NCT4 Tools and Test Equipment 16 Flashcards
SLM
Signal Level Meter
Signal Level Meter
A frequency selective receiver capable of tuning in a desired frequency/channel with a display showing the RF signal strength (dBmV).
The minimum signal level at the input to the customer’s television is
0 dBmV, with a maximum of 15 dBmV.
5 points to maintaining an SLM
Keep the battery charged.
Clean the battery terminals regularly.
Keep the SLM clean by wiping it gently; dry the display screen to prevent spots.
Do not use any type of cleanser or polish on the display.
A regular calibration should be made and logged.
DSAM
Digital Service Activation Meter
In miniscan mode, the Digital Service Activation Meter (DSAM) monitors up to
12 channels at a time.
MER
Modulation Error Ratio
MER is an
overall quality measurement that can be performed on a digital QAM carrier.
Ingress:
Passage of an outside signals into the cable; can result in noise and disruption of the desired signal.
BER
Bit Error Rate
BER detects
erorred bits in the system.
The DSAM measures BER by
tracking the bits sent, the number of errored bits (pre-FEC), and the number of bits that cannot be fixed by forward error correction (post-FEC).
Constellation Mode
displays a pattern of data points on a graph for easy interpretation, letting you detect and quickly diagnose sources of digital video problems.
DQI
Digital Quality Index
DQI is a simple indicator of
the overall quality of a QAM digital stream. This JDSU exclusive measurement is extremely effective in tracking intermittent problems.
DQI Signal quality readings of 6 or 7 indicate
that impairments are detected, but are most likely corrected by FEC and interleaving.
DQI Readings of 1 to 4 indicate
that the subscriber service is most likely being adversely affected by the impairments.
DQI Readings of 8 and higher are typically
not detected by FEC BER.
DQI also catches errors sometimes missed by BER and errored seconds measurements. To help troubleshoot intermittent issues, the index is plotted on a
180-second graphical history display.
DQI is a statistical measure of
the signal impairments that can cause uncorrected bit errors, resulting in packet loss. It also detects impairments that have not yet caused any pre-BER errors.
Because it samples QAM symbols, the decoder must acquire and maintain what?
QAM lock in order to obtain DQI readings.
A sweep trace reveals
every physical error in the network that influences transmitted signals.
The majority of all transmission errors can be detected by measuring the
frequency response of the network
sweep results are independent of transmission methods and formats, it is the most effective method to set up the right…
gain versus frequency.
Referencing active carriers, instead of transmitting sweep signals over active carriers, lets the meter sweep without…
degrading service quality.
DMM
Digital Multimeter
RMS
Root Mean Square Meter
Root Mean Square Meter
The RMS accurately measures AC voltages of signals other than pure analog sine waves.
Digital Multimeter
The DMM is a digital meter, which usually uses a LCD or LED display.
In general, signal leakage detectors have the following characteristics and functions:
Portable and powered by batteries
Usually fragile and expensive
Could have audible sound, LEDs, or a leakage strength meter/display when a leak is detected
May detect leaks at various frequencies, or on one specific frequency as determined by the operator
Usually has sensitivity control for finding the exact location of a leak
Uses a dipole antenna to detect a signal leak and determine its direction
Cable locators are used to find the
location or path of underground cables.
Most locators work by
inducing a tone into the cable. The technician then follows the direction of the cable with a receiver that monitors the tone.
A cable locator is made up of two parts:
Transmitter
Receiver
TDR
Time Domain Reflectometer
Impedance:
The resistance of a circuit (cable, passive devices are examples) to alternating current. Although impedance is measured in ohms, it can’t be measured with the ohm portion of a volt-ohm meter.
Impedance Mismatch:
The condition that results when two components of a system are operating at different impedance.
The TDR is used to determine the
distance of a known fault from a specific location.
A TDR is used to locate:
Bad or unknown splices Opens Shorts Kinked cable Crushed cable Water in the cable Any type of impedance mismatch
A short is a situation where the
center conductor comes in contact with the shield
A reflection with the opposite polarity indicates
that the fault is a short.
The worse the fault,
the larger the reflection will be.
A properly terminated cable will absorb all the TDR’s pulse energy, resulting in
almost no reflection.
Dead Zone:
A dead zone can be found at the beginning of the cable caused by the time lag needed for the pulse width to launch into the cable.
