Wavetek 3ST Specifiche Scaricare il pdf (Pagina 48)

4-24

Scale Adjustment

The UP and DOWN arrow keys can be used to adjust the reference

level on the analog meter. This is helpful when the audio and video

levels differ by large amounts.

To automatically scale the analog meter, press the FCN key followed

by the Scale second function key.

When in the TV channel mode, the level is represented using dual

analog meters; one for the video carrier and one for the audio carrier

(two in the video + dual audio channels mode).

When in the frequency mode or single channel mode, the level is

indicated by a single meter.

4.5 HOW TO MEASURE TILT - BALANCING AN AMPLIFIER

A cable system is designed for unity gain, and the output of each like

type of amplifier (trunk, bridger/line extender) should be as close to

identical as physically possible. The amplifiers are set up with

specified levels for signals at the high and low end of the spectrum

that are used for Automatic Gain Control (AGC) or Automatic Slope

Control (ASC). In the amplifier balancing process, these signals are

measured and adjusted to specification. Before making an adjust-

ment, ensure that there are no problems in the system that should not

be compensated with an adjustment but repaired instead.

To balance the amplifier, ensure that the AGC and ASC is switched

off. Tilt mode simplifies the actual balancing by displaying a bar

graph with a representation of up to nine different user selected

video carrier levels. Adjust the high pilot level to the specified level

using the gain control. The gain control tends to affect the overall

amplitude throughout the spectrum equally. Adjust the low pilot

level to the specified level using the slope control. The slope control

affects the low end of the spectrum more than the high end. Due to

the interaction between the two controls, repeat this process until the

pilots are "balanced". Then switch on the AGC and ASC, wait a

moment to measure the signal levels with the AGC and ASC acti-

vated.

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Wavetek 3ST Specifiche Pagina 48