ANTENNA QUALITY If your cell phone needs a boost, the first thing to consider is the quality of the antenna. Ask for a name-brand antenna that mounts in the center of the roof — not the glass — for a mobile application, advises Matt Larson of wps antennas.com. High-quality RG58 coaxial cable should be used to carry the signal inside the vehicle.

The first thing to look for in an antenna is the cellular frequency or frequencies it supports. Separate amplifiers are available for 824- to 894-megahertz (MHz) cellular band, or for both the cellular band plus the 1,850- to 1,990-MHz PCS band. Dual-band amplifiers make up a majority of the mobile amplifier offerings.

AMPLIFIER POWER Booster amps come in a variety of power ratings, ranging from 10 mW to 3W, a 300X power range. To make matters more complicated, power ratings sometimes are quoted in decibels using a dBm logarithmic scale. For example, a 10-mW amplifier is rated at 10 dBm, a 100-mW amp produces 20 dBm, and 3W equals 34.6 dBm. (Search the Internet for a dBm-to-watt converter.)

As you might expect, a well-designed larger amplifier can boost weaker signals than a smaller amp can. However, depending on the use, a smaller amp may work as well as a larger amplifier, especially when a vehicle or home/office isn't extremely far from the cell tower.

SAFEGUARDS As you compare systems, be sure that the amplifier is designed to throttle back power as it gets closer to the cell tower, which disrupts communications for other tower users. The amp's circuitry also should be designed to prevent a feedback loop between exterior and interior antennas. This is called oscillation and is most likely to occur in a mobile installation.

KIT OPTIONS Systems designed for use in vehicles often can be purchased piece by piece, or as a complete system. Most systems can be moved easily from vehicle to vehicle.

Home/office systems often are sold as kits with antennas, coaxial cable and amplifiers packaged together. If your cell signal is especially weak, consider substituting a directional antenna for the omnidirectional antenna that comes with some kits, Larson advises.