Icom IC-A20MK II Service Manual page 8

3-1-10 VOR CIRCUIT (VOR UNIT)
From the AF signal, the VOR circuit detects a variable
signal (VORC) and reference signal (VORS) from a VOR
station. The VOR circuit sends these signals to the CPU
(1C3001).
When the transceiver is set in the navigation band
(108-117.975 MHz), the NAV signal (IC3001, pin 48)
becomes "LOW," turning the VOR circuit ON via Q4004.
Q4004 controls a 5 V power source for the VOR UNIT.
The signal from the AM detector (DETO) is buffer amplified
at the VOR amplifier (IC4001 (B)).
The DETO signal includes 30 Hz variable phase compo-
nents and 9960 Hz reference phase components.
The 30 Hz component passes through the 30 Hz bandpass
filter (IC4001(D)) and is converted to a square wave signal
at the VORC comparator (IC4004(A)). The square wave
signal is then applied to IC3001 (pin 44) as a variable signal
(VORC).
VOR CIRCUIT BLOCK DIAGRAM
100 u sec.
₪4 <<
24V
The 9960 Hz component passes through the 10 kHz
bandpass filter (IC4001(C)) These components аге FM
modulated with 480 Hz deviation and 30 Hz modulation.
Signals are then amplified at a limiter amplifier (IC4002(A))
and are detected at an FM detector (IC4002(B)) to obtain a
30 Hz reference signal. \
The 30 Hz signal is amplified at ІС4003(А). This signal is
passed through the 30 Hz bandpass filter (IC4003(B)) and is
converted to a square wave signal at the VORS comparator
(IC4004(B)). This signal is applied to IC3001 (ріп 42) as a
reference signal (VORS).
A portion of output from IC4001(C) is applied to the VOR
sensor (Q4001~Q4003). When the VOR signal is received,
04003 turns ON апа 1C3001 (pin 43) receives "LOW" to
display the course deviation needle.
ІС4001 (А) applies the bias voltage fixed by R4008, R4009
to each IC.
DETO signal
from AM
detector
D1003
LIMITER
AMP
1C4002(A)
FM
DET
1C4003(A) 1C4002(B)
VORS
COMP
1C4004(B)
VORS signal VORD signal
to IC3001 pin 42 to 1С3001 pin 43
33.5 msec: Com.band :48У
шш Мау. рапа :0У
33.3 тѕес.
1C4001 (B)
VORC signal
to IC3001 pin 44
33.6 msec.
Fig. 3-4