selected determines the vertical
input characteristics of the 7S12. The right-hand compart-
ment (labeled PULSE GENERATOR) accepts S-series pulse
generators, trigger recognizers or trigger count-down heads.
The 7S12 has the following features: The vertical de-
flection factors, i.e., millivolts/div and millirho/div, are
from 2to 500 in a1-2-5 sequence. The time/div is cali-
brated from 20 ps/div to 1ys/div in a1-2-5 sequence. The
DC OFFSET control offsets the display in a±1 Vrange.
The HI RESOLUTION switch reduces the waveform noise
and jitter by signal averaging with acorresponding re-
duction of sweep rate. The LOCATE switch increases the
time/div and intensifies aportion of the display to locate
the time window relative to the total waveform. Front
panel outputs include OFFSET OUT (±10 Vrange),
VERTical SIGnal OUT and SWEEP OUT. Modes of sweep
operation include SINGLE sweep, REPetitive sweep,
MANual scan and EXTernal sweep IN.
The TIME-DISTANCE scale is calibrated for round-trip
time measurements of 0to 10 ys and one-way distance
measurements up to 4900 feet (1500 meters) air dielectric
or 3200 feet (975 meters) polyethylene dielectric. The
POLY scale may be calibrated for transmission lines which
have avelocity of propagation equal to or greater than that
of polyethylene. The Time-Distance scale may be ordered
with distance calibrated in metric units.
SECTION 1
ELECTRICAL CHARACTERISTICS
Characteristic Performance Requirement Supplemental Information
Deflection Factor
Accuracy Within 3%
Range 2units/div to 500 units/div irt a1-2-5
sequence. Units/div are labeled on the
sampling head.
Units/Div VARIABLE Range 'Provides continuous coverage from 1
to 770 units/div (mV or mp)
pCAL Range Allows calibrated reflection coefficient
(p) with pulse generators supplying
from 200 mV to 1Vpulse amplitude.
DC OFFSET Range Offsets display at least -M Vto —1 V.
OFFSET OUT
Range At least -MO Vto -10 V. OFFSET
OUT =10X (DC OFFSET) within 2%
Source Resistance 10 kfi within 1%

Characteristics—7S 1
2
Characteristic Performance Requirement Supplemental Information
VERTical SIGnal OUT
Amplitude 200 mV/div of signal display within
2%
VARIABLE control must be in CAL
position.
Source Resistance 10 within .5%
SWEEP OUT
Amplitude 1V/div of horizontal deflection within
2%
Range 0Vto greater than 10V
Source Resistance 10 kfi within 1%
TIME/DIV
Accuracy Within 3%
Range 20 ps/div to 1ps/div in a1-2-5
sequence
Time/Div VARIABLE Range Provides continuous coverage to at
least 8ps/div.
Display Modes
SINGLE Sweep Each sweep is initiated by pushing and
releasing the START button.
REPetitive Sweep Normal resolution: sweep rate is
continuously variable from at least 1
sweep in 20 ms to less than 1sweep in
5s.
HI RESOLUTION: sweep rate is con-
tinuously variable from at least 1
sweep in 200 ms to less than 1sweep
in 50 s.
MANual Sweep Any portion of the display may be
observed by manual operation of the
SCAN control.
EXTernal Input
Deflection Factor 1V/div within 5% to at least 15 V/div
Input Resistance 100 kfi within 10%
Maximum Input Voltage 150 V(DC +peak AC)
FINE (ZERO SET) Range Moves an unmagnified waveform at
least .9 div.
1-2

Characteristics—7S 1
2
ELECTRICAL CHARACTERISTICS
SYSTEM PERFORMANCE WITH S-6 AND S-52
Characteristic Performance Requirement Supplemental Information
Risetime 35 ps or less for the incident step, 45 ps
or less for the displayed reflection from a
short-circuited 1ns test line
Pulse Amplitude At least +200 mV into 50 0,
Input Impedance Nominal 50
Jitter Less than 10 ps (without signal averaging)
Aberrations Not more than +7%, —7%, total of 10%
P-P within the first 1.8 ns of the step edge
with the reference level at 1.8 ns from the
step edge; not more than +2%, —2%, total
of 4% P-P after 2.5 ns from the step edge
with the reference level at 0.3 ps from the
step edge.
TIME-DISTANCE Scale Time scale indicates round-trip time.
Distance scales (AIR and POLY
dielectrics) indicate one-way distance.
The usable TIME-DISTANCE ranges
for TDR measurements are limited by
the S-52 pulse duration.
Accuracy TIME scale within 1% of full scale. Distance scales are calibrated for the
nominal velocity of propagation of the
AIR and POLY dielectrics.
TIME-DISTANCE Multiplier
X.1 XI X10
TIME Range .1 ps 1AS lOps
i
Maximum of about 150
ns one-way cable delay.
AIR Dielectric Distance 49 feet 490 feet 4900 feet
Range 15 meters 150 meters 1500 meters
1
Maximum of about 150
feet (46 meters) cable
length.
POLY Dielectric Distance
Range
32 feet 320 feet 3200 feet
9.75 meters 97.5 meters 975 meters
Maximum of about 100
feet (30 meters) cable
length.
1-3

Characteristics—7S 12
Characteristic Performance Requirement Supplemental Information
PRESET Permits the calibration of the POLY
scale for dielectrics having avelocity
of propagation between those of poly-
ethylene and air.
Characteristic
Risetime
Pulse Amplitude
Input Impedance
Jitter
Aberrations
TIME-DISTANCE Scale
Accuracy
TIME Range
ELECTRICAL CHARACTERISTICS
SYSTEM PERFORMANCE WITH S-5 AND S-54
Performance Requirement
1.5 ns or less for the displayed reflection
from ashort-circuited test line
At least -t400 mV into 50
Less than 20 ps (without signal averaging)
Not more than -r4%, —6%, total of 10%
P-P within the first 17 ns of the step: not
more than +1.5%, —1.5%, total of 3%
after 17 ns.
TIME scale within 1% of full scale.
Supplemental Information
Nominal 50 ^2
Time scale indicates round-trip time.
Distance scales (AIR and POLY
dielectrics) indicate one-way distance.
TDR events out to 20 /ts (round-trip
time) may be viewed. This corresponds
to 9800 feet (3000 meters) in AIR
dielectric and to 6400 feet (1950
meters) in POLY dielectric. This
distance is the sum of the displayed
time window (10 ps maximum) and
the TIME scale readout (10 ps maxi-
mum).
Distance scales are calibrated for the
nominal velocity of propagation of the
AIR and POLY dielectrics.
TIME-DISTANCE Multiplier
X.1 XI X10
.1 ps 1ps 10 ps
An additional time range may be
viewed.
1-4

Characteristics—7S 12
Characteristic Performance Requirement Supplemental Information
AIR Dielectric Distance
Range
49 feet 490 feet 4900 feet
15 meters 150 meters 1500 meters
An additional distance range may be
viewed (in terms of time).
POLY Dielectric Distance
Range
32 feet 320 feet 3200 feet
97.5 meters 9.75 meters 975 meters
An additional distance range may be
viewed (in terms of time).
PRESET Permits the calibration of the POLY
scale for dielectrics having avelocity
of propagation between those of poly-
ethylene and air.
PHYSICAL CHARACTERISTICS
Characteristic Performance Requirement
Finish Anodized aluminum front panel
Weight
Net 4.7 lb
Domestic Shipping 7.2 lb
Export Packed 11.7 lb
Dimensions
Length (ex-
cluding knobs) 13.383 in
Width 5.464 in
Height 4.988 in
ENVIRONMENTAL CHARACTERISTICS
Characteristic Performance Requirement
Temperature
Operating 0°C to -t50°C
Non-operating -40°C to -i-65°C
ENVIRONMENTAL CHARACTERISTICS (cont)
^
1
Characteristic Performance Requirement
Altitude
Operating To 15,000 feet
Non-operating To 50,000 feet
Vibration
Operating 0.025 in P-P displacement at 55 Hz
Shock
Operating To 20 g's, 1/2 sine, 11 ms duration
Humidity
Non-operating
and Operating 5cycles (120 hours) to 95% relative
humidity referenced to
MIL-E-16400F (Paragraph 4.5.9
through 4.5. 9.5.1, Class 4)
Transportation Qualifies under National Safe
Transit Committee test procedure
1A, Category II
1-5

7S12
SECTION 2
OPERATING INSTRUCTIONS
General Information
This section of the manual provides the basic infor-
mation required for operation of the 7S12 TDR/Sampler
including installation, front panel information, and First
Time operation instructions.
The 7S12 is acombined horizontal and vertical,
double width sampling unit for use in any 7000-series
Oscilloscope. The 7S12 accepts two plug-in heads, a
sampling head and agenerator head, which determine
the characteristics of the TDR system. If atrigger recog-
nizer head such as the S-53 is used in the 7S12 gener-
ator head compartment, general purpose sampling can be
accomplished using the S-53 to trigger the 7S12 sweep.
INSTALLATION
The 7S12 can be powered by any Tektronix 7000-
series Oscilloscope. Since the 7S12 is acombined hori-
zontal and vertical unit, it must be installed in the
center two compartments of a7000-series Oscilloscope
containing 4 compartments, or into the right two com-
partments of a7000-series Oscilloscope containing 3
compartments. Avertical unit such as a7S11 can be
installed in the left compartment of either Oscilloscope
for dual-trace operation. Then J641 (a fixed shoe
connector) provides astrobe connection to the 7S1 1.
Three methods of installation are shown in Fig. 2-1.
Part Ashows the 7S12 installed in the center two com-
partments of a7504 Oscilloscope. The 7S11 and samp-
ling heads are shown for TDR and dual-trace use. Part
Bshows the 7S12 installed with the 7S11, 7M11, and
sampling heads for General Purpose Sampling and dual-
trace use. Part Cshows the 7S12 installed with the
7S11 and sampling heads in the 7403N (or 7503)
3-compartment Oscilloscope for TDR and dual-trace use.
For General Purpose sampling, use the 7M11 outside the
Oscilloscope, and the sampling heads as shown for
installation B.
Installing the 7S12 in the Oscilloscope
Insert the 7S12 into avertical and ahorizontal com-
partment of a7000-series Oscilloscope (See Fig. 2-1).
Slide the 7S12 completely into the two compartments.
The 7S12 will lock into place with aspring loaded latch
knob.
To install ahead into one of the two 7S12 compart-
ments, insert the head into the compartment with the
latch knob free to move until completely in the 7S12.
Then push the latch to lock the head in place. To
remove, pull the latch knob away from the panel, then
pull the unit from the 7S12.
Mating
The 7S12 vertical output amplifier gain must be
matched to the oscilloscope deflection factor for
accurate gain measurements. The VERT GAIN control, a
screwdriver adjustment on the front panel, adjusts the
vertical output amplifier gain of the 7S12. Adjustment
of this VERT GAIN control using the Oscilloscope Cali-
brator as asignal source is shown under First Time
Operation in this section of the manual.
The 7S12 horizontal gain must be matched to the
horizontal deflection factor of the oscilloscope. Hori-
zontal gain is set by the SWEEP CAL adjustment lo-
cated on the 7S12 front panel. The adjustment is made
for full rotation of the SCAN control for 10 divisions
with the MAN button pushed in. The HORIZ POS
adjustment is used to position the spot on the CRT.
The HORIZ POS control is also located on the front
panel. The adjustment method is discussed in First Time
Operation.
CONTROLS AND CONNECTORS
Abrief description of the function and operation of
the controls and connectors of the 7S12 follows. Fig.
2-2 shows the 7S12 front panel with asampling head
and apulse generator installed.
Vertical Section
DC OFFSET ±1 VPositions the display vertically by
applying an internal offset voltage
REV. B, JULY, 1976 2-1

Operating Instructions—7S1
2
Pulse Generator Heads
such as S-50, S-52,
and S-54
Choice of
Sampling Heads
S-1 through S-6
(A) Installed in 7504 Oscilloscope for TOR arxl dual trace use.
Trigger Recognizer
Heads such as
S-51 and S-53
Choice of
Sampling Heads
S'1 through S-6
(B) Installed in 7504 Oscilloscope for General Purpose sampling with 7M1 1Delay Line and 7S1 1for dual trace use,
Pulse Generator Heads
such as S'50, S-52,
and S-54
Choice of
Sampling Heads
S-1 through S-6
(C) Installed in 7503 (or 7403N) for TOR and dual trace use. For General Purpose Sampling, add the 7M11 (a passive unit) external to
the Oscilloscope and use Heads as in IB).
Fig. 2-1. 7S12 Installation Information.
2-2 (S

Operating Instructions—7S1
2
VAnlAMt CAl IM
TIME/OIV
riNC
DC OFFSET tIV
S-6 SAMPLING HEAD
LOOP THPO
losioa
2V/DfV lOkO
TOR/SAMPLER
Fig. 2-2. 7S12 front panel.
of up to ±1 volt to the sampling
head. The input signal zero refer-
ence (related to the CRT) is the
DC offset voltage instead of
ground. This control permits all
portions of a±1 volt input signal
to be positioned through the
CRT graticule area vertically even
at adeflection factor of 2units
per division.
FINE Provides fine control of the DC
Offset function. Control is con-
centric with the DC OFFSET ±1
Vcontrol.
Units/Div Selects calibrated deflection fac-
tors from 500 units/div to 2
units/div in a1, 2, 5sequence.
The actual deflection factor is
determined by the sampling head
used and the "mV", "mp"
switch.
VARIABLE Provides uncalibrated, continu-
(CAL IN) ously variable deflection factor
23

Operating Instructions—7S12
mV and mp
pushbuttons
pCAL
HIGH RESOLUTION
VERT GAIN
OFFSET OUT
±10 V10 kf2
VERTSIG OUT
.2 V/DIV 10kJ2
Horizontal Section
TIME/DISTANCE
Control
FINE Control
LOCATE Switch
from less than 0.65 to at least
2.5 times the calibrated setting.
Concentric with the Units/Div
switch. PRESET Switch
Permit selecting either mV/Div or and Control
mp/Div as the basic unit of verti-
cal measurement.
Screwdriver adjustment permits
calibrating the display for use TIME/DIV Switch
with pulse amplitudes between
200 mV and 1V.
Reduces the displayed noise by
approximately 10 times and slows
the display rate by 10 times.
Screwdriver adjustment permits
calibration of the vertical output
amplifier gain to match the oscil-
loscope CRT deflection factor.
Miniature connector provides an
output voltage proportional to
the internal DC offset voltage.
Unless otherwise specified on the
sampling head front-panel, the
open circuit voltage at this con-
nector is ten times the internal
DC Offset voltage as set by the
DC OFFSET control. The output
resistance is 10 kJ2.
Miniature connector providing a
real-time reproduction of the sam-
pling display. Permits anon-
sampling type oscilloscope to
monitor the facsimile signal. Out-
put resistance is 10 kfZ.
VARIABLE (CAL
IN) Control
TIME/DISTANCE
Multiplier
HORIZ POS
Control
SWEEP CAL
Control
SWEEP OUT
Jack
Crank-handle drive positions the
display over the full TIME/
DISTANCE range selected by the
Multiplier switch.
Variable SCAN
The FINE control provides a10% Control
position range with a10 turn
potentiometer for calibration of
initial step.
Provides adisplay of the location
of the position control setting on
adisplay equal to twice the nor-
mal position range. The width of REP Pushbutton
abrightened portion approximates
the TIME/DIV setting and starts
at apoint on the displayed sweep
corresponding to the setting of
the TIME/POSITION control.
Provides ameans of calibrating
the POLY scale to accommodate
the dielectric constants between
Poly and air.
A9position switch used in con-
junction with the 3position
Multiplier switch. The 27 combi-
nations of TIME/DIV and Multi-
plier switches provide 15 different
calibrated TIME/DIV settings,
from 20 ps/div to 1jus/div, in a
1, 2, 5sequence.
Provides continuously variable,
uncalibrated time/div by reducing
the time/division. Concentric with
the Multiplier and TIME/DIV
controls.
Provides aX10, XI, X.1 range
multiplier for the TIME-
DISTANCE tape dial. Switches
Time/Distance ranges. Concentric
with the TIME/DIV and VARI-
ABLE (CAL IN) controls.
Screwdriver adjustment for setting
the horizontal position of the dis-
play.
Screwdriver adjustment that sets
the horizontal gain to match the
deflection factor of the oscillo-
scope.
Pin jack providing an output vol-
tage proportional to the hori-
zontal display amplitude. Provides
1Vfor each division of display
with an output resistance of 10
kf2.
Provides an internal voltage for
adjusting the scan rate in the
REP mode and SINGLE mode.
Provides the manual scan voltage
in MAN mode and can be used
to calibrate the horizontal gain.
In the EXT mode this control
serves asavariable attenuator.
Provides repetitive scanning of the
display. The scan rate is adjusted
using the variable SCAN control.
2-4

Operating Instructions—7S12
Provides single scan display for
photographic use. Scan rate is ad-
justed using the variable SCAN
control.
Starts the single scan display after
the SINGLE pushbutton is pushed.
Provides manual operation of the
scan function using the variable
SCAN control.
Allows scanning the display using
an external signal. In this mode
of operation, the variable SCAN
control serves as a variable gain
control.
Pin jack provides the input facil-
ity for externally scanning the
display. Requires 1Vfor each
division of display into an input
resistance of 100 kS2.
The three position switch is located
near the top rear edge of the Hori-
zontal card inside the 7S12. The
Correction Memory circuit provides
automatic base line correction for
pulse generator heads and trigger
heads.
On (front position) This switch position is used when
automatic base line correction is
desired for trigger heads installed in
the Pulse Generator compartment
for DC stabilized sampler applica-
tions.
Normal This is the normal operating switch
(center position) position. The Correction Memory
circuit provides automatic base line
correction only for pulse generator
heads installed in the Pulse Gen-
erator compartment.
SINGLE
Pushbutton
START
Pushbutton
MAN Pushbutton
EXT INPUT
Pushbutton
EXT INPUT Jack
Correction Memory
Switch
Procedure
1. Insert the 7S12 TDR/Sampler into the center two
compartments of the 7504 Oscilloscope. Any Tektronix
7000-series Oscilloscope may be substituted for the
7504. (See the installation information in this section.)
2. Install the S-52 in the 7S12 Pulse Generator com-
partment.
3. Install the S-6 in the 7S12 Sampling compartment.
4. Set the controls as follows:
7504 Indicator Oscilloscope
AIntensity CCW
BIntensity CCW
Vertical Mode Right
Horizontal Mode A
7S12 with S-6 and S-52
(Two center compartments, the right vertical and
the Ahorizontal compartments)
TIME-DISTANCE dial
Multiplier
TIME/DIV
VARIABLE
FINE (ZERO SET)
REP
SCAN
LOCATE
mV
mV/Div
DC OFFSET (& FINE)
0
X10
1ns
CAL IN
Fully clockwise
pushed in
Midrange
pushed in
pushed in
100
Midrange
5. Turn the Oscilloscope Power on. After about 5
minutes warmup time, advance the AIntensity until a
free running trace is observed. Center the trace on the
CRT with the 7S12 DC OFFSET control.
Adjust VERT GAIN
Off (rear position) This switch position disables the
Correction Memory circuit. This
position is also used when a
sampling head gate balance control
is being adjusted.
FIRST TIME OPERATION
6. Install aSMA 1ns coaxial cable (supplied with
the S-52) with a50 termination connector to the S-6
Loop Thru (upper) connector. Install aSMA (3 mm) to
BNC adapter on the Loop Thru (lower) connector. Use
aBNC cable to connect the 0.4 V(into 50 Q,) Calibra-
tor Output signal to the adapter installed on the S-6
Loop Thru (lower) connector.
General Information
This First Time Operation procedure shows the basic
operation of the 7S12 controls for TDR operation using
the S-52 Pulse Generator Head and the S-6 Sampling
Head. Additional operating information follows the First
Time Operation procedure.
7. Use asmall screwdriver to adjust the VERT GAIN
(on the 7S12 front panel) for asquare wave display of
4divisions. Note that the sweep is free running and its
repetition rate is determined by the setting of the
SCAN control. Remove the BNC cable and the BNC to
SMA (3 mm) adapter.
S2-5

Operating Instructions—7S1
2
Adjust SWEEP CAL &HORIZ POS
8.
Push the MAN button and turn the SCAN control
fully counterclockwise. Aspot should be observed at
the left edge of the graticule. If not, use asmall screw-
driver to adjust the HORIZ POS control (located on the
7S12 front panel) to position the spot at the left edge
of the graticule. Rotate the SCAN control to its fully
clockwise position. The spot should have moved exactly
ten divisions to the right of its previous position. Use a
small screwdriver to adjust the SWEEP CAL control
(located on the 7S12 front panel) for ten divisions of
movement when the SCAN control is turned from one
extreme to the other. Readjust the HORIZ POS as
necessary in this adjustment. Push the REP pushbutton
and set the SCAN control to its approximate midposition.
9.
Use 50 nsemi-rigid cable (u-shaped, supplied with
the 7S12) to connect the S-52 Pulse Output signal to
the Loop Thru (lower) connector on the S-6. The upper
Loop Thru connector is connected to a1ns semi-rigid
coaxial cable in part 6.
NOTE
Connectors at both ends of the coaxial cable
should be firmly connected to mating connectors
or accessories. Tighten slightly more than finger
tight using a5/16 inch wrench. Agood connec-
tion is necessary to minimize reflections at the
junctions of connectors.
10.
Observe the S-52 waveform shown in Fig. 2-3A. The
positive pulse in the center of the screen is used in the S-52
to automatically reset the tunnel diode bias for the next
pulser trigger from the 7S12. The S-52 output pulse is not
visible on the screen due to the additional 7S12 trigger
delay with X10 Multiplier.
Change the 7S12 Multiplier setting to XI and observe
the S-52 output pulse shown in Fig. 2-3B. The width of the
pulse top will determine the maximum time (round trip
time) of the reflection from the leading edge that can be
observed with XI. Fig. 2-3C shows the leading edge of the
pulse on the X.1 position of the Multiplier. Use the lowest
Multiplier range setting to observe areflection.
Observing Risetime
11.
To observe the leading edge of the S-52 Output
Pulse, set the TIME-DISTANCE Multiplier to X.1, and
the TIME/DIV to a sweep rate desired up to 20 ps; Use
the Time-Distance knob to position the leading edge of
the pulse to the center of the graticule. Use the 20 ps
sweep rate for risetime display (Incident risetime) arx)
(A)
1(X) 1pS
\
i
1
^I
c5
:1
(Bl
100 mV :190n i
1
•
i
io6 mv :1)nS
1244-01 1
Fig. 2-3. First Time Operation showing Multiplier setting (Al X10,
(Bl XI and (C) X.1.
use the mV/Div VARIABLE knob to set the leading
edge for 5divisions on the graticule. See Fig. 2-4. Note
that the 5-division points on the display are about one
Tf time from reference point 1for 0% level and about
one Tf time from reference point 2for the 100% level.
2-6 REV JAN 1985

Operating Instructions—7S1
2
Fig. 2-4. Risetime measurement IT,) information (upper) and typi-
cal risetima display (lower). Note that Reference point 1and 2are
selected at the corners where the rate of change of the slope is maxi-
mum (where the radius of curvature is least).
12.
To observe the reflected edge (Reflected risetime)
of the S-52 Output Pulse, remove the 50 termination
from the end of the 1ns semi-rigid coaxial cable con-
nected to the S-6 Loop Thru (upper) connector, and
connect ashort-circuit termination to the cable.
Change the Time-Distance knob to move the Pulse
leading edge to the left and off the CRT until the re-
flected edge display is centered on the CRT. See the
typical waveform in Fig. 2-5. The Reflected risetime is
measured in the same way as the Incident risetime.
FINE (ZERO SET)
Turn the FINE (ZERO SET) control and note that
the control will change the horizontal position of the
display. This control can be used as a fine position con-
trol, or can be used by the operator as azero set for
the TIME-DISTANCE dial. Since the reflected edge
Fig. 2-5. Reflactad ritotima display.
represents the end of the 1ns line where the test line
will be attached, adjust the FINE control so the reflec-
ted edge of the pulse is displayed at the center of the
screen (or areference point selected by the operator)
with the TIME-DISTANCE dial set to zero.
13. Change the TIME/DIV to .1, and change the
Time-Distance knob to position the reflected pulse to
the graticule centerline. See the typical waveform in Fig.
2-6A.
14. The negative reflection is caused from the short
circuit termination. This reflection therefore has avoltage
reflection coefficient of about —Ip or —1000 mp.
15. Remove the short circuit termination. Change the
DC OFFSET control to position the display to show
the positive reflection due to the open line. This reflec-
tion as shown in Fig. 2-6B has avoltage reflection co-
efficient of about +1 por -FlOOO mp.
CAL Adjustment
16. Terminate the 1ns semi-rigid coaxial line with a
50 SI termination. Change the TIME/DIV to .2 ns, and
change the Time-Distance knob to position the leading
edge of the pulse to the center of the graticule. Push
the mp button in, and set the mp/Div to 200.
17. With asmall screwdriver, adjust the pCAL con-
trol for a5division displayed step amplitude.
Voltage Reflection Coefficient
As shown in Fig. 2-6, the reflection coefficient p
(rho) is taken from the top of the incident pulse from
IB 2-7

Operating Instructions—7S12
Fig. 2-6. Diiplay of ashort circuit tarminatad lina (A) and untar-
minatad lino (B).
the pulse generator. Apositive reflection (referenced
from the top of the incident pulse) indicates an imped-
ance greater than the impedance of the line. Anegative
reflection indicates an impedance less than the imjjed-
ance of the line. With aknown p, resulting from aresis-
tive load, the resistance of the load can be found by
the following formula:
Rl =Zo
Impedance Scale Overlays
For each mp amplitude discontinuity displayed on the
CRT, the indicated impedance Ri_ can be calculated by the
above formula. Impedance Scale Overlays are available for
the CRT face showing direct reading of the Impedance at
each graticule setting for 6different mp/Div settings. Three
overlays are required to cover 5, 10, 20, 50, 100 and 2(X)
mp/Oiv settings. Two sizes of three overlays each are
included in the 7S1 2accessories.
To use the Impedance Scale Overlays, select the overlay
for the mp/Div setting you are using, and install it in posi-
tion over the graticule on the Oscilloscope; read the
impedance values under the proper mp/Div scale listing for
the amplitude of the reflection. Note that the graticule
center is used as the 50 SI reference line.
In addition to impedance values, the overlays include a
POLY distance scale in cm using the 100 ps/Div time. For
further information, read the Time or Distance Measure-
ment Procedures later in this section.
TIME OR DISTANCE MEASUREMENTS
General Information
The TIME-DISTANCE dial setting can be considered to
be adelay in time before the operation of the display time
(except in LOCATE). The display time has 3multipliers or
ranges, which also multiply the TIME-DISTANCE dial read-
ing. The display time includes aTIME/DIV (magnification
of 1to 500 times), and aTIME/DIV VARIABLE control
which provides avariable uncalibrated time by reducing the
time per division.
When the LOCATE button is depressed to release (out
position), the displayed time is twice the time (magnifi-
cation of 0.5) labeled at the CCW position of the TIME/
DIV switch. Then the TIME/DIV switch controls the length
of the bright portion of the display to show the position on
the display relative to the pulse edge. The Oscilloscope
readout of the Time/Div will show the correct reading when
the LOCATE button is depressed (in position).
Time/Div
Fig. 2-7 shows the TIME/DIV settings for the Multiplier
settings. The Multiplier changes the scale factor of the
TIME-DISTANCE dial readings. The TIME-DISTANCE dial
readings are not generally used when in LOCATE. The
LOCATE position display is intensified by the Display Win-
dow time as controlled by the TIME/DIV and the TIME/
DIV VARAIBLE controls. The Display Window time be-
comes the normal display time when the LOCATE button
is depressed.
Fig. 2-8 shows the Display Window time for two settings
of the TIME/DIV control and three settings of the TIME-
DISTANCE dial.
With the TIME/DIV setting CON (.1 ps/Div), shown in
Fig. 2-8A, the TIME-DISTANCE dial is set for aMultiplier
of XI. Note that adelay from zero time to 1ps dial setting,
with the additional time of the Display window results in a
total of 2ps from the zero time. Accordingly, the duration
of the Pulse Output from the Pulse Generator head must be
at least 2ps. Use of the Multiplier of XI with the S-52 is

Operating Instructions—7S 12
Multiplies
Time-Distance
dial reading
VARIABLE control
(reduces Time/Oiv)
TIME/DIV
control
Multiplier
control
Fig. 2-7. Time/Div control information.
limited due to the short duration S-52 output pulse, shown
in Fig. 2-3B. Also, use of the X10 Multiplier is restricted
due to the 7S12 pulser trigger delay and the S-52 short
pulse. Using the Multiplier of X10 with apulse generator
head with along pulse duration (for example S-54 with a
pulse duration of 25 ps) the total time of about 20 ps is
available.
As the TIME/DIV is changed toward the CW positions,
the Display Window time is less and the total time from
zero is less, as shown in Fig. 2-8B.
Time or Distance Measurement Procedures
Procedures for Time or Distance measurements can be
shown in three general methods;
(A) On the screen, where measurement points are lo-
cated ashort distance apart.
(B) Between two points on the TIME-DISTANCE
dial.
(C) From dial zero, on the TIME-DISTANCE dial.
(A) On the Screen. The distance between two measure-
ment points or discontinuities on the screen may be deter-
mined more readily than from the TIME-DISTANCE dial.
Measure the time separation on the CRT screen, note the
horizontal calibration (TIME/DIV) and use Table 2-1 to
determine the distance separation. This table is an aid in
making measurements for short distances, where the TIME-
DISTANCE dial's resolution is limited. The column "Separ-
TABLE 2-1
On Screen Time vs. Distance (Separation)
Time is for round trip, and Distance is
for one way, in inches or cm/div.
TIME/DIV Separation in
AIR
Separation in
POLY Separation in PRESET (Spans
AIR to POLY)
20 ps/Div .12 inch/Div
.3 cm/Div
.08 inch/Div
.2 cm/Div
50 ps/Div .3 inch/Div
.75 cm/Div
.2 inch/Div
.5 cm/Div
100 ps/Div .6 inch/Div
1.5 cm/Div
.4 inch/Div
1cm/Div
2-9

Operating Instructions—7S12
Fig. 2-8. Effect of the Time/Div setting in relation to the three settings of Time-Distance dial. The time or distance represented in the time
windows shown is determined by the Multiplier setting.
ation in PRESET (Spans AIR to POLY)" can be filled in or
noted by the operator. The PRESET distances will be deter-
mined by the setting of the PRESET control (a screwdriver
adjustment on the front panel) when the PRESET button is
pushed in. The adjustment is set by the operator for cable
propagation velocities between air and Poly.
(B) Two dial points. This method uses the net dial read-
ing to determine the distance between the two points or
discontinuities. Observe one of the two discontinuities and
note its reference point on the screen (or set the FINE
control to position the discontinuity to the center or refer-
ence point on the CRT). Record the Time-Distance dial
setting (TIME, POLY, or PRESET POLY). Change the
Time-Distance knob to position the other discontinuity to
the same reference point on the CRT. Record the TIME-
DISTANCE setting. Subtract one recorded reading from the
other, to determine the net dial reading. The net dial read-
ing, times the Multiplier setting, v/ill result in the round trip
time or one way distance between the two discontinuities.
(C) From dial zero. In order to make measurements
directly from the TIME-DISTANCE dial, the zero point
must be determined. The FINE (ZERO SET) control is
useful for afine positioning control, and to set the dial
zero.
2-10

Operating Instructions—7S12
For example, use the S-52 and S-6 with aMultiplier
setting of X.1. Set the TIME-DISTANCE dial to 0, the
TIME/DIV to 2ns, and the FINE control fully clockwise.
Use the open or short circuit termination at the end of the
1ns line connected at the S-6 Loop Thru (upper) connec-
tor, to display the zero point or reference on the CRT.
Then, use the FINE control to position this reference point
to the left side of the graticule. Check other TIME/DIV set-
tings especially at 20 ps/Div. The TIME-DISTANCE dial
reading time 0.1 will then be the round trip time or one
way distance from the reference point. The same procedure
applies with the XI Multiplier (limited by the S-52 Output
pulse duration). When using the S-54 Pulse Generator head,
the risetime is less; however, the same procedure applies,
but on all Multiplier settings.
NOTE
The 1ns semi-rigid coaxial line (Tektronix Part No.
015-1023-00) should he used when making time or
distance measurements because S-6 and S-52 wave-
form discontinuities are in the first 2.0 ns. The
junction of the transmission line and the sampling
head connector is found by partially disconnecting
the line under test from the sampling head connector
to produce an inductive discontinuity (see Fig. 2-9) at
the junction. Adjust the FINE control to place the
discontinuity, abump, at aconvenient reference
point for the measurement and then fully reconnect
the transmission line.
High Resolution
Smoothing is always switched into the circuit in the 5
and 2positions of the units/Div switch. High resolution, a
separate pushbutton switch on the front panel, can be selec-
ted whenever smoothing of the display is required. The
displayed noise is reduced by about 10 times, and the scan
Fig. 2-9. TEST LINE connector iunction location obtained by par-
tially engaging the line to the connector.
Connect
"Test Line'
(A) "Loop Thru" connections for short and medium length
cable TOR measurements. The "Test Line" is connected to
the end of the 1ns semi rigid line for minimum aberrations
and fast risetime. Use the 7S12 Multiplier settings of X.1 and
XI (limited by the S-52 pulse duration).
1nsSMA
semi rigid
coaxial cable
015-1023-00
(supplied
with S-52)
750 ps SMA
semi rigid
coaxial cable
(supplied
with 7S12)
Adapters as required SMA (3 mm)
coaxial cables
(8) "In Liite" connections for short length cable TOR
measurements. The transmission system uitder test must have
two ports with low attenuation between them. SMA (3 mm)
semi rigid cables are used with the proper adapter to the
device under test. Use the 7S12 Multiplier setting of X.1.
Fig. 2-10. Application connections for "Loop Thru", and "In Line"
TDR.
rate is reduced about 10 times. Afurther reduction in the
scan rate may be necessary (by changing the SCAN control)
to avoid oversmoothing the display.
Single Sweep Operation
The SINGLE and START front panel controls are used
in the single sweep operation for recorders.
Before recording, set the controls for the desired display
in the normal repetitive mode. Set the desired scan rate for
the recorder. Connect the recorder to the 7S12, using the
VERT SIG OUT and the SWEEP OUT as required by the
recorder.
REV. B, JULY, 1976 2-11