Wavetek 147 Specifiche Scaricare il pdf (Pagina 349)

Application Notes: Reverse Sweep and Balance

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• 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.

• Keep all proceeding actives terminated for return sweeping. Don’t pre-

stuff the reverse pad and EQ. The noise funneling may hamper your

ability to sweep properly. A high value pad or terminator is

recommended.

• Terminate all low value tap ports. Even an unterminated splitter in a

subscriber’s house a few thousand feet away can cause standing waves.

Coax attenuation at the lower frequencies is slight, which allows the

reflected wave to make it back without much loss.

• 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 that test leads, connectors, F-81 barrels, etc. are good. 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 -1 MHz for reverse sweep. This lowers the

probability of inadvertent, overlapping sweep points and transients. A

sweep point every 1 MHz is sufficient in most situations for reverse

sweeping. It also creates a faster sweep update.

• Verify proper setup, levels, no overlapping sweep and actual channels,

etc.

• Avoid common problem areas (strong off-air shortwave, ham, and CB)

No Communication

• Check forward sweep to confirm communication path between the

transmitters and field unit.

• Set to "Single User" for Tx return sweeping and "Multiple User" for Rx.

• It could be collisions with other people reverse sweeping on the same

Tx. Use a Rx if warranted.

• Verify the appropriate telemetry, keep it high & located in the passband.

Watch out for sharp diplex filter roll-off and old 550 MHz passives in a

750 MHz system. The minimum level for forward telemetry is

approximately 15 dBmV, but can also overload with greater than

approximately +12 dBmV. We sometimes lose communication on input

test points because of the lack of gain from the active and the test point

loss. Use the spectrum mode with "max hold" on to verify the existence

of the telemetry and the level. Make sure test point compensation is 0.

• Check return path continuity. Verify test equipment connections, amplifier

continuity, active gain, and that no terminators are installed. Look at the

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Wavetek 147 Specifiche Pagina 349