Cisco Cisco 1 GHz GainMaker Amplifier インストールガイド
4022872 Rev B
5
Factors Affecting Network Frequency Response
Factors Affecting Network Frequency Response
In an HFC network, a variety of factors can affect the overall frequency response.
The amplifiers, connectors, cables, and other passives in the network each have
inherent frequency response characteristics, or signatures, that contribute to the
overall response.
The amplifiers, connectors, cables, and other passives in the network each have
inherent frequency response characteristics, or signatures, that contribute to the
overall response.
Additionally, undesired conditions such as loose connectors, loose seizure screws,
and water-damaged components can produce abnormal frequency response. The
effects of these undesired conditions can be seen during a frequency-response sweep
as sharp dips in response, commonly referred to as suck-outs, or excessive low- or
high-frequency losses. The conditions creating such abnormal frequency response
should be tracked down and corrected.
and water-damaged components can produce abnormal frequency response. The
effects of these undesired conditions can be seen during a frequency-response sweep
as sharp dips in response, commonly referred to as suck-outs, or excessive low- or
high-frequency losses. The conditions creating such abnormal frequency response
should be tracked down and corrected.
The magnitude of the cumulative frequency response resulting from the
characteristic signatures of all of the plant components may become great enough to
be considered excessive. To address this, many amplifier vendors, including
Scientific Atlanta, have produced optional plug-in trim networks that can be
selectively deployed in amplifier stations to shape and improve the overall network
frequency response.
characteristic signatures of all of the plant components may become great enough to
be considered excessive. To address this, many amplifier vendors, including
Scientific Atlanta, have produced optional plug-in trim networks that can be
selectively deployed in amplifier stations to shape and improve the overall network
frequency response.
In some cases, the overall shape of the cumulative frequency response may be found
to be more or less frown-shaped. This shape may have various causes, including
some degree of low- and high-frequency rolloff in plant components. Additionally,
the frown shape may be accentuated if there is down-tilt produced between
amplifiers that does not have the same smile shape as that of coaxial cable.
to be more or less frown-shaped. This shape may have various causes, including
some degree of low- and high-frequency rolloff in plant components. Additionally,
the frown shape may be accentuated if there is down-tilt produced between
amplifiers that does not have the same smile shape as that of coaxial cable.
For example, most HFC network taps and passives have down-tilted frequency
response characteristics. Their down-tilt may not have the characteristic smile shape
associated with coaxial cable, and may instead be more linear or have some degree
of frown shape. The cumulative down-tilt produced by the passives must be
counteracted by the equalizers in the network.
response characteristics. Their down-tilt may not have the characteristic smile shape
associated with coaxial cable, and may instead be more linear or have some degree
of frown shape. The cumulative down-tilt produced by the passives must be
counteracted by the equalizers in the network.
Because cable equalizers are designed to fully offset only the smile shape associated
with cable, they do not typically offset any non-smile shape that might be associated
with the passives. In this example, some degree of frown-shaped response may
become apparent as a result. This frown-shaped response may become more
pronounced in the deeper sections of the network which contain the greatest
quantities of taps and passives.
with cable, they do not typically offset any non-smile shape that might be associated
with the passives. In this example, some degree of frown-shaped response may
become apparent as a result. This frown-shaped response may become more
pronounced in the deeper sections of the network which contain the greatest
quantities of taps and passives.