Avideo signal generator is a type ofsignal generator which outputs predeterminedvideo and/ortelevisionoscillation waveforms, and other signals used in thesynchronization of television devices and to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses (in analog) or sync words (in digital). Generators ofcomposite video signals (such asNTSC andPAL) will also include acolorburst signal as part of the output.

Video signal generators are primarily classed according to their function. In addition, they may be classified according to the video formats and interface standard they support—one generator may generate composite analog signals (typicallyNTSC,PAL, or both), another may generateCCIR 601, and a third may generateMPEG streams over anASI.

Many manufacturers sell signal generation platforms, which can be populated with multiple modules providing the above capabilities (and supporting different formats). Many such platforms also include audio generation capability (as television includes audio as well as video), supporting eitherembedded audio or standalone audio formats.

Atest signal generator generatestest patterns, and other useful test signals, for troubleshooting and analyzing television systems. These devices are generally intended for off-line use (test patterns are seldom broadcast, unless a station is not operating properly or is off the air at the time), as they output complete television signals. Examples of signals output by such a device include:

• Color bars, one of several test signals used to verify the proper reproduction of a TV system'scolor gamut, and/or that a television signal or plant is compliant with the appropriate analog transmission standards
• Flat fields, a signal consisting of nothing but a specific color (typically white, black, a shade of gray, or one of theprimary colors (red, green, and blue) at maximum saturation). A red field is especially important inPAL applications, as it is the "red difference" portion of the chroma signal whose phase alternates every line; the red field should appear as a solid block of color, with no visible "bands" going across the screen.
• Multibursts,sweeps, andpulse signals, used to test the frequency response of a television system
• Ramp signals andstaircase signals, used to check the voltagelinearity of a television system
• Crosshatch patterns, used to check and calibrate alignment, aspect ratio, convergence, and both vertical and horizontal linearity
• Thebowtie signal, used to check the relative (inter-channel) timing of a component video signal.

Some generators achieved a relative popularity, due to channels broadcasting test cards for long periods where no programming was scheduled. Patterns associated with Philips^[1] (PM 5540, PM 5552,PM 5544,PM 5644), Grundig VG 1001^[2] (FuBk)^[3][4] SMPTE (Color Bars), or Snell & Wilcox (Zone Plate)^[5][6] generators are generally well known.

A few specialized signals are used indigital environments:

• ThePLL test signal is apathological test signal used to stress thephase-locked loop of a serial digital receiver; this is done by outputting a bit pattern which, after passing through thelinear feedback shift register used to scramble serial digital signals, resulting (with a high degree of probability) in a long strings of zeroes or ones, followed by a long string of the opposite polarity, on the digital (NRZI) signal; an issue which can cause poorly designed PLLs to unlock.
• Theequalizer test signal is another pathological signal, consisting of a long string of zeroes or ones, followed by a single bit of the opposite polarity. It can cause poorly designedcable equalizers to malfunction.
• TheSDI Checkfield signal, standardized bySMPTE RP178 (for SD) and RP198 (for HD), is a test signal which contains one of the above signals in the upper portion of the video, and the other in the lower portion of the video.

In addition, sophisticated signal generators may allow modification of the video timing, adjustment of the gains of the various components (including out of range), the introduction ofjitter orbit errors (into digital signals), the introduction of motion, or other effects.

Avertical interval test signal inserter, orVITS inserter inserts test patterns into thevertical interval of a television signal. Unlike test signal generators; a VITS inserter is used to insert the test signal into live programming, so that inline measurements of a transmission chain can be made while the chain is operational. (As the vertical interval is typically not visible on end-user televisions, this can be done without producing any artifacts noticeable to viewers). Since VITS signals can often be transmitted, it is also possible for a television station to receive its own on-air feed, and use the VITS to detect and troubleshoot problems in on-air transmission.

Async pulse generator (SPG) is a special type of generator which produces synchronization signals, with a high level of stability and accuracy. These devices are used to provide a master timing source for a video facility. The output of an SPG will typically be in one of several forms, depending on the needs of the facility:

• Acontinuous wave signal
• In standard-definition applications, abi-level sync signal, often with acolorburst signal in facilities that have analog equipment. Typically, this is either inNTSC orPAL format. As the resulting signal is usually indistinguishable from an all-black television signal of the same format, this sort of reference is commonly known asblack orblack burst.
• In some high-definition applications, a 'tri-level sync' signal is used instead. This signal is virtually identical to the synchronization signal used incomponent analogue video (CAV); and is similar to the synchronization signals used inVGA (the main difference being, in VGA the horizontal and vertical syncs are carried on different wires; whereas TLS signals include both H and V syncs).

Logo inserters are devices used to insert a television station's logo, or other fixed graphics, into a live television signal. Often called a "Bug Generator."

• Video display controller
• Philips PM5540
• Telefunken FuBK
• ETP-1
• Test card

• Tektronix, Inc.A Guide to Digital Television Systems and Measurements
• Tektronix, Inc.NTSC Systems Television Measurements
• Tektronix, Inc.PAL Systems Television Measurements
• Video Products, Inc.Usage of Video Test Pattern Generator
• Philips TV Measuring Equipment, 1980Archived 2022-02-08 at theWayback Machine

• Film and video technology
• Electronic test equipment

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