Nokia NSE-3 SERIES, Service Manual

Page: 62 / 217

PAMS
Technical Documentation
NSE–3
System Module
Original 11/97
Page 3 – 56
AFC function
AFC is used to lock the transceivers clock to frequency of the base sta-
tion. AFC–voltage is generated in COBBA with 11 bit AD–converter.
There is a RC–filter in AFC control line to reduce the noise from the con-
verter. Settling time requirement for the RC–network comes from signal-
ling, how often PSW ( pure sine wave ) slots occur. They are repeated af-
ter 10 frames , meaning that there is PSW in every 46 ms. AFC tracks
base station frequency continously, so transceiver has got a stable fre-
quency, because changes in VCTCXO–output don’t occur so fast ( tem-
perature ). Settling time requirement comes also from the start up–time
allowed. When transceiver is in sleep mode and ”wakes” up to receive
mode , there is only about 5 ms for the AFC–voltage to settle. When the
first burst comes in system clock has to be settled into +/– 0.1 ppm fre-
quency accuracy. The VCTCXO–module requires also 5 ms to settle into
final frequency. Amplitude rises into full swing in 1 ... 2 ms, but frequency
settling time is higher so this oscillator must be powered up early enough.
Receiver blocks
RX interstage filter
Parameter Min. Typ. Max. Unit
Passband 935 – 960 MHz
Insertion loss 3.8 dB
Maximum drive level +10 dBm
1st mixer in CRFU_1a
Parameter Min. Typ./
Nom.
Max. Unit/Notes
Supply voltage 2.7 2.8 2.85 V
RX frequency range 935 960 MHz
LO frequency range 1006 1031 MHz
IF frequency 71 MHz
Output resistance (balanced) 10 k ohm
1st IF–filter
Parameter min. typ. max. unit
Operating temperature range –20 +75 deg.C
Center frequency , fo 71 MHz
Maximum ins. loss at 1dBBW 11 dB