What is Antenna Separation and Why it’s Important
Posted on 12/2/2015 by Nicholas Jones
When installing a cell phone signal booster system, antenna separation is important because when the tower (outside) antenna and device (inside) antenna are located too close together they will pick up each other’s signals and create a feedback loop – a condition called oscillation.
You’re already familiar with the negative effects of oscillation. That ear-splitting screech that results when a public address system microphone is placed too close to a speaker is a consequence of oscillation.
If a signal booster system oscillates you won’t hear any noise, but the equivalent of that PA system screech will be picked up by all nearby devices on the cellular network.
Oscillation interferes with cell signal transmission and reception, and left uncorrected it can damage the cellular network. For this reason, the FCC requires all signal boosters to auto-detect oscillation. When oscillation is detected, FCC regulations require that the signal booster immediately take corrective action.
When a booster detects oscillation it will automatically power down its gain, or signal boosting power, in an attempt to correct the oscillation condition. This gain reduction will reduce the booster’s indoor signal coverage area. Moreover, if reduced gain does not correct the oscillation condition then the booster, by FCC regulation, must shut itself off. All this happens within a few hundreths of a second.
Obviously we want to avoid oscillation-caused gain reduction and booster shutdown. These can be prevented by locating the tower and device antennas far enough apart from each other. weBoost refers to this as the Minimum Required Separation Distance, or MRSD.
Getting to MRSD
First step to preventing oscillation by observing MRSD is to find best location for your tower antenna. Here’s a blog post and a video that explain how to find the best location for your tower antenna.
The Installation Guide that comes with your signal booster explains the MRSD for your specific model. If needed, you can download an Installation Guide here. INSTALLATION GUIDES
Below are some general rules of thumb for MRSD and preventing oscillation.
When you install your booster system’s device antenna, you should ideally keep 25-30 feet of VERTICAL separation from the tower antenna. If this vertical separation distance is not possible, you can employ horizontal separation to achieve MRSD.
But be aware – the horizontal separation distance required to reach MRSD is greater than the vertical separation needed to get MRSD. Using a combination of vertical and horizontal separation to achieve MRSD is perfectly acceptable. Also, facing the tower and device antennas 180 degrees away from each other will help you reduce MRSD. And a roof or wall between the two antennas may also help you reduce MRSD.
Some Final Thoughts
Of course if you are using an omnidirectional tower antenna, you can’t face it in the opposite direction from the device antenna because the omni has a 360-degree beamwidth. That means omnidirectional antennas require greater MRSD than directional antennas do.
To find out if a booster is oscillating, look at the lights on the front of the booster unit. Red lights indicate oscillation. If you see red lights, increase the separation distance between the two antennas to correct the condition. To learn more about what the lights on a booster mean, watch this video.
A final reminder: failure to observe MRSD will result in your signal booster reducing gain or shutting down. If your booster shuts down due to oscillation, it will not restart until the oscillation condition has been corrected.
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