Tektronix 7S11 User manual

Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon
070-0985-00
Product Group 42
IbktroniX'
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL
7S11
SAMPLING
UNIT
INSTRUCTION MANUAL
97077 Serial Number
First Printing FEB 1970
Revised MAY 1985
vii 'nte’ ti'tm’ P-im- ’•/

Copyright ®1970 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 apahel 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

7S11
TABLE OF CONTENTS
SECTION 1
SECTION 2
SPECIFICATION Page
General Information 1-1
Electrical 1-1
Environmental Characteristics 1-2
Physical Characteristics 1-2
OPERATING INSTRUCTIONS
General Information 2-1
Installation 2-1
Mating 2-1
First-Time Operation 2-2
Equivalent-Time Sampling Operation 2-2
Controls and Connectors 2-2
Basic Operating Information 2-2
Basic Applications 2-9
THE FOLLOWING SERVICE INSTRUCTIONS ARE FOR USE BY OUALIFIED PERSONNEL
ONLY. TO AVOID PERSONAL INJURY, DO NOT PERFORM ANY SERVICING OTHER
THAN THAT CONTAINED IN OPERATING INSTRUCTIONS UNLESS YOU ARE QUALI-
FIED TO DO SO.
SECTION 3BASIC SAMPLING PRINCIPLES
Introduction 3-1
Basic Sampling Techniques 3-1
Effective Sampling Time 3-4
Traveling Wave Sampling Gate 3-5
Dot Response (Loop Gain) 3-5
Smoothing 3.5
Smoothing of Random Noise 3-6
Tangential Noise 3-6
Display Sensitivity —Deflection Factor 3-7
DC Offset 3-7
Real-Time Sampling 3-8
Sweep Rates 3-8
REV FEB 1984 I

7S11
TABLE OF CONTENTS (cont)
SECTION 4CIRCUIT DESCRIPTION Page
Introduction 4-1
Block Diagram 4-1
Feedback Loop and Pulse Amplifier Chain 4-1
Vertical Output Amplifier 4-1
Sweep Unit Drive 4-1
Readout Logic 4-3
Circuit Description 4-3
Trigger Logic 4-3
Post Amplifier and Attenuators 4-3
Memory 4.5
Output Amplifier 4-8
Real Time Oscillator 4-8
Gate Generator 4-9
Readout Logic 4-11
Power Distribution and Decoupling 4-11
SECTION 5MAINTENANCE
Introduction 5-1
Preventive Maintenance 5-1
General 5-1
Cleaning 5-1
Lubrication 5-1
Visual Inspection 5-1
Calibration 5-1
Parts Identification 5-1
Parts Replacement 5-2
Troubleshooting 5-4
Introduction 5-4
Troubleshooting Aids 5-4
Troubleshooting Techniques 5-5
Transistor Checks 5-5
Diode Checks 5-5
Field Effect Transistors (FET) 5-6
Repackaging for Shipment 5-7
SECTION 6PERFORMANCE CHECK/CALIBRATION
Introduction 6-1
Test Equipment Required 6-1
Short Form Procedure 6-2
Preliminary Procedure 6-3
Check —12.2-Volt Power Supply 6-5
Check Interdot Blanking 6-6
Check Dot Response and Smooting 6-7
Adjust Memory Gate Width (R460) and
Memory Gain (C275) With Normalizer Head 6-7
Adjust Memory Gate Width (R460) and
Memory Gain (C275) With Sampling Head 6-8
II REV FEB 1984

7S11
TABLE OF CONTENTS (cont)
Adjust Variable Balance (R305) and
Smooting Balance (R245)
Check Deflection Factor Accuracies,
Variable Control Range and Adjust GAIN
Check Memory Overdrive Recovery
Check Vertical Signal Out
Check Vertical Gain Change in SMOOTH
Check Memory Slash
Check Delay
Check/Adjust Real Time Sampling (R415)
Check DC Offset and Adjust Position (R325)
Check Real-Time Trigger Amplifier Output
SECTION 7ELECTRICAL PARTS LIST
Abbreviations and Symbols
Parts Ordering Information
Index of Electrical Parts List
Electrical Parts List
SECTION 8DIAGRAMS AND MECHANICAL PARTS ILLUSTRATIONS
Diagrams
Mechanical Parts Illustrations
Repackaging Instructions
SECTION 9MECHANICAL PARTS LIST
Mechanical Parts List Information
Index of Mechanical Parts Illustrations
Mechanical Parts List
Accessories
CHANGE INFORMATION
Abbreviations and symbols used in this manual are based on or taken di-
rectly from IEEE Standard 260 “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.
Page
6-9
6-10
6-11
6-11
6-11
6-11
6-12
6-12
6-12
6-14
REV FEB 1984

7S11
SAFETY SUMMARY
The general safety information contained in this summary is for servicing personnel. Specific warnings and cautions will be
found throughout the manual where they apply, but may not appear in this summary.
IN THIS MANUAL
TERMS
CAUTION statements identify conditions or practices that could result in damage to the equipment or other property.
WARNING statements identify conditions or practices that could result in personal injury or loss of life.
AS MARKED ON EQUIPMENT
CAUTION indicates apersonal injury hazard not immediately accessible as one reads the marking, or ahazard to property
including the equipment itself.
DANGER indicates apersonal injury hazard immediately accessible as one reads the marking.
IN THIS MANUAL
SYMBOLS
Static-Sensitive Devices
This symbol indicates where applicable cautionary or other information is to be found.
AS MARKED ON EQUIPMENT
DANGER—High voltage.
AProtective ground (earth) terminal. ATTENTION—refer to manual.
WARNINGS
POWER SOURCE
This product is intended to operate from apower source that will not apply mare than 250 volts rms between the supply
conductors or between either supply conductor and ground. Aprotective ground connection by way of the grounding conduc-
tor in the power cord is essential for safe operation.
USE THE PROPER POWER CORD
Use only the power cord and connector specified for your product. Use only apower cord that is in good condition.
GROUNDING THE PRODUCT
This product is grounded through the grounding conductor of the power cord. To avoid electrical shock, plug the power cord
into aproperly wired receptacle before making connections to the product input or output terminals. Aprotective ground
connection by way of the grounding conductor in the power cord is essential for safe operation.
IV ADD FEB 1984

7S11
DANGER ARISING FROM LOSS OF GROUND
Upon loss of the protective-ground connection, all accessible conductive parts (including knobs and controls that may appear
to be insulating), can render an electric shock.
USE THE PROPER FUSE
To avoid hazard, use only the fuse specified in the parts list for your product, and which is identical in type, voltage rating, and
current rating.
DO NOT OPERATE IN EXPLOSIVE ATMOSPHERES
To avoid explosion, do not operate this product in an atmosphere of explosive gases unless it has been specifically certified for
such operation.
DO NOT SERVICE ALONE
Do not perform internal service or adjustment of this product unless another person capable of rendering first aid and
resuscitation is present.
USE CARE WHEN SERVICING WITH POWER ON
Dangerous voltages exist at several points in this product. To avoid personal injury, do not touch exposed connections and
components while power is on.
Disconnect power before removing protective panels, soldering, or replacing components.
SILICONE GREASE HANDLING
Handle silicone grease with care. Avoid getting the silicone grease in your eyes. Wash hands thoroughly after using silicone
grease.
ADD FEB 1984 V

FINE
DC OFFSET ±1V
DELAY
nons RANGE)
INVERT
VARIABLE (CAL IN!
DOT RESPONSE
NORMAL
mVOLTS/DIV
TYPE S-5
SAMPLING HEAD
+1V TO -1V
100V MAX DC
COUPLING
VERT SIS OUT
.2V/DIV flJKO
GNO
TEKTHONIX®
TEKTRONIX® SAMPLING UNIT
Fig. 1-1, 7S11 Sampling Unit,
7S11

7S11
SECTION 1
7S11 SPECIFICATION
Change information, if any, affecting this section will be found at the rear of the manual.
General Information
The 7S11 Sampling Unit is asingle channel vertical
amplifier plug-in unit designed for operation in Tektronix
7000-Series Oscilloscopes. The 7S11 accepts the S- Series
Sampling Heads. The Sampling Head determines the input
characteristics and the availability of atrigger pickoff.
The S-Series Sampling Head used can be plugged into the
7S1 1or used remotely on an optional extender cable unit.
The 7S11 provides the power for the sampling head.
Interconnections to the sampling head circuits are provided
by the connector in the sampling head compartment of the
7S11.
The 7S11 and a7T11 Sampling Sweep Unit operated in
the center plug-in compartments of a7000-Series
oscilloscope provide a single channel sampling system. Two
7S11's and one 7T11 provide dual-trace sampling, using the
electronic switching in the oscilloscope vertical amplifier.
X-Y operation is provided by two 7S11's operated in the
center plug-in compartments of the oscilloscope.
If atrigger pickoff is provided in the sampling head,
interconnections between two 7S11's and the 7T11
through the fixed and movable shoes provide atrigger
selection circuit to trigger the 7T11. An internally
reconstructed signal is provided to trigger areal-time
time-base such as the 7B50.
Sampled signals are presented to both the oscilloscope
vertical amplifier and to the front panel connectors for
external use with auxiliary equipment such as pen
recorders.
TABLE 1-1
ELECTRICAL
Characteristic Performance
Deflection Factor
Units/Division
Range
2to 200 in seven steps in 1, 2, 5
sequence. The Units/Division are
those labeled on the sampling head.
TABLE 1-1 (cont)
Characteristic Performance
Gain Accuracy
(Ratio to add
to accuracies of
source, oscillo-
scope, attenu-
ators, etc.)
Within 3% when NORMAL/
SMOOTH function is NORMAL,
with GAIN adjusted at any Units/
Division switch setting. Within 6%
when NORMAL/SMOOTH func-
tion is SMOOTH.
Units/Division
Variable Range Extends deflection factor from 1 unit/division or less to at least 400
units/division.
GAIN Range Permits adjustment of deflection
factor at any Units/Division switch
setting for all, 7000-series oscillo-
scopes.
DELAY Range At least 10 ns.
Memory Slash 0.1 division or less at 20 Hz for
ambient temperature of 0°C to less
than 30°C.
DC OFFSET
Range
-t1 volt to —1 volt or more.'
OFFSET OUT
Range -flO volts to —10 volts or more.
Relation to
actual Offset
Actual Offset =(0.1) (Offset Out)
within 2%.
Source resistance
(related to
actual Offset)
10 kn within 1%.
VERTical SIGnal
OUT
..,, , 200
(Signal input in volts) (. ,.j
Units/Div
within 2%. 2.4 volts peak-to-peak
maximum.
Amplitude in
volts
(Referenced
to input)
Deflection factor
(Referenced
to CRT)
200 mV/displayed division within
3% in +UP or INVERT.
Source resistance 10 kfii within 0.5%.
'unless otherwise stated on sampling head front-panel.
1-1

Specification—7S1
1
ENVIRONMENTAL CHARACTERISTICS
Storage-altitude up to 50,000 feet or 15,000 meters and
—55 C. Operating characteristics are the same as those
listed in the 7000-series oscilloscope manual.
PHYSICAL CHARACTERISTICS
Dimensions
Height 5inches (12.7 centimeters)
Width 3inches (7.6 centimeters)
Length 14 1/2 inches (37 centimeters)
Approximate dimensions including knobs and connec-
tors.
Finish Front panel is anodized aluminum.
Weight
Net About 2pounds (0.9 kilogram).
Shipping About 31/4 pounds (1.46 kilo-
grams).
STANDARD ACCESSORIES
Standard accessories supplied with the 7S1 1are listed on
the last page of the Mechanical Parts List section. For
optional accessories available for use with this instrument,
see the Tektronix, Inc. catalog.

SECTION 2
OPERATING INSTRUCTIONS
Change information, if any, affecting this section will be found at the rear of the manual.
General Information
This section discusses installation, first time operation,
function of front panel controls and connectors, basic oper-
ation and applications of the 7S11. If you are unfamiliar
with sampling, it may be helpful to read Section 3, Basic
Tektronix Sampling Principles, before proceeding with this
section.
The 7S11 is asingle-channel sampling unit for use in a
sampling system consisting of aTektronix 7704 or 7504
Oscilloscope mainframe, asampling sweep unit (7T11) or
real-time time-base and a7S1 1-sampling head combination.
The 7S11 accepts an S-series sampling head which deter-
mines the input characteristics of the sampling system and
(except for the Type S-3 Sampling Head) provides atrigger
pickoff.
The 7S11 can be used for real time operation with real-
time time-base units such as the 7B71 or 7B70 with the
7704 Oscilloscope, or the 7B51 or 7B50 with the 7504
Oscilloscope. An internal trigger source from the display
signal is provided for real time operation. Nevertheless, the
maximum useable sweep rate is about .1 ms/div (with a1
kHz signal), since at higher frequencies the horizontal dot
size increases and the number of dots per division becomes
less than three.
The vertical deflection factors of 2to 200 are calibrated
to the units labeled on the sampling head. Three-foot and
six-foot sampling head extender cables are available to
operate the S-series sampling heads remotely. Order the
three-foot sampling head extender cable by Tektronix Part
No. 012-0124-00. Order the six-foot sampling head ex-
tender cable by Tektronix Part No. 012-0125-00. Contact
your local Tektronix Field Engineer or Representative for
price and availability of these optional accessories.
Installing the 7S11 in the Oscilloscope
Insert the 7S11 into the Right Vertical opening of the
oscilloscope and slide the 7S11 completely into the com-
partment. The 7S11 will lock into place with the spring
loaded latch knob.
Insert the sampling head into the 7S11 with the latch
knob free to move until completely in the 7S11, 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 7S11.
The 7T11 Sampling Sweep Unit, normally used with the
7S1 1, must be installed in the AHorizontal opening next to
the 7S11 to make connections between the two units
through side connectors (the movable and fixed shoes).
Mating
The 7S11 Vertical Output Amplifier gain must be
matched to the oscilloscope CRT deflection factor for accu-
rate gain measurements. The GAIN control, ascrewdriver
adjustment on the front panel, adjusts the Vertical Output
Amplifier gain of the 7S11. Adjustment of this GAIN con-
trol using the Type 284 Pulse Generator as asignal source is
shown under Equivalent Time Sampling Operation which
follows. For further Gain information, refer to the Gain
Adjustment instructions later in this section.
Fig. 2-1 .Equivalent time sampling system.

Operating Instructions—7S1
1
FIRST-TIME OPERATION
Equivalent-Time Sampling Operation
Equivalent time sampling operation as described here is
provided by asystem consisting of the 7504 Oscilloscope,
the 7S11 Sampling Unit, the Type S-1 Sampling Head, and
the 7T11 Sampling Sweep Unit. The system is shown in
Fig. 2-1. Operation of the oscilloscope, sampling head, and
the sampling sweep unit is covered more fully in each in-
strument's manual. In this description, aType 284 Pulse
Generator is used as asignal source.
Set the Oscilloscope Vertical Mode switch to Right, the
ATrigger Source switch at Right Vert, and the Horizontal
Mode switch to A. Other oscilloscope controls may be in
any desired position.
Set the 7S1 1controls as follows:
DELAY Midrange
-t UP/INVERT -HUP
DC OFFSET and FINE Midrange
VARIABLE Pushed in
Units/Div 200
DOT RESPONSE Midrange
NORMAL/SMOOTH NORMAL
Set the 7T1 1controls as follows:
Time Position and Fine
Slope
Trig Level
Stability
Random/Sequential
Trig Amp
Variable
Time/Div
Sweep Range
Int/Ext
Scan
Rep/Man/Ext Input
Fully clockwise
-I-
Midrange
Fully counterclockwise
Sequential
X10
Pushed in
.1 /ts
5Ids
Int
Midrange
Rep
Type 284
Center the trace on the graticule with the DC OFFSET
control and adjust the Trig Level and Stability controls on
the 7T11 clockwise for astable display. The GAIN adjust-
ment is properly set if the amplitude is 5vertical divisions.
If the amplitude is not correct, adjust the GAIN control
with asmall screwdriver for 5divisions of vertical deflec-
tion.
NOTE
Operating the sampling head without the input con-
nector terminated by a50 El resistor or coaxial cable
will cause afew millivolts vertical shift to the zero
signal baseline. This occurs because of the strobe
kickout signal is reflected from the open input con-
nector. The kickout signal arrives back at the samp-
ling bridge during sampling time, while the bridge is
still conducting. To avoid this baseline shift, connect
the input circuitry, then set the display zero reference
point. Use at least 20 cm of airline between the Type
S-1 input and afast generator (such as a tunnel diode
pulse generator) or circuit that is sensitive to the fast
Strobe kickout signal.
CONTROLS AND CONNECTORS
Abrief description of the function and operation of the
controls and connectors of the 7S11 follows. The control
setup chart. Fig. 2-2, shows the front panel with an S-series
sampling head installed. This figure may be reproduced and
used as a test setup record for special applications or pro-
cedures, or it may be used as atraining aid for familiari-
zation with this instrument.
DELAY (10 ns Varies the time position of the ap-
RANGE) plied signal in relation to displayed
signals from other vertical instru-
ments operating in the same main-
frame.
-t-UP/INVERT In the +UP button setting, aposi-
tive input signal deflects the CRT
beam upward. In the INVERT push
button setting, the displayed signal
is inverted, anegative signal deflects
the CRT beam upward.
Square Wave Amplitude 1.0 V
Period 1jUs
Mode Square Wave Output
Lead Time 75 ns
Connect the Square Wave Output signal of the Type 284
through a5ns coaxial cable (Tektronix Part No.
017-0512-00) to the input connector of the Sampling Head
installed in the 7S1 1
.
DC OFFSET ±1 VApplies internal signal offset volt-
age of -H to —1 volt to the samp-
ling head. The input signal zero
reference (related to the CRT) is
the DC Offset voltage instead of
ground. Permits all portions of a
t-Tvolt input signal to be posi-
tioned through the CRT graticule
area vertically even at adeflection
factor of 2units per division. Verti-
2-2 (k)

Fig. 2-2. Control Setup Chart.
©2-3

Operating Instructions—7S1
1
FINE
Units/Div
VARIABLE
(CAL IN)
DOT RESPONSE
GAIN
NORMAL/SMOOTH
cal deflection total is 16 mV with aINT TRIG
deflection factor of 2mV/Div, and
1.6 Vwhen the deflection factor is
200 mV/Div. The front panel OFF-
SET jack allows accurate slide-back
voltage measurements to be made
of part or all of asignal at 10X the
actual offset voltage applied to the
head.
Push button selects internal trigger
operation between two 7S11's. In-
ternal triggering is canceled when
associated time base in the same
7000-series mainframe is switched
to external triggering. Lights up
when internal triggering is restored.
Provides vernier control of the DC
Offset function. Concentric with
the DC OFFSET ±1 Vcontrol.
Selects calibrated deflection factor
from 200 units/div to 2units/div in
a1-2-5 sequence. The units are se-
lected and named on the adjacent
S-series sampling head. For ex-
ample, with aType S-1 Sampling
Head, the Units/Div switch set at
100, each major division of deflec-
tion corresponds to 100 millivolts
of applied signal at the S-1 input
connector when the VARIABLE
control is at the (CAL IN) position.
Provides uncalibrated, variable ver-
tical deflection factor between
labeled values of the Units/Div
switch. When the VARIABLE con-
trol is rotated from the counter-
clockwise position, displayed ampli-
tude varies from less than 0.5 to
more than 2.5 times the calibrated
displayed amplitude.
Permits adjustment of loop gain for
optimum dot transient response
when the N0RMAL/SMOOTH
switch is in the NORMAL position.
OFFSET OUT Unless otherwise specified on the
X10 10kl2 sampling head front-panel, the open
circuit voltage at this miniature con-
nector is ten times the internal DC
Offset voltage as set by the DC
OFFSET control. The output resist-
ance is 10 kfZ.
VERT SIG OUT Afacsimile signal (the same Mem-
.2V/DIV10kTZ ory output signal that drives the
Vertical Amplifier) is available at
this miniature connector. The .2
V/DIV label applies only when the
VARIABLE control is at its CAL
IN position and is limited to about
2.5 Vmaximum. (The VARIABLE
control alters the CRT deflection
factor but does not change the sig-
nal amplitude fed to the VERT SIG
OUT miniature connector.) Output
voltage swing is not limited to the
magnitude displayed on the CRT,
Permits anon-sampling type oscillo-
scope to monitor the facsimile sig-
nal. Output resistance is 10 kf2.
GND Miniature connector provides acon-
venient front-panel ground point.
BASIC OPERATING INFORMATION
Screwdriver adjustment permits cal-
ibration of the vertical output am-
plifier gain to match the oscillo-
scope CRT deflection factor.
Selects unity loop gain at the NOR-
MAL push button setting. Reduces
the loop gain to 0.3 or less at
SMOOTH push button setting.
NORMAL provides the correct loop
gain required when measuring rise-
time. SMOOTH reduces the effect
of random noise on the display
while requiring high sampling dot
density for the correct displayed
risetime.
Dual Trace
The dual-trace features of the 7504 Oscilloscope Vertical
Mode permits observation of two 7S11 displays simultane-
ously. This is useful for comparing amplitude, risetime,
waveshape, and time relationship of two signals. The sweep
can use either 7S1 1as the internal trigger source. Be sure to
trigger from the 7S11 with the earliest signal event. Use
input signal cables with equal delays to preserve the time
relationship of the two signals.
The DELAY control adds avariable to the time coinci-
dence of the two signals to accommodate small time differ-
ence in cables or sampling heads, so that both signals can be
displayed in the correct time relationship.
2-4

Operating Instructions—7S1
1
.A \
<1
[
ywaaKssss- -N •
1)sA#
k
1til!
Fig. 2-3. Dual trace operation.
Dual-trace sampling operation requires two 7S11 Samp-
ling Units, a7T11 Sampling Sweep Unit, and two S-series
sampling heads installed in the 7504 Oscilloscope. As with
single-trace operation, the 7T11 must be installed in the A
Horiz opening adjacent to the 7S11 for internal triggering
connections. The second 7S11 is installed in the Left Vert
opening. See Fig. 2-3. Set the controls as follows:
7S11 Sampling Units
DELAY
-tUP/INVERT
DC OFFSET and FINE
VARIABLE
Units/Div
DOT RESPONSE
NORMAL/SMOOTH
Midrange
-t-UP
Midrange
Pushed in
50
Unity loop gain
(Fig. 2-5)
NORMAL
Type 284 Pulse Generator
Mode Pulse Output
Lead Time 75 ns
Set the 7504 Oscilloscope Vertical Mode switch to
Chop. Connect the Type 284 Pulse Output signal to the
sampling head input connectors through apower divider
and two 5ns coaxial cables. Connect the Type 284 Trigger
Output signal to the 7T11 Trig Input connector through a
50 SI coaxial cable and 3mm to BNC adapter, supplied
with the 7T1 1
.
Adjust the 7T11 Trig Level control for astable display.
Center both traces on the graticule vertically with the DC
OFFSET controls. This properly triggered dual-trace dis-
play will be similar to Fig. 2-4A.
Time Position. To show DELAY control operation,
change the 7T11 Sweep Range switch to 5and the
Time/Div switch 2 ns. Turn the Time Position control
counterclockwise to place the rising portion of the pulses
on the graticule. Time difference between the two displays
should be eliminated by adjusting one or both DELAY con-
trols.
Add
The algebraic addition of two signals can be obtained
with the Oscilloscope Vertical Mode switch set in the Add
position. The DELAY control can be used to compensate
for small time differences between displays before making
accurate algebraic addition of the two signals. For accurate
algebraic addition, both sampling heads should be same
type. Use the same display as described under dual-trace
time positioning.
The two signals can be superimposed using the DC OFF-
SET and DELAY controls for most accurate time coinci-
dence setting. Set the Oscilloscope Vertical Mode switch to
Add. The superimposed signals at dual-trace will be similar
to the display of Fig. 2-4B.
7T11 Sampling Sweep Unit
Time Position and Fine
Slope
Trig Level and Stability
Random/Sequential
Trig Amp
Variable
Time/Div
Sweep Range
Int/Ext
Scan
Rep/Man/Ext Input
Fully clockwise
+
For triggered display
Random
XI
Pushed in
5fxs
50 /US
Ext 50 2VMAX
9o'clock setting
Rep
Push the INVERT switch on one 7S11. The display
shown in Fig. 2-4C is nearly astraight line indicating equal
and opposite signal amplitude. Rotate the DELAY control
of either 7S1 1and notice that any time difference between
the two displays will appear as a pulse, either positive or
negative depending on the time position relative to the time
coincidence.
Dot Response. The loop gain of the sampling unit is
changed with adjustment of the DOT RESPONSE control.
Random process sampling (available with the 7T11) or

Operating lnstructions—7S1
1
multiple triggering (with areal-time time-base) are conven-
ient ways to adjust the DOT RESPONSE control to aset-
ting of unity loop gain (each sample responding to the full
signal amplitude). 100 millivolts with the Type 284 Pulse
Output signal applied to two inputs through the power divi-
der (keeping the same signal connections as above) would
use the Random mode of the 7T1 1
.
Fig. 2-4. Dispiays of dual-trace (Chop) and Add operation.
Push the +UP switch and the Oscilloscope Vertical Mode
switch Left or Right button. Observe the display as the
DOT RESPONSE control is rotated clockwise and counter-
clockwise. Asetting of unity loop gain occurs when the
random dots do not overshoot or undershoot the display,
see Fig. 2-5.
Fig. 2-5. Loop gain adjustment, triple exposure.
Vertical-Horizontal (X-Y)
Two 7S11 Sampling Units operated in the center com-
partments (Right Vert and AHoriz) of the 7504 Oscillo-
scope will produce the X-Y display for phase difference
calculations. See Fig. 2-6A. Any time-related signals which
do not exceed sampling head input specifications may be
used at the input connectors.
The 7S11 in the Right Vert compartment controls the
vertical deflection and the 7S1 1in the AHoriz compart-
ment controls horizontal deflection. Set the Oscilloscope
Vertical Mode switch at Right and the Horizontal Mode to
AHoriz. To produce aLissajous figure, apply asine wave to
both input connectors through the power divider and 5ns
coaxial cables. The Type 284 1ns Sine Wave Output can be
used. Set the Units/Div switches at 10 and VARIABLE
controls for a6division display both vertically and horizon-
tally; the DELAY control of either 7S1 1can be used to give
acircle display (90° out of phase) cy adiagonal straight line
(0 or 180° out of phase) for setting the 6divisions. Set the
DELAY control for the diagonal straight line to eliminate
phase difference at the 5ns coaxial cable inputs.
After these adjustments, the system is ready to show
accurate phase difference displays over awide range of fre-
quencies. Connect the signals to the 5ns coaxial cable in-
2-6 (A)

Operating lnstructions-7S1
1
puts. Fig. 2-6C shows amethod for calculating the phase
difference between the two signals.
A. Installed Sampling Units.
B. In phase display.
C. Calculation of 0method.
Fig. 2-6. XYoperation.
©1
Real Time Sampling
Never operate the real-time time-base without the
side covers in place because of possible damage to the
movable shoe contacts or to parts in the time-base
unit.
Real Time Sampling operation uses the three slowest
ranges of the 7T1 1Sweep Range switch or areal-time time-
base unit such as the 7B50, 7B51 ,7B70 or 7B71 .The 7S1
1
provides oscillator controlled Strobe Drive pulses to the
sampling head, independent of the real-time time-base unit.
The repetitive Strobe Drive pulses are turned on when the
7T1 1Sweep Range switch is at the 50, 5, and .5 ms ranges
or when the time-base unit is areal-time time-base unit.
Real time internal triggering is available even when the
sampling head does not contain atrigger pickoff circuit.
Install the 7S11 and real-time time-base units in the center
compartments (or the Left Vert and BHoriz) of the oscillo-
scope.
The 7504 Oscilloscope Calibrator Output of 1kHz,
Amplitude switch at 0.4 Vinto 50 may be used as the
signal source. Connect the Calibrator Output to the samp-
ling head input connector through a50 coaxial cable and
BNC to GR adapter. Set the Units/Div switch to 100 and
the time-base unit Time/Div switch to .5 ms. Obtain a
stable display with the Level/Slope control or the Trig
Level and Stability controls.
Real time sampling offers DC offset capabilities matched
with good overload recovery. Random noise in the display
can be reduced through smoothing with the DOT RE-
SPONSE control and SMOOTH operation.
NOTE
Type S-5 Sampling Head vertical noise may be re-
duced for real time sampling by lowering the oscil-
lator frequency by adjusting Rep Rate control
(R415). This also will lower the dot density.
Gain Adjustment
The GAIN control (a front-panel screwdriver adjust-
ment) matches the gain of the 7S11 vertical output ampli-
fier to the Oscilloscope CRT deflection factor. The gain
should be checked and adjusted each time the 7S1 1is used
with adifferent oscilloscope. A1% difference is possible
between channels.
An accurate voltage source should be used into the input
connector of the sampling head. The signal source imped-
ance must be considered when it drives the input of a50 L2
sampling head.
For 50 El input sampling heads, the Tektronix Type 284
(within 0.5% at 10 ps and 1ps), the 50 El Amplitude Cali-
brator within 0.25%, or aprecision chopped voltage can be
2-7

Operating Instructions—7S1
1
7S11 7S11
DELAY Midrange
+UP/INVERT +UP
DC OFFSET and FINE Midrange
VARIABLE Pushed in
Units/Div 200
DOT RESPONSE Midrange
NORMAL/SMOOTH NORMAL
DELAY
+UP/INVERT
DC OFFSET and FINE
VARIABLE
Units/Div
DOT RESPONSE
NORMAL/SMOOTH
Midrange
+UP
Midrange
Pushed in
100
Unity loop gain
NORMAL
7T11 7T11
Time Position and Fine Fully clockwise Time Position and Fine Fully clockwise
Slope +Slope +
Trig Level Triggered display Trig Level Triggered display
Stability Triggered display Stability Triggered display
Random/Sequential Sequential Random/Sequential Sequential
Trig Amp XI Trig Amp XI
Variable Pushed in Variable Pushed in
Time/Div .2 ps Time/Div .5 ms
Sweep Range 50 JUS Sweep Range 50 ms
Int/Ext Ext Int/Ext Int
Scan 9o'clock position Scan Optional
Rep/Man/Ext Input Rep
Type 284
Square Wave Amplitude 1.0 V
Rep/Man/Ext Input Rep
7504
Period 1JUS Calibrator Volts 4V(0.4 V
Mode Square Wave Output into 50 fZ)
Lead Time Optional Rate 1kHz
used. The Oscilloscope Calibrator output, with an accuracy
within 1%, can be used also.
Using the Type 284. Set the controls as follows using
the Type 284, accuracy withing 0.5% producing 7S11
deflection factor better than 3.5%, as the signal source to
check or adjust the GAIN control of the 7S11 and 50 Li
sampling head:
Connect the Square Wave Output signal from the Type
284 to the sampling head input connector through acoaxial
cable. Connect the Trigger Output signal from the Type
284 to the 7T11 Trig Input connector through acoaxial
cable and BNC to 3mm adapter.
Adjust the 7T11 Trig Level control for astable display.
Center the trace on the graticule with the DC OFFSET
controls and observe the square wave amplitude. If the
amplitude is not 5 vertical divisions, adjust the GAIN con-
trol with asmall screwdriver for 5vertical divisions.
Using Oscilloscope Calibrator. Set the controls as
follows using the Oscilloscope Calibrator as the signal
source to check or adjust the GAIN control of the 7S11
and 50 LZ sampling head. The 1kHz, 0.4 Voutput has an
accuracy of ±1%, producing a7S11 deflection factor
accuracy better than 4%.
Apply the signal from the Oscilloscope Calibrator Volts
output connector to the sampling head input connector
through aBNC coaxial cable and BNC to GR adapter.
Adjust the Trig Level control for astable display of the
square wave. Set the DOT RESPONSE control to unity
loop gain (no overshoot or undershoot at the leading front
corner).
Center the trace on the graticule with the DC OFFSET
controls and observe the amplitude. If the amplitude is not
4vertical divisions, adjust the GAIN control with asmall
screwdriver for 4vertical divisions.
Vertical Signal Output
Acomposite signal is available at the Vertical Signal Out-
put jack (VERT SIG OUT). This signal is taken after the
sampling process and is aproportional representation of the
display signal rather than the input signal itself. In real time
sampling, the output signal voltage follows the rate of the
internal real time oscillator. The open circuit voltage at the
jack is 200 millivolts per division of display when the
VARIABLE control is pushed in. The output resistance is

Operating Instructions—7S1
1
10 kll. The signal is not affected by the Oscilloscope Verti-
cal Mode switch. The signal is changed by the Units/Div
switch, the DC OFFSET controls, and the NORMAL/
SMOOTH switches. The INVERT switch does not invert
the signal. Output voltage swing is limited to 2.5 volts peak
or about 6divisions above and below the graticule center
depending on the actual position. The Units/Div switch is
active but the output voltage is always proportional to the
CRT display (0.2 V/Div) up to 12 divisions maximum peak
to peak. Since the signal at the Vertical Output jack is an
equivalent time signal, it is useful for pen recorder applica-
tions when the sampling sweep unit external input is driven
by the recorder.
The OFFSET OUT monitor jack permits accurate
measurement of the DC voltage set by the DC OFFSET
controls. The output voltage has arange of -^10 to —10
volts. Unless otherwise specified on the sampling head front
panel, the monitor jack output voltage is ten times the
internal DC offset voltage. The output resistance is 10 kT2.
BASIC APPLICATIONS
Vertical Deflection Measurements
Vertical displacement of the trace on the CRT is directly
proportional to the signal at the sampling head input con-
nector installed in the 7S11. The amount of displacement
for agiven signal can be selected with the Units/Div switch.
To provide sufficient deflection for best resolution, set the
Units/Div switch so the display spans alarge portion of the
graticule. Also, when measuring between points on the dis-
play, be sure to measure consistently from either the
bottom, middle, or top of the trace. This prevents the
width of the trace from affecting the measurements.
To make avertical deflection difference measurement
between two points on the display, proceed as follows:
1. Note the vertical deflection, in graticule divisions,
between the two points on the display. Make sure the
VARIABLE control is in the CAL position.
NOTE
The vertical deflection factor is determined by the
Units/Div switch and the value of the units of
measure as stated on the sampling head front panel.
The ratio of the input signal to the resultant deflec-
tion is called the deflection factor. For example, with
the sampling head unit values stated as mV/Div, and
the Units/Div switch set to 20, the vertical deflection
factor will be 20 mV/division.
2. Multiply the divisions of vertical deflection by the
deflection factor, and the external attenuator or probe
attenuation factor (if any). The product is the voltage
difference between the two points measured.
For example, suppose you measure 4.4 divisions of de-
flection between two points on the display and the Units/
Div switch is set for 20 mV/Div. Multiply 20 millivolts/
division by 4.4 divisions, the product is 88 millivolts. This is
the voltage difference at the input connector between the
two points on the display. Now assume there is a10X
external attenuator (probe) between the input connector
and the signal source. To determine the actual signal voltage
at the source, multiply 10 (the attenuation factor of the
probe) by 88 millivolts; this product (880 millivolts or 0.88
volts) is the actual voltage at the signal source.
It is also possible to measure an instantaneous (or DC)
voltage to ground from the display. This measurement is
accomplished in the same manner, except that with no sig-
nal applied, you must first establish aground-reference
point on the CRT.
NOTE
To establish the ground reference point be sure the
input connector is either terminated by a50 El resis-
tor or coaxial cable connected to the Input.
To do this, trigger the sampling sweep unit with the
signal source and display atrace. Then, position the trace so
it is exactly aligned with one of the graticule lines. The
actual graticule line you select will be largely determined by
the polarity and amplitude of the applied signal. After
establishing the ground reference, make no further adjust-
ments with the DC OFFSET control.
Apply the signal and measure the voltage in the manner
previously described. Make ail measurements from the
established ground reference point. Accuracy of this meas-
urement is within ±3%.
If the applied signal has a relatively high DC level, the
ground-reference point and the actual signal may be so far
apart that neither will appear on the CRT. In this case, refer
to the following discussion on "Voltage Measurements
Using the DC Offset Control."
Voltage Measurements Using the DC OFFSET
Control. Unless otherwise stated on the sampling head
front panel, the DC offset voltage cancels the effect of an
applied DC voltage of up to ±1 volt at the sampling head
input. Also, accurate slideback amplitude measurements of
the applied signal can be obtained by positioning the dis-
play at various points and measuring the amount of voltage
change at the OFFSET OUT monitor jack.
2-9

Operating Instructions—7S1
1
Source resistance for the voltage at the OFFSET OUT
monitor jack is 10 kTi; therefore, meter loading may be a
factor if other than an infinite-impedance meter is used.
The accuracy of the DC offset voltage measurement
depends on the accuracy and the loading effect of the meas-
uring device. The following measuring devices are recom-
mended, in order of preference, for monitoring voltage at
the OFFSET jacks.
(1)
Differential, non-loading DC voltmeter accurate within
0.2% or better. This type of device provides absolute
offset voltage measurements accurate within 2%. Meas-
urements of small changes in offset voltage can be
made more accurately than 2%.
(2)
Vacuum-tube voltmeter with an input impedance of at
least 10 megohms. Accuracy of the VTVM should be as
high as practical.
(3)
Zero-center ±1 mA milliammeter with as high an accur-
acy as practical. The milliammeter should be connected
directly between the OFFSET OUT monitor jack and
ground. When using amilliammeter, 1milliampere is
equivalent to 1volt of the actual offset voltage. The
loading effect is within 2% +the error percentage deter-
mined by: 100 (Rmeter/10000).
Slideback Measurement Procedure. To measure the volt-
age difference between two points on awaveform (such as
peak or peak-to-peak volts), proceed as follows:
1.
Set the DC OFFSET control to about midrange.
2.
Apply the signal to be measured to the sampling head
input. Adjust for astable display with about 7divisions of
vertical deflection between the two points of the signal to
be measured.
3. With the DC OFFSET controls, move one of the
points to be measured to the center line of the graticule and
measure the voltage at the OFFSET OUT monitor jack. Use
one of the measuring devices mentioned previously.
4. With the DC OFFSET control, move the display so
the other point to be measured is aligned with the center-
line of the graticule and again measure the voltage at the
OFFSET OUT monitor jack.
5.
Find the difference between the voltage measured in
step 3and the voltage measured in step 4, and divide by 10.
The result is the voltage difference, in volts, between the
two points on the waveform. This voltage tolerance is ±2%
of the input signal plus the tolerance and loading effect of
the measuring device.
Use of Smoothing
Random process sampling does not generally permit the
use of smoothing. This process requires unity loop gain to
construct acoherent display from the samples taken at ran-
dom. When using random process sampling, operate the
7S11 with the NORMAL switch pushed in, and adjust the
DOT RESPONSE control to unity loop gain.
Normal process sampling does permit the use of smooth-
ing. Time and amplitude noise may sometimes be objection-
able when operating at minimum deflection factors or max-
imum sweep rates. For Smoothing operate the 7S11 with
the SMOOTH switch pushed in.
This will reduce the random noise by about one half by
decreasing the gain of the sampling feedback loop. Fig. 2-7
shows the advantage of using smoothing when observing a
low-amplitude signal.
Dot Density. Normally the risetime of the display will
not be significantly affected in smoothed operation if the
dot density is sufficient. If, however, the display waveform
shape is affected when the SMOOTH switch is pushed in, a
compromise must be made between smoothing and dot
density. Fig. 2-7C illustrates the effect produced when the
dot density is low with smoothed operation. This effect can
be compared to the high dot density of the same input
signal as shown in Fig. 2-7B.
"False" Displays
Because sampling displays only afraction of any one
cycle of arepetitive signal, it is sometimes possible to
obtain afalse equivalent-time display of the signal. The
incorrect equivalent-time display occurs when the sampling
rate is an exact multiple of the signal rate. Each sample
vertical position represents the correct signal amplitude, but
an incorrect number of samples is taken, causing the false
equivalent-time display.
False equivalent-time displays can be detected by chang-
ing the sampling sweep unit Scan control; i.e., changing the
dot density. Occasionally such afalse equivalent-time dis-
play occurs when the sampling sweep unit triggering circuit
is adjusted to free run, and at the same time the triggering
signal amplitude synchronizes it falsely. Any time the dis-
play equivalent time changes when changing the dot den-
sity, alter the Time/Div switch to obtain adisplay with an
2-10