Cisco Headend System Release 2.5 User Guide

78-738186-01 Rev B 

DHCT Status Reporting Utility 

1-39 

The DHCT sign-on process includes establishing the transmission level to use when 

communicating with QPSK modulators and demodulators. DHCTs transmit at 

various levels and the QPSK demodulator then measures the quality of the signal. 

Based upon these measurements, the QPSK modulator then sends a transaction to 

the DHCT that provides the DHCT with a target transmit level. The DHCT then 

attempts to communicate with the modulator by using the target transmit level. The 

DHCT may make several attempts to communicate by increasing the transmit level 

until the DHCT is able to maintain a communication lock with the modulator. 
Over time, however, with the addition of other DHCTs to the network, signal-to-

noise ratio issues are likely to affect the performance of the network. Likewise, 

attenuation issues are likely to surface as network configuration changes. DHCT 

transmission levels that were first established when the DHCT was added to the 

network may no longer be valid and the system may require adjustment. System 

operators can use the DHCT Transmit Level Saturation Report to view data 

pertaining to the transmission levels of DHCTs on the network and can use the data 

to adjust their system, if necessary. 
Notes:   
• 

DHCT transmit levels are expressed in terms of dBmV. The translation of dBmV is 

decibels with respect to 1 millivolt over a characteristic impedance of 75 ohms. 

• 

Attenuation refers to the decrease in intensity between transmitted and received 

signals. The loss in intensity is usually a natural consequence of signal 

transmission over long distances. 

• 

A signal-to-noise ratio is a measurement of signal strength relative to background 

noise. Competing transmissions from other DHCTs on the network tend to 

increase the background noise, thereby decreasing the signal-to-noise ratio. 

• 

All demodulators assigned to a specific modulator should be configured to expect 

approximately the same transmit level from DHCTs. Compensate for variations in 

DHCT transmit levels by padding and combining. Do not configure transmit 

levels manually from the front panel of the demodulator.