Matrix Amplification XT2000 Dokumentacja Pobierz pdf (Strona 8)

Digital Services Activation Meter (DSAM)

www.jdsu.com/nse

Bit Error Rate Measurement

The BER measurement speeds detection of impulse interference in the

system by revealing when information is lost or corrupted at the bit

layer. The DSAM measures BER by tracking the number of errored bits

detected before FEC, known as pre-BER, and the number of post-FEC

uncorrected bits, known as post-BER.

Errored Seconds and Severely Errored Seconds Measurement

For troubleshooting intermittent bit error suspected connections,

technicians use the DSAM to capture errors that have occurred over

time. If an error has occurred during any second of elapsed time, the

number in the errored seconds eld increments by one. When one

error or multiple errors occur in the same second, this counts as one

errored second. If more than 1 bit in 1 million received bits has errors

occurring in the same second, the severely errored second register

increments by one. The errored seconds elds are conveniently

included in the standard digital level display.

Constellation Mode

Various elements within a network can compromise digital video

quality. Based on the patterns of data points displayed on the DSAM’s

constellation mode graph, technicians can quickly and easily interpret,

detect, and diagnose sources of digital video problems.

Patterns in the constellation graph display show network impairments. Tech-

nicians can gure out the probable cause of the impairment by identifying the

pattern.

Modulation Error Ratio Measurement

Low MER can be the earliest indication of transmission quality

degradation resulting from noise, ingress, and composite distortions.

An expression of signal-to-noise ratio (S/N) plus all other non-transient

distortion signals, MER also shows phase and amplitude distortions

that may have been passed from the headend. JDSU has perfected

this valuable measurement by optimizing both custom hardware

and proprietary software algorithms. The result is measurement

accuracy that far exceeds that of customer premises equipment (CPE)

embedded diagnostics.

QAM Sensitivity Setting

The QAM sensitivity setting allows adjustment because all CPE

does not function equally. The meter has a congurable high-

sensitivity digital setting to provide objective measurements that

help technicians track CPE-reported MER/BER issues in the network.

The DSAM has a normal mode to measure standard RF network

performance as corrected by distortion mitigation technology within

the CPE. The high-sensitivity setting turns o the various digital

processing technologies that correct for various impairments found

on the network, thus revealing pre-correction signal quality. The QAM

sensitivity conguration setting is global and aects all MER and/or BER

measurement modes, including DOCSIS mode.

Automatic Gain Control (AGC) Stress Indicator

The AGC stress indicator on a digital channel level measurement icon

appears when the DSAM detects rapidly varying AGC levels. This rapid

network amplier AGC variation can cause tiling, blocking, freezing,

slow cable modem throughput, and/or packet loss. The AGC stress

indicator indicates that there is a network problem upstream from the

tap. The AGC stress indicator is viewable in the digital level Autotest and

as well as the overall results section.

dB Delta (intermodulation limit)

The dB Delta measurement compares highest and lowest carrier levels

at the test point to determine maximum dierential throughout the

spectrum. This comparison provides an early indication of potential

intermodulation distortion caused by largely dierent carrier levels

overdriving a CPE’s tuner, which may result in tiling, blocking, or

packet loss. Root causes can include excessive tilt and/or cable loss

or excessive power on a given channel. The DSAM integrates this

calculation into the Video AutoTest and Home Certication results

display.

The DSAM itself can overcome dB Delta situations to provide accurate

measurements. The DSAM is congurable to anticipate normal,

medium, or high dB Delta conditions to minimize overdriving and

allow proper measurements.

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