Wavetek 147 Especificaciones descargar pdf (Pagina 261)

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Description and Basic Operation of the SDA-5500 and 5510: Basic Modes of Operation

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Measuring Hum

Hum is undesirable modulation of the television video carrier by power line

frequencies and harmonics (e.g., 60 or 120 Hz), or other low frequency

disturbances (FCC limit: < 3%). To measure hum, simply press the Hum key

when tuned to any non-scrambled channel (see Fig. 13-12). In the Hum

mode the hum modulation of the tuned channel or frequency will be

displayed in either % or dB as selected by the operator. Soft keys allow the

operator to select 60, 120 (50, 100 Hz), or <1,000 Hz filters for this

measurement to help in troubleshooting. A 60 Hz modulation component

suggests a possible corroded connector, a 120 Hz component tends to

indicate a possible failure related to the DC supply in the amplifier—possibly

a capacitor going bad and aggravating the ripple. A proprietary DSP

technique enables hum measurements on modulated carriers (non-

scrambled channels).

Fig. 13-12 The HUM Measurement Screen

Stealth has the capability of measuring the 1Hz hum component. To activate

this feature, set the fundamental hum frequency in the MEASUREMENTS

setup screen to 1Hz. The filter options on the hum screen will then become;

1Hz, <50Hz, and, <1kHz.

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