Wavetek 147 Especificaciones descargar pdf (Pagina 365)

Application Notes: Proofing and Testing

341

by power pack filter failure, bad solder connections, corroded connectors,

impulse noise, etc.

Diagnosis for 1 or 2 bars slowly scrolling up on the TV is as follows: If it’s one

hum bar (50/60 Hz), check for bad connections where voltage is ac. If it’s 2

hum bars (100/120 Hz), check the dc power pack for proper ac input, check

for power-pack ripple (possible filter cap or diode failure). This is achieved by

using an ac-coupled voltmeter and measuring ac voltage on the dc test

point. It should be < 15 mVac. Two hum bars can be produced by any power

supply that rectifies ac into dc and could include battery chargers.

If hum is only on 1 channel, suspect the headend. If it's only on a few lower

channels, it could be a bad power transformer humming along outside. If it's

on one house and not the neighbors, or on a digital channel, suspect the

house grounding.

Headend Tests [76.605(a)(11)]

Headend proofing consists of chrominance-luminance delay (<170 ns),

differential gain ( < ± 20 %), and differential phase (< ± 10 degrees). This is a

triennial test requirement.

Leakage – Rule [76.609(h) & 76.605(a)(12)]

This measurement can be taken directly from an aircraft above the system

and reported directly. 90% of leakage points shall not exceed 10 uV/m at an

altitude of 450 meters.

Measurements may be taken on the ground and entered into a formula that

simulates the interference it would cause at aircraft altitudes. The former

method is called the fly-over and the latter is called cumulative leakage index

(CLI).

If you opt to perform CLI instead of the fly-over, you must include at least 75

percent of the strand mileage of the cable, including all the cable that can be

expected to have the least leakage integrity. You must substantially cover

the plant in three months for a quarterly test.

A dipole antenna must be used 3 meters from the leak and 3 meters above

the ground. The dipole should be rotated about a vertical axis and the

maximum reading recorded.

Other conductors must be 10 or more feet away from the measuring

antenna. See 76.609 through 76.616 for the complete regulation series.

A single source of radio-frequency leakage must not exceed a certain field

strength, measured in microvolts per meter at a given distance with a "cut

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Wavetek 147 Especificaciones Pagina 365