PDI Communications, Inc.: Glossary of

A convenient socket on the back of headend processing equipment for obtaining AC power for auxiliary units.

(AGC) Circuitry in a headend processing device that adjusts the gain keeping the output level constant regardless of input level.

A device that is powered from a source other than the input signal and increases the operating level of the input signal. In cable systems its use is to rebuild the signal attenuated by cable and passives.

A class of devices or circuits where the output varies as a continuous function of the input.

When audio is placed onto an aural carrier by frequency modulation. To minimize over-modulation, which would cause distortion, the frequency deviation is set to ±25kHz deviation for monaural sound and ±50kHz deviation for stereo.

It is generally 600 ohms balanced or unbalanced. This is the matching point between the audio source and the modulator.

This control sets the ratio between video and audio levels. The setting usually is between 15dB and 17dB below the video carrier.

The connection point for the audio source information.

It is the difference between the audio level and the video level. Once set the ratio remains the same for any setting of the video RF level.

A control point at 41.25MHz for inserting scrambling or other audio information into the modulator.

Refers to the undistorted reproduction of the audio signal.

Is the vehicle for the transmission of audio information by modulation.

The frequency spectrum occupied by all of the transmitted signals used to modulate a carrier.

This refers to the Broadcast Television System Committee. It is an Electronics Industries Association Committee that created the analog TV stereo system we use.

Is the relationship of carrier amplitude to noise voltage amplitude. It is expressed in decibels (dB).

A segmented light emitting diode display that shows the TV channel in operation.

A device used to combine 12 or more TV channels into a single cable. It exhibits high isolation between ports and good return loss to maintain picture fidelity.

The distortion caused by the difference in time for the arrival of the black and white and the color signals. The result is the color is shifted with respect to the black and white causing a mis-registration effect like seen in some color comic papers.

A connection point on a modulator containing both audio and video information at IF frequencies. It is used to connect emergency alert or scrambling encoders.

A processing unit that takes modulated video and audio signals at RF and converts them to baseband signals.

The degree to which a video carrier wave is modulated. It is usually 87.5%.

The variance in gain of the chroma signal measured in relation to the luminance level.

The variance in phase of the chroma signal measured as a function of the luminance level.

A class of devices or circuits in which the output varies in discreet steps. Binary code is used to represent information.

Is an abnormal change in the desired waveform of a signal causing unfaithful reproduction of audio or video signals.

A device that converts signals or data into a desired form. In CATV it is used to insert messages or scramble TV pictures.

The gain verses frequency characteristic of a device or a system relative to the ideal. It is also referred to as peak to valley response.

The operating bandpass or frequency width of a device or system beyond which the power output is attenuated below a specific limit.

Is the degree to which electronic components and equipment can maintain a constant frequency through variations of temperature, voltage, current and similar factors. It is usually expressed in kHz or in parts per-million (ppm).

An increase in power when a signal is transmitted from one point to another. It is usually expressed in decibels.

The mixing together of two frequencies to produce two other frequencies equal to the sum and difference of the first two.

The effects of low frequency electromagnetic fields or currents exhibited as vertically moving horizontal bars on a television screen.

The total opposition a circuit offers to the flow of alternating current at a given frequency. Its symbol is "Z." Its measurement unit is the ohm.

Is the connection point on a modulator for controlling scrambling encoding for both the video and audio signals.

This is an integrated receiver-decoder. It consists of a satellite receiver and a descrambler.

This is the International Standards Organization quality standard covering manufacturing.

A single chip used as part of an automatic control system that contains a control unit, central processing circuitry, arithmetic and logic functions. It instructs other logic chips as to what to do.

A device for combining two signals with the result that a part of one signal (the carrier) is varied in step by the other, called the modulating signal.

A waveform containing six packets of special frequencies, 0.5MHz to 4.1MHz. It is useful as an indicator of a modulator’s or processor’s in-band frequency response and flatness.

An unwanted frequency current or voltage signal appearing over a wide frequency spectrum and having no useful purpose.

The middle of a value range. The input range of a processor may be 0 to 10dB. Nominal input is 5dB.

Refers to the National Television System Committee. This organization developed the television standard currently in use in the United States, Canada, Japan, South America and elsewhere.

In CATV the frequency offset required by the FCC, 12.5kHz and 25kHz, to keep leaking cable signals from interfering with aeronautical communications.

The recommended temperature of a device during its operation.

Refers to Phase Alternate Line. This is the television system used in Europe and other parts of the world. The subcarrier derived from the color burst is inverted in phase from one line to the next to help cancel out phase errors which affect the hue in color transmissions.

(PLL) A very efficient corrective circuit that acts as a phase detector. It compares the frequency of a known oscillator with a received signal and uses the output of the detector to keep the oscillator in phase with the incoming frequency.

Generally a transformer, rectifier and filter assembly that produces the power needed to operate an electronic device.

In FM, a process designed to selectively emphasize the magnitude of some of the frequency components prior to transmission. Its purpose is to reduce noise and distortion.

An amplified network inserted into a scrambler to emphasize one range of frequencies.

In CATV, a headend channel control device that receives a TV channel at RF, cleans up the signal at IF then converts the channel to a desired frequency and outputs the signal at a controlled level to a combining network and into the cable system.

In CATV, a signal level meter that measures output in dB.

A device used at the end of a communications link to accept a signal and process it for local use.

Refers to Systeme Electronique Couleur Avec Memoire. This standard is used in France, Russia, eastern European and some African countries. It uses an 819-line scan picture that offers better resolution than NTSC (525) or PAL (625). The three systems are not compatible.

In stereo operation, the degree the information on one channel is away from the other. It is expressed in decibels. The higher the dB number is, the better.

Is the relationship of signal amplitude to noise voltage amplitude. It is expressed in decibels (dB).

In CATV headend processing equipment, the unwanted output signal appearing on a frequency other than the fundamental signal frequency. When this signal is down 60 dB or better it has no effect on the desired TV pictures.

A switch used to eliminate the pre-emphasis network in a modulator when an external stereo encoder is connected.

(SAW) A very effective filter used at IF frequencies in CATV headend equipment to set the ideal bandpass response to prevent adjacent channel interference.

A port to connect signal meters or test equipment to measure equipment parameters without affecting primary operation. The measured levels will be down either 20 or 30dB.

In an amplitude modulated signal, the part of one sideband remaining after going through a selective filter.

In television, amplitude modulation of the carrier wave with pulses and waves corresponding to the picture, sync and blanking signals.

The port on a modulator where, at baseband, the picture portion of a television broadcast is inserted.

A control point at 45.75MHz for inserting scrambling or other video information into the modulator.

Is the force that causes current to flow through an electrical conductor.