Icom IC-720A Instruction Manual page 29

LOGIC UNIT BLOCK DIAGRAM
*DISPLY DATA
TUNE
MODE-FUNCTION
to
PLL
SW.
PLL UNIT BLOCK DIAGRAM
From D/A Сопу. (10Нг Control)
This output signal is divided by 100 (131.5KHz ~ 231.4
KHz) and used for the reference frequency of the main
loop. Thus, this loop provides 100Н2 steps on the operat-
ing frequency.
The second loop puts out 39.6 ~ 69.6MHz with 100KHz
steps. This output signal is used for the local oscillator of
the main loop, and mixes down the VCO frequency to
131.5 ~ 231.4KHz.
The third loop, i.e., the main loop, puts out 39.7315 ~
69.8314MHz, as the 151 Local Oscillator, with 100Hz steps,
for the entire band.
The crystal oscillator is a VXO (Variable Xtal Oscillator),
and provides 10Hz steps. This output is multiplied Бу З
and puts out 30.72MHz for the 2nd Local Oscillator.
6-10 RTTY UNIT
In transmit, this unit provides the FSK (Frequency Shift
Keying) signals for RTTY. The crystal oscillator generates
9.0106MHz for the MARK and 9.01077MHz for the
SPACE. These signals are sent directly to the 2nd mixer of
the RF unit, and mixed with the 2nd Local Oscillator
30.72MHz, and puts out 39.7315MHz IF signals.
6-11 LDA UNIT
This unit converts the digital band signals which are put out
from the CPU, to analog band control signals for external
control such as the IC-2K L, linear amplifier.
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