VOLUME 1 NUMBER 2
2H 1 µs/div, fully CW
1 µs/div, mid range 1 µs/div, fully CCW
Figure 2-1. Action of the horizontal position control in the
1 µs/div SWEEP setting.

An important aspect of composite video signal s p e c i f i c a t i o n s i s t h e d u r a t i o n a n d r e l a t i v e timing of sync and blanking pulses. For this reason, the time base selections built into the waveform monitor are specifically tailored for the purpose.
The 2H time base discussed previously is just
127 µs long to display two raster lines. The next lower pushbutton in the SWEEP group of the 5860C is marked 1 µs/div. Pressing this button in magnifies a section of the 2H display and the timebase is at one microsecond for each m a j o r d i v i s i o n on t h e c a l i b r a t e d horizontal graticule line at zero IRE. But it’s more than just a faster timebase. It’s actually a s p e e d e d - u p p i e c e o f t h e 2 H d i s p l a y . T o c h e c k t h i s , r o t a t e t h e c o u r s e h o r i z o n t a l position control ( ) throughout its range.
Y o u w i l l b e t a k i n g a w a l k t h r o u g h t h e 2 H waveform from its beginning to its end. Refer to Figure 2-1. This means you can examine in close detail any part of the 2H display and each p a r t that y o u ’ r e l o o k i n g at is one microsecond per major division.
H Sync and Blanking Wi d t h s
The 1 µs/div SWEEP setting makes it easy to measure timing events at the H rate. You can measure H blanking and H pulse widths. But the edges of all video signal excursions are not perpendicular to the timebase, so where e x a c t l y do you m e a s u r e p u l s e w i d t h ?
F o r t u n a t e l y, signal specifications such as are found in the FCC rules and EIA RS-170A tell you exactly where to measure them. (Note:
FCC rules and RS-170A are not the same; the l a t t e r i s a t i g h t e r s p e c a g r e e d t o b y E I A c o m m i t t e e m e m b e r s ) . T h e l a t t e r s p e c , f o r example, specifies the width of horizontal sync as 4.7 µs ± 0.1 µs at -20 IRE; that’s at half sync amplitude.
To put the -20 IRE point on the calibrated zero
IRE line, we reset the vertical position to put sync tip at -20 IRE. Since sync is 40 IRE units h i g h , t h i s p u t s t h e h a l f w a y mark o n t h e calibrated graticule line. (Check to make sure s y n c i s 4 0 I R E u n i t s d o w n f r o m b l a n k i n g before making this measurement.) Now, set the FINE horizontal position control to put the leading edge of sync on one of the major graticule marks. Read the distance from the l e a d i n g e d g e t o t h e t r a i l i n g e d g e o n t h e c a l i b r a t e d g r a t i c u l e l i n e . F i g u r e 2 - 2 , f o r e x a m p l e , s h o w s a n H s y n c p u l s e w i d t h o f
4.7 µs. That is four major divisions and two and one half minor divisions of 0.2 µs.
Horizontal blanking width is measured at +20
I R E a c c o r d i n g t o R S - 1 7 0 A . T o m e a s u r e H blanking, we reset the vertical position control to put blanking at -20 IRE. This puts the part of the b l a n k i n g to be m e a s u r e d on the c a l i b r a t e d g r a t i c u l e l i n e . To make this measurement, however, we need video at both start and end of blanking that’s higher than 20
I R E . F o r c a m e r a s , t h i s i s e a s y t o d o b y focusing the camera on a flat white card or wall. Figure 2-3 shows the waveform from a
L e a d e r 4 1 1 g e n e r a t o r u s i n g t h e 1 0 0 % f l a t white raster signal.
Following the same procedure with the FINE horizontal position control, the example shown in Figure 2-3 shows an H blanking width of
10.85 µs. This is within the RS-170A spec of
10.9 ± 0.2 µs.
The Phantom Pulses
If you look closely at the 2H display in Figure
2-1, you will see a faint, narrow sync pulse halfway between the horizontal sync pulses. Is this an aberration, just something wrong? It isn’t but to understand what is is you have to realize that we are not looking at just two lines
Figure 2-2. Horizontal sync pulse width measured at
4.7 µs.
Figure 2-3. Horizontal blanking width measured in
10.85 µs.

Figure 2-4. Detail of the vertical blanking interval showing leading and trailing equalizing pulses.
in the raster. We are looking at two, then the next two, the next two, and so on. We see all the lines in the raster superimposed one over the o t h e r. You can tell this because the 75% white chip appears on the top 3/4ths of the color bar picture. That 100% white chip that straddles the chroma peaks for yellow and cyan is in the lower
1/4th of the picture. Okay, we see all the lines in the raster, what are those phantom pulses? They are the mid line equalizing pulses that appear in front of and just after vertical sync. Refer to
Figure 2-4. The equalizing pulses are about half as wide as H sync pulses and there are six, spaced at half-line intervals before and after V sync. It’s those half line pulses that we see halfway between the H sync pulses. They are faint because there are only six in each vertical field. Thus, they are refreshed at the field rate, not at the line rate and that makes them dim.
Refer to Figure 2-5. You can use the procedure for measuring sync pulse width to check the width of the equalizers. the RS-170A spec for these is 2.3 µs ± 0.2 µs. The faint positive-going pulse just to the left of the equalizer is the halfline serrations in the V sync pulse.
Field Rate Checks
Pressing the 2V button in the SWEEP group presents the waveform of Figure 2-6 where two fields are displayed. The 2V MAG button works the same way to blow up the display horizontally.
And once again, the horizontal position control permits you to explore those two fields in detail.
Figure 2-7 shows the expanded part at mid range of the position control where the center V blanking period of the 2V waveform is shown expanded. Compare this waveform with the sketch of Figure 2-4. Here you see the six leading and six trailing equalizing pulses. Note that they are narrow and spaced at half-line i n t e r v a l s . T h e V s y n c p u l s e i t s e l f i s 3 H i n duration but serrated by positive going holes at half-line intervals. These holes serve to keep the horizontal oscillator in your TV set in sync during the brief vertical sync period. It is easier to measure vertical blanking width in raster lines rather than in time units. The FCC specifies a maximum of 21. Over that, and a broadcaster faces a citation although there is recent talk of
Figure 2-5. The mid-line area at the 1 µ/div time base permits a faint image of the mid-line equalizing pulses.
Figure 2-6. The 2V waveform display shows two vertical fields.

Figure 2-7. The 2V MAG display gives a detailed view of the V sync area.
relaxing the rules. The RS-170A specifies 20 lines for blanking. To measure V blanking, find line 10.
that’s the first line following the trailing equalizing pulses that’s equipped with color burst. See
Figure 2-7. Then count the remaining lines to the right until you get to the end of V blanking. In
Figure 2-7, that’s 21 lines.
Which Field?
The V blanking period shown in figure 2-7 shows the start of Field 1. We can spot it because there is a full line of video just before the start of V blanking. That full line is the last complete line of the 525 line raster. Also, the last line in V blanking is a full line.
Figure 2-8 shows the start of Field 2. This was obtained by leaving all settings a s i s a n d interrupting sync by pressing the SYNC (INT-
EXT) button a few times. It’s a fifty-fifty chance which field will come up. Here you see a half line of video just before the start of V blanking. Count six equalizing pulses back from V sync and you will see that half-line of video just to the left of the first equalizer. Similarly, the last line of V blanking ends in mid line for the blanking period at the start of Field 2.
1H/1V Sweeps
Model 5860C offers the operating options of 1H and 2H sweeps. The 1H sweep is found by pushing 2H and 1 µs/div simultaneously. Similarly, the 1V sweep is set up by depressing 2V MAG and 2V simultaneously.
Both 1H and 1V sweeps double the amount of detail that can be observed. But things also look d i fferent. Burst and chroma take on a totally different appearance. Look closely at Figure 2-9.
There appears to be twice as many cycles in burst and the cycles are peaks in opposite
Figure 2-8. The V sync area at the start of field 2.
directions. That’s because of the timing relation of line and subcarrier frequencies. The subcarrier frequency is actually an odd multiple of half the line frequency: Fsc = 455/2 • Fh. This was arranged from the beginning of NTSC to minimize the dot pattern caused by sub-carrier cycles in black-and-white pictures. (Subcarrier is trapped out of the Y signal in color sets). Because of this relation there are 227 1 /
2 cycles per raster line and the half cycle difference causes positive peaks on one line to above negative peaks on the next.
Thus, the subcarrier cycles in burst show two sets
180° apart in phase. (You see the same thing on conventional oscilloscopes synced at the line r a t e . ) H o w e v e r , t h e 2 H d i s p l a y s h o w s t w o consecutive l i n e s s i d e b y side, instead of superimposed and burst looks like the textbook model. One of the reasons why the 2H display has been standard on waveform monitors since the dawn of NTSC. (1H and 1V displays are relatively recent).
Figure 2-9. 1H sweep.