Circuit Descripiton; Receiver Circuits (Rf Unit) - Icom IC-R6 Service Manual

SECTION 4.

4-1 RECEIVER CIRCUITS (RF UNIT)

EARPHONE ANTENNA
When using the connected earphone as an antenna, RX
signal from the earphone is applied to the RF circuits (except
0.10–1.895 MHz band), through the earphone antenna SW
(D101 and D109).
ATTENUATOR CIRCUIT
When the attenuator is activated, the PIN diode (D68)
is forward-biased and a 10 dB (approx.) attenuator is
composed.
The switching of D68 is carried out by Q521 with the control
signal "ATT."
RF CIRCUITS
The RX signal from the antenna is applied to appropriate
RF circuits, according to the RX frequency.
• 0.10–1.895 MHz
When using an external antenna;
The RX signal from the antenna connector (CHASSIS; J1)
is applied to the RF AMP (Q505) through the band SWs
(D66, D67 and D73) and LPFs.
When using the internal bar antenna;
The RX signal from the internal bar antenna (CHASSIS;
EP2) is applied to the RF AMP (Q505) through the ANT SW
(D76).
The amplified signal is passed through the band SWs (D71
and D72), and then applied to another RF AMP (IC18).
• 1.9–14.995 MHz
The RX signal from the antenna connector (CHASSIS; J1)
is applied to the RF AMP (Q505) through the band SWs
(D65, D70 and D73), LPF and the BPF.
The amplified signal is passed through the band SWs (D71
and D72), and then applied to another RF AMP (IC18).
• RF CIRCUITS
ANT CONNECTOR EARPHONES ANTENNA
J1(CHASSIS)
Q521
ATT
ATT
D68
EARPHONE
Q514,
ANT SW
D101,D109
D13,D31,
0.10-29.995 MHz
D73,D75
BAND
LPF
SW
118-174.995 MHz
D3,D11,D74
330-469.995 MHz
BAND
SW
470-832.995 MHz
30-117.995 MHz
175-329.995 MHz
833-1309.995 MHz
CIRCUIT DESCRIPTION
BAR
J2
EXT SP
ANTENNA 0.10-1.895 MHz
0.10-
LPF
1.895 MHz
1.9-14.995 MHz
ANT
Q510,D76
SW
BPF
D63,D65,D66
15-29.995 MHz
BAND
SW
HPF
Q14
RF
BPF
AM P
Q35
RF
BPF
AM P
Q24
RF
BPF
AM P
Q36
RF
BPF
AM P
Q26
RF
BPF
AM P
• 15–29.995 MHz
The RX signal from the antenna connector (CHASSIS; J1)
is applied to the RF AMP (Q505) through the band SWs
(D63, D64 and D73), LPF and the HPF.
The amplified signal is passed through the band SWs (D71
and D72), and then applied to another RF AMP (IC18).
• 30–117.995 MHz and 175–329.995 MHz
The RX signal from the antenna connector (CHASSIS; J1) is
applied to the RF AMP (Q36) through the band SW (D13) and
the BPF. The amplified signal is passed through the band SWs
(D34 and D71), and then applied to another RF AMP (IC18).
• 118–174.995 MHz
The RX signal from the antenna connector (CHASSIS; J1)
is applied to the RF AMP (Q14) through the band SWs (D74
and D75) and BPF. The amplified signal is passed through
the tuned BPF (D1 and D2) and band SWs (D25 and D71)
and then applied to another RF AMP (IC18).
• 330–469.995 MHz
The RX signal from the antenna connector (CHASSIS; J1)
is applied to the RF AMP (Q35) through the band SWs
(D3 and D75) and the BPF. The amplified signal is passed
through the tuned BPF (D4 and D5) and band SWs (D29
and D71), and then applied to another RF AMP (IC18 ).
• 470–832.995 MHz
The RX signal from the antenna connector (CHASSIS; J1)
is applied to the RF AMP (Q24) through the band SWs (D11
and D75) and BPF. The amplified signal is passed through
the band SWs (D32 and D71), and then applied to another
RF AMP (IC18).
• 833–1309.995 MHz
The RX signal from the antenna connector (CHASSIS; J1)
is applied to the RF AMP (Q26) through the band SW (D13)
and BPF. The amplified signal is passed through the band
SW (D36), and then applied to another RF AMP (IC18).
The signal from the RF AMP (IC18) is applied to the 1st IF
circuits.
Q505,Q527
RF
BAND
AM P
SW
D64,D67,D70
D1,D2
TUNED
BPF
D4,D5
TUNED
BPF
D25,D29,D32,
SW
BAND D34,D72
D36,D71
IC18
RF
BAND
AMP
SW
4 - 1
RF UNIT
To the 1st IF circuits