If a function command only was sent (no PTT tone
after the function tone), no low appears at TP1 during
the 62-ms timing period of U8B, and the decode logic
returns to the initial state awaiting the next command
sequence.
Monitor Function Decoder
When a monitor-function command is sent, the
guard-tone detection at TP1 triggers the 240-ms timer
U2A, which enables audio-signal passage through ana-
log gate U10A. U4D and U3A are both high-gain
stages and, therefore, the function-tone signal at U3A-1
is a rail-to-rail squarewave. The squarewave function-
tone signal from U3A-1 is applied to the monitor band-
pass filter U3B,C,D through R32. Monitor-bandpass-
filter output is rectified by CR3 and, after filtering, is ap-
plied to comparator opamp U1A at U1A-3. U1A-1 goes
high, triggering the 50-ms timer at U8A-5 through
U9F-6,11. Upon 50-ms timer timeout, the 62-ms timer
is triggered, but, since TP1 is high due to the absence
of PTT tone, the PTT relay is not energized.
The low-to-high transition at U1A-1 triggers the
monitor timer U2B at U2B-12 through R31. U2B-10
goes high and energizes the monitor relay K1 through
U9A-1,16 for a timed period. If a PTT command is
de-coded before timeout of the monitor timer, the high
at U6B-4 resets the monitor timer at U2B-13 through
R47 and U6D-12,11.
In the latched mode of operation, JP1 is in the B
position, and, when U2B is triggered, U2B-7 goes low,
effectively
short-circuiting
the
C16
charging
path
through R30, R28, and R46, preventing C16 from
charging to timeout potential. Upon a PTT command,
U6B-4 goes high and resets the monitor latch at U2B-
13 through R47 and U6D-12,11. U2B-10 goes low and
monitor relay K1 is deenergized.
In the refresh-monitor-timed mode of operation with
JP1 to A, JP2 to B, and JP3 to B, upon the decode of
any valid command, TP7 goes high, triggering the
monitor timer at U2B-12 through JP3. A PTT command
will not reset the timer in this mode, because the reset
path is short-circuited by JP2.
224B/PCB Function-Tone Decoder Module
Operation of the frequency-select function-tone de-
coders is identical to that of the monitor-function de-
coder, except that the frequency-select decoders are
tuned to a different frequency.
The decoder output at U3A-1 is a high which is ap-
plied as a low to the F1-latch set input at U4A-1
through U5A-1,18. Simultaneously, a low is applied to
the F1 latch reset input at U4B-6, and, if JP2 is in the
Tone-Remote Station Adapters
5
M
O
D
E
L
R
C
-223C
-2
M
O
D
E
L
R
C
-223C
-2
M
O
D
E
L
224B/
P
C
B
M
O
D
U
L
E
ADDI
TI
ONAL
224B/
P
C
B
MODUL
ES
AMP
FULL DUPLEX
RX
NOTCH
FILTER
RX
TX
AMP
TX
M
O
D
E
L
R
P-
223C
4/
6/
8
2-WIRE LINE
IN/OUT
4-WIRE LINE
ROMANS
4-WIRE LINE
INPUT
AMP
*
*
RX AUDIO
TX AUDIO
PRE-FILTER
2175Hz
FILTER
2175Hz
FILTER
DETECTOR
RX
TX
TIMER
LIM
AND
DVR
PTT
RELAY
2050Hz
FILTER
DVR
RELAY
MONITOR
PWR
S MONITOR
TIMER/LATCH
TIMER
TIMER
HOLD
DETECTOR
AMP
1950Hz
FILTER
DETECTOR
1850Hz
FILTER
DETECTOR
S F1
R LATCH
S F2
R LATCH
PWR
RELAY
DVR
DVR
RELAY
F1
F2
ANY
V
AL
ID
DECODE
RESET
IN
/O
UT
LI
NE
RC-223C/RP-223C
*RX AUDIO, TX AUDIO TRANSFORMERS ARE OPTIONAL
UP TO THREE ADDITIONAL 224B/PCB MODULES FOR F3 TO F8
RC-223C/RP-223C block diagram.
