Wavetek 147 Specifikace stáhnout pdf (Strana 356)

Application Notes: Return Path Troubleshooting

332

misleading. If there’s a reference carrier present, you can

make a relative measurement, such as desired-to-

undesired ratio (D/U).

The field unit has a "noise/ingress" feature, which can be used for

troubleshooting. This displays the noise seen in the headend with optimum

resolution of 280 kHz. This simplifies reverse troubleshooting and testing of

headend reverse noise or ingress. The headend unit will transmit/broadcast

the ingress from all the return amplifiers connected to it back to the field unit.

This transmits the ingress seen in the headend on the forward telemetry

frequency. So if no reverse communication is achieved, you will still get a

display of the noise/ingress floor. The noise mode on the multiple user

reverse receiver (Rx) transmits the total noise in the headend also, but with a

resolution based on the return channel plan resolution.

NOTE: The Noise mode can take up to a minute to track if

the reverse is not connected.

NOTE: The Spectrum mode is not the same as a true

spectrum analyzer. The RBW is set at 280 kHz and a VBW

> 1 MHz. This is optimized for analog carriers and burst

noise measurements. It has a peak noise detector so the

noise reading may be significantly higher than a normal

spectrum analyzer with the same RBW setting.

Be sure forward input levels to the headend transmitter (Tx) are between 4

and 12 dBmV. If levels are too high, distortions will be created in the Tx,

which appear as common path distortions (CPD) when you're viewing the

Noise mode.

Listening to Ingress for Identification of the Source

• Use FM demod for the audio of forward channels and certain shortwave

radio.

• Use AM demod for reverse interference and ingress, such as CB, Ham,

and shortwave radio.

This may give you some insight into the location of the source or at least the

nature of the source. You may be able to get the call signs of a ham radio

operator or a mile marker from a truck driver using his CB. This could aid in

pinpointing the ingress location.

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Wavetek 147 Specifikace Strana 356