Wavetek 147 Specifiche Scaricare il pdf (Pagina 293)

SDA-5500/SDA-5510 Sweep Configuration: Forward Sweep Configuration (SDA-5500)

269

The SDA-5500’s output can be injected using a directional coupler at the

output of the combining network, or it can be injected at an input to the

combining network. With an output level set such that the sweep is 14 to 16

dB below video carrier level, good response measurements can be made

without interference to subscriber TV pictures.

CAUTION ! It is important that the IN connection be

downstream from the OUT connection for proper operation

in all modes.

It is also very important to use correct signal levels when

connecting a sweep transmitter. Worksheets 1 and 2 below

provide guidelines for calculating the value of couplers and

pads when you’re installing an SDA-5500 for proper

forward sweep.

Properly connecting the SDA-5500 and establishing the right sweep and

telemetry levels are probably the two most critical steps in installing the

Stealth sweep system. Mistakes in SDA-5500 connections or wrong levels

on either input or output can cause the SDA unit to produce erroneous or

inconsistent results. A simple and common method of connecting the SDA-

5500 in the system at the headend works for both forward and reverse

sweeping.

Setting Levels

In Sweep mode, the SDA-5500 input should never see video or carrier levels

above +12 dBmV. The forward sweep points being inserted into the system

by the SDA-5500 should be 14 to 16 dB below the video carrier levels at the

SDA-5500 input. The forward telemetry signal generated by the SDA-5500

should be 4 dB higher than the sweep insertion points, or 10 dB below the

video carrier levels. Figure 14-3 shows a graphical display of the relationship

of the system’s video carriers, the sweep insertion points, and the forward

telemetry signal. When you are sweeping, you can see this relationship on

the SDA-5500 display, except for telemetry.

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Wavetek 147 Specifiche Pagina 293