External directional antenna
Although some of the less expensive models do not include an external directional antenna they are crucial to providing significant signal strength gain. This is because the antenna can be oriented and located outside to provide the best possible signal, usually aligned with the nearest cell tower. Generally speaking the larger the external antenna the better the signal - although even a small, correctly oriented external antenna should provide better signal than the internal antenna on any cell phone. These can either be fitted by professionals or will include a signal strength monitor for easy alignment.The better systems will generally include an internal monopole antenna (although the type of antenna is far from standardised) for rebroadcasting the signal internally - the advantage of using a monopole antenna is that the signal will be equally distributed in all directions (subject, of course, to attenuation from obstacles).Because all radio antennas are intrinsically polarized, cell phones perform best when their antennas are oriented parallel to the booster’s antenna - although within reasonable proximity the booster’s signal will be strong enough that the orientation of the cell phone’s antenna will not make a significant difference in usability.All modern models will include a signal amplifier. Even the cheaper home-use models now provide around 30dB gain and many of the more expensive models provide over 50dB. However, it should be noted that since the decibel scale is measured on a logarithmic scale a 30dB gain represents a one thousandfold signal power increase - meaning the total amplification of a repeater with greater than around 50dB is likely to be useless without a good, well aligned antenna. This is due to the difficulty of filtering the correct signal out from the background noise, which will be amplified equally, and the limiting maximum signal power of the amplifier (typically from around 5 dBm or 3.2 mW).