Dsp Receiver Circuit; Af Amplifier Circuits; Main Speaker Output; Sub Speaker Output - Icom IC-7800 Service Manual

3-1-7 DSP RECEIVER CIRCUIT

(DSP-A AND DSP-B BOARDS)
The DSP (Digital Signal Processor) circuit enables digital
IF filter, digital noise reduction, digital PSN (Phase Shift
Network)/Low Power/Phase demodulation, digital automatic
notch, etc.
• RX-A AND RX-ONLY CIRCUITS (DSP-A BOARD)
The 36 kHz 2nd IF signal from the 2nd IF amplifier
(RXPLL-A unit, IC1506) passes through the analog switch
(IC331, pins 1, 7) with limiter function, and is then applied
to the buffer amplifiers (IC301, pin 2, IC341, pin 2, IC371,
pin 2) to convert to balancing signal. The signal is applied
to the A/D convertor (IC401, pins 4, 5).
The converted digital signals are applied to the DSP IC (IC1)
to do filtering, demodulate and so on. The demodulated
digital signals are applied to the D/A convertor (IC551) to
convert into analog AF signals.
The converted analog AF signals pass through the low-
pass filter (IC601, pins 3, 6, IC651, pins 3, 6), and are then
applied to the buffer amplifier (IC701, pins 2, 3) to convert
into unbalancing signals.
The signals are applied to the AF amplifier circuit.
• RX-B CIRCUIT (DSP-B BOARD)
The 36 kHz 2nd IF signal from the 2nd IF amplifier
(RXPLL-B unit, IC1506) passes through the analog switch
(IC331, pins 1, 7) with limiter function, and is then applied
to the buffer amplifiers (IC301, pin 2, IC341, pin 2, IC371,
pin 2) to convert to balancing signal. The signal is applied
to the A/D convertor (IC401, pins 4, 5).
The converted digital signals are applied to the DSP IC (IC1)
to do filtering, demodulate and so on. The demodulated
digital signals are applied to the D/A convertor (IC551) to
convert into analog AF signals.
• AF AMPLIFIER CIRCUIT
IC101
5
DRAF 6
DSP-A board
7
IC100
5
6
DSP-B board
7
"CROSS" signal
SQL
1
IC102
SW
Q101
Amp.
Amp.
"CROSS" signal
SQL
1
SW
Q100
The converted analog AF signals pass through the low-
pass filter (IC601, pins 3, 6, IC651, pins 3, 6), and are then
applied to the buffer amplifier (IC701, pins 2, 3) to convert
into unbalancing signals.
The signals are applied to the AF amplifier circuit.
3-1-8 AF AMPLIFIER CIRCUITS (MAIN UNIT)
The AF amplifier circuits amplifies the AF input signals to
the suitable driving level for the speaker.

• MAIN SPEAKER OUTPUT

The AF signals from the DSP-A and DSP-B boards are
applied to the AF switch (MAIN unit: IC100, pin 7 for
DSP-A, pin 6 for DSP-B), and pass through the SQL switch
(Q100) which is controlled by "SQLM" signal. The signals
are applied to the buffer amplifier (IC102, pin 3), and are
then amplified at the VCA (Voltage Control Amplifier) circuit
(IC105, pin 14). The amplified signals from the VCA circuit
(pin 11) are applied to the AF power amplifier (IC140, pin 1)
to obtain the suitable driving level for speaker. The output
signals from pin 13 pass through the mute switch (Q141,
RL140), and are then applied to the internal speaker jack
(J142, pin 1) via the MAIN speaker phone jack (J140).

• SUB SPEAKER OUTPUT

The AF signals from the DSP-A and DSP-B boards are
applied to the AF switch (MAIN unit: IC101, pin 6 for
DSP-A, pin 7 for DSP-B), and pass through the SQL switch
(Q101) which is controlled by "SQLS" signal. The signals
are applied to the buffer amplifier (IC102, pin 5), and are
then amplified at the VCA (Voltage Control Amplifier) circuit
(IC105, pin 1). The amplified signals from VCA circuit from
pin 4 are applied to the AF power amplifier (IC140, pin 2)
to obtain the suitable driving level for speaker. The output
signals from pin 12 pass through the mute switch (Q141,
RL140), and are then applied to the SUB speaker jack
(J141).
IC105 IC140
VCA
PA
VCA
PA
VCA
AF
VCA AF
IC180 IC182
"PHI" signal to the Front CPU.
3 - 4
[Sub SP out]
Mute
[Main SP out]
Int. SP
CHASSIS unit
FRONT unit