Icom IC-R7O Maintenance Manual page 14

SECTION 5 CIRCUIT DESCRIPTION
5-1 RF UNIT
1. RF stage
The signal (1.6 ~ 30 MHz) received from the antenna connector (ANT2) is fed to the input selecting
circuit.
Usually, the TRH signal from the logic unit is "L" level, so Q1 is turned ON, D3 is turned ON, current
flows to R7, and the signal from the antenna connector signal is fed to the BPF (band-pass filter).
Note that current flows from Q1 to R3, D1 and R8; D1 is turned ON; and the input signal from the
converter terminal is shunted to ground through C2.
If the converter terminal is used, Q1 is turned OFF because the TRH signal from the logic unit is "H"
level; D5 is turned ON, D2 is also turned ON, current flows to R7, and the signal from the converter
terminal is fed to the BPF.
The TRH signal also flows to R5, D4 and R2; and the input signal from the antenna connector is shunted
to ground through C4.
Good isolation is provided between the antenna connector and the converter terminal by this circuit.
The signal received from the input-selecting circuit is fed to the BPF, where unwanted signals outside of
each band width are removed.
BPF switching signals from the logic unit are supplied to J5, the BPF input/output switching diodes
(D8 ~ D25) are turned ON according to each band, and the BPF corresponding to the band is selected,
causing the received signal to pass. .
The received signal which has passed through the BPF is fed to the PREAMP/ATT
switching circuit.
These can be selected by a switch on the front panel.
PREAMP
FRONT
PANEL
THROUGH
S16 OPRE
OFF
OATT
Boo
T8VO
ee ee eed
ATT
036