Wavetek 147 Especificaciones descargar pdf (Pagina 337)

Application Notes: Forward Sweep and Balance

313

NOTE: The "max/min" displays the peak-to-valley

between the markers. The delta displays the difference in

level and frequency at the markers.

In forward sweep, the field unit has a max input of approxi-

mately 20 dBmV/ch for a fully loaded system. This is usu-

ally not a problem on the high loss test points, but could be

an issue when connecting directly to a seizure screw.

256-QAM is a more complex modulation scheme and

requires a higher C/N than 64-QAM. It also doesn’t have as

much guardband. The default option is to dwell on the

carrier (Stealth unit must have digital option installed),

which could slow down the sweep update time depending

on the total number of carriers.

Common Forward Sweep Problems

Standing Waves

• Use a directional test point if available. Standing waves could still occur if

a mismatch is severe and close enough.

• Read from a tap. Some lower value taps may still give reflections

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

• Use a plug-in test point not a probe. Probes will always be bi-directional

unless they are in series with the circuit and a directional coupler is used.

• Install a terminating tap (4 port 8 or 8 port 11) if you have the luxury. It’s

an easy way to isolate the system.

• Verify test leads, connectors, F-81 barrels, etc. Use an in-line pad to see

if the standing wave goes away. If so, there is a reflection being created

between the field unit and test point.

Spikes

• Keep the resolution to approximately 6 MHz for forward sweep. This

lowers the probability of inadvertent, over-lapping sweep points and

transients. A sweep point every 6 MHz is sufficient in most situations for

forward sweeping. It also creates a faster sweep update.

• Verify proper setup, levels, channel types, no overlapping sweep and

actual channels, etc.

• Avoid common problem areas such as strong off-air broadcasts and

certain FM channels.

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Wavetek 147 Especificaciones Pagina 337