When the signal level is insufficient, the image may display snow-like noise or random dots. At this point, a trunk amplifier must be used to boost the signal level. This issue occurs repeatedly when the signal strength is too low, and the only solution is to amplify the signal using a trunk amplifier.
The main function of an amplifier is to increase the signal level of each transmitter in the cable by 25–30 dB. Therefore, the placement of the trunk amplifier plays a crucial role in maintaining signal quality. If it's placed too close to the source, the nearby transmitters might have excessively high levels, which can cause interference for the distant transmitters. In such cases, the signal level at the receiver could exceed 20 dB above the minimum, leading to issues like adjacent channel interference, horizontal lines, or other types of noise.
On the other hand, if the trunk amplifier is placed too far from the source, the transmitters located farther away might have a signal level that is too low, resulting in poor reception or signal degradation.
To ensure proper signal distribution, it's essential to use a field strength meter to measure the signal levels of all transmitters along the cable. Typically, this measurement is taken at a specific point, such as where cables connect or before the signal reaches the distributor. Once the lowest signal level is identified—ideally around 75 dB—it indicates that the system is balanced. At this stage, the power levels of all transmitters should be adjusted to approximately 75 dB, a process known as level equalization, before connecting them to the trunk amplifier.
Note 1: It's often difficult to reduce the signal level of transmitters near the trunk amplifier to exactly 75 dB, since most transmitters can only lower their output by about 20 dB. As a result, their output might still be above 110 dB. To achieve proper level equalization, an attenuator or splitter (as discussed in other articles) is typically used to force the signal down to the desired level.
Note 2: When installing the trunk amplifier, the trunk line should be connected first, and all transmitters in the cable should be powered on and adjusted to the correct signal level. Afterward, the signal is sent to the distributor. Ideally, all transmitters connected to the amplifier will have a signal level of around 75 dB. After amplification, this level increases by 30 dB, reaching 105 dB. Other transmitters connected to the distributor will also be close to 110 dB, ensuring that both newly added and existing transmitters maintain a consistent signal level across the network.
This careful setup ensures stable and clear signal transmission throughout the entire system.
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