Vktech GSM DCS 900/1800MHz Dual Band Cell Phone Signal Booster Repeater Please make sure distance above 10M between indoor and outdoor antenna, its better divides one from another by a wall. Please try to choose a good signal place to set up the outdoor antenna. Please sure that there are good signal 4-5 bars on your outdoor, or it will not work on your room. It could only strengthen cell phone signal, it could not produce cell phone signal,if there is no cell phone signal at all in your area, there is no need to use it. Suitable : 500 square meters around ( it will be different according to your using condition )