Cisco Cisco 1 GHz GainMaker Amplifier Guide De Montage
4022872 Rev B
3
Traditional Equalizer Usage
Linear Equalizer Usage
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.
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.
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.
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.
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.
Both Equalizers Working Together
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.
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.