Icom IC-R7O Maintenance Manual page 19

1. Reference oscillation circuit and 2nd LO circuit
The output (20.48 MHz) obtained at the oscillation circuit (composed of X1 and Q12) is used as the 2nd
LO and the Local Oscillator and reference frequency for the 3rd loop.
The oscillation output of Q12 is tripled at Q13, and 61.44-MHz 2nd LO output is obtained.
The oscillation output of 012 also is fed to the Q11 buffer-amplifier and is supplied to IC6. Here there is a
2-stage 1/2-frequency divider, and the 10.24 MHz obtained at the first stage is output from pin 9 as LO
for the 3rd loop; the 5.12 MHz obtained at the next stage is output from pin 5 as the reference frequency
of the 1st loop and the 2nd loop.
2. 3rd loop
This loop is a mixed-down type PLL composed of IC3, IC4, Q1, etc.
IC4 has a built-in oscillator circuit, DBM and amplifier circuit.
Relationship of 3rd loop PLL and oscillation frequency
Display Oscillation
frequency frequency Remarks
(kHz) (MHz)
00.0 13.15 Oscillation frequency = 10.24 + 0.01 x N
00.1 13.16
00.2 13.17
01.0 13.25 N changes 1 for each 100-kHz change of display
02.0 13.35 frequency.
10.0 14.15
20.0 15.15
30.0 16.15 For information concerning the offset of the display
90.0 22.15 frequency and the oscillation frequency in each
99.0 23.05 mode, refer to the "Display unit" section.
99.9 23.14
Vcc vec
ciss
5 23.14
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Py bs aT &
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z 10.24MHz
5. 12MHz