This document explains how to set up a Tektronix 465M oscilloscope to display horizontal scan lines of an NTSC, PAL or similar analog TV signal generated by a Tektronix 1410 video test signal generator. The information is set up in a specific series of steps, each of which builds on the previous.
If you have a different oscilloscope or video test signal generator, your steps will be different. At minimum you will need an oscilloscope with a delayed sweep feature and some kind of steady video source with an easily identifiable horizontal border.
The primary objective of these instructions is to show the difference between a scan line with color information and one without color information. The secondary objective is to give a quick introduction to the Tektronix 1410 video test signal generator and the Tektronix 465M oscilloscope and to demonstrate one of the tweakier features of the oscilloscope.
All connections are made with coaxial cable with BNC connectors or coaxial cable with RCA connectors and RCA-to-BNC adapters.
The NTSC monitor should show color bars in the top half of the screen and an 8-bar monochrome gradient in the bottom half of the screen.
Now you should see the entire frame of the video signal. It should be fuzzy in the left half and show distinct levels in the right half of the display.
In this exercise we will zoom in on two scan lines: the last color scan line and the first monochrome scan line.
Press HORIZ DISPLAY - A INTEN in
Rotate the DELAY TIME POS knob CW. Notice that the left part of the display gets dark, leaving the right half bright. (You may need to adjust the INTEN control to optimize this display.) Rotate the knob until the bright part of the display begins just to the left of the change, in the middle of the display, from fuzzy to distinct levels.
Pull out the grey A and B TIME/DIV collar. Rotate it to 20uS. Notice that the bright part of the display now covers only the transition.
Press B DLY'D/
Slowly rotate the DELAY TIME POS knob until you see three scan lines: The first two should show a fuzzy stairstep and the last should show distinct stairsteps.
The A TRIGGER section is using the vertical sync signal from the 1410 to start the main sweep at 2 mS/div.
The DELAY TIME POS sets the delay after the A SWEEP begins, to start the B SWEEP.
The DLYD SWEEP PULL (Grey collar) sets the delayed sweep speed to 20 uS/div.
HORIZ DISPLAY A - uses the sweep signal set by A.
MIXED - uses A, then after period set by DELAY TIME POS, B.
B DLY'D - uses only B, at its higher sweep speed, to show ~3 scan lines.
The fuzziness displayed in the traces in the left half is the high-frequency color subcarrier of the composite signal. As you can see, they are superimposed on the signal in the color half of the image and absent in the grayscale half. A further exercise would be to use the oscilloscope to zoom in closer onto the subcarrier signal itself.
It is beyond the scope of this document to explain how the subcarrier encodes color information.