When installing a mobile repeater system, it is important to ensure that the signal is “balanced” from all the operators.
Firstly, take a signal measurement on the roof of the building. The equipment required for this is a spectrum analyzer. We recommend using the Stella Doradus TestTool which has a spectrum analyzer as one of its modes.
In our example we shall call the operators, A, B and C. (see Diagram above)
Oftentimes, the signal of one operator will be stronger then the others. You can see in the diagram that operator C is much stronger then operator A. C is located only 50m from our building whereas A is 1000m. B is somewhere in the middle at 500m. These are big differences in distance and this results in big differences in received power also.
In Diagram 1, an Omni-directional antenna receives the signal from all 3 operators and does not favor one operator over the other. The result is that unequal signal is sent to the first repeater in the system. The repeater does not differentiate between each of the operators. All it sees is the most powerful operator, in this case, operator C. If the signal level of operator C is above a the threshold level set in the repeater, the repeater will attenuate the power of operator C to a safe level. The repeater does this to ensure no overpowered signal enters the system.
The drawback to this is that, those weaker operators also get attenuated by the same amount and sometimes this means they are attenuated so much as to be useless. (See image 1, output of repeater)
You can see in diagram 1 that operator A has been reduced to zero. Operator B is redueced very low and only operator C is perfect. Overall, this is not an satisfactory result.
So how do we avoid this?
Take a look at diagram 2 above.
In this situation, we use a Yagi directional antenna instead of the omni used in diagram 1. A Yagi antenna can focus its power in one direction whilst reducing it elsewhere. By placing the Yagi strategically on the roof, in this case behind a big wall to block out the most powerful operator C and pointing it towards operator A, we can balance the 3 operators more effectively. Even though the signal being sent to the repeater is a bit overpowered, this is no problem, the repeater can attenuate it a little to reach the safe level. The main point is that the signal from each operator is roughly balanced. The repeater will then distribute this balanced signal through out the building.
If you need every more direcionality, take a look at our new Laser antenna.