NEC DB2000, Service Manual

Page: 100 / 199

Part 3.3: The UHF VCO and Synthesiser
The UHF VCO and Synthesiser can be checked with the receiver set to the same
setting as previously described. Obviously being a dual band product DB2000
has two UHF VCO’s, so therefore both VCO’s need to be checked. Please refer to
figure 3.2: UHF VCO’s and Synthesiser, for signal levels and control voltages.
Figure 3.2: UHF VCO’s and Synthesiser
RX Channel VCO Input Voltage Output Level in dbm’s VCO Frequency
1 2.5 V.d.c -21dbm 1205 Mhz
62 2.8 V.d.c -21dbm 1217.4 Mhz
512 1.8 V.d.c -11dbm 1535 Mhz
698 2.5 V.d.c -11dbm 1572.4 Mhz
DIV
65
LOOP
FILTER
PRE-
SCALER
IC201 LMX2331L RF-PLL
(IC202/3)
PHASE
COMPARATOR
IN
OUT
3 2
4
3
5
PHASE
DIFFERENCE
(CURRENT)
PHASE
DIFFERENCE
(VOLTAGE)
13MHz
CLK
8
VCC
GND
1
NC
V_VC01/2
5
11,12,13
SERLT
SERDA
SERCK
EG:1205Mhz (GSM)
200Khz 200Khz
GND
GND
UHF VCO
I/P
+ 5 V.d.c
O/P
See table below for levels
See table below for voltages