Chapter 8 Measure Mode – Basic Tab
Constellation
176 DSAM Help User Guide Rev. 001
Digital Performance
The area displays the high sensitivity indicator, modulation error ratio
(MER) and bit error rate (BER) before and after (pre/post) forward
error correction (FEC).
Interleaver Depth
Interleaver depth is displayed immediately to the right of the BER lock.
The DSAM supports the following interleaver depth values:
–1,128
–2,64
–4,32
–8,16
–16,8
–32,4
–64,2
– 128,1
– 128,4 (additional purchase required)
Deep interleaver channels (such as 128,4) require DSAM model 2600,
3600 or 6000. If you are using a different model, only the level and
BER appear.
Impairments
The dots representing QAM symbols on the constellation grid should
be well within the grid lines (decision boundaries). When the dots
approach or exceed these boundaries, significant errors are occurring
in the transmission of the signal. Impairment types are described as
follows.
Thermal (system) Noise
Thermal noise impairments cause the dots on the graph to spread out
toward the grid lines (decision boundaries), indicating significant
errors such as low levels into amplifiers or too many amplifiers in
cascade. The zoom feature would display more detail about the posi-
tion of these dots in relation to the grid lines
NOTE
If the displayed interleaver depth is greater than the interleaver
depth supported, the BER values are displayed as dashes (-----).
The frequency, level, MER and constellation display remain accu-
rate.
21128026 R001 DSAM Help User Guide.book Page 176 Thursday, February 5, 2009 2:02 PM
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