Icom IC-R7000 Service Manual page 17

4.3 PLL CIRCUIT (PLL UNIT)
This circuit generates the 1st LO signals (778.70-
DATA
(FROM LOGIC
UNIT)
,----------,
I
DIVIDER Fret PHASE
I
I
I
I
I
1/1024 (5kHz) DETECTOR
PROGRAM·
MABLE
DIVIDE
1/N
LOOP
FILTER
06, 013,
019
I
' - - - H I
CONTROL
I
COUNTER
-~.,-1
COUNTER
1/10,1/11
~:__
_ _ _ _ _ _ _ _ _ _J
X2
J_
X5
025
(51.2MHz)
c::::i _ _ _ ...
T
J_
c::::J
Tx1
X3
010
X4
016
XS
025
12MHz
band
(153.6
MHz)
(204.8
MHz)
(256
MHz)
X3
015
X2
012
X2
018
X3
027
1290.699MHz) for the 1st mixer, and 2nd LO signals
(256 or 768 MHz) for the 2nd mixer.
vco
1
01, 02
vco
2
03, 04
IC8
(307.2MHz)
(409.6MHz)
(768MHz)
(256 MHz)
Fvco X2
D1, D2
Fvco
Fe
F1stLo
Fig. 7
4·3·1 REFERENCE OSCILLATOR CIRCUIT
This circuit consists of crystal X1 and 024.
The output (51.2MHz) of Q24 is used to make for
the reference frequency of the PLL (Fret), the LO
frequency in the PLL loop (Fa), and 2nd LO signal
(F2nd LO).
In addition, the output of Q24 is divided into 1 /10
at IC?, and then fed to IC3.
4·3·2 2No LO CIRCUIT
(a) 256MHz 2nd LO SIGNAL CIRCUIT
The signal from Q24 is multiplied by five at 025,
and passes through L41-L43, Q26, and 029. Q29
outputs a 2nd LO signal (F2ndL0=256MHz, OdBm).
(b) 768MHz 2nd LO SIGNAL CIRCUIT
The signal from Q26 is multiplied by three at 027,
and 028 outputs the another 2nd LO signal (F2nd Lo
=768MHz, OdBm).
The band signal (BS) switches the above two kinds of
2nd LO signals according to the receive frequency.
Q20 and Q21 turns OFF according to the MUTE signal
when in an unlocked condition or by the BLK signal
when in blank memory channel.
4.3.3 PLL LOOP SYSTEM
This circuit generates the 1st LO signal for the RF
UNIT.
(a) VCO CIRCUIT
The VCO circuit consists of the >..-resonator circuit
with a micro-strip line. This allows for a variable
range of 389.35-645.35MHz by two VCOs.
IC3 controls oscillation frequencies of this circuit.
The VCO selector (VS) signal switches VCOs accord-
ing to receive frequencies.
4-7