RF Oscillation and RF Overload in Building Cellular Amplifiers.

Posted by on July 21, 2016

Fix oscillation and overload situations in an in-building cellular amplifier using tips provided in this post. When someone is attempting to make a call on their cell phone, radio-frequency (RF) signals are sent and received between their device's antenna and the closest cell tower. Making a phone call is no problem at all if there’s a strong signal; but if that signal is somehow blocked, or even weakened, then the result will be low signal quality, poor reception, or dropped calls. A safe and reliable solution to these signal issues is to use a Cell Signal Booster, but you should be aware that there're some troubleshooting practices to observe. If you’re a reseller or an installer, you need to familiarize yourself with potential issues like oscillation and overload, in addition to knowing how to recognize and respond to complaints about these conditions. In short, you need to be prepared!

RF Oscillation and RF Overload in Building Cellular Amplifiers.

Explaining "Oscillation".

Oscillation, otherwise known as feedback, can occur when installing a cellular signal booster (also known as an Amplifier). Oscillation occurs when outside (donor) antenna and inside (broadcast) antenna are situated too close to one another. This close proximity means that crosstalk occurs between the two antennas, thus causing oscillation – or a feedback loop. This is a serious condition which can not only damage the cellular signal boosting system, it can also disrupt the cellular network. It is for this reason that the Federal Communications Commission (FCC) has ruled that all cell signal boosters must be able to auto-detect oscillation and immediately shut down or reduce power to correct the condition. You will know that oscillation has occurred if an amplifier is displaying a solid red light, which means that the signal booster will have either shut down or reduce the power. If you want to find out more about the signal in your building, then you may need a site survey.

Fixing Oscillation.

In order to correct oscillation, the first step is to increase antenna isolation. This is a simple matter of putting more space between outside and interior antennae. Ideally, you will be able to move the inside antenna to another part of the room or a different room altogether in the building. You may be able to turn down the gain on an amplifier unit by using the adjustable knobs, however this will depend on the booster model. This will help in reducing feedback by limiting ability of an amplifier to boost the signal. You should be aware, though, that when you reduce a booster’s gain, you may also be reducing the coverage area of an amplified signal.

Explaining "Overload".

If a donor antenna located outside the building is too close to a cell tower, another problem can occur: Incoming signal can be too strong, which will result in signal overload. Regardless of whether you’re attempting to amplify signal from that tower, or not, this problem can occur with any carrier’s tower. You will know if overload has occurred if you see a blinking orange light on an amplifier.

Fixing Signal Overload.

Your initial course of action should be to redirect the donor antenna. If you’re using a directional antenna, then that antenna should be aimed away from offending cell tower until such time as the lights on the booster revert back to green. Another solution might be to move your exterior antenna to a different location, perhaps on the side of a building where it will be shielded from the cell tower, or on the roof of the building. Sometimes, though, redirecting the donor antenna won’t solve the problem. For example, let us assume that your customer is utilizing the AT&T cell phone service, which means that the donor antenna should be aimed towards the nearest AT&T tower. However, there could well be a Verizon tower located between the building and that AT&T tower, so the booster is being overpowered with the Verizon signal. You will lose connection with the distant AT&T tower if you redirect the antenna, but because the Verizon tower is too close, the signal booster will shut itself down due to signal overload.

Installing a Channel Filter.

When you have a problem with competing towers like the one described above, the logical answer is installation of a frequency filter. These filters are easy to install, and they come with various options for whichever frequency range is creating the overload issues. Simply attach the filter between the donor antenna and an amplifier, then connect the cable from the donor antenna to the filter. Next, to the other side of the filter you should connect a short jumper cable (two-feet) and attach it to your outside antenna connection on the booster. Using above example, the filter will then reduce the strength of the signal being received from offending Verizon tower, thus allowing the desired AT&T signal to be amplified by the booster.

Choosing the Right Filter.

In order to determine which filter will best suit your needs, you first need to work out which carrier(s) are being used by the people in the building. You then need to use a signal meter to determine which frequencies, channels and bands those carriers are using, and which ones are creating the overload condition. Now you will know which filter to use to decrease the offending frequency range.

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