Icom ID-800H, Руководство по обслуживанию, Страница: 13 / 59

4 - 3
The ceramic filters (FI1, FI2) are switched by W/N switches
(IC9, IC10) that is controlled by “WN_SEL” signal from the
main CPU (IC505, pin 99).
The filtered signal is applied to the AM or FM detector circuit
separately.
• IN CASE OF FM/DV MODE SIGNAL RECEIVING
The filtered 2nd IF signal from the W/N switch (IC10, pin
1) is applied to the limiter amplifier section of the FM IF IC
(IC8, pin 5). The amplified signal is applied to the quadrature
detector section (IC8, pins 10, 11) to demodulate the 2nd IF
into AF signals and then passed through the AM/FM switch
(IC5, pins 1, 7).
While operating in DV mode, the switched AF signals from
AM/FM switch (IC5, pin 1) are applied the CODEC circuit via
J507 (pin 4).
While operating in FM mode, the switched AF signals from
AM/FM switch (IC5, pin 1) are applied the AF circuit via the
A/D switch (IC516, pins 1, 6).
• IN CASE OF AM MODE SIGNAL RECEIVING
The filtered 2nd IF signal from the W/N switch (IC10,
pin 1) is applied to the AM detector (Q13, Q16) to demodu-
late the 2nd IF signal into AF signals and then passed
through the AM/FM switch (IC5, pins 1, 6).
The switched AF signals from AM/FM switch (IC5, pin 1) are
applied to the AF circuit via the A/D switch (IC516, pins 1, 6).
4-1-7 CODEC CIRCUIT (CODEC BOARD)
The switched AF signals “DETS” from the AM/FM switch
(MAIN unit; IC5, pin 1) via the J301 (pin 22) are amplified at
the buffer amplifier (IC251, pins 1, 2). The amplified signals
are applied to the GMSK modem (IC252, pin 11), and are
then applied to the CODEC CPU (IC204) as clock synchro-
nizer digital signal. The digital signals from the CODEC CPU
(IC204) are applied to the AMBE voice CODEC IC (IC151)
to process code extension, and are then applied to the lin-
ear CODEC IC (IC50) as 32 bits digital voice data. The digi-
tal signals are converted into the analog AF signals at the
D/A converter section (IC50), and are then applied to the
AD switch (MAIN unit; IC516, pin 7) via the J301 (pin 22) as
“DAFOUT” signal.
The output signals from the CODEC board are applied to
the AF circuit.
4-1-8 AF AMPLIFIER CIRCUIT (MAIN UNIT)
The AF amplifier circuit amplifies the detected audio signals
to drive a speaker. The AF circuit includes an AF mute cir-
cuit for the squelch.
The audio signals from the AD switch (IC516, pin 1) are
passed through the low-pass filter (Q5), and are then
applied to the electric volume (IC508, pins 1, 2). The level
adjusted AF signals are output from pin 2 and amplified at
the AF power amplifier (IC510, pins 1, 4) after being passed
through the AF mute switch (Q512).
The power amplified AF signals (IC510, pin 4) are applied to
the internal speaker that is connected to J505 via [EXT SP]
jack (J506).
A portion of the demodulated audio signals from the low-
pass filter (Q5) are applied to the 8-pin data jack J504 (pin 6)
for packed operation, etc.
4-1-9 SQUELCH CIRCUIT (MAIN UNIT)
• NOISE SQUELCH
A noise squelch circuit cuts out AF signals when no RF sig-
nals are received. By detecting noise components in the AF
signals, the squelch circuit switches the AF mute switch.
Portion of the AF signals from the FM IF IC (IC8, pin 9) are
passed through the active filter section in the FM IF IC (IC8,
pin 8). The active filter section filters and amplifies noise
components. The amplified noise signals are converted into
the pulse-type signals at the noise detector section. The
detected signals output from pin 14 (SQL) via the noise
comparator section.
The "SQL" signal from the FM IF IC is applied to the main
CPU (IC505, pin 39). Then the main CPU analyzes the noise
condition and output the AF mute signal as "AF_MUTE"
from pin 55 to the AF mute switch (Q512).
• TONE SQUELCH
The tone squelch circuit detects tone signals and opens the
squelch only when receiving a signal containing a matching
subaudible tone (CTCSS/DTCS). 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.
Linear
CODEC
Buffer
IC253B
Buffer
IC251A
Buffer
IC251B
6
6 7 5
1
16
11
7
1
3
IC50
IC151
IC351
"232C_RX" signal
to the J504 , pin 7
"232C_TX" signal
to the J504, pin 4
"DAFOUT" signal to
the AD switch (IC516)
"DMOD" signal to
amplifier (IC3)
"DETS" signal from
AM/FM switch (IC5)
"DAFIN" signal from
buffer amp. (IC3)
IC204 IC252
AMBE
CODEC
CODEC
CPU
Modem
RS-232C
• CODEC CIRCUIT