Atec Acterna-DSAM-6000 - Manual (Page 3)

Digital Quality Index™ (DQI) Mode
DQI is an indicator of the overall health of a QAM stream. This measurement
does a great job tracking intermittent problems and is unique only to JDSU. It is
represented by an easy to understand Index rating from "1" to "10" with ten being
the highest quality. DQI also catches errors sometimes missed by BER and Errored
Seconds measurements. It also displays a 90 second graphical history.
MER Mode
Modulation error ratio (MER) is the earliest indication of transmission quality
degradation resulting from noise, ingress, and composite distortions. An expres-
sion of signal-to-noise ratio plus all other non-transient distortion signals, MER
also shows phase and amplitude distortions that may have been passed from the
headend. MER is the best overall quality measurement that can be performed on a
digital QAM carrier. JDSU has perfected this valuable measurement by optimizing
both custom hardware and proprietary software algorithms (Patent Nos. 6,061,393;
6,233,274; 6,278,730 and 6,385,237). The result is accurate readings that far exceed
those reported from customer premise equipment such as digital settops.
BER Mode
Bit error ratio (BER) helps to quickly detect impulse changes in the system by
revealing when information is lost or corrupted at the bit layer. The DSAM-6000
measures BER by tracking the number of errored bits that are seen before forward
error correction (FEC), known as pre-BER, and the number of bits that cannot be
fixed by FEC, known as post-BER.
Errored Seconds and Severely Errored Seconds Measurement
For troubleshooting connections that are suspected of intermittent bit errors, the
technician needs a means of capturing the presence of errors that have occurred
over a period of time. If an error has occurred during any second of elapsed time,
the errored second field increments by one. One error or multiple errors in the
same second is counted as one errored second. If more than 1 bit in 1 million bits
has errors occurring in the same second, the severely errored second register in-
crements by one. The errored seconds fields are conveniently included in the
digital level display.
QAM Ingress Mode
Detecting the presence of ingress within the digital tier of carriers on the
downstream path is nearly impossible without turning off the service. The tightly
spaced QAM carriers hide any visual presence of unwanted forward ingress such
as CSO and CTB. An MER test will indicate that an issue exists but with the
DSAM-6000 and the patented JDSU QAM Ingress mode the technician can
inspect what is actually going on beneath the digital “haystack” while still
remaining in service.
Return QAM Generator
Standard on the DSAM-6000, the Return QAM Generator is a mobile 16 QAM
transmitter. The ability to transmit a QAM-16 modulated signal back to the
headend is helpful for proving line capabilities for future data and voice channels
and for troubleshooting return path issues in the network.
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DSAM-6000 DIGITAL SERVICE ANALYSIS METER
QAM Ingress test allows the technician to see what is
going on underneath a live digital carrier which is
usually not viewable due to the presence of the
“haystack”.
In the level mode on a digital channel, the signal’s
level and MER are measured and the channel’s BER
and errored seconds are tracked.
The Return QAM Generator eanables operators to test
and prove upstream network performance.
DQI will display intermittent, short duration impair-
ments missed by MER and BER as well as steady state
issues typically captured by MER and BER.