When the signal level is insufficient, the image may display snowflake noise. In such cases, a trunk amplifier must be used to boost the signal level. This same issue occurs when the signal level is too low, causing the image to show snowflake patterns, and again, a trunk amplifier is required to increase the signal strength.
The primary 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 the amplifier is placed too close to the source, it may raise the signal level of nearby transmitters excessively, leading to overloading and interference on the far-end transmitters. This can result in issues like adjacent channel interference, horizontal lines, or other types of distortion.
On the other hand, if the trunk amplifier is placed too far from the source, the signal level for distant transmitters may drop below the minimum required level (typically 75 dB). This can cause poor reception and degraded image quality.
To ensure optimal performance, it's important to use a field strength meter to measure the signal levels of all transmitters along the cable. At a specific point—usually at the connection between cables or before the signal reaches the distributor—measure the levels. If the lowest level is close to 75 dB, that’s considered standard. Then, adjust the power of all transmitters so their levels are around 75 dB. This process, known as level equalization, ensures consistent signal strength across the system before connecting the trunk amplifier.
Note 1: Transmitters near the trunk amplifier often have difficulty reducing their output level to 75 dB because their internal adjustments can only lower the level by about 20 dB. As a result, the output level of most transmitters tends to be above 110 dB. To achieve proper equalization, an attenuator or a splitter (as discussed in other articles) is usually used to force the signal level down.
Note 2: When installing the trunk amplifier, it's essential to connect the main trunk line to the amplifier first and power up all transmitters to their correct levels. Once the signal levels are balanced, connect the distributor. After amplification, the signal level increases by 30 dB, reaching around 105 dB. Other transmitters connected to the distributor should also be close to 110 dB, ensuring that newly added transmitters match the signal level of those on the main line.
By following these steps, you can maintain consistent signal quality throughout the entire system, preventing interference and ensuring a clear, stable image.
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