REPORT RESUMES
ED 016 389 EN 005 639 A COMPARATIVE STUDY OF VIDEO TAPE RECORDINGS. BY WIENS, JACOB H. WEINS ELECTRONIC LABS., WOODSIDE, CALIF. REPORT NUMBER SA-3055 PUB DATE 20 OCT 66 CALIFORNIA STATE DEPT. OF GEN. SERVICES,SACRAMENTO EDRS PRICE MF50.50 HC -$4.03 100P.
DESCRIPTORS- *INSTRUCTIONACTELEVISION, *VIDEO TAPE RECORDINGS, *EQUIPMENT MANUFACTURERS, *EQUIPMENT EVALUATION, TAPE RECORDERS, *COMPARATIVE TESTING, EDUCATIONAL EQUIPMENT, SCHOOLS, KINESCOPE RECORDINGS
THE COMPARATIVE EFFECTIVENESS OF PRESENTLY AVAILABLE VIDEO TAPE MACHINES IS REPORTED, FOR THE CONVENIENCE OF SCHOOL ADMINISTRATORS PLANNING TO USE SUCH EQUIPMENT IN EDUCATIONAL PROGRAMS. TESTS WERE CONDUCTED AT THE WIENS ELECTRONIC LABORATORIES. MACHINE BRANDS TESTED WERE AMPEX, CONCORD, MACHTRONICS, PRECISION, RCA, SONY, AND WOLLENSAK. A DETAILED MECHANICAL COMPARISON IS GIVEN IN CHARTS AND GRAPHS. AVAILABILITY OF INSTRUCTIONAL TELEVISION MATERIAL IS SHOWN ON A TABLE OF PRODUCTION CENTERS AND DISTRIBUTING LIBRARIES. (MS) I
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A S U.S. DEPARTMENT OF HEALTH, EDUCATION & WELFARE
OFFICE OF EDUCATION
THIS DOCUMENT HAS BEEN REPRODUCED EXACTLY AS RECEIVED FROM THE
PERSON OR ORGANIZATION ORIGINATING IT.POINTS Of VIEW OR OPINIONS
STATED DO NOT NECESSARILY REPRESENT OFFICIAL OFFICE OF EDUCATION
POSITION OR POLICY.
A COMPARATIE STUDY OF VIDEO TAPE RECORDERS
by
Dr. Jacob H. Wiens Director, College of the Air College of San Mateo
Prepared under Standard Agreement No. 3055 by Wiens Electronics Laboratories 130 Crest Road Woodside, California October 20, 1966 CONTENTS
FOREWORD iv PREFACE
CHAPTER 1 I INTRODUCTION 3 IIAVAILABILITY 8 IIICOST OF KINESCOPERECORDINGS 10 IVTHE RECORDINGSYSTEM
TAPE RECORDERS. . 16 VTHE PRINCIPLESOF TESTING VIDEO 16 The Multiburst Test ...... 17 The Window Test , 17 The Stairway Test
PHOTOGRAPHS. . . 19 VIANALYSIS OF WAVEFORMOUTPUT TEST
DESCRIPTION OF TESTSET-UP AND EQUIPMENTTESTS VII 25 ON INDIVIDUALMACHINES 79 VIIIMECHANICAL COMPARISON
COMPARATIVE VITALSTATISTICS IX 81 AS SUPPLIED BYMANUFACTURERS 86 XCONCLUSIONS 88 SELECTED REFERENCES 89 APPENDIX A--Lighting 91 APPENDIX B--VisualAids 94 ACKNOWLEDGEMENTS iii
FOREWORD
In keeping with the policy of making information available concerning various aspects of educational television in California, the Department of General Services has published this report for appropriate distribution throughout the State. The tremendous interest in the qualifications of the various video recorders now available indicates the need to make the kind of information this report contains readily accessible.
The comparisons and tests presented in this publication were developed and carried into effect at the Wiens Electronic Laboratories by a team of electronics specialists headed by Dr. Jacob H. Wiens under contract with the Bureau of Audio-Visual and School Library Education of the State
Department I Education. The conclusions do not necessarily reflect the official recommendations of any State agency.
General Andrew Lolli Director Department of General Services iv
PREFACE
The =i different kinds of video tape machines currently being manufactured by various companies throughout the world pose a serious dilemma for school administrators in selecting program equipment whether they are planning to record or playback television programs. This report of the effectiveness of presently available video tape machines has been prepared to assist school personnel to make more realistic appraisals of the capabilities of the machines before making a selection.
The results of the taste described in this study are not considered to be comprehensive or all-inclusive.All the recorders were volun- tarily submitted for testing by the manufacturers. It is possible that some of the machines submitted were demon3tration models rather than off-the-line models; they were tested juTt as received. Therefore, in studying the report, it should be kept in mind that different machines of the same kind might have exhibited other characteristics under identical tests.
The tests on the machines were conducted at the Wiens Electronic
Liboratories at the request of the State Department of Education, Bureau of Audio-Visual and School Library Education in consultation with the
Public School Instructional Television Committee and the office of the
State Coordinator of Educational Television.Special acknowledgements should be made for the work of the team of electronics specialists which conducted the tests. The team was composed of Dr. Jacob H. Wiens, Director of the College of the Air; Thomas J. Brames, Electronics Department;
Francis J. Morgan, Chief Engineer, KCSM-TV; and Walter J. Nichol, Techniciani, KCSM-TV; all fromanMateo College, San Mateo, California.
Harry J. Skelly, Chief Lawrence T. Frymire, Executive Secretary Bureau of Audio- Visual and Television Advisory Committee' School Library Education State of California Chapter I
INTRODUCTION
So much has been written abeat the benefitsderived from television that the school administrator is interested in investigatingthe use of television in instruction.
There are advantages to be gained by the use oftelevision, but there are also problems that school systems mustavoid when applying television to their situation.
Television is a unique tool that can be usedeffectively. Television will not improve unimaginative teaching norwill it hold the attention of students when the subject matter is dull oruninspiring. The fact that a program is presented on the television screendoes not necessarily improve the quality of the program and, in manyinstances, may bring out the negative rather than the positive properties.
Great care must be taken in theselection of the personnel who appear on television. All teachers in a school system are notnecessarily able to project as a televisionteacher. The personnel who appear must relate well to the audiences to whom they are speaking.
A toievised class sessionrequires a most careful analysis of the objectives of the lesson, arrangement of subject matter toillustrate each objective, and how the lesson is finallypresented.
Mq0 PohOol systems, withlimited budgets, are simply not in a position to produce high qualitytelevision courses. To produce an inadequate television lesson and record it on a video tapemachine may decrease the effectiveness because oflimitations of technical skill in the use of the recording equipment. The production of television lessons -2- by a school system is a complex operation and should be daielpted to 3 people who are experts in the field and who have the necessazy equipment.
Schools wishing to make use of television in their teaching program must, therefore, either use programs available to them over the local broadcast television channels or reproduce their own programs in their schools by means of a video tape recorder or use materialobtained from a tape library. In any event, the school systems ere increasingly dependent on a means to reproduce video material fromvideo tape.
A very important consideration in the matter of video tape recorders is making satisfactory dubs or second generation tapes. The errors, such as frequency response, increase not in an additive fashion, but in an exponential fashion or by multiplication. That is, if there is a 50% drop in frequency response at 2 MHz, the second generation or first O dub will show a 257. frequency response. Phase-shifts, on the other hand, are purely additive. The combination of errors introduced in the second generation in a machine that may multiply t rapidly that the dubs made from the master become virtually useless. It is, therefore, necessary to keep the quality of the tape recorder which will be used for making copies at the highest level of perfection possible in order to beable to produce satisfactory copies of the video tape.
It is hoped that this report will be of some help to administrators who are planning for the use of television, and particularly video tape recorders, in their educational programs. -3-
Chapter II
AVAILABILITY OF'INSTRUCTIONAL TELEVISION MATERXAL
For a school district that does notcontemplate producing all of its own material, it is helpful to investigatethe availability of instructional television material for thevideo tape machine under consideration. Questionnaires were sent out to the majorproduction centers and distributinglibraries in the United States to determine the medium by which their material isdistributed: 16mm film or tape for quadraplex or helical-scan. No attempt has been made to assure full and complete coverage of the existingproduction centers.
In addition to the material that isavailable as indicated in this report, certain of the educationalmaterial distribution centers act as a recording-duplicatingfacility and will make'tape'available. for any machine. The Great Plains RegionalInstructional Television
Library of Lincoln, Nebraska, operates inthis manner and presently has the quadraplex, Ampex 660B, Dage, Sony200, and AmpeX VR7000 machines:'
Schools may request tapes for other machines bypaying the expenses involved in rental of the video tape machineplus the recording fee.
Additionally, it should be noted that manyschool districts can arrange withbroadcasting stations to record programs off-the-air.Most educational stations offer this type of service toschool districts for a nominal fee.
.r -4-
INSTRUCTIONAL TELEVISIONMATERIAL SOURCES FOR THE MACHINESCHECKED IS AWAILABLE FROMTHE FOLLOWING
16mm .QUADRA- AMPEX NAME OR PRODUCTIONCENTER FILM PLEX 6608 OTHER OR DISTRIBUTINGLIBRARY
California KCET . Channel 28 Community TV ofSouthern California 1313 North VineStreet Los Angeles,California 90028
KQED - Channel 9 525 4th Street San Francisco,California 94107
KTEH - Channel54 . 70 West Bedding Street Sar Jose, f:alifornia95110
KVIE - Channel 6 P. O. Box 6 Sacramento, California95801
Los Angeles CitySchools 1061 Temple Street X Los Angeles,California 90012
Pasadena City, Schools 351 South Hudson Avenue Ampex VR-7000 PasaCiena, California91109
Regional ETV AdvisoryCouncil 155 West WashingtonBoulevard Los Angeles,California 90015
College San Diego State X San Diego, California92115.
Valley InstructionalTelevision Assoc. c/o KVIE - Channel 6 P. O. Box 6 Sacramento, California95801
Western Radio &Television Assoc. 633 Battery Street Sony EV-200 San Francisco,California 94111
Florida WUFT-TV University of Florida X Gainesville, Florida32603
WFSU-TV Florida State V4versity 202 Dodd Hall X Tallahassee, Florida -5-
NAME OF PRODUCTION CENTER 16 mm QUADRA- AMPEX OR DISTRIBUTING LIBRARY, FILM PLEX 6608 OTHER
Illinois WSIU-TV Southern Illinois University Carbondale, Illinois 62903 X
Indiana NAEB/ETS Program Service Bloomington, Indiana 47402 X
Midwest Program, Airborne Television .Instruction, Inc. Purdue University Lafayette, Indiana X
National Center for School & College TV Bloomington, Indiana 47402 X Sony EV-200
Maine WMEB-TV University of Maine Orono, Maine 04473
Massachusetts Commission on English Boston, Massachusetts X
Heath DeRochemont Corp. Boston, Massachusetts X
Northeastern Regional Instructional Television Library Cambridge, Massachusetts X
Michigan University of Detroit .Detroit, Michigan X
Minnesota College of Saint Teresa Winona, Minnesota X
KTCA-TV 1640 Como Avenue St. Paul, Minnesota 55108 X X
Minneapolis Public Schools Minneapolis, Minnesota X X
Nebraska Great Plains Instructional Telev. Lib. University of Nebraska Ampex VR-7000 Lincoln, Nebraska X Sony EV-200
KUON University of Nebraska IIIAmpex VR-7000 and 40th and W Streets will make dubs for Lincoln, Nebraska 68501 X X X any other machine -6-
NAME OR PRODUCTION CENTER 16 am QDADRA- AMPEX OR DISTRIBUTING LIBRARY FILM PLEX 660B OTHER
New Hamatime WENH-TV X Box 2 Durham, New Hampshire 03824 X
New York RAETA Rochester, New York
University of New York Albany, New York X X Ampex VR7000
WHNT - Chanftl 14 Schenectady, New York
WNDT - Channel 13 304 West 58th Street New York, New York 10019 X X
Ohio Ohio State University Columbus, Ohio X
Oregon School District No. 4 Eugene, Oregon X
State of Oregon System of Higher Education orvallis, Oregon X
Pennsylvania DepartmenL of Public Instruction State of Pennsylvania Harrisburg, Pennsylvania X X Ampex VR7000
WQED-WQEX Metropolitan Pittsburgh 4337 Fifth Avenue Pittsburgh, Pennsylvania 15213 X
South Carolina South Carolina ETV Center Columbia, South Carolina X t. Tennessee Memphis Community TV Foundation Memphis, Tennessee X X X
WDCN - Channel 2 P. O. Box 6188 Nashville, Tennessee 37212 X X -7-
NAME OF PRODUCTION CENTER 16 mm QUADRA- AMPEX OR DISTRIBUTING LIBRARY FILM PLEX 660B OTHER
Texas KERA - Channel 13 3000 Harry Hines Boulevard Dallas, Texas 75201 X
KLRN Southwest Texas Educational TVCounCil Austin, Texas X
KUHT - Channel 8 4513 Cullen Boulevard Houston, Texas 77004
Texas Educational Microwave Project University of Texas Austin, Texas X
Washington KCTS-TV - Channel 9 University of Washington. Seattle, Washington 98105
School District No. 1 Seattle, Washington X
University of Washington Seattle, Washington 98105 X
Washington, D. C. FETA - Channel 26 Washington, D. C. X
Wisconsin WHA-TV 3313 University Avenue Madison, Wisconsin 53706
Wisconsin School of the Air Madison, Wisconsin -8-
Chapter III
COST OF KINESCOPE RECORDINGS
A large number of firms in the United States are in a position to reduce video tape to kinescope recordings.The resulting kinescopes can be projected on a conventional motion picture projectorand can likewise be used for television presentations.
Typical among the companies engaged in this function are Technicolor
Corporation of America, 823 North Seward Street, Hollywood,California, and Acme Film Laboratories, Inc., 1161 North Highland Avenue, Hollywood,
California. While their prices change without notice, cur' :ent available, costs of transfer services are approximately as follows:
Tele View Recording Services, Inc.
Single System Sound/16 mm Negative and One Print 10 minute transfer 93.56 15 minute transfer 113.36 30 minute transfer 171.00 60 minute transfer 2141.56
Double System Sound/16 mm Negative-Separate Track and One Print 10 minute transfer 121.28 15 minute transfer 153.68 30 minute transfer 248.00 60 minute transfer 495.28
16 mm Release Prints 1 minute 4.00 5 minutes 10.00 10 minutes 17.50 15 minutes 25.00 30 minutes 50.00 60 minutes 95.00 -9"
Acme Film Laboratories, Inc.
Transfer Video Tape to16 mm Film Direct Positive 140 minutes 9.50 per minute 11-20 minutes 7.50 per minute 21-44 minutes 6.00 per minute 45-60 minutes 5.50 per minute Minimum Charge 50.00
Transfer Video Tapeto 16 ram Film Single System (Includes compositenegative and one print) 2-10 minutes 10.50 per minute 11-20 minutes 8.50 per minute 21-44 minutes 7.50 per minute 45-60 minutes 6.50 per minute Minimum Charge 50.00
Transfer Video Tape to 16 mm Film Double System (Includes. picture negative, RCA Area Track Negative and one print) 2-10 minutes 12.00 per minute 11 20 minutes 10.50 per minute 21-44 minutes 9.50 per minute .45-60 minutes 8.50 per minute Minimum Charge 60.00 -10-
Chapter IV
THE RECORDING SYSTEM
There are sexer:II:separate and identifiable' factors necessary to produce a satisfactory recorded television program. 'These include the studio facility, the studio camera, the studio mixing equipment, the video
tr tape, the video tape recorder, the televisionplayback equipment, and the television receiver.
In order to produce a professional quality television lesson, it is necessary to provide for the necessary highlighting level (see appendix A) with adequate attention to such factors as badk lighting, uniformity of front lighting, visual aidg, and rear screen Projectors.
This report will not deal with television cameras per se, but the successful television production facility should be equipped with a camera capable of producing a resolution which is in excess of the capability of the television receiver. The difference in cost of a low quality Vidicon television camera with resolution in the order of 300 to 400 lines and a camera with adequate resolution is so little that the studioshould not be handicapped by having an inferior camera. Many manufacturers are presently able to offer cameras with resolution of 700 lines in the center and 500 to 600 lines in the corners--resolution which exceeds that of the other pieces of equipment in the complete system.
The art of manufacturing of video tape has reached a point at which video tape generally is no longer the limiting factor in the production center. At least three highly reliable manufacturers of video tape can furnish any type of video tape as required by the various models of video tape recorders. Video tape is manufactured withthe magnetic granuleslaid length-
of the wise or perpendicular tothe video tape. T he magnetic properties
primary magnets laid down onthe tape are affected by thedirection in
which a magnetic field is appliedwhen the tape is manufactured. One
orientation of the magneticmaterial is designed for thequadraplex machine
where the magnetic line isperpendicular to the tape and theother is
designed for the helical-scan machineswhere the magnetic track is .aid
in a direct slant across thetape, (but generally in alongitudinal direction).
plagued by In the early productionof video tape, manufacturers were
minute areas on the tapethat were not covered by theiron oxide coating.
This coating, less than amil thick, must be spreadabsolutely-uniformly
with no pinpoint holes largerthan the tip of a needle.A hole in the
oxide coating one micron indiameter (one millionth of aninch) produces
part of a scanning line, an objectionablewhite smear for an appreciable
probably 2% of the screen width. This phenomenon is known inthe television
of how industry as "drop out" andmanufacturers guarantee tape in terms
many drop outs persecond the tape contains. Drop outs are undetected
until a signal is recorded andplayed back. Consequently, manufacturers
select reels that are do not generally detectdrop outs in tape except in
used for quality control.
Additionally, manufacturers are nowcoating the oxide side of thevideo
The iron oxide used in video tape with an extremelythin layer of plastic.
the thin plastic tape is an exceptionallyhard and abrasive material and
coating does much to decreasethe head-wear as therecorder's video head
increased by rubs across the oxidecoating. The recording level must be The 10% to 157. when the video tapemachine is using plasticcoated tape.
state of the art ofthe production of video tapeis such that television
by the video tape. programs reproducedfrom tape are not limited -12-
The limiting factor in installations using the best recording
techniques and equipment is the television receiver.While it is possible
to purchase televisicn monitors that can exhibit a resolutionof 600 lines per inch, the cost of such monitors is sohigh that most educational
institutions will choose to purchase readily available economy models of
broadcast television receivers. Receivers in this category are available
for UHF, VHF, and for a direct video input..
The standard television set with.a video input is a relatively new
item on the commercial market. Television installations have long
"jeeped" television sets for a video input. This is done by adding a
Switch in the first video amplifier and switching this to a terminated
75 chm video input line. The resulting level to the first video amplifier
is of the order of .5 to 2 v. p-p, and this generally is notsufficient to
provide adequate contrast.All commercial models frequently add a stage of
amplification to raise the standard video input signal to the properlevel
before switching into the video circuit.
The electronics and the television cathode ray tube are the limiting
factors in a standard television receiver. The economy line of receivers
will reproduce from 300 to 325 lines at the center of she picture,and this
should be the practical limitation placed on resolution for educational purposes.
The last factor in the resolution and fidelity of the, video program is
the video tape recorder. The video tape recorder is required to transform
the video picture signal to a suitable magnetic signal which places a
series of north and south magnetic pacts along a narrow stripof magnetic
iron oxide on the video tape. The width of the magnetic track is from 3 to
10 mils (1/1,000ths of an inch).A similar very narrow guard band separates
one pass of the video recordinghead from the subsequent track. -13-
In the case of the quadraplex video taperecorder, a single pass of the recording head perpendicularly acrossthe video tape records 16.4
lines of picture information. The next head on the four-pole rotary assembly records the next 16.4 lines untilthe entire raster of 525 lines has been recorded.
In the case of the helical-scan,generally the entire first field
consisting of 262.5 lines isrecorded in one pass of the head across the
at the slant angle. The actual path length obviously varieswith the
width of the tape and the angle that thehead makes with respect to the
longitudinal direction of the tape. The second pass of the head records
the remainder of the 525 linesthat form the interlace second field.
In addition to the magneticislands that are deposited on the video
tape by the recording head, aminimum of two additional tracks must be
recorded by the machine. One track will contain the audioinformation
(and the techniques are identical tothose of the standard audio tape
recorder). The second track containsinformation which controls the speed
of the playback recorder so thatthe position of the tape will besynch-
ronized exactly with the positionof the video pick-up head. This is
naturally a requirement so that theplayback head will retrace the precise
path made by the recordinghead.
The total frequency spectrumrequired to reproduce a satisfactory
television picture is from 60 Hz(Hertz) to 4 MHz (megaHertz). The electrical
signals are converted to magneticfields by the recording head, and the
oxide coating retains a portionof the magnetic field,as distinct areasof
north and south poles. Onplayback, the north and south polessuccessively magnetic field to be set upthrough pass under theplayback head causing a
electrical signal. the playback coils. This in turn, produces an -14-
the original The electrical signalobviously must faithfully represent electrical field containingthe video information.
magnetic field is Since the electricalfield generated by a changing proportional to the rateof change of flux, there is aninversely propor-
fields. That is, tional voltage versusfrequency produced by the magnetic residual magnetic poles as thefrequency decreases,the strength of the the recording head is toremain must increase ifthe voltage produced in
varies by a factor of50,000 to 1, constant. Since the video frequency It is thus virtually the magnetic field mustalso vary by this ratio. solve this dilemna impossible to record videoinformation directly, and to
electrical information into afrequency it is necessary toconvert the video
modulated signal. signals are represented Since in frequencymodulation the electrical
the carrier frequency,low by the rate of excursionof the frequency from frequency of the recorded frequencies can be reproducedwithout changing the
frequency in most systems is signal appreciably. The nominal carrier system varies the close, to 3 megahertz, andthe frequency modulating
thereby assuring frequency above and belowthis by a limiting amount,
recording head is essentially that the electricalvoltage reproduced by the the resulting constant. The rate at which thefrequency varies determines of the excursion demodulated frequency of thevideo signal, and the amount
amplitude and pOlarity above and below the carrierfrequency determines the modulation used in of the reporduced videosignal. nie type of frequency
the video tape recordervaries from recorder torecorder. modulators and Most of the video taperecorders have separate
electronics demodulators built into theelectronics. To assure that the
provided which does is working properly, aloop-through arrangement is -15-
includes the modulationand not involve therecord - playback heads but that it may be monitored demodulation circuits. This output is arranged so through during recording to assurethat the signal isbeing properly routed
immediate playback without the modulator; it beingimpossible to provide an
duplicating the entire complexvideo record-playbackhead system. -16-
Chapter V
THE PRINCIPLES OFTESTING VIDEO TAPE RECORDERS
signals while The ideal video taperecorder must reproduce video maintaining the inputamplitude and phaserelationship.
Specifically, this meansthat the amplitude ofthe reproduced
video signal for allfrequencies signal will varyexactly as the input
It further means thatthe phase in the televisionvideo spectrum. remain unaltered inpassing relationship betweenall signals shall
through the recording process. number of tests that can The televisionindustry has developed a A series of threesimple well be applied tovideo tape recorders.
fidelity of the televisionsystem. tests will giveinformation on the multiburst or sine-wavefre- These three tests arereferred to as the
quency test,the window test,and the stairstep test.
The Hultiburst Test of constant In the multibursttest, a series ofsine-wave si7nals
amplitude but variablefrequency are fed into thevideo tape recorder
of seven gateddiscreet intervals The multiburst usedin the test is a set sinusoidal consisting of a wiliteflag or windowfollowed by six pure and 4.2 HHz frequency bursts of 0,5MHz, 1.5 HHz, 2 MHz,3.2 MHz, 3.6 Hilz,
frequency burst occupiesapproximately locked to line time. Each sinusoidal the signal werator sothat the eight microsecondsand is adjustable in
amplitude of eachsinusoidal burst can bekept constant. -17-
The reproduced multiburstwill yield the amplitude/frequency response of the system. When the signal output is down to70% of the original signal, it is down 3 db. A drop in signal to 50% Is down6 db.
The Window Test
The window test signal consistsof approximately 30 microseconds of 1007. modulated (white)signal level held constant over theperiod.
Only 150 lines toward the bottomof the television picture isaffected.
As seen on the "A" scope,the window is a pure whiterectangle occupying
approximately one-fourth of thelower left side on a dark screen. The
black portion of the screen isheld at blanking level and the whiteportion
is held at 1007. modulationlevel. The reproduced picture shouldbe
perfectly uniform in intensity overthe entire region with neithertrailing
black nor white at the left or rightedges of the rectangle.
The Stairstep Test
The stairstep test consistsof ten discreet constantsignal levels
occupying the entire pictureframe. The highest level is adjusted to
100% modulation (white) and thelowest level is at blankinglevel.
This test determines theoverloading characteristic of the system
the output and the reproduced signalshould increase at the same ratio as
should be of the test generator. Each portion of the stairstep pattern
level a degreeof pure gray level on the"A" scope starting with a black
and progressing to pure white or1007. modulation. Error in aperture can
be estimated by laying aruler along the stairstep patternand estimating
the deviation of theleading edges of the patternfrom a straight line. -18-
monitor are reproduced Calibration photographstaken with the waveform
This was done to providesimple in this report foreach machine under test. the signals from .the comparison between thecalibration test signals and
1-4, and Figure 1-7 areexamples equipment under test. Figure 1-1, Figure of the three input testsignals. -19-
Chapter VI
ANALYSIS OF WAVEFORM OUTPUT TEST PHOTOGRAPHS
Figure 1 shows a typical high frequency roll-off as depicted by the fact that the third, fourth, fifth, and sixth multiburst patterns are regularly decreasing inamplitude. This high frequency roll-off
*"
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Fig. 1High Frequency Roll-Off
was produced by introducing alow-pass filter which decreased the amplitude of the signal as the frequencyincreased.High frequency roll-off decreases the sharpness ofthe leading white line on the left side of all objects, andthis produces a black smear on the left side of all white objects. It likewise produces a white lag on the right side of allobjects, referred to es atrailing white smear. Fig. 2 Standard "A" Scope Display
Fig. 3 High Frequency Roll-Off Note lack of detail on all bursts
On a window, the result is as shownin Figure 4 where the leading edge of the square is significantlyrounded at the top left side and where the right side of thewindow as it approaches blanking levelis again significantly rounded off. The sync pulses, the downwardportion
of the picture, is likewisesignificantly rounded from the perfectly
square pulse patterns ofFigure 1-1.
MIL
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Fig. 4Waveform of Window With High Frequency Roll-Off Fig. 6 Normal Window"A" Scope
Fig. 7 Window with Blackand White Smear Caused by High FrequencyRoll-Off
Low frequency distortion hasits greatest effect onthe horizontal of portion of the window o' whiteflag. Depending on the time constant
oscilloscope the circuit involved, tbehorizontal bar on the waveform For example, a will show under-shoot,over-shoot, or horizontaltilt. is a drop in am- short time constant over-shootis a negative tilt that Figure 8 shows an example plitude from the leadingto trailing edge.
"A" scope, the gray levelsof large of the latter.When viewed on the Over-shoot, on the otherhand, out- areas changetoward the dark hues.
white or lighter colorghost. lines the left sideof all objects with a NOWA 41411111111.1114111111111111
Fig. 8Low Frequency Distortion Causing Horizontal Tilt
Fig. 9 Window ShowingHorizontal Tilt Effect
A third very common typeof effect that occursin a television
This can be system is due to echo ormulti-signal path in thesystem.
delay of some sort. caused by impedance mismatchtogether with a time times where the This effect is generally morepronounced at those -23-
signal level makes a wide excursionsuch as immediately after a sharp rise or a sharp drop in level.Figure 10 shows echoes or ringing super. imposed on a window. A sharp leading spike precedesthe actual damped ringing signal, and this produces aseries of ghosts that diminishin brightness as they progress towardthe right of the television screen.
8 II -----
I Mir" vwomrairowarmaminitp A4iValtleilinVIMW*11/11 "FMONWMMOMMWMWAMLAM .miasio. ask
Fig. 10Echo or Ringing and Overshoot
Fig. 11"A" Scope of Echo and Ringing -24-
A problem common to011 video tape recorders isthe presence of
Since the video carrier some unfilteredcarrier in the video output. and the highest frequencyto be transmittedby the video tape recorder are of the sameorder of magnitude, itbecomes increasingly difficult to reduce the carriersignal to an acceptable level.
The presence of the carrierfrequency on the video signalwill tend
It has the effect to blot out thefiner details of shading onthe picture. The of reducing the resolvingcapability of the televisionreceiver. presence of ahigh frequency extraneoussignal when combined with the
Since video signal will produce atype of distortionknown, as a.moire.
by some type of the high frequency extraneoussignal is often produced
oscillation effect in the systemthat is amplitude dependent,the resulting
moire effect will shiftand vary with time. This effect is most pronounced
on scenes made upof fine vertical orhorizontal lines. produces a type of The friction between thehead and the video tape
distortion that affects thevertical objects on thetelevision screen.
revolution due to Evidently the head velocitychanges slightly during a
non-uniformity of frictionbetween the head and the video tape This
edge of the results in a noticeable"S" shaped curve on the leading
follow the leading edge under-scanned picture. Since all vertical lines
therefore slightly of the under-scanned picture,all vertical objects are
the same effect is noted asthe "S" shaped. In the quadraplex machine,
skewing of the successive segmentsproduced by each head. This can be
partially remedied by adjustingthe tension control known asthe skewing
control.
In test, most of the videotape recorders exhibited acombination of
analyze each of the video the above factors, and anattempt has been made to
tape recorders'ith respect to the errorslisted above. -25-
Chapter VII
DESCRIPTION OF TEST SET-UP AND EQUIPMENT TESTS ON INDIVIDUALMACHINES
Diagram No. 1 shows the testoet-up used on thevideo tape recorders.
signal generator with the The sync generatorcontrols the Telechrome test The signal signal looping throughthe waveform monitor inthe A position.
the switch position then is fed to themodulator. In the record mode, and the monitor picture appears connects the demodulatorto the modulator,
This position makes itpossible on the Bposition of the waveformmonitor.
but, not the record-playback to check the loopthrough electronic circuit
monitor, the signal loopsthrough head configuration. From the waveform the "A" scope and theline is terminated in a 75ohm resistor. the video tape recorder In the playback mode,the function switch in
playback portion of thevideo is as shown onthe diagram and only the the demodulator, tape recorder isactivated. This signal feeds through
the waveform monitor,and through the "A" scope. obtained by means of a All photographs of thewaveform monitor were
Hewlett-Packard Model 1968Polaroid-Land camera.
photographs taken The photographs of the"A" scope are enlarged 35 mm
high contrast with a Nikon F 35 mm camera. Photographs were printed on
paper to show asmuch detail as possible. almost synchronizes Since the Nikon camera timesetting at 60 cycles
each of the with the playback videosignal, a phasing bar appears on
photographs from the upperleft -hand side to the rightside of the photograph.
An increased exposure Without perfect synchronization,this is unavoidable. possible loss of detail. For would involvemultiple-scanning lines with a maximum detail and the this reason, it wasdeemed desirable to maintain
subsequent phasing bar.
.74 -26-
TEST SET-UP
VTR UNDER TEST
Record /Playback Head
Modulator Demodulator
Waveform Monitor Test Signal Generator
Sync Generator
Diagram 1 EQUIPMENT USED: 1003-DIB VideoTransmission Test Signal Generator: Telechrome Model Test Signal Generator
Generator * Sync Generator: Riker Model 520 Sync Waveform Monitor Waveform Monitor: Tektronix RM 527
Video Monitor and "A" Scope: Modified High Resolution Conrac Model CVA-17Video Monitor
loaned for thisproject by * The Riker Model520 Sync Generator was Street, Hollywood,California S. S. Krinksy &Associates, 6311 Yucca -27- Machine 1, Ampex VR.660
This is the input signal into the machine before passing through any of the electronics. The flag burst is calibrated to 100%. Multiburst signals a_e calibrated to 50%.
Fig, 1-1 Calibration Multiburst
Output level 10% low. Output level starting at 3.2 MHz is reduced to less than one-half its original level. Leading edges of flag indicates high frequency roll-off plus slight ringing.
Fig. 1-2Multiburst Loop-Through
Output 'level 18% low. :Ugh frequency roll-off beginning at 1.5 MHz and num' is reduced to one-half :t Alifilhaik by nowinwr stiriown the original level 1 IILL: 3.2 MHz. Flag and sync signals show definite ringing. Haze in picture shows noise andcarrier leak through.
Fig. 1-3Multiburst Playback -28- Machine 1 Ampex VA -660
4
";:111124.._
Fig, 1.4Calibration Window
The output level is 5% low on loop-through with evidence of tilt due to high frequency roll-off.
NOMIIIIIWASSLY11110/M __MUM
Fig. 1-5Window Loop- Through
The output level IQ15% low. The window indt- cates definite ringing out not in excess of 3%. Approximately 3% tilt indicates high frequency roll-off. General noise 11,6.111. indicates possible carrier leak through.
Fig. 1-6 Window Playback Machine 1 -29- Ampex VR-660
Fig. 1-7 CalibrationStairstep
The stairstepoutput level is 6% lowwith indication of slight ringing. It may be noted that thecarrier leak through onplay- back is lessthan in the loop-through mode.
4
Fig. 1 -6 StairstepLoop-Through
The outputlevel is 16r, low. Slight ringing on allsteps. Differ- ential amplitudedis- tortion verylow.
Fig. 1-9 Stairstep Playback -30- Machine 1 Ampex 66oz
/MI
11
Fig. 1-10Multiburst "A" ScopeLoop-Through
Fig. 141 Multiburst"A" Scope Playback
660B is excellent withgood The loop-through responseof the Ampex Some detail isvisible in response through the3.2 MHz multibursts of extraneoussignals the 3.6 MHz burst.On playback the presence 3.6 MHz burst andinterference are visible asmoire patterns in the low "S" distortion on in the 3.2 MHz burst. This machine has a very the vertical bars. Machine 2 -31- t Ampex VR-1100
I
Fig. 2-1Calibration MultiblirA
The amplitude and phase relationship are faith- fully reproduced through the 3.2 MHz burst with the loop-through signal down not more than 30% at the 4,2 MHz burst frequency. inimr..u..limansimumula 111111011111
.
Fig. 2 -2Multiburst Locr.:-Through
T1:,1 dot:,!le pattern in Le 1.6wiz and 4.2 1,5iz
1 Milli pt..ttr-; indicate the .._1111111111111111111. prcen;e of extrane,ras 91 I Mk signals, probably carrier leak through.The system, however, passes these frequencies with signa] down proaUly I "4111111111111111111111iiiil igumall111111111111111111111111011 5O at the highest multi- burst frequency.
Fig. 2-3Multiburst Playback -32- Machine 2 Ampex VR-1100
Fig. 2-4Calibration Window
The electronic circuit on windowloop-through indicates over compen aation by over-shoot at the trailing edge of the window and over- shoot on the syncpulse. Referring to Fig.2-6, the window playback, the over compensation is necessary to over. come certainof the playback characteristics.
Fig. 2-»5 Window Loop-Through
The leading edgeof the window indicztes asmall degree cf highfrequency ro/L-cff and probably low frequencytilt. an entirely acceptable value intot-, categories.
Fig. 2.6Window Playback -33- Machine 2 Ampex VP-1100
Fig, 2-7Calibration Stairstep
The loop-through stairstep is entirely satisfactory.
Fig, 2.8Stairstep Loop-Through
elc /bac The leefm.threttgiT stair- step is entirely satis- factory anexhibits thh.n aperture distortion. A strai4nt edge laiu along the edge of the stair6te shows that t points come to a oerfectly strait line.
Fig. 2-9Stairstep Playback
A" --aW F.,*".4t44,0+1,4 -34.- Machine 2 Ampex VR-1100
MI*117E/a It
Fig. 2-10 Multiburst"A" Scope Loop- Through
u- Mrnal.
Fig. 2-11 Multiburst"A" Scope. ...;)7,ack
Of the machines tested, the Ampex VRI100 showedthe most favorable playback characteristics.The 3.6 MHz burst is clearly visible on the "A" scope and the moire effect indicates that asubstantial portion of the 4.2 MHz aignal is passed. However, with the inclus- ion of extraneous signals, probably carrier leak throughthat is also evident in the 4.2 MHz waveform monitormultiburst playback picture, see pageX.
ouf -35- Machine 3 Ampex VH-6000
EWE
I IllUan't
- 414 Y._
Fig. 3.1Calibration Multiburst
MN=
High frequencyroll-off _ beginning at 1.5 MHz. i91.1411 Level reduced toone-half !VOL &mamma original level by2 MHz.
Fig. 3.2Multiburst Loop.Through
61111111.1111.
CN roll.off 4.4.4,&...~011111111 High frequency beginning at 1.5Mft. Level reduced toone.half original level by2 Slight ringing onthe flag and carrier leak through.
Fig. 3-3Multiburst Playback Machine 3 Ampex VR-6000
Fig. 3-4Calibration Window
The output level is approximately 5% down.
Fig. 3-5Window Loop-Through
The output level is 51"/: down. The ringing is
3(:". Video noise on base line.
Fig. 3-6Window Playback -37- Machine 3 Ampex VR-6000
ame0111101111111111111110 111111esiefstavarma...... 41111111116.1M1.
Fig. 3.7Calibration Stairstep
Video noise or carrier leak through quite noticeable on all steps.
4.
Fig. 3-8Stairstep Loop-Through
Noise more noticeable than on loop-through and some ringing is noticeable.
Fig. 3-9 Stairstep Playback Machine 3 AmpexvR4opo'
I
Fig. 3.10 Mu ltiburst"A"gOieLoop-Throug
Fig. 3-11 Matiburst"A" Scope Playback
signals. by and playbackpictures-show extraneous Both loop-through cause' Errors'in, of sync pulses the moire patterns. the "A" difficulties in thehorizontalintervals ,near the tc? of pulses for successivelines in'. scope picture.The reproduced'sync uniform as one fieldis slightly' alternate fieldsevidently are not herringbone effect .on the 1.5MHz' and' delayed. This is seen as a. 2.0 MHz bursts= 'earthe top.dr,thepicture. -39- Machine4 Ampex VH-7000
Fig. 4-1 Calibration Multiburst
The. output leVel,is approximately 15% high. High frequency roll-off is 'noticeable at 1.5 MHz. Output level is 30% below
I normal by 2 MHz and very sharp drop to 60% down at 3.2 MHz. Carrier leak through.
Fig. 4-2Multiburst Loop-Through
The output leVel is normal. Noise and ringing on, fag, "' Roll-off beginning at 1.5 MHz. Level is 30% down at 2 MHz and 50% down at 3.2 MHz. Roll-off less sharp than in loop-through,
Fig. 4.3Multiburst Playback
r7,4:17.:1 -40- Machine 4 Ampex VR-7000
Fig.4.44-4 Calibration Window
Definite tilt on window indicating accentuated by frequency reiponse* Base, line noise indicates carrier leak through. The output level i8,10%
rermiresenblormslon..Y.Q high.
Fig, 4-5Window Loop-Through
.d11111.-
The tilt on window indicated accentuated :low frequency ,response* Approximately 3 ringing. %CETrier leak through and noise noticeable on bast line* T output level is approx:imate1.7 5%- high.
, . , , " , . s ... . ,
, -, ' ' . . , . ' ,
Fig. 4.6 Window Playback -41- Machine 4 Ampex VR..7000
Figs 4.7 Calibration Stairstep
Carrier leak through noticeable on all steps, Slight ringing notice- able on all steps., Slight differential gain distortion but not in excess of3%,
Fig. 4.8Stairstep. Loop-Through
The output, levelis ap- proximately 5%,lolf* Noticeable ringing .on all steps. Noise, carrier leak throughfand dlffer- ential gain are the same as in loop- through,'
Fig, 4 .9 Stairstep Playback -42- Machine 4 Ampex VR-7000
/
3 ^ v.,3
Fig. 4-10 Multiburst "A" ScopeLoop-Through
111L
Fig. 4-11 Multiburst"A' Scope Playback
The sync pulses on alternatefields are delayed in both theloop- through signals and the playback nearthe top of the"A" scope dis- picture. The playback picture wasadjusted for Minimum "S" tortion by means of the tensioncontrol..This type ofdistortion is still evident.Detail in the 3.2 MHz burst;'is almost:absent. Machine 5 Concord VTR-400
MIININI111111111
111111Pl".vittry". Novi1.I
61114111114111111 111YMIAMMI
Fig. 5-1Calibration Multiburst
The oiAtput level is, normal. The,bitrst, signal is 30% down at 0.5 MHz and 50% arrrakaffiraimisamh `.down at. :14 MHz. No burst Signal is visible from '3.2 MHZ' on. Hinging, on leading edge ofnag burst.
Fig. 5-2Multiburst Loop-Through
The output level is,:.normal. T.fie,buist'signatis10% down at 0.,5,MHz,and,50% ,-down at 1.5: MHZ, No burst signal iavisjb.e'from 3.2 MHZ. Oh, Ringing on leading edge of flag 'burst. ,Approximately 5% noise and Carrier leak through.
Fig. 5..3 Multiburst Playback -44- Machine 5 Concord VTR-600
411
Fig, 5J Calibration Window
Ringing on leading edge of window. Carrier leak through on base line.
Fig. 5-5Window Loop-Through
The output level is approximately 1. Approximately 3% to4% ringing on entire window. 10% noise and carrier leak through on base:Line,
Fig, 5-6Window Playback -45- Machine 5 Concord VTR-600
1.la am- 11111111MMEmmul1111111111111Imumnim
Fig. 5-7 Calibration, Stairstep
The output level is2% low. Differential gain good,Mild carrier leak through on all steps.
Fig. 5-8Stairstep Loop-Through
The'output level is 5% low. Noise, carrier leak through, and ringing adding to 10% visible on all steps.
Fig. 5.9Stairstep Playback -46- Machine 5 Concord. VTR-600
Fig. 5-10Multiburst "A" Scope Loop-Through
Fig. 5-11 Multiburst"A" Scope Playback "
No "A" scope detailis visibleii.the,playback of the 3.2 Milz'bur*,' uniform from top to The reproducedhorizontal sync pulses sr not bottom of the picture andalternate fields are displaced aOtice-, able degree. "5" distortion due to insufficientconirol'Overtho tape tension isevident. -47- Machine 6 Machtronics MVR-65
Fig, 6.iCalibration Multiburst
Flagindicates,high freq- uency peaking andringing. Irregular placement of multiburst signalsindi-
- cates Modulation or demod- ulhticn system distortion.
Fig. 6..2 Multiburst Loop-Through
Flag burst indicates high frdquency peaking and slight ringing. Irregular placement of muitiburst IL___Aa.AMV. signals less pronounced. lull High frequency response apprOximately '35% down at 3.2 MHz, Over 50% -down at 16 MHz. About 7%
, noise in carrier leak :through,
Fig, 6-3Multiburst Playback -48- Machine6 Machtronics MVR -65
_-
Fig, 6 Calibration Window
Window loop-through indicates high frequency peaking and ringing. Output level is about 5% low with some carrier leak through. .
100,...... 111 , .1C7
Fig. 6-5Window Loop-Through
Window playback indicates high frequency peaking and ringing. Output level is about 5% low and about 3% noise arid, carrier' leak throuh
Fig* 6.6Window Playback
ray -49- Machine 6 Hachtronic s MVR-65
Fig. 6.7Calibration Stairstep
Differential gain is very good. High frequency peaking noted on eachstep. Approximately 1-1/2% carrier 'leak throUgh.
: * '
Fig. 6.8Stairstep Loop-ThroUgh
Some high freVency peak- ing on each step.Differ- ential gain very good. About 4% noise andcarrier leak through.
4
.Fig. 6.9 Stairstep Playback -50- Machine6
S Machtronics,Ktrii45 . a:, "- ; :f; .,"
., .; ', 44S s r, ;..
, ,
1 ; -
NriormioNoml..' 'r
r
,
St
/4
Fig. 6-10 Multiburst"A"scope Loop-Thr9411
, -
Fig. 6-11 Multiburst"A"ScopePlayback
has excellentreproduction This video tape recorder Some : through 3.2 MHz with fairdeiail',uP'tOthe 3.6 MHz- burst. pattern leakage carrier or otherspuriousSignali'cause, the moire tension control: must be readjusted in the 3.6 MHZ burst.The tape scope to eliminate the skewof the upperportionof thene andshowsrthe'api,Slity. The bottom portion showsexcellentlinearity S55555 *
SS of the properlyadjusted machine... . . '. ,
' , :s -51- Machine 7 Precision PI-3V -=10.0,
Fig. 7-1 Calibration Multiburst
11.1.1 Flag indicates high frequency roll-off and slight ringing. Multi- burst signals indicate bad interference between video information and carrier frequency. Freq- uency response down to approximately 40% at 3.2 MHz. Extreme carrier leak through. Video level J113111111MMICEIVM 10% high. Sync level 15% short.
Fig. 7-2Multiburst Loop-Through
Video level about 7% high. Sync level' 20% low. Dis- tortion in multiburst signal due to interference between video information aad carrier frequency which would cause moire interfer- ence in picture.Response down to approximately 40% at 3.2 11Hz. liaise and carrier leak through ap-
proximately 9%. ,
Fig. T 3 qultiburst Playback -52- Machine 7 Precision PI-3V
leo
Fig, 7-4Calibration Window
,...... _ C
The loop-through signal is approximately 6% high. Some high freq- uency ringing indicated. Carrier leak through extremely bad, Sync level 15% low.
Fig. 7-5Window Loop-Through
Playback video level is 7% to 6% high. Noise and carrier leak through extremely bad. Sync level down 15%.
.114Sti MOM
Fig. 7.-6 Window Playback
;- *00.4,4.4114495F0WWIZZreallinal -53- Machine 7 Precision P1-3V
(7)
Fig. 7.7Calibration Stairstep
Loop-through level is 105 high. Differential gain distortion is ap- proximately 35. Carrier leak through extremely bad.
Fig. 7-8Stairstep Loop-Through
Playback level is about 11% high. Differential gain distortion is .about 2%. noise and carrier leak through is extremely bad.
Fig, 7.9Otairstep Playback. -54- Machine 7 Precision PI-3V
Fig. 7-10 Multiburst"A" Scope Loop-Through
I
Fig. 7-11 Multiburst"A" Scope Playback
tape recorder shows The electronicloop-through in the PI-3V video a breakup ofportions of the 3.2 MHz and3.6 MHz bursts--an effect which is time dependentin field time.The effect causes a total the bottom breakup in portiora ofthe bursts. The double lines on by portion of the 3,42 MHz burst onplayback are probably caused ringing in the Ilectronlcscaused:by. high frequencypeaking circuits. -55- Machine 8 Precision PI-4V
A
Fig.8-1Calibration Multiburst
Flag indicates ringing and high frequency roll- off. Multiburst indicates interference between video information and carrier. Response down approximately 28% at 3.2 MHz. Sync level is la short.Carrier feed 104=11111 through is approximately
I 8%.
Fig, 8..2 Multiburst Loop-Through
The output level is 7% low. High frequency ringing.Multiburst owIN signals indicate inter- ference between video c. information and carrier frequency. Sync level is approximately 11% low. Bad noise and carrier leak through.
Fig. 8.3 Multiburst Playback Machine 8 -56- Precision PI-4V
ti
Fig, 8.4Calibration Window
Window loop-through indicates ringing and carrier leak through.
Fig. 8-5Window Loop-Through
Window playback level is approximately5% low. Indicates high frequency ringing. Bad noise andcarrier leak through.
Fig. 8..6 Window Playback -57- Hachine Precision PI-.4V
NV. 1111111....
Fig. 8-7Calibration Stairstep
The differentialgain distortion is approxi- mately 5%.Bad carrier leak through.
.81
Fig, 8-8Stairstep Loop-Through
The differential gain t. distortion is approxi- mately 4%-to5%. Bad noise and carrierleak through.
a
Fig. 8.49 3tairstep rlayback -58- Machine 8 Precision PI-4V
ti
Fig. 8-10 Multiburst"A" Scope Loop-Through
, te A ii / .....-/ II II- II N1:111111111 Auintime :t..
Fig. 9-11Multiburst "A" ScJpePlayback
the field on loop- Extraneous s7Ignals areevident in a portion of the'upper portion ofthe through as sho'n bythe moire pattern on evidently related to theverti- "A" scope picture. The ringing is the lower portionof the cal sync pulse asit is not evident on that the picture. The frequency responseof the playback shows reproducing the 3.2 MHzbursts. video tape recorderis capable of reproduced as evidencedby The vertical syncpulses were poorly excessive. the vertical bar inthe picture. "S" distortion was 5n- Machine 9 RCA VTR-,
11 II. NI 1111111111,1111-
II 11111111MINS '1E111111' 1-
Ma- 111111111"'
Fig. 9.1Calibration Multiburst
The output level is approximately 10% down. Iv Frequency response
111111111111 excell-at to 3.6 MHz. Over 50% down at 4.2 MHz.
Fig, 9-2Multiburst Loop-Through
The output level is approximately 10% down. 111111111111111M Frequency response ex- 4E: cellent to 3.6 MHz. Over 50% down at 4.2 MHz. Some noise and carrier leak through. .11111
Fig, 9.3 Multiburst Playback -60- Machine 9 RCA VTR-5
ou.111111111111111111111101111111111111Ma 1111111111111MNIMUNIIIMMEN111180--
Fig. 9-4Calibration Window
The output level is approximately 15 down, Some carrier feed through,
Fig. 9.5Window Loop-Through
Output level is 10% down. Some noise and carrier leak through.
Fig. 9-6Window Playback Vachine 9 RCA VTR-5
Fig. 94Calibration Stairstep
The differentialgain is excellext. Some carrier leak through.
Fig, 9.33tairstep Loop-Through
Yak The differentialgain is excellent. Carrier plus noise leakthrough.
AR. 11111
aairstep Flayback -62-
Fig. 9-10Multiburst "A" Scope Loop-Through
Fig. 9-11 Multiburst "A" Scope Playback
Loop-through electronics was excellentthrough 3.6 MHz and the playback was equally good throughthe 3.6 MHz burst. Some moire patterns are seen on playback throughthe 4.2 MHz burst and these probably are caused by carrierfeed-through or other extraneoms signals. The effect differs with the severalrecord-playback heads. Each of the quadrapole heads canbe identified ov the slight skew or displacenientl for34 lines. -63- Machine 10 Sony PV-120U
11111111111
AM I Onr' INS
lift I i !1,q
Fig. 10-1Calibration Multiburst
High frequency peaking and ringing indicated. Mid-frequency of burst accentuated as compared III MEI to low and high freq- uency of burst. Output level is approximately 7% low.
(Note: As the video input level was changed, the fifth and sixth bursts went through a series of strange nulls.)
rig. 1010-2 -2 Multiburst Loop-Through
The output level is ap-
iit 11111111 proximately 8-1/2% low. Frequency response is approximately 30% at 111111111-:::""- 2 MHz. Irregular dis- tortion noticed in last three bursts. Some carrier plus noise leak through.
Fig. 10-3Multiburst Playback vianftraft.O.ftifima
-64- Machine 10 Sony PV-120U
..,.". ti
Fig. 10-4Calibration Window
Window indicates high frequency peaking and ringing.
.nrillAtaftlin=MMW
Fig. 10-5Window Loop-Through
Window indicates slight ringing cmd carrier plus noise leak through.
Fig. 10-6iindow Playback -65- Machine 10 Sony PV-120U
Fig. 10-7 Calibration Stairstep
The differentialgain is extremely good. Some carrier leak through.
11111104
Figs 10-8Stairstep Loop-Through
The differentialgain is good. Carrier plus noise leak through.
F ::,tairatep Playtaeli. -66- Machine 10 Sony PV-120U
Fig. 10-10 Multiburst "A" Scope Loop-Through
Fig. 10-11 Multiburst "A" Scope Playback
The electronic loop-through picture showssatisfactoryreproduction through the 3.2 MHz burst. On playback the 3.2 MHz burst is just visible and a small amount of carrier leak through orextraneous signal causes the moire. The absence of the moire pattern onthe 3.6 MHz and 4.2 MHz bursts is due to the lackof a sufficient signal in these frequencies to produce theinterference. Satisfac- tory horizontal sync pulses arereproduced to lock the horizontal drive oscillator. -67- Machine 11 Sony EV-200
Fig. 11-1Calibration Multiburst
Flag indicates some high frequency ringing plus low frequency accentuation. Freauency response 50% down at 3.2 MHz. Some carrier leak through;
(Note: The last three bursts on the multiburst went through a series of nulls with a change when the video input level was 1111111 changed.)
Fig. 11-2Aultiburst Loop-Through
High frequency ringing indicated on flag burst. Frequency response down 30% by 2 MHz. Noise and carrier leak through.
Fig. 11-3Multiburst Playback -68- !Nchine 11 tiony LV-200
qt
Fig. 11.4Calibration Window
Carrier leak through and' high frequency ringing.
jit:MIII
Fig. 11-5Window Loop-Through
High frequency ringing, carrier leak through, and noise.
Fir. 11-6 Window Flaybacl,. -69- Machine 11 Sony BV-200
ammikaorrnairmismiumnsimmiimmminimmimmuimr'""
Fig. 11-7Calibration AairStep .
The differentialgain is excellent.Carrier leak through.
Fig. 11-8Stairstep Loop-Through
The differentialgain is good. Carrier leak through plusnoise.
Fit. 11-93tairstep Playback 70- Machine 11 Sony EV-200
Fig. 11-10 Multiburst "A" Scope Loop-Through
Fig. 11-11 Multiburst"A" Scope Playback
"A" scope picture The Sony EV-200 produced aremarkably excellent electronics on bothloop-through and playback.The loop-through good a signal was verysatisfactory through 3.2MHz with almost as low for an economy on playback. "S" distortion, likewise, was helical-scan machine. -71- Machine 12 Sony SV.300
111111111111
Fig. 12-1 Calibration Ailtiburst
_11111111l Flag burst indicates high frequency ringing plus high frequency off. Frequency ,response 30% down at 4,9,f MHz. 50% or more at 1,5 MHz.
Fig, 12-2Multiburst Loop-Through
Flag burs: indicates high frequency ringing and high frequency roll- off. Frequency response 30% dovn at O, MHz. 50% or more at 1.5 MHz.
Fig. 12-3Multiburst Playback -72- Machine 12 Sony SV-300
4.1.,1111..M.11111...... 01.111110.10.1,
Fig. 12-4 Calibration Window
Indicates high frequency roll-off. Low frequency accentuation. Carrier leak through.
...... 211...111411116. Mb* .11111111C
Fig. 12-5Window Loop-Through
Indicates high frequency roll-off. Low frequency accentuation. Noise and carrier leak through!
Fig. 12 -6 Window Playback Machine 12 -73- =1K11111111 Sony 0-300
Pig. 12-7 Calibration Stairstep
The differential gain distortion is about 2%. Rounding edges of stair- step indicates ,high .frequency roll-off. Blur in picture indicates carrier leak through and/or noise:
Fig. 12-8Stairstep Loop-Through
The differential gain distortion is about2%. Rounding edges of stairstep indicates high frequency .roll-off. Blur in picture indicates carrier leak through and/or noise.
Fig. 12-9Stairstep Playback -74- Machine 12 Sony SV-300
nv.111
11.
Fig. 12-10Multiburst "A" ScopeLoop-ThrOugh
Fig. 12-11 Multiburst"A" Scope Playback
video not represented asbeing an education4 The Sony SV-300 was at 2 MHz and The loop-throughelectronics cut off tape recorder. The particular low at thisfreqgency on playback. was equally with the panel for test couldnot be adjusted, machine submitted portion of the"A" scope adjustments to preventbreakup of the top picture. -75- Machine 13 3M Wollensak VTR-150
1111 :A** Air. 0 1111111: 1 1 III MI 1111911111 I ill IIIRM17 MI
I 14111911
Fig, 13-1Calibration Multiburst
1111
Loop-through signals are through video amplifier and not through any type 11.111111111.111' Pit of modulation and demodu- lation system. Approxi- mately 15%.
IL -
Fig. :4u1tiburst Loop-Through
High frequency peaking at and ringing indicated. Amplitude of syn pulse extremely long. Freq- MIL" uency response approxi- mately 50% down at 1.5 MHz.
Fig, 13-3Multiturstila.'back Macnine 13 314 Wollensak WW-150
Fig. L3- Calibration Window
Loop-through signals are through video ampli- fier and not through any type of modulation arid demodulation system. .Approximately 15%.
Window playback extremely high frequency peaking and ringing indicated plus noise.
'UNA 1.1.1 -77- Machine 13 3M Wollensak VTR-150
Pig. 13-7 CalitionStairstep
Loop - through' signals are through videoamplifier and not through anytype of modulation anddemodu- lation system. Approxi- -ately 15%,
Pig. 13-8Stairstep Loop-Through
The differentialgain is extremely poor. Bad white compensation.'High frequency peakingand ik ringing indicated. Bad hi. hher bar lbrik noise on output. N.shat.
Mae
3-9 -.;tairstepP1aybae2k _ ...kkotwelowome .
-78- Machine 13 3M Wollensak VTR-150
11111hir...
Fig. 13-10Multiburst "A" Scope Loop-Through
Fig. 13-11Multiburst "A" Scope Playback
does not involve the The loop-through"A" scope picture evidently to be a direct modulation and demodulationcircuits as it appears of course, video amplifier loop.The resulting pictures are, electronics and so excellent but they do notrepresent the entire loop-through pictures. the picture cannot becompared with the other The playback signals cutoff very sharplyafter 1.5 MHz and the The horizontal sync pulses areaccordingly reproducedbut poorly. vertical lack of adequate horizontal syncpulses causes the uneven bars. .11 -79-
Chapter VIII
MECHANICAL COMPARISON
A detailed mechanical analysis of each video tape recorder was undertaken. The topand bottom plates of the recorders were removed and the unit was examined from the standpoint of routine maintenance of such items as belts, replacement of heads, accessibility of test points, soldering connections, etc. Chart No. 1 is a comparison of the mechanical construction of the video tape recorders tested based on a rating from "1" to "3", the numeral "1" indicating the molt*__' satisfactory condition for each factor considered.
In several of the recorders, it was evident that minor changes had been made after construction; and probably most of the units submitted for test were demonstration models rather than off-the-line models. Consequently, there is no assurance that a different set manufactured by the same company would not have exhibited other characteristics. 4.$ 14 '0,4 CD 0 41.4 0 00) 0C) 3 1 3 2 3 1 2 3 3 2 2 2 3 0 0 0 4 0 Z >1 4$0 c30 ' 44 114 0 0 $4 pf C.) 90' 0) Sri Z.4 240' 3 1 2 3 3 I 2 2 3 '1 2 3 1 3 12 22 2,2 32 1 11 22 33 21 21 23 22 bo Cd 2 1 3 2 2 3 2 3 2 1 1 2 1 41) 4.) .14Rf HW 0,0*I-I .00 44(4 3 2 3 2 2 1 2 3 2 1 2 2 2 *r1 4.) 03 CO4D 04 $23 COMPARISON 1 44 0 W to 0 1 1 3 3 1 1 1 1 1 1 3 1 1 -80- Chart 1 1 3 3 2 1 1 1 2 2 2 2 1 MECHANICAL 3 1 1 2 3 1 3 3 1 1 1 1
VTR-150 MVR-65 PI-3V PI-4V VTR-600 VR-1100 VR-6000 VR-7000 PV-120U EV-200 8V-300 VTR-5 Wollensak Ampex Ampex Ampex Concord Machtronics Precision Precision RCA Sony Sony Sony 3M COMPARATIVE VITAL CHAPTER IX STATISTICS NAME OF MACHINE PRICE HEIGHTINCHES WIDTH INCHESAS SUPPLIED LENGTHINCHES BY MANUFACTURERS WEIGHTPOUNDS v.VIDEO p-p IN VIDEO v. pia... OUT TAPEINCHES WIDTH TAPEIPS SPEED REELINCHNI....12-1/2 SIZE AmpexAmpex VR-660B VR-1100 $ 27,900 8,000 7414-5/8 42-1/429-7/8 2717-3/8 800100 1.0.5 - 2.0 .5 - 1.0 2.0 22 7-1/215 3.7or 14 Ampex VR-6000 1,4503,150 1015 2529 1418 6580 1.01.0 1.01.0 11 9.69.6 9 9.3/4-3/4 AmpexConcord VR-7000 4 VTR-600 1,150 10 -1/2 16-1/2 17 53 1.0 1.0 1/2 12 7 Machtronics MVR-65 11050 10-3/8 24-1/1624-7/16 13-7/3213-7/32 7584 0.5-1.40.5V.1.4 0.5-1.4 0.5-2.0 11 7.5 10.510-1/2 PrecisionPrecision PI-3V PI-4V 11,500 7,800 10-3/8 24-7/16 13-7/32 85 1,4 1.4 1 7-1/2 & 15 8.46 10-1/212-1/2 RCA VTR-5 18,905 8,950 3725 3317-1/2 2716-3/4 475150 0.8-1.20.5-1.5 1,00.5 -2.0 2200 4.25 7 SonySony PV-120U EV-200 3,550 17-7/8 11-1/8 26 88 0.5-2.0 0.5-2.0 1.0 7.87.5 8 Sony SV-300 Wollens a VTR-150 1,2501,495 11 9 1814 1519-1/2 4547 -.1 to 2 1 1 to1 2 1/21/2 7-1/2 7 AmpexNAME OFVR-6608 MACHINE NO. OF HEADS MILS HEAD7-1/2 WIDTH HEADu INCH GAP HEAD VELOCITY 650IPS MILSPROTRUSION DEGREESSLANT ANGLE HEAD SPEED RPM1800 Ampex VR-1100 42 lo - 15 5 - , 7-1/2 ips - 60 1500 35 90 9 14,400 Ampex VR-6000VR-7000 1 60 9555 1000 3 3600 MachtronicsConcord VTR-600 MVR-65 23 128 0.50.039 mils 645484 5.0 20 3.16 7 18001800 Precision PI-4VPI-3V 2 8 0.040.o4 mils 620 62o 88 4-1/2 18001800 SonyRCA. VTR-5PV-120U 2 5 & lo 7 4o.090 74o1561 3.0 8 17°17'17" 3.0 14,4003600 Sony EV-200 2 6 NA 590 6 18001800 3MSony Wollensak sv-ago-; VTR-150 NA-15, .189, 425 1.7 90521 3600 0 NAME. OF MACHINE HOURSHEAD LIFE BANDWIDTH ELECTRONICS PLAYBACK BANDWITTH SIGNAL,- TO -NOISE IN LINES RESOLUTION FCC TIMEBASE TRANSISTORS TEMPERATUREDtzetatIORATION 5% AmpexAmpex VR-1100 VR-660B 250100 3.04.0 MHz MHz 3/04.0 MHz MHz 4040 db 270350 YesYes AllAll AmpexAmpex VR-7000 VR-6000 500 3.03.5 MHz MHz 3.0305 MHz MHz 40 42db db 250310 NoNo AllAll ConcordMachtronics VTR-600 MVR.65 750250 3.53.3 MHz 2.63.5 MHz MHz 4042 db db 250320 YesYes 62193 1 15°C, 0 °C, h h50°C 45°C Precision PI-3V 250 3.5 MHz 3.5 MHz 30 30db db 300300 YesYes 8454 1 1 40°F40°F, h h 120°F120°F RCAPrecision VTR-5 PI-4V 250 3.54.5MHz2511z. MHz 25Hz-3.54.5MHz MHz 40 db 400 Yes 1 0°C, h 45°C SonySony PV-120U EV-200 500500 3.33 MHzMHz 3.33 MHzMHz 4240+ db db 330320 Yes 175100 1 110°C, 10°C, h h 40°c4o°c Sony, SV-300- 1 0 500 NA2 MHz 2,52 MHzMHz 4035 db db 180160 to 200 NoNo 5148 NAME, OF MACHIlly SLOWPOSSIBLE SPEED STOP POSSIBLE FRAME RACK MOUNT FOOTAGECOUNTER OFINTERCHANGE TAPE 'TRACKSAUDIO AUDIODISTORTION REMOTECONTROL AmpexAmpex VR-1100 VR-660B YesNo YesNo NoNo NoYes YesYes 22 1.0%1% YesYes AmpexAmpex VR-7000 VR-6000 NoNo YesYes NoNo YesYes Yes 1 1.0%1.0% NoYes Concord VTR-600 No Yes No Yes Yes 1 amplifierin monitor1% is YesYes Machtronic'sPrecision MVR-65 PI-3V YesNo YesYes NoNo YesYes YesYes 21. 3% Yes PrecisionRCA VTR-5 PI-4V YesNo NoYes NoNo YesNo YesYes 2I1 Opt.Std.. 3% 3% YesYes SonySony PV-120U EV-200 YesYes YesYes YesYes YesYes YesYes 22 Less6%3%Less than than Yes Sony3M SV-300 Wollensak VTR-150 No YesNo No YesNo YesYes .1" 1 NA3% No 1 NAMEAmpex OF VR-660BMACHINE MODULATIONHetrodyne SYSTEMModulator DEMODULATION&Pulse Low PassCounter FilterSYSTEM- Detector Ampex2220LOCAL CorporationBay ADDRESS Road, Redwood City, California 94063 AmpexAmpex VR-1100 VR-6000 MultivibratorMultivibrator &Pulse Low PassCounter Filter Detector AmpexAmpex22202220 CorporationBay CorporationBay Road, Road, Redwood Redwood City, City, California 94063 AmpexConcord VR-7000 VTR-600 MultivibratorDouble Side Band FM PulseDouble& Low Counter Pass Filter Filter Detector Ampex1935Concord2220 CorporationArmacostBay ElectronicsRoad, Avenue, Redwood Corporation Los City, Angeles, California 90025 California 94063 03 MachtronicsPrecision PI-3VMVR -65 FrequencyFM Modulation FrequencyPulse Counter Demodulator Demodulator PrecisionMVR3170470 Corporation SanPorter AntonioInstrument Drive, Road, PaloCompany Palo Alto, Alto, California California 94304 94306 RCAPrecision VTR-5 PI-4V HeterodyneFrequency ModulationModulator PulseFrequency Counter Demodulator Demodulator RadioPrecision4203170 TaylorCorpoiationPorter Instrument Street, Drive, of SanPaloCompanyAmerica Francisco, Alto, California 94304 California Sony EV-200PV-120U FM Modulation FM Demodulator Sony926926 Industrial CorporationIndustrial Avenue, Avenue,of America Palo Palo Alto, Alto, California California Sony3M SV-300Wollensak VTR-150 None bandFM with Recording Double Side- NoneatorLimiters Detector with Discrimin- 926Sony3203 Industrial MCorporation ShawCompany Road, Avenue, of Palo Alto, South San Francisco, America California California -86-
Chapter X
CONCLUSIONS
Comparison oftechnical vital statistics, From the datafurnished under
nocompatibility betweendifferent it is obviousthere is absolutely
exception: RCA and the Ampex manufacturers ofequipment with one of the machinesalmost without quadraplex machines. The remainder record tapewidth, head velocity, exception differin such categories as
FM carrierfrequency, slantangle, head width, typeof modulation, everysignificant electronic diameter of recordinghead, and virtually
characteristic. drawn that theproblem, willprobably A furtherconclusion can be that the near future. During the time increase ratherthan decrease in and execution stages,the Dage DV-300 this project wasin the planning replaced with a new project becauseit was to be waswithdrawn from the demonstrated a portablemachine at the NAB con- model. Westel Company prior to furnish aproduction model ference in Chicago,but was unable The followingadditionalcompanies are to theconclusion of thisproject. machines or have amachine that wasnot either in processof planning
available forexamination: and 2000) Ampex Corporation(Models Nos. 1200 Fairchild IndustrialProducts General ElectricCompany Ikegami ElectronicsIndustries, Inc. International VideoCorporation Matsushita (Panasonic)Company Inc. (NorelcoE1-3401A/54) North AmericanPhilips Company, Par, Ltd. No. TCV-2010) Sony Corporationof America (Mode Wesgrove Electronics,Limited Winston ResearchCorporation the presentlyavailable list, Since video tapemachines,are added to improved, it would seemrealistic others are delayed,and still others are for the State of California tohave a continuing testing program to examine machines as they aremade available to school systems. The results
could be an addenda to this report, and thismight enable the administrators
to keep up to date on the stateof the art. -88-
SELECTED REFERENCES
Ampex Corporation, "Methods of Waveform Testing, Pulse & Bar - 'K' Factor," ABC Laboratory Report No. 26
Foss, Stan, "Vertical Interval Testing with the New RM529 Waveform Monitor," April, 1965, Tektronix, Inc., Beaverton, Oregon
Hewlett-Packard Bulletin, "A New TV Waveform Oscilloscope for Pre- cision Measurements of Video Test Signals," Vol. 17, No.6, February, 1966
Hewlett-Packard Bulletin, "Precision Measurements of VideoSignals," February 15, 1966
Hewlett-Packard Bulletin FEN, "Television andSine-Squared Testing," Supplement, January 24s, 1964
Instructional Television Library Project,"Instructional Television Materials," Third Edition, 1964
Lewis, William C. "Television Tape Recorders" University of Colorado, April., 1964
Stucker, Howard & Winslow, Ken,"Specification and Selection of a Video Tape Machine for EducationalApplications"
WEie, Dr. Warren L., "The Selection and Purchaseof TV Systems and Related Hardware by Santa Clara CountySchool Administrators," February 14, 1963
Wade, Dr. Warren L., "TV Equipment,Systems, Facilities, and Personnel: A Guide for SchoolAdministrators," April, 1965
Wiens, Dr. Jacob R., "Planning forInstructional Television," January' 10, 1966 APPENDIX A
-89-
LIGHTING
The typical classroom has avarying light intensityfrom approxi minimum mately 10 foot-candles to 50foot-candles. This light intensity is
the typical classroom for Image Orthicon cameras. The light intensity in is wholly inadequate for aVidicon camera. While the present-day Vidicon camera can produce apicture at this light level, atleast two factors combine to produce a less thansatisfactory telecast.
the 1. As the light level decreases,the electronic circuitry in
Vidicon camera can be adjusted toproduce an electron signal
which compensates for thedecrease in lightlevel. This electronic
manipulation, however, decreases thesignal-to-noise ratio and
has the effect of increasingthe background randomlight pulses.
This effect is referred to as"snow."
be increased 2. The light level reachingthe camera tube itself may
by increasing the camera aperture. Increasing the camera
aperture decreasesthe depth of focus. The depth of focus is
measured by the number of feetthat the object may movetoward or
Thus, with a low away fromthe camera before the pictureblurs.
light level, the classroom teachermust remain within a foot or
two of the initialdistance from the lens ofthe camera in order
that the picture stay infocus. It is obvious that this is a
severe handicap tothe teacher and perhaps animpossible situation.
It may be entirelyimpracticable to bring in asufficient amount of
light into a regular classroom topermit televising the teacherin this
required for satisfactory situation. Approximately 200 foot-candles are
results with a Vidicaon camera. This would put a uniformlight intensity
over the floorof a normal classroom, andilluminate the chalkboard, -90-
This may possibly a map onthe side of thewall. the teacher'sdesk, and in turn watts oflight. This light intensity require asmuch as 15,000 in the room temperaturerises unduly and, generatesenough heat that the air-conditioning andrefrigeration to keep practical cases,requires roomcomfortable. the other hand,will operate with some The ImageOrthicon camera, on 100 foot-candlesof light. The Image degree of successwith from 50 to expensive instrumentand requires Orthicon camera,however, is both an for each telecastto producesatisfactory special adjustmentsand handling to safeguard of two personsis a minimum crew results. A technical crew of the ImageOrthicon camera. and to properly usethe capability APPENDIX B -91-
VISUAL AIDS
Programs that have proven to be effective for teaching by television make massive use of visual aids.A television lesson that is written on a blackboard in a dimly lit classroom will reproduce by television more poorly
than the same lesson produced live by the instructor.
Visual aids properly prepared and skillfully used are most effective.
The visual aids that some teachers may find difficult to prepare entirely
by themselves are:
1. Flip cards and other printed material. This requires access to
a printing press, paste-on type,photographed menu bulletins, and
hand-lettered material. Graphic material prepared on an ordinary
typewriter is so inferior when compared with what the child sees
in his favorite television show as to be ineffeetive and probably
negative in effect.
The use of animated devices. Most teachers are not familiar
with the various types of machine-operated gadgets, objects, and
figures that make a first-rate television program a success. The
Walt Disney approach to learning may be effective, but it requires
the imagination, skill, and ability found only in a limited number
of people. The absence of skillful visual aids turns an otherwise
good television lesson into an ordinary look-and-see program.
3. Objects and models. A good television lesson may require an
extensive use of models, objects, and other pieces of equipment to
illustrate the point. Most individual teachers have neither the
time to look for nor the knowledge as to where this kind of
equipment is available. One major difference between a television
lesson produced in a major studio and the ordinary classroom is the
access the studio has to countless sourcesof models and devices. -92-
is a small section 4. Motion Picture Clips. A motion picture clip photo- of motion pictureabstracted from a commercial film or
graphed by the studio. A school system rarelyhas the equipment
producing acceptable and the trainedtechnicians capable of only add to motion picture material. Such motion pictures not
situations that could the program butthey very often depict 1 usually impossible not be producedotherwise. For example, it is
in the breeze for the television camerato view a flag waving
seconds of the scene be directly. This requires that the few
that either photographeddirectly by a motion picture camera or
this portion be cutfrom a commerically madefilm.
great care must be If commercial filmis used for film clips, and that the taken that all commercialrights have been respected
institution has compliedwith the latest copyrightrules. One
district may use (in a of the present pertinentrules is that the motion purely closed-circuitsituation) material taken from a material is picture without paying aroyalty provided that this
complete production not used after sixmonths. This means that the and must be redone everysix months or the schoolmust carefully
meticuously check copyrightlaws and obtain releases.
for a For the above reasons, itbecomes virtually impossible
small operation to includemotion picture clips in atelevision
production.
picture clip, an In addition to the, matterof procuring the motion
technical equipment in entire new dimensionmust be added to the picture clips. order to make it possible toincorporate the motion
forA.,,n...... ore.,1 -93-
It suddenly becomes necessary to add a motion pictureprojector and the related camera, a switching system, andan operator to
incorporate the filmclip at theproper place.Few if any motion picture clipswill be used ina small school television system. r V1,4 -,4,-,t1WFTIRTTMK
-94-
ACKNOWLEDGEMENTS
I wish to acknowledge the cooperationand interest in this project given by the Public SchoolInstructional Television Committee of California headed by Mr.Roy C. Hill, Chaiiraan; sadalso the work of Mr. Guy M. Reinke, Consultantfor A -V, who firot conceivedthe project and assisted in getting theproject tinder way.