Icom IC-701

6-3 PLL (Phase Locked Loop) UNIT
6-3-1 LOCAL OSCILLATOR CIRCUIT
Q1-Q6 are local oscillator circuits for the conversion type
PLL. Each circuit, Q1-O6 is functional for each band
respectively; for example, Q1 is for the 1.8MHz band and
Q6 is for the 28MHz band. Each oscillator circuit is
basically the same, being a doubler with 3rd overtone
crystals.
XTAL OUTPUT
28 MHz 40.625MHz 81.25MHz
For example, X1 of the 1.8MHz oscillator is a 3rd overtone
crystal (27.125MHz) and has L2 in series, which is for the
X1 oscillating frequency adjustment. The output tuning
circuit Connected to the Q1 collector is tuned for 54.25
MHz, which is double the frequency of the fundamental
crystal oscillator frequency. The operation of Q2-Q6 is
exactly the same as that of 01, except the output fre-
quencies are different.
6-3-2 VXO (Variable Frequency Crystal Oscillator)
CIRCUIT
This circuit is for the oscillation, by 100Hz steps, of the
lowest two digits (0.0 - 9.9KHz) of the VCO output fre-
quency of the PLL circuit. The VXO circuit consists of
LS! BLOCK DIAGRAM
Output Data Selector
Q7, Q8, D9, X7, 18, etc. QO8 oscillates on the 15MHz
range using X7, D9, D10, and L18, and the oscillating
frequency is altered in 100Hz steps by the voltage supplied
from the D/A (Digital to Analog) converter.
Q7 triples the output signal from O8 and supplies about
45MHz signal to the mixer circuit of IC7.
6-3-3 MIXER AND AMPLIFIER CIRCUIT
The local oscillator output and VCO output are mixed by
IC6 and the mixed signal is taken from Pins 3 and 13 of
IC6. The output signal is filtered by L13 and L14, tuned
for 42-44Hz, to supply the signal to IC7. The output signal
of the VXO circuit is also supplied to IC7 to be mixed with
the signal from IC6. The difference of these two signals
(IMHz - 3MHz) is filtered by a low-pass filter and is
amplified by IC8 up to the level of more than 1.6Vp-p.
6-3-4 PLL LSI CIRCUIT
The output from IC8 is the input to the LSI, Pin 2. The
LS! contains PLL and control circuits. To drive the
reference frequency of the PLL, a SMHz crystal oscillator is
connected to Pins 3 and 4. This frequency is divided into
1/500 by the fixed frequency divider in the LSI and
becomes the accurate frequency of 10KHz. The input from
Pin 2 is divided by the Programmable divider in the LSI
from 1/100-1/299 which is decided by the controller, fed
into the phase frequency detector with the reference
frequency of 10KHz. The output is taken from Pin 40 in
the form of a pulse from the phase detector according to
these two input’s difference of phase. The controller
circuit consists of two sets of a 4-1/2 digit BCD up-down
B, A, DC BA, D, C, By A,D,C, B, A, D, CyB) Ag to Frequency Display
Ay i, Dy Cy By Ag D, C)B, A,
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UP/DOWN Control
UD
ByA,D; Ay
CK UP/DOWN Counter A
XYZ CL fy FF Fi Fo Koki KoKy Ky
EE
ei —
DIGIT
Counter
GANG Control GANG
G Control
COUNTER SWITCH COUNTER
SL Switch
Frequency control Pulse input
CLOCK
XYZ CL
STEP Switch
B, A, D; Ay
XYZ.
al
Divider
HI
FLKK KK,
Programmable Divider
UP/DOWN Counter B
Fy 3 Fo F, Fy Kok; Ko KyKy
Phase
Detector
Divide ratio
DIGIT
Counter
D IN
Oscillator q Crystal
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