Cell phone signal boosters, also called amplifiers or repeaters, work by capturing a weak cell signal outside the home, office, car, boat, warehouse, etc, bring it inside, amplify it, and redistribute it. The most popular products on the market contain four main components: the outside antenna, the amplifier (booster / repeater),the inside antenna, and the cabling to connect everything.
The Outside Antenna
The outside antenna can be omni-directional (can capture signal from all directions) or directional (works best when pointed directly at a cell tower). The benefit to omni-directional antennas is that they are easy to install and pick up/radiate signals in a 360 degree horizontal plane. They are great for picking up and transmitting to multiple towers for multiple carriers. You want to mount them as high as possible where the signal is strongest. A couple disadvantages of omni-directional antennas: 1) their gain is typically lower than directional antennas. 2) They are more prone to other RF interference. The Cellphone-Mate CM100-S is a good example of a popular omni-directional outdoor antenna.
The benefit to directional antennas (Yagi antennas) is that they typically provide more signal gain (power) than omni-directional antennas. They are also less prone to other RF interference. Because they provide more gain, the tower can typically be much further away than is acceptable for an omni-directional antenna. The Wilson 304411 Wide Band Yagi is a good example of a popular directional outdoor antenna.
Just about every amplifier (or booster) will have two values that basically define it. The first is “band”. Most amplifiers are classified as single band or dual band. With the exception of iDEN (Nextel), single band refers to either 850 MHz or 1900 MHz, meaning that the amplifier only boosts one of those two frequency ranges. Dual band on the other hand will boost both frequency ranges. While there are certainly reasons for purchasing a signal band booster, dual band boosters are more common and compatible with just about every carrier.
The second value is gain and just about every signal amplifier will have this specification published. Without getting too technical, gain is defined as the ratio of output to input. When specifying electrical power, gain is measured in decibels or dB. dB numbers are derived from a fairly simple logarithmic function; however all you need to know is that every increase in 3 dB doubles the power.10 dB = gain of 1013 dB = gain of 2016 dB = gain of 4019 dB = gain of 8020 dB = gain of 10030 dB = gain of 1,00040 dB = gain of 10,00050 dB = gain of 100,00060 dB = gain of 1,000,000If you have been shopping around for a cell phone signal booster then you have probably come across these numbers and were not sure exactly what they meant. Now, hopefully you have a better understanding.
When searching for an amplifier for your particular application, please reference the following:
20 dB – Automobile, Boat – 4ft. antenna separation or direct connect
30 dB – Automobile, Boat – 5ft. antenna separation or direct connect
40-45 dB – Large Auto, RV, Large Boat – 6ft. to 20ft. antenna separation
50 dB – Small Home, Townhouse, Office – 40ft. to 60ft. antenna separation
55 dB – Medium Home, Office – 50ft. to 70ft. antenna separation
60+ dB – Large Home, Office, Warehouse – 70+ft. antenna separation
Please keep in mind that this table represents general rules of thumb and the recommended applications and distances may vary by manufacturer. Antenna separation is very important and should not be overlooked when choosing or designing your system. Antenna separation is the straight line distance (in 3 dimensions) from the outside antenna to the inside antenna. In practice, these distances can be somewhat shorter than the rule-of-thumb distances listed above due to ceilings, walls, fireplaces, metal roofs, brick fireplaces, etc. blocking or inhibiting a straight-line signal path. The rule of thumb antenna separation distances are to keep your amplifier from going to oscillation. In the audio world, this is analogous to getting a microphone too close to a speaker and producing feedback.
The Inside Antenna
Inside antennas, just like outside antennas, come in different shapes and sizes, serve different purposed and can be omni-directional or directional. A lot of the products from Wireless Extenders (Wi-Ex) have a small omni-directional antenna attached to the amplifier itself. While this makes installation fairly simple, the unit must become part of your home dcor as it must be installed in a central location and will be visible. Most in-building products from manufacturers such as Cellphone-Mate, Digital Antenna, and Wilson Electronics will have a separately mounted internal antenna.This may sometimes make them more difficult to install, but having a separate indoor antenna allows for the most flexibility when choosing a central coverage point. The most popular antenna for providing omni-directional internal coverage is the ceiling-mounted dome antenna, such as the Cellphone-Mate, Inc. CM222. They even make low-profile dome antennas and even dome antennas which resemble light fixtures, which are less obtrusive and mesh well with any home dcor.
Inside antennas can be directional as well. Wall-mounted panel antennas provide directional coverage in typically a 90-120 degree radiation pattern. While coverage is only provided pretty much in front of a directional antenna they usually offer more gain than a dome antenna. With that being said, panel antennas are great for large but somewhat narrow rooms or hallways. They are also useful if you are not able to fully adhere to the antenna separation requirements. If the indoor directional antenna is pointed away from the outdoor antenna you will most likely be able to get away with a less than recommended antenna separation distance.
The cabling and connectors used to connect the outside antenna to the amplifier, as well as the inside antenna to the amplifier, play a crucial role in how your system will perform. Depending on the product, different types of cabling and connectors can be used. Some of the Wi-Ex and Wilson Electronics products use standard RG6 or RG59 75 Ohm coax. This is the same coax used for your cable TV or satellite system. While this type of cabling is less expensive, there are some drawbacks. For cellular and PCS frequencies, on average, RG6 will lose 6-10 dB of signal per 100ft.Depending on the actual length of cable you use, this can sometimes provide more signal loss than the outside antenna provides in gain. Remember, you want your amplifier to receive the highest level of signal possible. For this reason, it is recommended that runs using RG6 should be no longer than 50 or 60 ft. For most other in-building cell phone signal boosters LMR-400 50 Ohm Coax is the standard. In comparison, while LMR-400 is more expensive and thicker, it only loses about 3-6 dB per 100 ft for cellular and PCS frequencies respectively. Based on this, LMR-400 can be run further than RG6 before there is a decrease in system performance. For all three-piece systems (outside antenna, amplifier, inside antenna) it is recommended the amplifier be installed as close to the external antenna as possible, using the shortest cable possible. Ex. If the external antenna is installed on a roof, it is recommended the amplifier be installed in the attic as opposed to the basement. The shorter the cable length between the external antenna and the amplifier, the better. Remember that there is no separation requirement between the antennas and the amplifier, only between the antennas.
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