Cell
phone boosters, or BDA's ( Bi-directional Amplifier) are useful and do improve
service to a degree. The article linked to is mostly accurate, except for a few details. Most importantly, these devices should be installed properly. Typically there's a donor antenna and a server antenna. The donor is the one that talks to the cellsite and should be mounted outside as high as possible. The server antenna is the one that talks to your phone. It is typically mounted inside a building, vehicle, or
cabin. It's extremely important that the two antennas are far enough away from each other to avoid self oscillation. That's where the donor antenna is picking up the server antenna's output and redirecting through the amplifier and back out the server antenna, and so on. This is a serious issue for wireless providers. The
noise generated is severe and affects performance at any nearby cellsites adversely. call quality goes down for everyone in the area, especially those weak signals from distant customers, like a
boat several miles out.
Some BDA's have circuitry to detect this and cut back the amplifier, but I'm not so certain how effective the consumer class BDA's are at this. They are common on tugs and workboats that traverse the
Mississippi River between Baton Rouge and
New Orleans. The
interference, at least for one carrier, has forced the carrier to install very expensive active dsp filtering at cell towers along the river that will search for the
noise and filter it out, or rather try to filter it out.
The ACtive
Captain article tries to explain how cellphone networks are designed, but missed the most important part. Every carrier has a limited frequency band for customers and they must reuse those frequencies in a manner that doesn't cause
interference problems on the other side of town. This is why cellsite footprints are smaller. They don't broadcast signals in a circle around towers either. There are typically three sectors on a tower that usually are oriented in three 120 degree areas. There will be directional antennas that cover just that area. It's technically a different cellsite in each sector. This configuration is a loose
rule amongst cell company RF engineers and they will re-orient those antennas, or use wider/narrower antennas due to traffic or terrain. This might include not intentionally covering near-shore, a large lake, or bay. Don't even think about off shore. Their licenses do not allow it. The problem is there are no obstructions over the
water and is another big concern for interference when trying to reuse the limited frequencies. This is also why you might get 5 miles
offshore and still have coverage from a site designed to reach out about a mile on shore.
There'[s a couple of misconceptions here in previous posts, boosters do indeed work and you don't have to be 2" from the server antenna, unless you have a model that requires your phone be in a
cradle, such as the models made for automobiles.
Timing Advance ( aka propagation delay 3G networks) could be used to limit long distance comms, but isn't used much for that, rather it's a statistical reporting tool. For example, I have seen where timing advance was used to help locate the position of many users whose calls registered drops on a particular cellsite. The TA indicated 2.3 miles out, but that was very rural area and not possible to have as many calls as were taking place. It turned out, the actual location was a small town courthouse that was actually 1.2 miles from the tower.
70dB isn't 3M watts in this case because there is no direct coupling with these devices and they're max
power out is limited by FCC law.
Bottom line is these things do indeed work, as long as they're installed properly and are designed for the
network you have. VZ and ATT put their 4G LTE primarily on specific and discreet portions of the 700MHz band and a BDA designed for one, may not work on the other, or may not cover all the bands these carriers operate on. It's another link that could tie you to a particular carrier and make you less likely to dump one for the other if it means having to
purchase another $300+ BDA.
Commercial versions are used in many, many office buildings and hotels in cities to improve
service inside. Many of those are connected to elaborate distributed antenna systems that incorporate multiband
low power radios that several carriers can all share - similar to the way
WiFi is distributed in a
hotel, some systems include
wifi too.
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