Cellular amplifier: what is the maximum cable length?

Cellular amplifier: what is the maximum cable length?

"What is the maximum length for the cable of my cellular amplifier?"

It's a perfectly legitimate question that we hear often. And there is no one answer, for every GSM amplifier at home or in the office we find a different situation. In each case it depends (also) on the signal available outside and its level of intensity before amplification.

  1. A coaxial cable always induces some loss, it is normal
  2. As a general rule, the cable to the external antenna should be as short as possible
  3. Cunning to use long coaxial cables


1.A coaxial cable always induces some loss, it is normal

A wave is, in essence, an electromagnetic field picked up by an antenna. The antenna "transforms" this electromagnetic field into an electric current. This electric current is routed from the antenna to the electronic circuit, in this case our cellular amplifier, through a coaxial cable.

This electric current is rather weak, and its passage along the cable causes its intensity to decrease, degrading with distance. This is a completely normal electrical phenomenon and we call it cable loss.

There are different types of coaxial cables, also for various uses. We propose 3 types of GSM 3G 4G amplifier cable, with different lengths. Below are the technical specifications of the three types of coaxial cable:

Specifications 5D coaxial cable  -----    Specifications 7D coaxial cable  -----    Specifications 12D coaxial cable



2.As a general rule, the cable to the external antenna should be as short as possible

As we saw in the previous point, each cable induces a signal loss depending on its length.

In addition, since the radio signal (electromagnetic wave) is transformed by the antenna into current (electrical signal), signal quality (= current level) is directly proportional to the received signal.

Thus, keeping the cable short between the outdoor antenna and the GSM amplifier ensures that the signal reaching the box is still good enough to be re-amplified and then distributed by an indoor antenna(s). If the signal received by the antenna is too weak, the antenna can convert only the little signal it receives, and the available current will be very very low. It is therefore difficult to make it travel a few more meters on the cable, otherwise--there will be no signal to amplify when it reaches the GSM amplifier!

Referring to the external part of the signal amplifier, the maximum length of the cable is 30 meters, if there is a very strong external signal. Otherwise, we do not recommend using cables of this length (and even 20 meters). In the standard GSM repeater kit you will find an external coaxial cable of 10 meters.

3.Cunning to use long coaxial cables

With this information we are able to calculate the maximum length the cables should be:

1. the power of the repeater in dBm
2. the length of cable you want to use connect each of the internal antennas;
3. the loss value of the coaxial cable;
4. the desired power between 7 and 9 dBm at the input of each internal antenna,

It is worth mentioning that choosing the right power repeater depends on the amount of internal antennas we want to connect.

Since everything technical is a bit complicated or time-consuming, contact our team for more information and send us some information about your project (square footage, external signal quality).

We will do all the calculations for you and propose a system that will work exactly according to your needs, specially designed for your premises.