Antenna Tuning And Switching Controls (Ctrl Unit); Tx Amplifier Circuits (Pa-A Units); Tx Filter Circuits (Pa-A Unit); Resistance Detection Circuit - Icom IC-7410 Service Manual

TX AMPLIFIER CIRCUITS (PA-A UNITS)

The TX signal from the BPF UNIT is sequentially amplifi ed
by the pre-drive AMP (Q201), drive AMP (Q221, Q222), and
power AMP (Q241, Q242).
The amplifi ed TX signal is applied to the TX fi lter circuits.

TX FILTER CIRCUITS (PA-A UNIT)

The amplified TX signal from the power AMP (Q241,
Q242) is passed through one of LPFs, depending on the
transmitting frequency, to remove harmonic components
contained in the TX signal.
The fi ltered TX signal is applied to the CTRL UNIT.
• TX AMPLIFIER AND TX FILTER CIRCUITS
RL801
3.5/3.8/4.63 MHz
RL501
RL601
RL1001
RL1101
RL901
From the
Q201 Q221/Q222 Q241/Q242
BPF
RL701
circuits
PRE
PWR
DRIVE
DRIVE
AMP AMP
PA-A UNIT
HF ANT1 HF ANT2
RL501
D401
IC431
IC701
CURRENT ANTI
AMP
DET
RL351
1.8 MHz
RL802
NETWORK
LPF
UNIT
TUNING
NETWORK
RL502
LPF
TUNER
5/7 MHz
RL602 CPU
LPF
RL301
10/14 MHz
RL1002
D251
D151
LPF
D152 IC171
R
RESIST
AMP
18/21 MHz
DET
RL1102
LPF
IC171
24/28 MHz
P
PHASE
RL902 AMP
DET
LPF
IC31
50 MHz
RL702
FOR/REF
SWR
LPF
AMP
DET
D11/D12
CTRL UNIT
ANTENNA TUNING AND SWITCHING CIRCUITS
(CTRL UNIT)
The TX signal from the PA-A UNIT is passed through
4 detection circuits on the CTRL UNIT, before being applied
to the antenna connector [ANT1] or [ANT2].
Refering to the detected parameters, the tuner CPU (IC701)
controls the tuning networks on the NETWORK UNIT, to
match the transceiver and connected antenna.
SWR DETECTION CIRCUIT
The forward wave is rectified by D12 at the current detect
transformer (L11). The rectified voltage is amplified by the
DC AMP (IC41), and then applied to the A/D port of the
tuner CPU (IC701).
The refl ected wave is rectifi ed by D11 at the current detect
transformer (L11). The rectified voltage is amplified by the
DC AMP (IC41), and then applied to the A/D port of the
tuner CPU (IC701).
REACTANCE DETECTION CIRCUIT
The TX signal which is picked up at the current detect
transformer (L101), and the TX signal which is picked up by
C101, C105 and R105, are rectifi ed by D102 and D101, and
amplifi ed by C-MOS IC (IC111).
The amplifi ed signal is applied to IC131, through the buffer
(IC121) for phase comparison. The resulting signal of phase
comparison is rectifi ed by D131 and D132, and composed
and amplified by IC51, then applied to the A/D port of the
tuner CPU (IC171).

RESISTANCE DETECTION CIRCUIT

A portion of the TX signal is picked up by L151 and C152,
and rectifi ed by D152 to be converted into DC voltage.
Another portion of the TX signal is rectifi ed by D151 to be
converted into DC voltage too.
And these voltages are the same when the connected load
(=antenna) is matched to 50 Ω. Thus the difference of these
voltages represents the resistance components.
By comparing the difference of these voltages, the
transceiver detects the resistance components.
The detected resistance components are buffered by Q151
and amplifi ed by IC171, and then applied to the A/D port of
the tuner CPU (IC701).
CURRENT DETECTION CIRCUIT
A portion of the TX signal is picked up by L401, rectifi ed by
D401, and applied to IC431 to be level-compared with the
voltage from the SWR detection circuit.
When the resistance of connected load (=antenna) is less
than 10 Ω, the TX signal is bypassed the NETWORK UNIT,
through the tuner compulsorily switches (RL301 and RL351),
to protect the circuit on the NETWORK UNIT from refl ected
waves.
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