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Application Notes: Reverse Sweep and Balance

324

Find the highest number and set the Sweep and Telemetry close to this. For

instance, the highest number is 45.5 so they are set for 46 dBmV.

Store a reference at the node with a 7 dB in-line pad installed. This will

automatically knock down the sweep and telemetry level without having to

change the generator output and the associated problems with doing that

(explained later). Store a reference and record the telemetry.

Go to the trunk amp, disconnect the in-line pad, and reverse balance to the

same reference and telemetry. Go to the bridger amp and install an in-line 2

pad. Balance to the same telemetry and reference. Go to the LE and install a

4 dB in-line pad. Balance back to the same reference of 0 and telemetry that

was recorded when the reference was stored.

The one caveat to this is the inconsistency with in-line pads. One more

variable is added to the equation!

Considerations

There are some things to consider when changing the sweep and telemetry

levels on the field unit for different balancing scenarios. This may influence

your balancing method.

1. Changing the sweep insertion level on the field unit does not change

where the sweep is displayed. The display is gain or loss, not the

headend unit received.

2. Changing TP compensation changes where the sweep is displayed

on the screen.

3. Changing the telemetry insertion may not have a 1 for 1 effect, and it’s

only in 2 dB increments.

NOTE: Because this is a sweep, ingress can affect the

outcome. It may be advantageous to terminate all reverse

port pads or keep all amplifiers terminated until activation.

Common Return Sweep Problems

Standing Waves

• Use a directional, injection test point if available. Standing waves could

still occur if a mismatch is close and severe enough.

• Inject into a tap. Some lower value taps may still give reflections

depending on port-to-port isolation and port-to-output isolation.

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Wavetek 147 Dokumentacja Strona 348