(Last Updated On: June 26, 2021)
What Is Adjustable DB Gain?
A repeater is a small cellular signal amplifier that can be installed anywhere where the signal from the carrier’s base tower is insufficient. The repeater is a bi-directional amplifier. It picks up a weak incoming cellular signal from the base station, amplifies it, and transmits it to the user’s mobile device. Similarly, the repeater also broadcasts the radio signal outgoing from the user to the operator’s tower.
The repeater generates a minimum of its noise (it does not interfere with the base station) during operating in normal mode and provides the maximum coverage area according to its technical characteristics.
If the received signal is too strong, the automatic gain control module allows you to correct the operation of the equipment and the weak signal to make it sufficient. In addition, AGC performs a protective function of the cellular network against interference in uplink and downlink channels, preventing oscillations (self-excitation) of the repeater.
Most problems with cellular amplifiers are caused by feedback that occurs between the indoor and outdoor antennas. With a weak connection, self-excitation will not happen, but the overall noise of the entire system will increase. Thus, the link will be unstable, although the phone will show 4-5 bar.
Self-excitation can occur on both the internal antenna and the external one. The mobile phone will have a full scale in the first case, but the connection will be unstable, and you will not talk. Repeater gain is a value that shows how many decibels the signal at the output of the amplifier will grow relative to the input.
Consider a repeater with a gain of 60dB and a maximum output level of 19 dBm. Ideally, when there are no other input signals in the gain range, the repeater will amplify ONE input channel by a factor of 60 dB. However, in reality, there are always several channels at the input and noise and interference.
With a large number of simultaneously talking users, a drop in power occurs at the amplifier’s output stage because the repeater begins to use a larger number of carriers to serve all users. Therefore, the coverage area will be minimal, and in some cases, the signal may disappear altogether.
Each additional channel reduces the gain by 10Lg (N / 2). For example, for four channels at the input, the device’s gain will drop by about 3 dB, and for 16 input channels, this value will already be 9dB. Accordingly, the maximum output level will already be 19-9 = 10d Bm. It is essential to know that the repeater gain depends on the number of amplified channels. At night, due to the small number of users, the gain will be maximum, and during the day, it will significantly decrease. The presence of interference also reduces dB gain.
Amplifiers with DB gain less than 60 dB are effective only for installation in apartments located near the repeater and provided there are no dead zones.
AFC – amplitude-frequency characteristic – dependence of the repeater gain on frequency. It is always non-linear and will amplify some channels better, and some will be worse. In addition, the frequency response has blockages at the boundaries of the ranges of 3-8 dB. Therefore, it is necessary to pay particular attention to the channels located on these limits.
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