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The 2nd IF signal from the 2nd mixer (IC4, pin 3) passes
through the ceramic filter (FI1) (during wide channel spacing
selection or passes through FI2 during narrow channel
spacing selection; [W/N] only).
4-1-6 AM/FM SELECTOR CIRCUIT (MAIN UNIT)
IC-2200H can receive AM and FM signal. The 2nd IF signal
is detected AM or FM detector circuits respectively.
(1) AM DETECTOR CIRCUIT
The filtered signal is applied to the AM detector circuit (Q37,
Q38) to demodulate 2nd IF signal into AM AF signals. The
AM AF signals are applied to the AF circuit via the AM/FM
selector switch (IC12, pin 6).
(2) FM DETECTOR CIRCUIT
The filtered signal is amplified at the limiter amplifier section
(IC4, pin 5), and is then applied to the quadrature detector
section (IC4, pins 10, 11 and X2) to demodulate the 2nd IF
signal into FM AF signals. The FM AF signals are output
from pin 9 (IC4) and are then applied to the AF circuit via the
AM/FM selector switch (IC12, pin 7).
4-1-7 AF CIRCUITS (LOGIC UNIT)
The AF circuits are composed of digital and analog AF cir-
cuits. The AF signals are amplifies the demodulated AF sig-
nals to drive a speaker.
(1) IN CASE OF DIGITAL AF SIGNALS
The digital AF signals are applied to the optional digital unit
(UT-115*) via the J4 (pin 23) by the “DETO” line. The audio
signals that are converted to analog signals at the UT-115
are applied to the analog selector circuit (IC525, pin 8) from
the optional digital voice unit passed through the J4 (pin 22)
via the “AFOUT” line. The signals pass through the high-
pass filter (IC3c, pins 8, 9) from the analog selector (IC525,
pin 9), and are then applied to the analog switch (IC6, pin 1).
*Refer to “4-6 UT-115 CIRCUIT DESCRIPTION” (page 4-7 )
in detail.
(2) IN CASE OF ANALOG AF SIGNALS
The analog AF signals are applied to the analog selector
(IC525, pin 11), and pass through the high-pass filter (IC3c,
pins 8, 9). The filtered signals are applied to the analog
switch (IC6, pin 1).
The audio signals are applied to the AF mute switch (MAIN
unit; Q29) via the VOL adjust pot (R61). The signals are
amplified at the AF amplifier (MAIN unit; IC9, pin 1) to obtain
2.4 W audio output power after being passed through the
emphasis switch (MAIN unit; Q41). The amplified AF signals
are applied to the speaker via the J4 (MAIN unit) and J6
(MAIN unit).
4-1-8 SQUELCH CIRCUITS
(MAIN AND LOGIC UNITS)
•
NOISE SQUELCH
The noise squelch circuit cuts out AF signals when no RF
signals are received. By detecting noise components in the
AF signals, the squelch circuit switches the AF mute switch.
A portion of detected audio signals from the FM IF IC (IC4,
pin 9) are applied to the active filter section of the IC (IC4,
pin 8) as “SQLIN” signal, after passing through the D/A con-
verter (IC5, pin 12). The active filter section of the IC ampli-
fies and filters noise components. The filtered signals are
applied to the noise detector section in the IC and output
from pin 13 as the “NOIS” signal.
The “NOIS” signal from IC4 (pin 13) is applied to the CPU
(LOGIC unit; IC1, pin 26). The CPU analyzes the noise con-
dition and outputs “AFMUTE” and “FILC” signals via the I/O
expander IC (LOGIC unit; IC2) to toggle the AF mute (Q29)
and emphasis (Q41) switches.
Even when the squelch is closed, the AF mute switch (Q29)
opens at the moment of emitting beep tones.
• TONE SQUELCH
The tone squelch circuit detects AF signals and opens the
squelch only when receiving a signal containing a matching
subaudible tone (CTCSS). When tone squelch is in use, and
a signal with a mismatched or no subaudible tone is
received, the tone squelch circuit mutes the AF signals even
when noise squelch is open.
AF signals from the FM IF IC (IC4, pin 9) are applied to the
AM/FM selector (IC12, pin 6 or 7), and then pass through
the analog selector (LOGIC unit; IC525, pins 10, 11). The
signals pass through the low-pass filter (LOGIC unit; Q3) to
remove AF (voice) signals, and is applied to the CTCSS
decoder inside the CPU (LOGIC unit; IC1, pin 1) via the
“CTCIN” line to control the AF mute switch.
Analog selector
(IC525)
Analog switch
(IC6)
Optional unit
(UT-115)
"DETO" AF signal from the AM/FM
selector (MAIN unit; IC12, pin 1)
11
1
R61
11
IC3
Q29
Q41
8
15
9
9
10
8
AF
IC9
Speaker
(SP1)
HPF
LOGIC unit
MAIN unit
AF
mute
Emphasis
switch
AF
volume
• AF CIRCUIT