Analog Video Test Signals

Test signals are a vital part of what keeps an analog video system working at it’s peak. Some are general purpose and others have very specific jobs. Some were intended just the transmitter testing while others helped television sets to adjust them selfs. If you compare a test signal at the input to the device it’s applied to and the output of that device any differences between the two are caused by miss-adjustment or a fault in the equipment. Below is an assortment of analog test signals and what they are used for.

Color Bars on a Waveform Monitor

Color Bars on a Picture Monitor

Color Bars - these are the most widely used test signal. The on screen display shows all three primary colors (Red, Green & Blue) and the secondary colors (Cyan, Magenta & Yellow) as well as black & white. Vector scopes have markers to show where these six colors should be in relation to the color burst. A quick look at a monitor would tell any engineer if the video was correct or not. Color bars was always placed at the start of any video tape or video feed so it could be evaluated and adjusted.

Color Bars on a Vector Scope

SMPTE Color Bars - are specially designed to help engineers properly setup color monitors. The reverse set of color bars towards the bottom and the pluge bars in the black region are all used to set a monitor’s Brightness, Contrast, Phase and Chroma Levels.

Composite on a Waveform Monitor

Composite on a Picture Monitor

Composite Test Signal - is comprised of several different tests. The first is the modulated stair step used for testing for differential Gain and Phase. Next is the Pulse to test for ringing and over and under shoots. Then the modulated Pulse to show delay differences between luminance and chroma. (see close up)

Lastly is the White Bar which can once again be used to look for over and under shoots.

This signal would be used in testing transmission systems or individual pieces of equipment. .

Close-up of Pulse & Mod Pulse

Multi-burst on a Waveform Monitor

Multi-burst on a Picture Monitor

Multi-burst - is just that, a series of burst of progressively higher frequencies. It starts at 500KHz and moves up to 4.5MHz. It provides a quick and accurate evaluation of a system’s bandwidth or more commonly Roll Off. If you send it through a length of cable you will see the attenuation of the high frequencies caused by the cable.

Sweep on a Waveform Monitor

Sweep on a Picture Monitor

Sweep - is a sweep of frequencies from low to high. It is similar to Multi Burst but does not skip frequencies. It can show you if there are any dips or peaks within the video bandwidth where as Multi Burst may not show this as it shows only discreet frequency bursts.

Gray Field on a Waveform Monitor

Gray Field on a Picture Monitor

Gray Field - is a mid level luminance only signal. It is usually accompanied by Black and full White signals that test the equipment’s luminance levels with a full screen or Frame of that level.

Red Field on a Waveform Monitor

Red Field on a Picture Monitor

Red Field - is for testing a CRT monitor’s Purity. If the convergence as well as the focus coils and small magnets are not aligned properly the Purity of the monitor would be off. You would see this as areas of colors on the screen when it is displaying full red. Not used with today’s monitors.

Multi-pulse on a Waveform Monitor

Multi-pulse on a Picture Monitor

Multi-pulse - for testing Group Delay, where different frequencies are delayed through a system by different amounts. Mostly used for testing analog transmitters.

NTC 7 on a Waveform Monitor

NTC 7 on a Picture Monitor

NTC 7 - also called the Pink Panther, combines the multi-burst, modulated pedestal for testing transmission links.

VIR on a Waveform Monitor

VIR on a Picture Monitor

VIR - the VIR or Vertical Interval Reference, was used for a very special reason, it was inserted within the vertical blanking period above the picture to provide a reference for the television set. WIth it’s 40 IRE of chroma and 50 IRE gray and 7.5 IRE pedestal it provided a way for the television set to adjust it’s self when receiving an over the air broadcast. It was never intended to be used full screen.

(Sin x) / x - is a very specialized test signal used only for on the air transmitter testing. The unique features of this signal produce a kind of sweep signal in an on air television broadcast. With the use of a spectrum analyzer the frequency response can be measured.

(Sin x)/x on a Picture Monitor

VITS - VITS or Vertical Interval Test Signals is a way to provide test signals even while a television program was in progress. These signals reside above the picture during the vertical interval. The two photos to the left show VITS in place.

Any number of different test signals can be used but the most common were the VIR, Multi-burst and Composite.

Using both Fields up to 6 different test signals could be used at once.

VITS in the Vertical Interval

Close-up of VITS