Posted by Admin on March 28, 2016
Antenna separation is important when installing a cell phone signal booster because, if the tower (outside) antenna and the device (inside) antenna are located too closely together, they will create a feedback loop known as oscillation; caused by picking up each other’s signals.
Most of you will already be familiar with the negative effects of oscillation: Remember that ear-splitting screech when a Public Address System microphone is placed too close to a speaker? Well, that is a consequence of oscillation! You will not hear any spoken voice if oscillation occurs; However, the equivalent of that terrible Public Address System screech will be picked up by all nearby devices.
Uncorrected oscillation can damage the cellular network because it interferes with cell signal transmission and reception. That is why the FCC requires that all signal boosters must auto-detect oscillation. And when oscillation does occur, FCC regulations demand that corrective action be taken immediately by the cell phone signal booster.
When oscillation is detected by a booster, it automatically powers down its gain (signal boosting power) in an attempt to rectify the oscillation condition. This gain reduction reduces the indoor signal coverage area of the booster. However, if reduced gain does not correct the oscillation condition, then, by FCC regulations, the booster must shut itself down. Remember that this entire process occurs within a few hundredths of a second!
Therefore, the aim is to avoid gain reduction caused by oscillation and booster shutdown, and this is achieved by ensuring that both the device and tower antennas are located a sufficient distance apart from each other.
This is referred to as the MRSD – Minimum Required Separation Distance.
The first step in preventing oscillation by observing MRSD is to determine the best location for the tower antenna (or "outside antenna"). Our blog post regarding installation of tower antennas explains the easiest way to find the correct location for your tower antenna. In addition, the Installation Guide that you received with your signal booster clearly explains the MRSD for your specific model. If required, download installation guide and instructions for external antenna.
Ideally, one would keep 25 to 30 feet of vertical separation from the tower antenna when installing the device antenna for your booster system. It is quite acceptable to employ horizontal separation in order to achieve MRSD if a vertical separation distance is not possible. Remember, though, that the horizontal separation distance needed to meet MRSD will be greater than the vertical separation needed to get MRSD, but it is possible to use a combination of both in order to achieve MRSD. In addition, if you face the tower and device antennas 180° away from each other, this will help to reduce MRSD; and of course a wall or roof between the two antennas can also help.
Obviously, if you’re using an Omnidirectional tower antenna, you can’t face it in the opposite direction from the device antenna because the Omni antenna has a 360° beamwidth; meaning that Omnidirectional antennas do require a greater MRSD than directional antennas.
Check for red lights on the front of your booster to determine if oscillation has occurred. Red lights mean oscillation, so you need to increase the separation distance between the two antennas in order to correct this condition. Learn more about what do various color lights on a booster mean?
If you fail to observe MRSD, your signal booster will reduce gain, or simply shut down. If it shuts down due to oscillation, it will not restart until oscillation has been corrected.
Now you know why antenna separation between exterior/ external and interior/ internal antenna within a cell phone signal booster system is very important in ensuring that it continues to optimally boost reception indoors.