What is a Wideband CATV Attenuator


A Wideband CATV AttenuatorA Wideband CATV Attenuator is an application used to normalize the level of the high dynamic range multichannel TV signal. The input signal level may vary from 0 to 20 dBmV (-49 to -29 dBm) depending on the local cable network layout and standards. As a result,the attenuator should provide at least 20 dB of low distortion attenuation.
Application note APN1003, A Wideband General-Purpose PIN.In cable TV line amplifiers and set-top applications, a variable attenuator is used in front of an LNA as an AGC. Figure 1 shows a block diagram of a typical transceiver used in a set-top box. The wideband attenuator is different from the  forward path attenuator.The Wideband attenuator increases the power on your upstream it must of been low and there wasn’t a spear tap at cab or something.CATV attenuators are circuits that reduce the power level of a signal by a certain amount (gain) with little or no reflection. They reduce the output signal with respect to the input and measure the power reduction in decibels (dB). There are two basic types of RF attenuators: fixed and variable.

To improve the high-frequency isolation, a simple and robust compensation circuit was developed, as shown in Figure 5. The compensation circuit requires only one or possibly two additional components and uses existing parasitic components of a PI attenuator. The series connected C1–LC1 and C2–LC2 are the existing RF ground capacitors with their respective parasitic inductors, LC1 and LC2. Since the values of C1 and C2 are usually very large at the high-frequency end of the CATV band, they may be neglected. Capacitor CB, a necessary addition for the compensation circuit to work, is represented with its parasitic inductance LB. Resistor RB represents the loss of capacitors C1, C2, CB (about 0.6 W) which may be added to the compensation circuit if more flatness at the high-frequency response is desired.

In-line attenuators can be inserted in coaxial cable feeds to reduce signal levels. Attenuator signal loss ranges from 3dB to 20dB and available with power passing and high return loss options. Combinations of attenuators may be used together to create the exact signal loss needed.

The Model 2507-10 75-ohm Terminator (10-pack) provides a 75-ohm load that can be used on unused splitter output ports in order to maintain uniform signal levels.

Note: Do not use terminators on unused distribution amplifier outputs.



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