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How a vehicle repeater can fool you
It is possible for a repeater to appear to work and improve signal when a phone is in close proximity to a tower. This appearance is caused by the two following phenomena:
a) the repeater amplifies the signal that is generated by the tower and sends it to the inside antenna of the vehicle. The increased signal that is broadcast to the inside of the vehicle causes the signal bars on the cell phone to increase and since most people equate an increase of the signal bars with improved performance and range it looks like the repeater is beneficial, however this is not the case. An increase in signal bars is simply a measure of the signal level (strength) that is generated by the tower and reaching the phone. Although in normal conditions when a phone is not connected to a booster and there is not a repeater present, an increase in the signal bar meter of the phone indicates closer proximity to the tower and hence the chances of a successful call are increased, this does not hold true when any type of amplification device is used. It is possible to increase the signal bars on a cell phone with the use of amplifiers or RF noise generators (like a poorly designed or manufactured booster or repeater) while simultaneously not improving and sometimes even degrading the phone's ability to transmit and the user will not know it without the use of sophisticated RF diagnostic instruments.
b) the cellular network regulates the power that a cell phone transmits with power commands that are sent to the cell phone by the tower. If the phone is close to a tower, the network commands the phone to transmit at low power and as the cell phone gets progressively further from the tower it is commanded to transmit with increasingly more power. When a call is engaged near a tower, the transmit power from the phone is very very low and even though the repeater is present the signal that is transmitted by the phone is not powerful enough to cause the repeater to oscillate, hence there are times when a repeater will not cause harm to signal and since the signal bars displayed by the phone are greater with the repeater turned on than turned off it seems that the repeater is useful and working OK, however a repeater would not be required under these circumstances since the tower is close by and the phone is adequate by itself. When the distance from the tower increases and the phone is commanded to increase its power, the increase in power will make the repeater start to oscillate at some point. This is usually when amplification is required but instead of increasing power the repeater causes call degradation through oscillation and "RF noise".
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