scoop on scopes

11
Why, when, and how to use a waveform monitor and vectorscope, and what they can tell you: a basic primer. ' Nancy Dykl Kelly I o vouw NR installed a new studio facility. or expanded your existing one, and the technical consultant or sales rep who sold you the new equjpmcnt said you had to have a waveform monltor and a vec~rxope. You dutifully ordered them, and the servtce technician htalled them -now what? Let's dissect the waveform monitor first. You can use this helpful tool at several locations in the video chain,e.g.. one for each camera control unit (CCU), one at the vidco ~wttchcr/SEG (special effeco generator). one on the line output before the video goes into the videotape recorder, or one at the output of the time base corrector CTBC) in your ed- iting suite or at the TBC in your master control room where the tape is played back for your closed~lrcuit, cable, or b~dcastsystcm. No matter where It b found, Lts purpose is the same: it makes sure that your video signal bas good as it ccu! k prior to belug recorded or distributed. R EFORR you AYTEMIT to take any readings. flnd the internal/extemal knob or switch. If you are ob- serving the signal from In-house video sources Ufre vldtoupe playback, a crmera,and so onset rhfs control ro the C~xtemal" porttion.Thls will Insure that the waveform montrnr Is locked m the external. incoming reference source. urd b maklng accurate, sublc measurements based on the signal from that source. The "lntcmal" setting will lock the wavcfom monltor to a self-generated slgnal. and is used mainly to provide a stable readlng for nonsynchronow swarmoutside of your fhctllty,like a remote m c k or satelUte. Murr wavefcrm monitor screens use two vertical scales tormeasuring.Thcone up the rightside is thestandard scale of the Federal CommunIcat1ons Commission (FCC), an6 Is calibrated in percent of modulation. For most studlo appl1- cad on^. thb xale Ls not relevant because It refers to the modulation of a broadcast transmitter carder. he one you will wc Is the scale on the left, which is calibrated in 1EEE units (from the Institute of Electrical and Electronics En- 6ince~~ fomerly known as the Institute of Radio Engineers or I RE, and.usual&referrerd to as the "Eye triple E". i. Vectorscope Displaying Colorbars Using this scale. you can measure one of the most Im- portant characteristics of the video signal, its lumlnance level, or "light Intensity." Any white objects that are in the xenc should cause lumlnance level peaks in the signal that fall in the area of +I00 IEEE unirs (at the top of the scale). Any black objects should have a video level of around +7.5 IEEE uniu, and the levels for m t of the colon wlll fall be- tween these two value. Toset a standard value for white at + 100 IEEE units, or if you want to do general morittoringof overall levels while working in master control, it is better to use the IRE xnlng on the scope.The IRE scttlnglets you see only the brightness (luminance) infonnaon In the signal. If you need to know whether color splkes go above the +100 IEEE level, or be- low 0 IEEE unfts,or ifyou need toobserve thecolorburst (be patient, I11 explain that in a IIttIe-while), use the "flat"sct- ting. It pmvida a slgnal that hcluda all the color Cchromln- ance) information as well as lumlnance. Ushg the IEEE scale, one very important application of a waveform monitor Is to set the 'contrast" of the video slgnal. If your picture look muddy and lacksdetait the cxVcr- all video level is probably un, 1ow.A glance at the wavefonn monitor wlll probably reveal that the%hiteU peaks are dos- er to +SO IEEE unlts than they arc to + 100. To improve the picturc quality, bring up the video level at the sou= you are measuhg - the camera Iris, switcher output, 'LBC video out, and so on - ti11 white measum + 100 IEEE unb, and watch the image become c l e a r and more detailed on your picture monltor. On the other hand, if the video monltor shows "hot spots" Ln the lmage or a plcture that appears to bum and tear ad has Httle detail,check to see If the level isexceeding the + 100 IEEE mark. Again, adjust the level at the source until white measure +l00on the waveform monitor and watch the detail return to the Image while the teadng disa~pcdn- he chart lists the acceptable limits (In lEEE units) the FCC has dcflned for each of the parameten in a vldeo signal.

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Page 1: Scoop on Scopes

Why, when, and how to use a waveform monitor and vectorscope,

and what they can tell you: a basic primer.

' Nancy Dykl Kelly I o vouw NR installed a new studio facility. or expanded your existing one, and the technical consultant or sales rep who sold you the new

equjpmcnt said you had to have a waveform monltor and a vec~rxope. You dutifully ordered them, and the servtce technician hta l led them -now what?

Let's dissect the waveform monitor first. You can use this helpful tool at several locations in the video chain,e.g.. one for each camera control unit (CCU), one at the vidco ~wttchcr/SEG (special effeco generator). one on the line output before the video goes into the videotape recorder, or one at the output of the time base corrector CTBC) in your ed- iting suite or at the TBC in your master control room where the tape is played back for your closed~lrcuit, cable, or b~dcastsystcm. No matter where I t b found, Lts purpose is the same: it makes sure that your video signal bas good as it ccu! k prior to belug recorded or distributed.

R EFORR you AYTEMIT to take any readings. flnd the internal/extemal knob or switch. If you are ob- serving the signal from In-house video sources

Ufre vldtoupe playback, a crmera,and so onset rhfs control ro the C~xtemal" porttion.Thls will Insure that the waveform montrnr Is locked m the external. incoming reference source. urd b maklng accurate, sublc measurements based on the signal from that source. The "lntcmal" setting will lock the wavcfom monltor to a self-generated slgnal. and is used mainly to provide a stable readlng for nonsynchronow swarmoutside of your fhctllty, like a remote mck or satelUte.

Murr wavefcrm monitor screens use two vertical scales tormeasuring.Thcone up the rightside is thestandard scale of the Federal CommunIcat1ons Commission (FCC), an6 Is calibrated in percent of modulation. For most studlo appl1- cad on^. thb xale Ls not relevant because It refers to the modulation of a broadcast transmitter carder. he one you will wc Is the scale on the left, which is calibrated in 1 EEE units (from the Institute of Electrical and Electronics En- 6 i n c e ~ ~ fomerly known as the Institute of Radio Engineers or I RE, and.usual& referrerd to as the "Eye triple E".

i .

Vectorscope Displaying Colorbars

Using this scale. you can measure one of the most Im- portant characteristics of the video signal, its lumlnance level, or "light Intensity." Any white objects that are in the xenc should cause lumlnance level peaks in the signal that fall in the area of + I 0 0 IEEE unirs (at the top of the scale). Any black objects should have a video level of around +7.5 IEEE uniu, and the levels for m t of the colon wlll fall be- tween these two value.

Toset a standard value for white at + 100 IEEE units, or if you want to do general morittoring of overall levels while working in master control, it is better to use the IRE xnlng on the scope.The IRE scttlng lets you see only the brightness (luminance) infonnaon In the signal. If you need to know whether color splkes go above the +100 IEEE level, or be- low 0 IEEE unfts,or ifyou need toobserve thecolorburst (be patient, I11 explain that in a IIttIe-while), use the "flat"sct- ting. It pmvida a slgnal that hcluda all the color Cchromln- ance) information as well as lumlnance.

Ushg the IEEE scale, one very important application of a waveform monitor Is to set the 'contrast" of the video slgnal. If your picture look muddy and lacksdetait the cxVcr- all video level is probably un, 1ow.A glance at the wavefonn monitor wlll probably reveal that the%hiteU peaks are dos- er to +SO IEEE unlts than they arc to + 100. To improve the picturc quality, bring up the video level at the sou= you are measuhg - the camera Iris, switcher output, 'LBC video out, and so on - ti11 white measum + 100 IEEE unb, and watch the image become c l e a r and more detailed on your picture monltor.

On the other hand, if the video monltor shows "hot spots" Ln the lmage or a plcture that appears to bum and tear a d has Httle detail, check to see If the level isexceeding the + 100 IEEE mark. Again, adjust the level at the source until white measure +l00on the waveform monitor and watch the detail return to the Image while the teadng disa~pcdn- he chart lists the acceptable limits (In lEEE units) the FCC has dcflned for each of the parameten in a vldeo signal.

Page 2: Scoop on Scopes

I Vldeo TW LOW

I Resun No contrast; Seen: plcture muddy.

Video Too High

Plcture has hot spot8 & ?earsn.

I Good Vldeo Levels I Picture look. good. I

USING TEST EQUIPMENT

T HEXE ARE TWO rates a waveform monitor can use to xm a video signal. As you are probably aware. the American standards for a video picture call for the

htcrlacing of w o separate packets of l ina. called fields. Ficldonc is created by x a n n h g the uneven lines in the 525- line video image (1.3.5,. . .525),and field two is mated by scanning the even l i n a (2.4.6,. . .524). These two packets are then interlaced so the complete frame contains all 525 line. and this happens 30 t i m a every sccond.The waveform monitor lea you x e both fields side by side (the vcnlcal rate, or "wo field" xning) or it can show you just two lines (the horizontal rate, or "two line" setting).

In the vertical, two-field mode, you see one complete frame of video with the individual lines from field one ap- pearing vertically and conxcutively at one side of the dis- play, and the lines from field two appearhg in the same way at the other side. The h t ten or so iines on the left of cach field represent rhc vertical sync and blanking interval where the encoded test signals and synchronizing pulses arc located. All the other l i n e are t h o x in the vlsible TV picture. Wou can't xc the f i t ten lines of any field on a well adjusted video monitoc thcy willbc out of view at the top of the picture. You can xe them only when the monitor is un- derxanned and shaws all the picture edges on the xrcen.)

By expanding the waveform monitor display horizon- tally, you can see the individual l l n a In more detail. The horltonal.or two-line, rate leu you view the equivalent of two l ine of vidco. In thIs mode. you can distinguish the charactcriffta of the individual lines much more clearly. Achully, me looking at a rcprescncatlon of the entire pfmre frame because the waveform monitor will overlay dl 525 lines so you can set overall video levels. Some of the slightly mom sophisticated Cand more expensive) waveform moniton wlll let you view each llnc individually.

l N ~ L H O R ~ ~ T A L mode, hex b what you see, reading fmm fcft to fight on the waveform monitor display. F i m there b the bknklng area, which gets I t s name

fwmthe function it serves. It blanks the video screen during the retraceperiod rathat the electron beam that 'draws" the picture can get from the end of the line it Just furlshed to the kgInnlng oi thc next l n c . Ut "draws"cach line from left to right) The blanking level is 0 IEEE unlu on the waveform monitor's screen.

The next vbiblr mrnpancnt is a heavy llne, slttfng at -40 IEEE units, which reprcscnts horizontal sync. This

synchronizing pulse occurs at the beginning of every hori- zontal line, all 525 of them. The only video source h a t will not give you a sync display comes from camera control units that don't i n x n sync. If the display is short, 1.e.. falls above the level of -40 IEEE unlts, you might have a problem that could rcsult in an unstable picture. Chcck your sync source (sync generator, videotape recorder. remote source); it may require adjustment or servicing.

Following another small blanking interval, you will see the yellow-greenish color bum. (Why yellow -grccnlsh? I11 explain that in the vectorscope section.) You must use the "flat" xtting that provida chrominancc information to get this color burst display. A proper burst signal centen on the blanking 1wel.O.and extends from +20 above that level to -20 bclow It, for a total of 40 IEEE units. The FCC specifies that there should be eight cycles of color bunt,anC if you expand the waveform display horizontally, it Is possi- ble to count them.

The color burst signal is extremely important to the TV receiver in the home; it provides the standard of reference that the receiver locks to so it can acurately reproduce the color elements in the picture. Not only must It have the proper number of cycles, they must also exhibit the proper level. When the color bunt level is too low, 1.e.. less than 40 IEEE unitsethe home receiver may wander, searching for a reference, and the rcsult could be rainbows or random color in the picture,or no color at all. It is a good idea to check for proper color bunt levels at cach point in the video chain.

After another brief blanking interval, the bulk of the &play shows the individual picture elcmcnn.The wsveform monitor portrays them as relative values of lighmess and darkness. As I already pointed out, the trace should lie be- twttn+7.5 and+ 100 IEEE units. Note thataTvblack"isnot really black; the blackest object in the picture is still above the 0 blanking level (at +7.5 optimally, but the FCC will ac- cept levels between +5 and + 10 IEEE units). When the eye compares thk level to the rest of the levels in thc picture, it xes black, but compared to sync at -40 IEEE units (which the eye doesn't see), tt is actually gray. Sync is the blackest black. This +7.5 value is referrrd to as the "setup," and repre- xna the separation bctwccn blanking and rcfcrcnce black.

0 NE OTHERPARAMETER YOU can observe on awave- form monitor Is horizontal timing.which isvery important If your facility uses multiple vldeo

sources. No doubt, when switching berween two sources

Page 3: Scoop on Scopes

like the camera and YTR or camera and slidcchaln, you haveat some tlmc seen the plctum appear to)urnpsidcw.ys. Rnhably this was the result of a timing uror and indicates lhrt :he horitsntal tlrnlng was not set properly.

Scanning ofa video line takes a fixed amount of dmc. 63.5 micmbcconds. and aU elements within that line must occur in their prqpcr relative time intervals. A shin in this timing in either dirrcdon. earlier or later, results in m error that can knoticedon thcvldm monitor if it islargeenough. TO avoid such rnon. the horizontal. timing must k set so it will bc Identical on all of the video sources you will use to- gcihcr. If one source docs not pcrmit horizontal timing ad- just mcnts, w it u the dercncc and set all the other sources to cen form 80 it.

You will find the sa le used to set horizontal timlng abnp the 0 XEEE unit b a d h e . It reads horizontally from kft to right 03 the waveform monitor satcn. To use it, set rhc waveform monitor to 1 mlclo~cond per division; each t r w division on the scale will then equal, 1 mictolsccond. US the 2-line (horizontal) rate and thc flat (chroma) Ktttng.

When Ktdng timing. or 'phasinga a system, ust a wave- f91.m mnimr that b located at the switcha output. This makes it easy to check and p b ~ ~ all of your video murccs indi\.idually. Before suning, the wavefonn monitor nttds te be fed a reference sync signal, which was probably done

rhr q u i p e a t was installed initially. When you ad- just the timlng el your quipmcnt, you will see the display an the paticult (calibrated screen) of thc wavefonn monitor # u l l y mevc te the left 0r rlght. Bc sure, however, that the w w c f ~ menitor i s aperating in the external sync mode; If b sa to Internal, the display on the monitor's graticule nlll mat nmwe rat4 you won't bc able ta, measure your timing id)upunmtr.

Using the slmrl h m your reference source, set the ~ ~ a g eQOc d l e hmbaut sync on one of the luee 4h4shs. Thh wlll $vc ysu r reference mark M, US in p h b g 1 1 the 4thtr swcs UB confern. (some wrvcf@m

my have the herbnu1 crUBrrtlons dong the -# at@ NEE la H units. By defSnltlsn, m H unit kcme kcefddm,w63.5 m i ~ @ n & d Bcfere wd@rn- &tketkere$u@mslat Is ysur system wysur rcfmaeck sw W W Smw sacctr PCC ~uImm4nu. Thew cUtc that the h k a n ~ I qac p3# plus rtrc bsdqwreh Umm the -ins tu*e end dehc dlm bha- iertarpd ~ Q I dtbct * elw-~et bunt) SIIOUI~I mcistm 9.54 @-.rhr, , . wi* a ulermn eif f.31 te c.3) ntkrtwccolrQ.

'

L- wr rwitchcr te select yeur vidco wrtrcrs, one at a ~ ~ ~ . . s l l J u s t each fer he&@nul timing so that the lead*

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IEEE Unit, FCC 9 ol MhdNtlCW

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loo 12.6%

7.5 70% o - - - - - - - - -IS%

-4Q 106%

-uma&m@d @mkr

*mas* WM.

-Ik(owl#Bkdc -8knnng Wtuvl

-8yna

(llnea 1,3,5, . . .) (Llnoe 2,4,6, . . . )

mPanded.D@play fpr-tlrying '. - ,

I"m-bipt) -j ., . . ., . - 100

+HorkontaI S y n w +Back Porch*

1 1 1 1 1 4 1 1

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b ' - '

Page 4: Scoop on Scopes

c

Abow Is a wavelorn of the i-nfofmatkn In thapktvr* that tho camom -8

from your reference source, as shown o i the waveform monitor display. This calibration assurcs that each uzlt Is now in phase (timed to coincide) with every other unit. If you find that the widths of the horizontal sync from your various sources are different, or if the sync from your refer- ence source docs not meet FCC regulations, you may need additiond technical assistance.

N ow.WHAfA80VT the VCC~O~SCO~C? A v~ctors~~pe's primary p u r m is to give you information about the color,orchroma, portion of the video signal.

Before going further. I need to say a word about NTbC color. To bc sure that allsignals would be compatlble,the Na-

tional Television Systems Committee developed and s@- ficd the standards by which color W would be created and aansmitted in the United States. The NTSC system (which engineers affectionately refer to as "Never The SameColor7 is different from the standards used In Europe or other countries. In NTSC.color Iscreated asa function ofa v-ng p h a x angle. referenced to O". Each color occurs at a defined paskion around the circle, from 0 to 3W, which fs why the gradcuie on the face of the vectorscope Is in the shape of a circle,

When you lookat the faceofa veaorscope,adot in the center of the circle, wlth no other dlsplay. indicate that no color is prexnt -you are dealing with a monochromcsfg- nal. When color is present, the color burstvector,a greenish- yellov/lsh fine and the reference signal for all the other cot- on, lies along the 1 W line, polnting to what would be the "9" posftion on a clock face. CThe O" measurement 1s at 3 o'clock.) 7he angle readings arc around the outer perlphcr~ of the circle on the face of the vcctorscopc.

If your signal has color that will meet FCC standards, ; the color bar vcctots fall wlthln the large boxes on the 1 graticulc. When the NTSC standards were set up, now 2 than 25 yean ago, the smatler boxes indicated the.iocatIon

of the truest rcprertntation of each hue: ff the vectors fall Within the bfg boxes but miss the small ones, you will see thc proper colors on your vldeo monitor, but there may bc 3 slight hue vrriadons.

$ Some of the color erron that a vectoacoge will dlsplay kj .,art: 1) Vectors that arc too short and don't reach their boxes.

- --

I (right, with the vldeo Nne dlsplawd shown by the horlronfel tub).

In &Is case, the picture on the video monitorwill look washed out -the colors will not have enough saturation (intensity) and will look **pastelisha and vague. 2) Vectors that are too long andovenhoot theirboxcs.On a monitor,a p i m r e with this problem will have colors that are over-saturated, forex- ample, Caucasian skin tone will be too red,as though the per- son had a healthy sunburn. 3 ) Vectors that are rotated out of their boxes, in either direction. The picture will have color, but it will not be true color. If the rotatlon is to the right, a banaria will lwkorangish insteadofyellow; if It's to the left, that same banana will look greenish.

EFORE YOU TRY to use the vectorscope for making .any needed adjustrneilu on your equipment. be sure its dlsplay Is accurate. It should be in the

external sync mode oust like the waveform monitor) and the color burst vector, whlch Is usually shorter than the colorbar vectan.should fall exactlyalong the 180" reference line. If it doesn't. look for a control knob marked "phase"or "positioning" and use it to move the vector to i ts proper position.

Now look at the colorban from each of your video sources -stud lo swI tcher colorban, camera-generated coI - orbars, or the playback of colorban from a videotape. If the colorbar vectors do not fall In their proper boxes, adjust the chroma phase at each source until they do.This is essential ff your color reproduction ls to be accurate. When you switch to active Qlvt) video. the colors will be separated out and displaucd tn their rrspcctfvc regions on the vexoncope screen. For examplc,a football field will have a large packet of sig- nal In the green area,skin color for a Caucasian face will fall between yellow and red,or a beach scene may give you a tot of signal In the bluc/cyan region.

When you are reading the vectorscope, If the display rotates rapIdly it is an Lndlcatlon that you are looking at a non-synchronous source, Ix., one that is not locked to the studio sync system. Such signals could come, for example, from a remote truckthat i s feeding back to thestudio via mi- crowave or cablc,or from a satellite. You can read non-SYn- chronous slgnaIs by putting the vectoncope in the htemal sync modc,but you won't be able to phase them to the studio. system as discussed in the next paragraphs.

Page 5: Scoop on Scopes

Color Burnt W o

V ~ C ~ O ~ S t00 ahon: colors are washed out and vague.

Voctors loo long; coloro ars wer-tmturatad and too brlght.

Vectors rotatod out of boxes; colors have hue errors. I

Much like uslng a waveform monitorfo adjust dmlng in muItiple video sauces, you can use a vcctozsmpe to adjw system burst phase (or sub-canicr phase). and for the same reasons -so that all of your video sources will bt accurate with reference to each other. ThIs will prevent aotfceable s , W In color values when yau switch fhm one source to an- other. The adjumncnt Is made by laying the bwstslgnal b m each source on top of h e sigaal fmm all the others so that they all are on the same reference line.

As with thewaveform monitor. be sure the vectorscope is in the exttmal sync mode. As a reference. choose a signal that will not change, cg, svvitcher black, colorbars from a test generator.or whatever source you wbh to use as the one ta which all thcothea arc to be phased.AlSgn the colorburst vector exactly on the 180" line (uslng the vcctorscope's phasing knob to make any necessary adjustments). then switch through the othcr sources, one by one -your cam- eras. the character generator. theTBC while vfdco Ls playing back from the recorder. the filmchain. and so on. Use the sub-carder phase or system phase control on each source to lay the wctor from its color burst signal exactly on topof the one from your rrfercnce source. .

Once all of the equipment is adjusted, you wlll not see a n y color shifts when you dissolve from one camera to an- other.ormlrch fmm the filmchain to the playback from the W'R, or use the character generator or anather keying source to do a supedmposftion. SwItchcr black is a good source to use as your rcfercnce. It docs contab color butst,and durlng production, you usually will fade to and from bhck, there- fore uslng It as rhc reference wtll assure that gohg from one source to another wlU not cause color shlfts.

~NCE u RULES are made to be broken. there art F arc drcumstancts in which even thcx guide- U ncs should be Ignored, or perhaps a better word

is " ched.'*Toobtaln clcar,dIstinct video,you sometimes must push dtfinitbns to thdr liml~s.

that one.small spot peak at a level chat exceeds +I00 IEEE unitson the waveform monitor Lfyou want to maintain the propcr levels ln the rest of the video. Try a ten recording with the offending object in the shot. ~f the picnrrc doesn't "lear" when you play it back, 11 will probably be OK.

Another example, at the opposite end of rhc spxmm. Is a production which uses black talent. Because of variations in lightlng,set configuration. and individual differences in skin tonesthe faces ofsome black people will appear to lose all dctall if your refcrencc black level is set at the FCC's rtc- ommcnded4-7.5 IEEE units.Try mnnhg the black level !??1 thccamera up closer to -t 10 XEEE units and see STthat helps. Donyt be afraid to experiment with the tools and skills in using these testing units that you have acquired!

FLnaUy, k rurc your teu cquipmenr is working properly. Read the manuals to become familiar wlth the built-in cali- bration checks. Most wavcfom monitors will have a "Cali- brate" knob that displays onevolt of video, which supplies a signal that should measure from -40 to 4 106 IEEE units if the waveform monitor is set properly. Be sure to check and calibrate periodically before you u y t makc any measurc- menu on other equip mcnt Once a week is a good schedule. and cemlnly anytime your waveform monitor Is moved. I f you suspect the unL has a problem, check it each rime you use k uirtil the trouble b soIved or the unit repaired.

lfyour wavefom monitor and veccocscopc are both at the same locatfon In the video chain. c.g.. at the output of the switcher, familiarhe yourself wlth how the display on one looks relatlve to the display on the other in different slnia- dons. If the waveform monltor shows normal video levels,

, !he vtcto~xy)pc should have vectors in the proper boxes. IS, however, the peak lcvcl on the wavcfonn monltor docs not ~ch+100IEEE,arrthc venonstiU in theltboxa.ordo they falIshon7After you become accustomed t~ using them, you will wonder how you ever got along without these two pro- duction tools. t 0

For cwmple, lf you arc shooting a xcne with one brlght, shhy djed In it -the rrnKtlon from comeone's ycslasscs, for Innilncc -and you 1) can't remove the objca, 2) canlga

ofthe reflcnion by adjurtlng the lighting, or 3) can'l a 1 Nann) ~ y k l u.5 ia r licensed te*fi8lon enginwr ceb'e dam ~e -1---x-- - . - 8 - - A . . l# t - - -----. ..-.. --..L .,. let -.-.-- ,- b - - - I - - a*l-b.s---

. . . . a . . -

Page 6: Scoop on Scopes

r

WAVEFROM MONITOR DISPLAY ANALYSIS 1 .

In the 2H mode the waveform monitor displays two horizontal scan l ines a t 8 time Though only two l ine3 a r e visible, the process happens so f a s i that a l l 525 l ines

arc shown every 1 /30 o f a second.

I . .

I f t he l i ne s a r e then c o m p r e s ~ e d ...4

and then compressed egain ... 4

and then f l lnally cornpre~ led until ell 525 l ines are visible e t the time, then one complete frame will be vi~ible, This i s what i~ displayed in the 2Y m d e .

Page 7: Scoop on Scopes

WAVEFROM MONITOR DISPLAY ANALYSIS 1

I n t h e 2Y Mag posit ion the center p o r t i o n of the 2V display i s magnified to s h o w t h e v e r t i c l e sync signal w i t h f i n e detai l . This makes i t post ib le to measure

t h e v e r t i c l e b lank ing i n t e r v a l t o de te rm ine i t s width.

In t h e 1 Microsecond p e r d i v i s i o n pos i t ion t h e cen te r p o r t i o n o f t h e 2H d i s p l a y . i s magnif ied t o 3 how t h e .hor izonta l sync s ignal with f i n e detai l . T h i s w o r k s . - - .. - . -

much li ke the 2Y Meg mode. T h i s maker i t possi b le t o measure t h e h o r l z o n t s l b l ~ n k i n g i n t e r v a l t o de te rm ine i t s width. 11 13 called 1 Microsecond p e r . .

d i v i s i o n because t h e sweep ir ca l ib ra ted t o t o r r e s p o n d to the m a j o r m a r k e s o n t h e blanking line ofthe gr8 t icu le .

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f- >

Gray Yellow Cyan Green egente Red Blue

77%

I I

I White Q Black 100% 7.5% .

FULL FIELD.

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A P U T FUELD COLOR BARE5

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Horizontal Blanking Interval

Right side o f picture Left side o f picture

J v v T

Front Po rch Sync Pulrr Back Porch I

I---- Horizontal Blanking Interval I 10.9 Hicro S e c o d r f 0.2 Micro Seconds \

The width of the horizontal blanking interval i s measur.ed on your waveform monitor graticult using the flat response mode and the 1p s e e / D\V position of the sweep switch. In the 1p stc/DIV position the graticule is calibrated .so tha t the major marks a r t 1 micro second wide and the minor marks a r e 0.2 micro seconds. Position the t race on the graticule and s e t the f a r le f t point a t which t h t picture just ends on the l e f t most major mark. Then count the major graticule marks until you reach the point a t which the picture just begins. This interval should fall between 10.7 micro seconds and 11.1 micro seconds. Note: the signal from your-switcher will be much cleaner and easier to measure than that coming from a tape machine. If the signal i s wider than the specification then ad just your horizontal blanking w i d t h control until the spec ts mat. Each video source by it. self must m e t this rpcc.

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' . . test line at First 14 ne at

bottom of picture . t o p o f picture

t . 1 T

I f

J

Equalizing'sync Equalizing pulses . . . Pulse pulses

. . \ v

I

. . . . .. ' . Vertical Blanking Interval

~pecification: Vertical blanking interval t 2OHorizontal l ines plus lH, minus OH.