What can we do when repeater self-excitation?

What is the mobile signal repeater self-excitation?

Self-excitation means that the signal amplified by the repeater enters the receiving end for the secondary amplification, resulting in power amplifier work in a saturated state. The repeater self-excitation only appears in the wireless repeater. Because the fiber optical repeater is coupled base station signal directly, so the fiber optical repeater will not generate self-excitation, suppose the fiber optical repeater has a signal. But if you can’t make a phone call or poor call quality in fiber optical repeater. In that case, it is recommended to check the uplink and downlink attenuation and repeater hardware.

What is self-excitation:

For example, temperature changes cause the change of amplifier gain, isolations, and the base station parameters; then, it will cause an increase in the input of the repeater. When you debug the repeater, please do not excessively pursue the amplification and adjust the gain too significantly. You must leave some room for it. For the repeaters with fault records, it is challenging to detect self-excitation in the reverse channel of the repeater. Because the forward channel of the repeater always has signal input from the base station, if the repeater is self-excited, the forward amplifier may be overloaded. Some repeaters detect that the amplifier is overloaded three times. They will turn off the repeater immediately and give a clear record of the failure. It is easy to find. However, the input signal of the reverse channel amplifier varies greatly. The mobile phone transmitter is not always in the transmitting state, and the distance is not always the same.

In some cases, it will cause the reverse channel amplifier self-excited. The amplifier returns to normal due to the sudden loss of input. The self-excitation of the reverse channel amplifier is not only a few seconds short and irregular. Sometimes it does not self-excite once for several hours, which is extremely difficult to fix the fault.

If the repeater is installed, the mobile phone can typically answer the local phone if the mobile phone communicates with the local telephone. Still, the local telephone is disconnected when answering the mobile phone, and the sound quality is inferior. It may be caused by the self-excitation of the reverse channel amplifier of the repeater.

When the repeater is installed improperly, the transceiver antenna isolation is not enough. The gain of the whole repeater is too significant. The output signal will be fed back to the input after a delay, resulting in severe distortion of the repeater output signal and self-excitation. The frequency spectrum of the signal self-excitation will occur. After the self-excitation, the quality of the signal wave becomes worse, which seriously affects the call quality and causes call drops.

There are two ways to overcome the self-excitation phenomenon. One is to increase the isolation between the donor antenna and the retransmission antenna, and the other is to reduce the gain of the repeater. When the coverage of the repeater is required to be minor, the gain can be reduced. When the repeater is required to cover a large area, the isolation should be increased.

- Increase the horizontal and vertical distance of the antennas

- Add obstructions, such as installing shielding nets, etc

- Increase the directivity of the donor antenna, such as using a parabolic antenna

- Select a retransmission antenna with a stronger direction, such as directional angle antennas

- Adjust the angle and direction of the donor and the retransmitting antenna so that they are as far away from each other as possible.