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Dual Band GSM (Model BST850): Urban Areas: GSM coverage is normally deployed as follows: in major cities GSM850 and GSM 1900 are both deployed at the same time. The Cellular Network uses a method called "channel hopping" to command the phone to use a particular channel on one of the two frequencies at any given time. The network will give preference to channels in the GSM1900 frequency when the phone reports that it is receiving any channel in this frequency at a pre-determined signal level that the network deems acceptable. When the phone reports signal below the pre-determined acceptable level in GSM1900 frequency, then the network commands the phone to use a channel in the GSM850 frequency. When the phone next reports that it is receiving GSM1900 at an acceptable level again, then the network will command it to use a GSM1900 channel. This switching of channels (channel hopping) occurs very frequently, in the order of as frequently as a few seconds. If the phone does not report acceptable signal in either of the two frequencies, then the network will keep it on a GSM850 channel until the signal improves or the call fails. Rural Areas: Rural areas are almost always covered by GSM850 only and when signal deteriorates it is in the GSM850 frequency. Given the way the GSM dual band cellular providers have deployed the networks and how they use the channels allotted to them, the last frequency that will be in use by a phone before a "dropped call" will be in the GSM850 band, therefore a BST850 booster that amplifies the 850 band is the only booster that is required. |
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