This criteria is not catered for in DIY kits

A building or a bridge could have been built in between the BTS and the home or business shielding it totally. Because high frequencies are LOS dependant, these factors can change and individuals can be affected drastically. All these factors should be measured and recorded.
The RSSI measurement should be done at a height of not less than 7 meters from the ground. This is the minimum installation height of an outdoor antenna on a cell extender. Ground level RSSI is irrelevant for this purpose. It is imperative that you do have some signal on the site of installation - if there is no signal there is nothing to amplify. But, no signal at ground level does not mean there is no signal, there could be good signal just above the tree line.
What must be achieved? These measurements are curtail in determining what the outdoor gain should be. How many BTS towers in the coverage aria and their situation is information needed in selecting the correct antenna type to communicate between the BTS and the jammer. This criteria is not catered for in DIY kits. Antenna types, their radiation patterns and their strength (Gain) are not common knowledge to the layman. Once this is established, a link budget calculation can be calculated and the correct cell extender recommended. This will ensure a cell extender that does what it is designed to do and that is to give you indoor coverage. Incorrect calculation and unqualified installation will very probably lead to a system that oscillates, creates noise on the network and gives very limited coverage.
Typical signal strength evaluation One bar signal on you cell phone can be amplified to full strength with a cell extender. Signal strength is measure in dBm. Here is a rough guideline that could assist. Remember, this is what the user is experiencing at ground level. He may have full signal on a hill 100 meters from home.
Theoretically using a Coiler TG900 27dBm cell extender with 60dB gain and selected antennas a site with -90dBm can be amplified to -27dBm which will provide coverage to a normal sized home. Between 7~10met radius on the GSM900 frequency is common. Much larger coverage arias have been achieved regularly but one tends to be very careful in sketching coverage when RF is being applied as it is not very predictable and so many variations apply.