Cisco Headend System Release 2.5 User Guide

78-738186-01 Rev B

DHCT Status Reporting Utility

1-41

DHCT Transmit Level Saturation Report,

Continued

Understanding the DHCT Transmit Level Saturation Report

There are two parts to the DHCT Transmit Level Saturation Report:
•

A graphical representation of the distribution of the various transmission levels of

DHCTs assigned to each QPSK modulator on the system
Note: Read Graphical Distribution of DHCT Transmission Levels, next in this

section, for help in interpreting the graphical representation.

•

A numerical analysis of the graphical representation of the various transmission

levels of DHCTs assigned to each QPSK modulator on the system
Note: Read Transmit Level Analysis, later in this section, for help in interpreting

the graphical representation.

Graphical Distribution of DHCT Transmission Levels
The first part of the DHCT Transmit Level Saturation Report contains a graph that

shows the distribution of the various transmission levels of DHCTs assigned to a

specific QPSK modulator. In the following example, the modulator is QPSKMOD1.

The horizontal axis of the graph plots units of dBmV; the vertical axis (not marked

on the report) plots the relative number of DHCTs transmitting at each dBmV level.

DHCT Transmit Level Saturation Report - QPSKMOD1

Current Tuner Input Attenuation Level: 2 (-5 to 11

dBmV

)

|-------------------------------------------------------------------------
| T T
|   T|T |
|      T||| |T T
| T |||| || |T
| | ||||T|| || T
|   T T| |||||||T|| |
| T T| ||T||||||||||T|T
|   T T| ||T||||||||||||||||TT  T
| T TT TT TTTT|T||T|||||||||||||||||||||TT|TTTT
|---------+T--T---T+-T--+----+---------+--------+----+----+--------+--------
|
10 20 25 30 40 50 55 60 70

=================>|<==>|<==========================>|<==>|<=================
  ^ ^
  | |
  Settop Signal Core Population Settop Signal

Too Weak (25-55

dBmV

) Too Strong

Cisco engineers have determined that DHCTs communicate best with QPSK

modulators and demodulators when the DHCT transmits at a level between 25 and

55 dBmV. Notice the bell curve depicted in the illustration (and highlighted in bold

for easy recognition). The peak of the bell curve centers around 40 dBmV, the

midpoint between Cisco’s recommended transmission level of 25 and 55 dBmV. This

graph represents a healthy system; the vast majority of DHCTs assigned to this

QPSK modulator transmit within Cisco’s recommended range of 25 to 55 dBmV.