Multiple Generations on Video Tape Recorders

1 DOCUMENT RESUME EM 000 327 ED 022 369 By- Wiens, Jacob H. MULTIPLE GENERATIONS ON VIDEOTAPE RECORDERS. and School LibraryEducation. California State Dept. of Education,Sacramento. Bureau of Audio-Visual Spons Agency-Office of Education(DHEW), Washington, D.C. Repor t No- ESEA -5; NDEA -3 Pub Date 68 Note-43p. EDRS Price MF -S025 HC-S1.80 EVALUATION, EQUIPMENTMAINTENANCE, Descriptors-COSTS, EDUCATIONALEQUIPMENT, *EQUIPMENT DESIGN, *VIDEO TAPERECORDINGS EQUOvENT STAMARDS,*EXPERIMENTS, RESEARCH 6401, Sony EV200, Sony Identifiers-Ampex VR6000, AmpexVR7000, Ampex VR7500,Concord VTR600, Craig PV120U, Sony SV300, WollensalcVTR150 recorders were testedfor their dubbingcharacteristics Helical scan video tape two in order tomake selection dataavailable to mediapersonnel. The equipment, by the manufacturers.The test was recorders of each typetested, was submitted of a single tape, designed to producequality evaluationsfor three generations levels of probable use inthe school situation.The experiment thereby encompassing all playing the recording tested four conditions:making a recordingand playing it back; making a copy of therecording and playing itback; and back on a second machine; in the study making a recording ofthe copy and playing itback. This representation waveform monitor, whichhas meaning forthe appears in twoforms: on the standard For each engineer; and on apicture monitor,which has meaning tothe media specialist. conditions, still photographsof the waveformoscilloscope of the four experimental performance and for image and the picturemonitor image weremade to analyze the recorders studieddetermine reproduction in the report.Various design elements in of their value for various uses.The conclusion is thatthere are three groupings quality and price range.When the intended usehas been recorders based on picture from one of the determined, the appropriategrade of machine maythen be selected groups.(PIT) 0 0

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CALIFORNIA STATEDEPARTMENT OF EDUCATION SUPERINTENDENT OFPUBLIC INSTRUCTION MAX RAFFERTY 1968 SACRAMENTO 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.

MULTIPLE GENERATIONS ON VIDEOTAPE RECORDERS 0

Prepared by Jacob H. Wiens Director, College of the Air College of San Mateo

For the Bureau of Audio-Visual and SchoolLibrary Education California State Department of Education This manuscript was prepared under Standard Agreement No. 3404 by Wiens Electronics Laboratories 130 Crest Road Woodside, California

It was reproduced with NDEA, Title III, and ESEA, Title V funds. PREFACE

the dubbing characteristics The purpose of thisstudy was to investigate personnel may have of helical scan video tapedevices so that media make more graphically presented dataavailable to allow them to The representa- realistic appraisals ofmachines underconsideration. which has meaning tion in this study is on astandard waveform monitor which has more meaning tothe to engineersand on a picture monitor reproduced electricalcharacteris- media specialist. In the former, the visual or pictorial tics are represented;and in the latter, a representation is presented. by the manufacturers The equipment examined wasvoluntarily submitted invited to supervise thetests and for testing.Their engineers were to assure thatthe equipment wasfunctioning properly. for by the StateDepartment of The tests on themachines were arranged National Defense Education Education and werefunded in part by the should be made for thework of the team Act. Special acknowledgments the tests under the of electronicsspecialists which conducted Audio-Visual and SchoolLibrary direction of Guy M.Helmke, Bureau ot of Dr. Jacob H. Wiens,Director of Education. The team was composed Chief Engineer, KCSM-TV; the College of theAir; Francis J. Morgan, from the College of and Walter C. Nichol,Technician, KCSM-TV; all this report do San Mateo, San Mateo,California. The conclusions of recommendations of anyState not necessarilyreflect the official agency

Harry J. Skelly,Chief Donald E. Kitch Bureau of Audio-Visualand Acting Chief Education Division of Instruction School Library Preface

Introduction 1

Helical Scan Tape Recorders 1

Video Quality Test 2

The Test Procedure 3

The Test Sony EV-200 6 Sony SV-300 9 Sony PV-120-U 11 Ampex VR-7500 13 Ampex VR-7000 17 Ampex VR-6000 20 Wollensak VTR-150 22 Concord VTR-600 25 Craig 6401 28

Equipment Reliability 31

Tape Guides 31

Cleanliness 32

Cleaning Solution 32

Tape Tension 33

Tape Interchangeability 33

Standard Tape Format 33

Tape Costs 34

Gre lings Among Tape Recorders 34

Video Tape Recorders Tested 36

Test Equipment Used 37 Multiple Generations on Video Tape Recorders

Introduction

Video tape recorders have now become an integral part of oureducation program. The video tape recorder makes it possible to record material for review and instruction, as well as.to provide the means for storing instructional material for subsequent playback. Ideally, the video tape recorder should be capable of playingback the recorded material without degradation. This means that the picture as viewed on a picture monitor on playback would be as good as the original picture.

The state of the art has advanced to the point where it is physically possible with the highest quality equipment to produce a recorded picture that cannot be distinguished by the eye from the original picture. The cost of this equipment, however, is high and, the attention of many school administrators is focused upon the less expensive and more portable helical scan type of video tape recorder.

Moreover, in addition to making ehe initial video tape, educators see a need to make copies of tapes. Any deterioration of picture quality in the process of recording and playing back will have a negative effect on the final product.

It is hoped that this test may serve as an aid in determining whichof the helical scan video tape recorders present capabilities which promise to fulfill the planned needs of educational programs.

Helical Scan Tape Recorders

The equipment investigated and studied in this report is limited to the helical scan type video tape recorder. In the helical scan machine, the signal is laid down on a slant across the video tapl. The industry is currently producing helical scan video tape recorders in the two- inch, one-inch, and half-inch format. The two-inch format machine tested in this series is the Sony PV-120-U.

A large number of mechanical configurations are used to make contact between the video tape and the recording head. A simple configuration uses a 1800 tape-wrap and two recording heads so that one head is constantly in contact with the video tape. This configuration requires a head switching assembly thatcomplicates the mechanical adjustment.

In another configuration, the tape wraps entirely around the drum of the head using a conical wrap. This is sometimes referred to as an alpha wrap because of its similarity to the Greek letteT a. The alpha- wrap machines generally employ asingle head.

The most common tape configuration, the omega wrap, uses a wrap which makes a loop around the head very similar to the Greek letter "omega" fl. This type of machine usually uses a single head. encountered machines isthe difficulty fault in allhelical scan impossible A common track to thenext. It is virtually in switchingfrom one slant from ehe endof one with ehe headin passing to maintaintape contact is easily next line. This difficulty line to thebeginning of the in whichehe configuration inthe omega wrap observed fromthe tape in passingthrough of contactwith the tape head iscompletely out In the AmpexVR-7000 of the tapetraverse. the smallbottom segment lines aremissing approximately eightfull video series, forinstance, 57. with the tape, seeFigures 55 and due to lossof head contact with thevideo machine thehead loses contact Since in thehelical scan reproduced bythe of time, no syncpulses are tape for asmall segment time, themonitor or this timeinterval. During this of recorder for by virtueof the behavior to afree-running state receiver reverts When the syncpulses are again oscillator circuit. period of time the horizontal oscillator huntsfor a short transmitted, thehorizontal time is a the syncpulses. The recovery before againlocking with oscillator drivecircuit of thehorizontal function of thetime constant involved. and differswith thecircuitry of the local pulses and thesubsequent hunting The momentaryloss of sync the videopicture results in adisplacement of horizontal oscillator video picture, in the upperportion of the and sometimesin a "hook" depends uponthe dura- of thisdistortion see Figure53. The severity adjustment onthe video pulses, thetension tion of theabsence of sync tape, andehe electroniccircuitry. the videopicture is drop-out withrespect to The locationof the head to occur near drop-out in allmachines is made important. The head is justbefore pulses and themostfavorable location the vertical sync With the headdrop-out located of vertical syncpulses. oscillator has the the series the horizontal point in thetime sequence, information of the at this the firstpicture longest time tostabilize before next fieldis reproduced. phenomenon is animportant head drop-out The problempresented by the head-to-tape material. The loss of one inmaking copiesof the video time material shouldfall at the same contact onehe re-recorded not occur,the original recording. If this does sequence asin the increase with aresulting aggravation number of missingsyncpulses will of the videopicture hook.

Video QualityTest excellence in termsof engineer measurespicture The electronics factor,bandwidth, relates distortion, andnoise. The first bandwidth, device. produced bythe electronic to thefrequencies of a multibursttest signal response ismeasured by use The frequency produces a seriesof signalsconsisting generator. This generator white flag andfollowed signal referredto as a first of awhite level 1.5 MHz, 2.0 MHz, frequency burstsof o.5 MHz, by six puresinusoidal to linetime. See Figute A. 3.2 MHz, and4.2 MHz, locked

-2- s RIM 1111111111111111m '11

111111111111

Pig. A - Multiburst Standard

The second factor, distortion,refers to the preciseness with which the signal is reproduced by the entire system. If the output signal is exactly similar to the input signal, the systemis said to have no distortion.

The third factor, noise, in the signal is aform of distortion caused by extraneous, short duration pulseswhich produce sharp, white specks on the screen and are verydistracting to the eye.

The resolution chart as viewed on apicture monitor is most meaningful to the layman, see Figure 1. This chart has a series of circles in the four corners of the picture, a seriesof line wedges, a series of gray steps, and anothercircle at the center of the picture. From the numbers along the line wedges, it is possible todetermine the resolution in terms of lines. A deformation of fhe circles in the corners or in the center gives an indicationof the linearity of the entire system. Vertical elements will give informationabout the line rate stability of the unit.

The Test Procedure

To simulate a school use as nearly aspossible, the test consists of:

a. making a recording and playing it back, b. playing the recording back on anothermachine, c. making a copy of the recording andplaying it back, and d. making a recording of the recordingand playing it back.

The real school situation might be thatof making a tape, playing it over a school closed-circuit system,recording the material off the air or otherwise at one of the participatingschools and then making copies of the tape to be used in other classrooms. The grade of video tape recorder equipment will depend upon the usemade of the third generation tape and the necessity for editingand duplicating.

Two identical video tape recorders ofeach type were used in the test.

-3-

a.' The entire test system was regulated by a TelemationBroadcast Syn- chronizing Generator, Model TSG-2000M.

The flag and multiburst test signal was producedby a Telechrome Video Test Generator, Model No. 3508-C2. The multiburst signals were calibrated by a Hewlett-Packard Waveform Oscilloscope, Model No.191A, and fed directly to the input terminals to thefirst video tape recorder. A two-minute sequence of the multiburstsignal was recorded.

The resolution chart was reproduced by using aTele-Pat light box and a RETMA Resolution Chart, No.TM-302. The television camera was a Blonder-Tongue TTVC-1B-SN with a 75mm, f 1.9 lens set atf4. The video level of the camera signal was calibrated by means of'Jae Hewlett- Packard waveform oscilloscope and the picturesize was adjusted to properly fill the screen on a Conrac Picture Monitor,Model No. CNB8/C. A two-minute sequence cf this material was nextrecorded.

The entire sequence was then played back byMachine No. 1 and the multiburst signal was reproduced on the Hewlett-Packard191A waveform monitor and photographed by a Hewlett-Packard 1798Polaroid oscilloscope camera using Polaroid No. 107 film.

The resolution chart was reproduced andexhibited on the Conrac picture monitor and was photographed by a 3-1/4 x4-1/4 speed graphic plate camera using Eastman pan film with a camera settingof Fll and 1/5 second. The picture monitor pictures were reproduced bystandard enlargement techniques.

The numerical identification refers to the model ofthe tape recorder. The letter designation refers to the picture sequence with"a" representing the playback of the material on the machine used forrecording.

The video tape was then transferred to Machine No.2 and a similar set of two photographs was made, these beingdesignated "b."

The video tape was then transferred back to the originalmachine and a second video tape was used to make a re-recording on Machine No.2. This sequence of pictures was marked "c."

The output of Machine No. 2 with tape No. 2 was then fedback to Machine No. I and a third dub was made on tape No. 3, Machine No.1. This sequence of pictures is identified as"d."

supervise the Each participating company was invited to have its engineers /// tests to insure that the equipment was functioningproperly. Sony, Ampex, and Concord were represented by field engineers.

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Fig. B - Test Set-Up

-4- CdTelchrome Test Signal Generator 1421 Telemation Sync I Oenerator Blonder-Tongue Vidicon Camera

Conrac Hewlett-Packard 7- Picture TV Waveform Monitor Oscilloscope

TV Video Recorder Under Test

Diagram No. 1 Equipment Arrangement forRecording

Recorder No. 1 Recorder No. 2 Record or Playback Playback Mode Mode

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1 Hewlett-Packard Hewlett-Packard TV Waveform Polaroid Oscilloscope ((t Camera 10

Speed Graphic Course Picture Plate Monitor Camera amp

Diagram No. 2 Equipment Arrangement forRe-Recording and/or Playback

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Calibration

Figure 1 is a photograph of the resolution of the camera system. The horizontal resolution is in excess of 600 lines at the center.

The multiburst standard is

HI not shown but each of the multiburst amplitudes were individually adjusted to 10 and 90 on the waveform oscilloscope scale. The 111111101111411110 white flag was adjusted to :41/1 ", 100 and the black flag to -40. Fig. 1 - Standard Resolution Chart

Sony EV-200 Series

Figure 2 is a playback of the resolution chart. This shows a horizontal resolution of 300 at the center with approximately the same corner resolution butwith some skewing of the lower half of the picture.

Fig. 2 - First GenerationResolution

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,4,-ottfi Figure 3 is the playback of the multiburst frequencies, 0.5 MHz, 1.5 MHz,

7 2.0 MHz, 3.2 MHz, 3.6 MHz,

Ty a fr and 4.2 MHz, The response is down approximately 3 db at 2.0 MHz and 6 db at 3.2 MHz with essentially no signal at4.2 MHz.

Fig. 3 - First GenerationMultiburst

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Figures 4 and 5 are identical to Figure 2 except that the tape was Fig. 4 - Tape Interchange played back on a different machine of the same model, The Sony EV-200 has excel- leat tape interchange capability as the two sets of pictures are virtually identical,

Fig. 5 - Tape Interchange

--mairimill0111121E111116 In Figures 6 and 7, the original tape was played back on Machine No, 1, recorded on Machine No, 2, and reproduced on Machine No. 2. This is a second generation picture.The resolution has decreased slightly as has the frequency response,

Fig. 6 - Second Generation Resolution '

The 0.5 MHz frequency has been accented and the 3.2 MHz frequency has suf- fered. The noise components of the video signal have increased due to the additional electronics and the last two multiburst signals are entirely masked by noise.

Fig. I - Second Genera ion Alltibnrst

Figures 8 and 9 were produced by re-recording the entire test sequence of Figures 6 and 7. This is a third generation picture. The horizontal resolution at this point is not more than 200 but the vertical linearity and the useful picture information has re- mained. The loss of detail is, of course, due to the decreased bandwidth as shown Fig. 8 - Third Generation on Figure 9 of the multiburst, where the noise level now entirely blanks the last three multiburst frequencies and where the 1.5 MHz response is down by approximately 3 db.The white flag shows remarkably little tilt and the leading edges of the sync pulses are clean and distinct. A pro- cessing amplifier would reproduce the sync pulses very satisfactorily.

End of Sony EV-200 series

Fig. 9 - Third Generatio n i iyur s t Ealy SV-300 Series

Figures 10 and 11 represent the initial playback onthe Sony SV-300. The record amplitude control was adjusted to themanufacturer's specifications but on playback there is both alow frequency displacement resulting in the centerline falling on 60 ratherthan 50 on the scale. The amplitude, furthermore,has decreased from 80 unitsto approximately 70 units on the 0.5 MHz frequencyand Generation Resolution Fig. 10 - First the signal has droppedby approximately 9 db at the 1.5 MHz frequency. The remaining multiburstsignals are masked bynoise. This resu4s in a poorhorizon-

tal resolution andthe . 200-line bars are almost totally obliterated.The picture linearityexhibits almost no verticalhooko

Fig, 11 - FirstGeneration Multiburst

Figures 12 and 13show good tape interchangecharacter- istics. The response on Machine No. 2 is nearly identical to that on Machine No. 1.

Fig. 12 . TapeInterchange ,e4 The sync pulse andflag are indistinct because of a

4,1(,T84 drop-out of the higherfre- c quency componentsof the signals and the slopeof the sync pulse madeit dif- ficult to prevent thepicture fromfluttering.

Fig. 13 - TapeInterchange

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Figures 14 and 15show the 40- -... ------,--= 5;- --1,...,.-- a="Ex: second generationpictures. -'''' ' .=:-.--'"" *At-4,- As will be noted,only the first multiburstfrequency, 0,5 MHz, is nowvisible and Fig. 14 - SecondGeneration Resolution all but the majorcomponents of the resolutionchart are blurred. It is doubtful that a televisionpicture with this limitedresolution is usefUl inclassroom instruction. Efforts to make a thirdgeneration were un- successful.

End of Sony SV-300series

Fig. 15 - SecondGeneration Multiburst -10- pony PV-120-U Series

Figure 16 is a playback of

Mon , the resolution chart, The .01.01. WHINNEMISRlia Sony PV-120-U can be adjusted to produce nearly perfect vertical linearity. The horizontal resolution is approximately 300 lines in the center and with each of the corners exhibiting roughly w. #--- the same resolution. The vex.- III # tical linearity is necessarily 4 limited by the 525-line format

A of the American television system. Th: gray scale shows 11111111111111111.1111111 at least six shades of gray. 111111111101111 'gra ,41 But this does not mean that the video tape recorder was at fault. The camera adjust- Fig, 16 - First Generation Resolution ment and the photographic equipment crowd together the shades beyond number seven and the reproduced PV-120-U picture is equal to the standard resolution picture in this respect.

Figure 17, the multiburst playback, shows evidence of high frequency peaking especially in the 1.5 MHz, 2.0 MHz, and 3.2 MHz bursts. The 4.2 MHz burst is masked by noise. The spikes on the leading and trailing edges of the sync pulses further show the effect of high frequency peaking. Fig, 17 - First Generation Multiburst

-PT"Z"Aq't ' .14 Figures 18 and 19 show that there is some difficulty in maintaining optimum tension when the tapes are played back on a second machine. Again, it would appear that careful adjustment of the == mechanism would minimize 5*****. this and that the same picture resolution could be

7X, obtained on a second machine as on the original. .1* mmmollo , 111.7-11r INNIMMININI 4 - nleimmis z 1- i-rr s

Fig. 18 - Tape Interchange In Figure 19, the multiburst, the high frequency peaking is not as predomin- ant as in the original ma. chine indicating that adjustable electronic circuitry is provided for this purpose.

Fig. 19 - Tape Interchange

Figures 20 and 21 show that excellent reproductions can be expected from theSony PV-120-4J. Furthermore, tapes played back on the machine used for producing the tape show betterverti- , cal linearity than the slam INNOMMIN " chine exhibited whenplaying back a tape made on another machine. The multibursts on Fig. 20 - SecondGeneration Resolution Figure 21 show the effect of two successive peaking circuits as the 1.5 MHz burst has exceeded the amplitudes of the original or theplay- back burst. The effect of high frequency roll-off is likewise in evidence as the 306 MHz burst is down by approximately 9 db. ,

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Fig. 21 - Second GenerationMultiburst -12- Figures 22 and 23 are the respective third generation resolution an& multiburst pictures.The additive effect of the vertical ir- regularities become evident as a general wavy line of the vertical components. Nevertheless, the horizontal resolution in the center section is very nearly 300 lines and the vertical resolution remains close to 500 lines, the theoretical maximum. The third pass through the peaking circuitry has 111.1011111 increased the amplitude of the 1.5 MHz and 2.0 MHz bursts completely out of Fig. 22 - Third Generation Resolution proportion but the amplitude of the 3*2 MHz burst is approximately normal. The spikes or overshoots on the sync pulses have increase& to excessive proportions and in some receivers this may cause malfunctioning of the horizontal sync circuits. The video tape recorder is capable of satisfactory high frequency response but a frequency selective attenua. tion system would improve the aver-all performance.

End of Sony PV-120-1,1 series Fig. 23 - Third GenerationMultiburst Am ex ...L.._:D.(M.SILAAnlaVEt*JosHi

Figure 24 is a playback of the ---,------: ----,-..--==------01.11wale17---- resolution chart showing in .--"-.....-- ---*,.. - excess of 350 lines center --...... 11.- - resolution an& 300 on the :43 While the vertical -.2-----,-- I --:::- . corners. ,:-' ;Z.-- - -.1-_---L - ----;:' ' lines show excessive hook, this is a function of the ZEML. tension adjustment and on subsequent pictures the hook was entirely elindnated by the proper adjustment. This then is more an operator's " error than amalfunctioning smic=7=-- 7--- ._--5:0-1111111111111111(k-AIM= of the equipment. .7"-"r i.-.*. ---7MIR-7,- IIIIMMmalT=7 Fig. 24 - First GenerationResolution -13- Figure 25, themultiburst playback, showsremarkable linearity in thefirst three buI:sts. The fifth burst frequency of3.6 MHz is down not morethan 4 db and the 4,2 MHzburst is down approximately6 db. This machine vasswitched to high band. a.texpl se

Fig. 25 - FirstGeneration Multiburst

Figures 26 and 27'show the performance of themadhine on tapeinterchange with the maximumresolution of approximately 350lines in the center.As will be noted, thetension adjustment hasvirtually cleared up thelinear picturehook. The multiburst ontape inter- Fig. 26 - TapeInterchange change issuperior to that of the originalmachine indicating that theremust be some highfrequency adjustment in themachine.Very . little sync pulsedistortion occurs viththe excePtionof slight ringing atthe trailing edges* This should not degrade thepicture quality.

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Fig. 27 - TapeInterchange lirri4r11,11_11FLI 41110",.;**N4144 414,.44.

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Figures 28 end 29 are the f second generation resolution and multiburst playback pictures. The vertical linearity is remarkably straight indicating that the nachine can be adjusted to produce **" excellent pictures.The resolution is still in excess of 300 lines center resolution and about the same in the four corners. Fig. 28 - SecondGeneration Resolution The multiburst amplitudes have decreased but little from the first generation tape and only a slightlow frequency roll-off isevi- dent, This low frequency roll-off does not affect the sharpness of the leading black edges of the resolution picture.

Fig. 29 - Second GenerationMultiburst

Figures 30 and 31 are the third generation resolution and multiburst respectively. The center resolutionstill remains at 300 lines and the nunbers on the chart are still readable.The resolution chart picture speaks for itself.

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Figures 37 and 38 show the operating characteristics on tape interchange.The Fig. 37 - Tape Interchange picture quality and the multiburst characteristics are essentiallyidentical,

Fig. 38 - Tape Interchange

Figures 39 and 40 are the second generation pictures of the resolution chart and multiburst. The reproduced picture is quite satisfactory and the machine can be adjusted to eliminate most of the picture hook.

Fig. 39 - Second Generation Resolution -18- The 3.6 MHz and 4.2 MHz bursts are badly distorted and the 2.0 MHz burst is down approximately 6 db below the 0.5 MHz frequency but only approximately 3 db t below the original reference signal.

Fig. 40 - SecondGeneration Multiburst

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. .33,ft.43:444, ' Nk Figures 41 and 42 are the third generation resolution and multiburst pictures. 4lK Atm a- 111,- The resolution chart shows some distortion and the additive effect of picture hook. The multiburst pattern shows excessive distor- Fig. 41 - ThirdGeneration Resolution tion in the 3.6 MHz and 4.2 MHz bursts with an ex- aggerated 0.5 MHz frequency as well as a generaldown- ward displacement of all of the bursts. This pattern clearly indicates some malfunctioning in the electronics or a misadjustment of the low frequency amplifiers in the equipment.

End of Ampex VH-7000series Fig. 42 . Third GenerationMultiburst -19- Ampex VR-6000 Series

Figure 43 is a first generation resolution chart indicating excellent vertical linearity and approximately 250-line resolution in the center and corners of the pattern. The gray level is satisfactory.

Fig. 43 - First GenerationResolution

Figure 44 is the first generation multiburst and it shows almost perfect reproduction in the 0.5 MHz burst but 3 db down at the 1.5 MHz frequency and a signal that is almost masked by noise at 3.6 MHz and 4.2 MHz frequencies.

Fig. 44 - First GenerationMultiburst

0010100111.111101010 MitailIPPWRommimper;Fpx7...,,----- Figures 45 and 46 show the ,,6.66mabaaugaaarii561101111111111111.iiit .0 tape interchange capability 0 of this model and, while the multiburst pattern is almost identical with that on the original machine, the resolution chart is less distinct in all areas. There are still 200horizontal lines clearly visible in the

, center region.

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, Fig. 45 - Tape Interchange -20- Fig. Tapc Tyltercha4;ee

Figures 47 and48 are second generationresolution chart and multiburstpictures. The resolution chartstill shows excellentlinearity and 200 lines horizontalresolu- tion in the center and corners. The multiburst picture shows the absence of the Fig. Second Genexation !eoLtt ion 3.2 MHz burst and the1.5 MHz and 2.0 MHz bursts aredown 6 and B db respectively. The sync pulses arestiil clear and distintt and show a remarkably low noise level or overshoot.

Fig. 48 - SecondUeneraticn - Figures 49 and 509 the third ^ generation resolution chart -eferra44KNOVA2. and multiburst, show a con- tIVIWAVOMOW0141M tinuing deterioration of the picture quality and frequency response. The horizontal resolution is now less than 200 lines. The amplitude of the 0.5 MHz signalcontin- ues to remainnormal and there is almost nodisplace- ment of the centerline of the multiburst signal.The noise level and overshoot characteristics are entirely satisfactory. The third generation would, however, ..-,,,,,tottrwrolkyr.rx yield picture quality that Figure 49 Fig. 49 - Third GenerationResolution lacks detail. shows the missing lines produced by lack of contact between the head and the tape due to the omega wrap feature as a white barat the bottom of thepicture.

End of Ampex VR-6000 series

Fig. 50 - Third GenerntionMultiburst

Wollensak VTR-150 S9rics,

Figure 51 is the first generation resolution chart of the Wollensak VTR-150.The resolution is less than 200 lines. The variation in black level mar beattributed to uneven head-to-tape contact.

Fig. 51 Arst GenerationResolution -22- 4_

.4 a II ;

z 0 4 * :

- a :

6 ; I 0

:4 a a I

: - a 4

5 * - 0

4 : " a 0 '"0 - 0

5 z : 11 : : : z : a , - o .. I 0 :. : a -: :

* f I . : I 4.

Z : Z

* 0 . a z

= , I 4

Z S : Figure 55 is the second generation of the resolution chart and it shows both distortion and missing lines at the top of the picture due to loss of head-to-tape contact. More lines are missing in this machine than in some of the other tape recorders and this effect increaseswith the third generation, Figure 57

Fig. 55 - Second Generation Resolution

Figure 56 shows that the peaking at 0.5 MHz is excessive as this level has increased by approximately6 db. The noise level and phasedis- tortion continues to worsen as can be seen bythe white flag and the droop in the to, signal level of the noise blanked last fourmultibursts.

Fig. 56 - Second GenerationMultiburst

4 ;fa Figure 57 is the third generation and it can be seenthat this picture is virtually un useable. The loss of additional horizontal lines at the top of the picturehas now obliteratedhalf of the upper corner circles.

Fig. 57 - Third GenerationResolution -24- Figure 58 shows a deter. ioration of the sync pulses and extraneous noise that produces the poor picture quality.

End of Wollensak VTR-150 series Fig. 58 - Third GenerationMultiburst Concord VTR-600 Series

Figure 59, the first generation resolution chart for the Concord VTR-600, isquite satisfactory for a half-inch machine. The horizontal resolution is less than 200 lines as can be seen by the wow. == 101101.014 ,A0.01. absence of vertical lines in xdoSNOW the center scale and the right and left edge resolution lines. The upper half of the resolution chart shows both a right and left curve that could not be corrected by thetension control. Fig. 59 - FirstGeneration Resolution

The first generation sync pulses show no signal beyond 2.0 MHz and the signal at this point is down by approximately 12 db. The signal at 1.5 MHz is down approximately 6 db and there is phase distortion on thewhite flag and sync pulses.

Fig. 60 - FirstGeneration Multiburst .

x Figure 61 shows the resolution chart on a tape inter- . change playback.The VAW4 apparent double exposure on the portion of this picture is produced by the two heads and the fact that either the adjustment is not perfect or the tension varies for each of the heads.

Fig. 61 - Tape Interchange

Figure 62 shows a frequency response that is very similar to the response found on the original machine.

Fig. 62 - Tape Interchange

The second generation resolution chart shows an increased double hook on the upper portion of the picture but does not exhibit the double exposure effect of Figure61. A. tape made on Machine No. 2 f',6 would reproduce satisfactorily .de while it would not satisfactorily play back a tape made on Machine No. 1. ":-/->v,,-% 4Y,

Fig, 63 - Second GenerationResolution -26- , Figure 64, the second generation multiburst, shows a deterioration of all but the 0.5 MHz burst.A small amount of signal in the 1.5 MHz frequency can be detected but the remaining multiburst frequencies are masked by noise.

Fig. 64 - Second GenerationMultiburst

, Figures 65 and 66 show the '," < ,,./,"!,,"4,

End of ConcordVTR-600 series Fig. 66 - ThirdGeneration Multiburst -27-

*<< Craig 6401 Series

Figure 67 is themultiburst sequence used on theCraig 6401 machine. This machine when the 74.1.4 was not available other tape recorders were tested and a differentmulti- burst generator, waveform oscilloscope, and resolution chart were used.Note that the multiburst standard amplitudes are different from those in the previousseries*

'415143SF

Fig. 67 Multiburst Standard forCraig 6401

Figure 68 shows theresolu- tion chart with solidbars rather than the shades-of- gray scale. The horizontal resolution is well in excess of 200 lines andthe vertical linearity is excellent.

Fig. 68 - FirstGeneration Resolution

FigurP 69, the first generao. 11111111 tion myLtiburstpicture, MEW shols r2.0 MHz frequency III dow by not morethan 6 db. The 0,5 MHz burstis almost identical to the inputfre- quency.

Fig. 69 - FirstGeneration Multiburst Figure 70, the resolution chart tape interchange picture, shows again the effect produced by the two record- playback heads in the Craig 6401 machine. This causes the apparent double exposure on the upper half ofthe picture indicating that dif- ficulties will be experienced on playback of tapes made on other machines.

Fig. 70 - Tape Interchange

Figure 71 shows almost the 111111itil v ^ identical frequency response as on theoriginal machine 1111Ifittl--- 11116,444I but again with a slightfre- quencydisplacement produced by the two record- At playback heads.

Fig. 71 - TapeInterchange

Figure 72, the second generation resolution chart, continues to show in excess of 200 lines in thecenter and all four cornersof the picture.While this resolution is not satisfactory for exactingapplica- tions, the secondgeneration has deteriorated verylittle.

Fig. 72 - SecondGeneration Resolution =Wit Figure 73 shows a marked AAP degeneration of the sync pulses and decrease in all but the 0,5 MHz frequency. The small signal in the 1.5 MHz frequency is respon-

112E111111111 sible for reproducing the 200-line resolution in the picture.

Fig. 73 - Second GenerationMultiburst

Figure 74 is the third generation resolution chart produced on this machine. The vertical linearity continues to be excellent and except for frequency response which resultsin loss of resolution, the third generation tape produced is quite satisfactory.

Fig. 74 - Third GenerationResolution

Figure 75 shows a continued degeneration of the sync pulses and white flag. The noise, however, has notin- creased out of proportion 111111111 and this results in the IMBUE high quality resolution MUM- chart picture. The machine can be adjustedto produce very favorablevertical linearity.

End of Craig6401 series Fig. 75 - Third GenerationMultiburst '"' .

.Bquipont_Reliability and low All video tape recorderstested employ solid-state circuitry is very low due to voltage power supply. Heat produced in the system Virtu- the low signal levelsand power supply voltagesin the system. ally all transistors are nowof the silicon variety. The low voltages place little strain oncapacitors and resistors andall of these factors result in high reliability. A properly engineeredsolid-state system should perform as wellafter ten years ofcontinual use as it performs in the initial stages.

factors. A tape The mechanical reliabilityinvolves many more complex recorder that relies on amultiplicity of rubber belts,friction drives, and other wearing surfaces maybe expected to requirefrequent attention. which result Rubber or neoprene beltsexhibit fatigue charactel:istics in increase of slippageand malfunctioning. Felt pads when used for brakes on rotating equipmentglaze and lose their stoppingability. Devices that rely heavily onfriction points for their operationneed frequent adjustment and inthe absence of properadmustments the circuits jerk, grab, or otherwisemishandle the video tape.

Video tape is made with a verystrong mylar base butfrequent jerks on the tape and impropertension will cause the tape todeform with the resulting misfit contact withthe recording heads. Most of the video tape machines haverecorded tracks on both edgesof the tape as well is otherwise as in fhe centersection. A tape that has stretched or deformed will make contact withcertain of the heads but mayhave inadequate contact with someother head. Video tape recorders equipped with multiple motor drivesinstead of a belt-driven transportand with braking accomplished by electrical means aregenerally more reliable than those depending on belts orfriction for these functions.

Tape Guides

The tape guides are used toalign the tape for the mostsatisfactory contact with the recordingheads. The most satisfactory tapeguide is a rotating onewhich usually exhibits aminimum of friction with respect when the guide makes contact to the tape. This is especially important with the oxide surface ofthe video tape.

The non-rotating tapeguides consist of variousconfigurations of guide is bars or stationary spools. In some instances, the tape adjustable, which permits theoperator to correctlyalign the tape. the tape by having By the same token, it isalso possible to misalign bottom edge the guides too close togetherin which event the top or allow the tape to of the tape is scratched. Too loose a guide will rise above or float belowthe proper position. In the hands of a layman, the adjustable guides areprobably undesirable. In any event, of operation guides should be examinedcarefully after every few hours removed from for signs of oxide and tapematerial that may have been the video tape by the guideduring operation.

-31- W!.

Since video tape recorders areto have thecapability of playing all tapes produced onthe identical makeand/or model, the tape transport seriously reduce the inter- system must not bemisadjusted as this will changeability of tape.

Cleanliness

Utmost care must beused to keep the video tapeand the tape transport Video tapes on system of the video taperecorder immaculatelyclean. capable of lifetime tests in carefullycontrolled environments are a 4,000 to 10,000 passes. The same video tape usedin questionable after 100 to 400 passes. locations often has deterioratedto uselessness irregularity in the A common fault in video tapeis a microscopic magnetic coating of the tape. This causes a drop-out or amomentary function white line on the picturemonitor. This irregularity may be a ashes, sand, of the manufacturing processbut specks of dust, cigarette A tape guide cloth fibers, and the likewill produce the sameeffect. deposit on the tape, and may produce asliver of polyester which can the tape, will result this chip, causing thehead to lose contact with in a momentary drop-out. and the various Periodic thorough cleaningof the entire tape transport machine operation. heads is most essentialfor satisfactory video tape each recording or play- The entire transportshould be cleaned before should be carefully wiped with an back. Each of the several guides approved cleaner and all ofthe head assembliesshould be cleaned to heads. remove specksof oxide and otherdebris that can clog the Microscopic specks of oxide mayform a bridge in the video tapehead which will make the headinoperative for either record orplayback. but, unfortunately, This irregularity isquickly observed on playback essential that all cannot be detected onrecord. It is, therefore, immaculately clean to avoid parts of the taperecorder assembly be head build-up. is an iron The oxide material used inthe fabrication of video tape found in nature. oxide; one of the hardestand most abrasive materials the oxide The binder used in themanufacture of the video tape causes to build up on theguides and on the heads. Such build-up can ruin the entire video tape in one passon the machineby irreparably scratch- ing it. properly It is doubtfulthat anyone except atrained technician can maintain a video taperecorder.

Cleaning Solution This will help The use of a goodcleaning solution ismandatory. guides and heads. Due remove oxide anddebris deposits from all tape and of the binder used in the to the chemicalcharacteristic of the tape manufacture, only a few commoncleaners are satisfactoryfor this by the majority of video tape manu- purpose. Freon TF is recommended volatile and the operator mustwork facturers. Freon TF is highly very fast to removethe oxide beforethe freon is evaporated.

-32- Those portions of the transportthat do not contain rubber maybe cleaned with xylene or a mixtureof 987 xylene and 2%,757-25% aerosol-glycerin. This material must not comein contact with thevideo tape or rubber but is effective on metalguides and easier to usethen freon. Great care must Rubber guides may becleaned by use of methylalcohol. be exercised that allsurfaces moistened with methylalcohol are thoroughly and completelydry before the video tapeis again threaded through the machine.

Tape Tension applied to the moving tape so A certain amountof tape tension must be motion of the head that a proper tip penetrationis maintained during the across the tape. Most video tape recordershave a fixed tension control The playback on recordand a variable tension control onplayback. tension control isadjusted for optimum picturequality which usually The occurs whenthe picture exhibits a minimum"hook" characteristic. Wollensak VTR-150 uses a simplenonadjustable felt pad for the tension control; and in the particularmodel tested, the qualityof the resultant picture would have improvedhad the control been variable. Similarly, the fixed tension control onrecording on some machinesmade it nearly impossible to correct for thepicture hook when the tape wasplayed back on a different machine. Evidently, some method ofstandardizing the record tape tensionwould be desirable in order toinsure the maximum tape interchangeability.

Tape Interchangeability

All of the machines testedin this project workedsatisfactorily with identical make and respect to interchanging tapewith a machine of the always obtained when the tape model. Admittedly, the best results are is played back on the samemachine used for recordingbecause the head alignment on record and playbackis then exact. On machines that have experienced in inter- no playback tensionadiust, difficulty can be be required changing tapes. A playback tensionadjust should, therefore, to insureinterchangeability of tape frommachine to machine.

Standard Tape Format

Several groups of machines now use acommon tape format. Foremost in used on the this is the Ampex VR-7000 serieswhere the same format is VR-7000, and Ampex machines used in this test, theAmpex VR-6000, Ampex introduced the Ampex VR-5000and the VR-7500. Additionally, Ampex has Ampex VR7800 in the identical tapeformat. The Ampex VR-7800, with a color and a tape full complement of accessories,is capable of excellent made on the Ampex VR-7800 maybe played back on anyof the other machines. Similarly, tapes made on any ofthe Ampex one-inchformat machines may be played back on any other type. For example, the testidentified as 4-6-a is a recording made onAmpex VR-7500 (lowband) and played back on the economyAmpex VR-6000 machines.

-33- The versatility of the Ampex one-onchformat lies in the fact that a single high quality machine like the AmpexVR-7500 can be used for recording purposes and the productionof copies. These copies can be played back on the economy Ampex VR-5000 machinein the classroom. The Ampex one-inch format is used on RaytheonModel RR-750 and Raytheon ModelRR-700 and machines. These machines appear to beidentical with Ampex VR-7500 Ampex VR-7000 and theinterchangeability of tapes extend tothese models.

The Sony EV-200 is available as apackage unit under severalother popular trademarks including GeneralElectric and RCA. Tapes made on any of these machines arecapable of playback on any otherof the same group.

The Raytheon machines, amnufacturedby Ampex, as well as the RCAand General Electric machinesmanufactured by Sony, were nottested in this project because of theirrelationship to the parent company.

Tape Costs

The per-hour cost of video tapeis an important consideration.While distributors have certain latitudesin establishing quantity-pricebreak, the following list cost of tapeis illustrative of thedifference in tape cost:

half-inchtape,60 minutes $40.00 one-inchtape,60 minutes 60.00 two-inchtape,60 minutes 75.00

Grot

There appear to be threenatural groupings in the helical scanvideo tape recorders. These groupings are apparent inpicture quality, price range, andpossible useage. The groupings are as follows:

the $4,000 to $8,000 price range. 1. The first group is generally in This equipment appears useablefor broadcast purposesprovided that certain precautions are taken. The picture quality is suchthat the third generation tape still isclearly useable. Of machines tested in this project, the SonyPV-120-U and the Ampex VR-7500(high band) would probably fall in this group.

$4.000 price 2. The second group of machineswould fall in the $2,000 to range. These machines did notexhibit the necessary time base stability required for broadcastand had more problems withpicture hook as well as a degradedpicture quality. The sync pulses were not sharply reproduced;and, in some instances, there wasmarked deterioration of the recordedmaterial. The machines, however, should find acceptance inschool systems for closed-circuitprograming where editing and making copiesof the material are not aprime pre- requisite. The machines that fall inthis group are the Ampex VR-7000 and the Sony EV-200. The third group ofmachines would fall in the$1,000 price range 3. These and these machinesshould be limited to recordand playback. machines typically are ofthe half-inch format and areeconomical in useful for dubbing from tape consumption. The machines likewise are Ampex a moreprofessional model. The machines in this group are VTR-150, and Craig 6401. VR-6000, Sony SV-300,Concord VTR-600, Wollensak

-35-

_ SELECTED STATISTICS OF THE TEST RECORDERS TABLE 1 TEST NO. 1 SonyNAME EV-200OF MACHINE $ 3,350PRICE VIDEONO. OF HEADS 2 HEADVELOCITY 590 ips WIDTHTAPE 1 in. SPEEDTAPE 7.8 ips $PERTAPE HOUR COST 6o.00 32 SonySony SV-300 PV-120-U 8,950 980 2 740425 1/2 2 4.257.5 75.0040.00 54 Ampex vii-7500VR-7000 3,4503,995 1 1000l000 1 9.6 6o.00 c"t...) 1 6 Ampex va..6000 1,595 1 l000 1 9.6 6o.00 1 7 Wollensak VTR-150 1,495 21 484180 1/2 12 7.5 40.00 98 PanasonicConcord(Only one VTR-600204 Panasonic 204 1,150 1/2 10 Craigthemachine test 6401 waswas availableabandoned) and 1,035 545 1/2 9.5 50.00 ACKNOWLEDGEMENT OF VTR EQUIPMENT USED IN PROJECT

Video Ta e Recorders Tested: prnished BE:

Ampex VR-6000, Serial No.4124 Ward/Davis Associates Ampex VR-6000, Serial No.4141 3921 East Bayshore Ampex VR-7000, Serial No,4189 Palo Alto, California 94303 Ampex VR-7000, Serial No.4454 Ampex VR-7500, Serial No.1869 Ampex VR-7500, Serial No.1872

Concord VTR-600-1, Serial No. 1999 Campbell Engineering Concord VTR-600-1, Serial No.2017 814 East 14th Street Oakland, California 94606

Craig Model 6401, Serial No.690098 Video Products Sales Craig Model 6401, Serial No.690095 Craig Panorama Inc. 2302 East 15th Street Los Angeles, California 90021

Sony EV-200, Serial No.1985 Sony Corporation Sony EV-200, Serial No.1874 926 Industrial Avenue Sony SV-300, Serial No. 1119 Palo Alto, California94303 Sony SV-300, Serial No.1276 Sony PV-120-U, Serial No,2656 Sony PV-120-U, Serial No. 2233

Wollensak VTR-150 Minnesota Mining and Manu- Wollensak VTR-150 facturing Company 320 Shaw Road South San Francisco,California 94080

Furnished By: Video Tape Used: Minnesota Mining and Manu- 3M Tape facturing Company 320 Shaw Road South San Francisco,California 94080

Ward/Davis Associates Ampex Tape 3921 East Bayshore Palo Alto, California94303

Video-Educational Distributors Memorex Tape 312 Brokaw Road,Suite 8 Santa Clara, California95050

Com-Tel EngineeringCorporation Sony Tape 1472 Oddstad Drive Redwood City, California94063

-37- Test E ui ment Used: Furnished B

Telchrome Test Signal Generator Telemet Company Model 3508-C2, Serial No. 717 3841 South Main Street Manufactured by Telemet Company, Santa Ana, California92705 Amityville, New York

Telemation Broadcast Synchronizing Telemation, Inc. Generator 2275 South West Temple Model TSG-2000, Serial No.201 Salt Lake City, Utah84115

Conrac Picture Monitor Reeves Electronics Model CNB8/C 405 Sherman Avenue Model No. 123849 Palo Alto, California Manufactured by Conrac Division, Covina, California

iHeWlett -Packard Oscilloscope Neely Enterprises Camera, Model 197A 1101 Embarcadero Road Serial No. 730-01126 Palo Alto, California94303

Hswlett -Packard TV Waveform Neely Enterprises Oscilloscope 1101 Embarcadero Road Model No. 191A Palo Alto, California

Blonder-Tongue Vidicon Camera Manufactured by Blonder- Model No. TTVC-16-SN Tongue Labs, Serial No. 1335 Newark, New Jersey

Speed Graphic Plate Camera

Pan X Film

Polaroid Type 107 Film

1e7-137 3-68 500

-38-