People often think that by installing an omni antenna in a city they will provide the best chance of catching the signal from all operators, and therefore achieve the best amplification.
However, the opposite is true for a number of reasons.
How antennas work.
Think of it like being at a party with hundreds of noisy people around you, and you are trying to focus on what just one person is saying. In this case, your ears are like an antenna – an omni directional antenna.
You would like to amplify the sound from just this one person while reducing the sound from all of the other people in the room.
If you add a hearing aid, or “amplifier”, the noise from every direction will increase and you might still not be able to hear the desired person – or at least, you might only catch a word here and there.
If you were to place a loud speaker (megaphone) to your ear however, and focus it at the desired speaker, you would increase the quality and signal level from that person while decreasing the background noise. This is like a directional antenna (Yagi or Laser).
This is the same for amplifying the signal from an operator’s mast.
The position and type of external antenna is crucial for a good signal result inside the building.
In large cities, there may be hundreds of masts visible to the antenna on the roof, but the phone connects to only one mast. If you install an omni antenna, the repeater will receive the signal from hundreds of masts. The combined downlink power received from all these masts means that the repeater only receives a fraction of the desired transmitter power, and the result can be a poorly amplified signal.
Ideally, you need to find a mast that is nearby and contains all of the desired operators, and point a very directional antenna (the Laser antenna) in this direction.
The Laser is a special parabolic narrow beam-width antenna made by Stella Doradus. This special antenna has an ultra narrow beam width with extremely reduced side lobes. The Laser antenna is able to strongly reduce the signal from all the other towers whilst increasing the signal from the tower in the main narrow beam.
