User Guide

PAMS
Technical Documentation
NSB–1
System Module
Original 06/98
Page 3 – 36
sults in over 28 dB of headroom which is required for the +/– 200 kHz
faded adjacent channel (approximately 19 dB) and extra 9 dB for pre–
monitoring.
AFC
The AFC is used to lock the MS clock to the frequency of the BS. An
AFC voltage is generated in COBBA_GJ with an 11 bit ADC. This voltage
then controls the center frequency of the 13 MHz VCTCXO module.
Software Compensations
Power Levels (TXC) vs. Channel
Power levels are calibrated on one channel in production. Values for
channels between these tuned channels are calculated using linear inter-
polation.
Modulator Output Level
For optimum linearity and efficiency the output level of the modulator is
adjusted in the production.
Power Levels vs temperature
In order to avoid the bias voltage variation of the detector diode ruining
the accuracy of the power control loop, the bias voltage of the detector is
measured when no RF power is transmitted. This voltage (DETLVL) is
fed to the A/D converter in CCONT where DSP uses this value to correct
the TXC voltage.
RSSI
Signal strength RSSI vs. input signal is calibrated in production, but RSSI
vs. channel is compensated by software. If DETLVL (A/D) is used as a
temperature sensor to correct for RX variations over temperature, the
diode characteristics are 1.2mV/C.