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Trouble Shooting Guide, Advanced
The information about the amplitude corresponds to the strength of the received RF-signal, i.e.
the RF-level at the antenna input of the receiver.
The antenna signal is converted and amplified in two steps, through the 1st IF 175 MHz down to
the 2nd IF 6.0 MHz.
To resolve the amplitude information the collector currents in three of the amplifiers are used in
a way that gives high dynamics in the amplitude scale.
The currents have a logarithmically positive relation to the amplitude of the RF-signal, which
gives the advantage of a linear proportional relation to the RF-amplitude measurement result
expressed in a dBm-scale.
The higher RF-signal (and collector currents), the higher RSSI-value.
RSSI is used for two measurement functions, electrical and numerical, mean value and
momentary value.
The electrical value of the RSSI is used to report the signal strength to the switch through the
base station as current RX-level.
The three collector currents RSSI1, RSSI2 and RSSI3 are converted to voltage by N800, then
added and forming a mean value in C826.
After amplifying the summed RSSI-voltage the value is A/D-converted and sent as electrical
RSSI serial data to the processor for processing.
The numerical RSSI-value is calculated and only used internally in the phone by the DSP.
The three collector currents RSSI1, RSSI2 and RSSI3 are converted to voltage in N800, A/D-
converted as momentary value bit by bit and then delayed and added.
No mean value is formed.
Information about the numerical RSSI is sent as serial data to the processor for processing.
The principles of the RSSI-function are shown below Fig.7.1.
Fig.7.1
4/00021-3/FEA 209 544/18 B
32(121)
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