Cisco GainMaker Optoelectronic Node 1GHz with 65 86 MHz Split Technical References

4022872 Rev C 

 

3 

 

Most HFC networks use up-tilted RF amplifier output levels, meaning that their RF 

output levels increase at higher frequencies. Today’s networks typically employ a 

linear output tilt, so that a plot of output level versus frequency is a straight line that 

tilts upward from low to high frequency. This linear output tilt is produced at the 

node using a passive network called a linear equalizer. 
The following illustration compares the straight-line loss characteristic of a linear 

equalizer with the frown-shaped characteristic of the cable equalizer described 

earlier. 

 

As shown above, both the linear equalizer and the cable equalizer introduce greater 

signal loss at lower frequencies. However, whereas the cable equalizer response is 

curved, the linear equalizer response is a straight line, indicating equal loss per unit 

of frequency. 
The dB value of a linear equalizer indicates the amount of tilt it produces, where the 

tilt is equal to its loss at lowest rated frequency subtracted from its loss at highest 

rated frequency. As with cable equalizers, plug-in linear equalizers are typically 

available in a wide range of fixed dB values. 

 

Traditional HFC network implementations combine the use of cable equalizers and 

linear equalizers to help achieve optimum overall frequency response. A linear 

equalizer at the node is used to provide the desired linear output tilt, while cable 

equalizers in the amplifiers are used to offset the down-tilt and shape introduced by 

the coaxial cable.