Trouble Shooting Guide, Advanced
4/00021-3/FEA 209 544/25 C
Ericsson Mobile Communications AB
21(78)
7.2
RX-fault
7.2.1
What is RX level-fault
The phone receive a signal from base station, the signal is mixed down to 67.71 kHz.
The received signal is measured with an ADC.
A high input signal gives a high value out from the ADC.
The phone is calibrated for input signals between -110 dBm and -40 dBm.
The phone compares the measured value and sends back the information about the signal
strength to the base station.
The base station calculate the RX-level value by comparing the systems lowest signal strength
according to the GSM-specification (-110 dBm) with the value of signal strength that the
phone sends back.
110 - (the absolute value of the value of signal strength from the phone) = RX level
E.g.: The phone measures the signal strength to -102 dBm.
RX level = 110-102 = 8
Table 7.1
When there is a RX-level fault the calculated value in the EEPROM does not correspond with
the input signal, i.e. the phone experience the signal to be stronger or weaker then its real
value.
7.2.2
This is how you can verify an RX-level fault
For EGSM900, connect a call toward the GSM test instrument at an optional channel
(1-124) with the input signal at -102 dBm and powerlevel 5.
For GSM1800, connect a call toward the GSM test instrument at an optional channel
(512-885) with the input signal at -102 dBm and powerlevel 0.
Read of the RX-level value on the GSM test instrument
Raise the signal strength to -68.5 dBm.
Read of the RX-level value on the GSM-test-instrument.
The RX level value for each of the channels should be as follow:
RX level
Min
Max
RX level at -68.5dBm
40
46
RX level at -102dBm
6
12
Table 7.2