Icom IC-R7000 Service Manual page 13

RECEIVE FREQUENCY 2nd LO FREQUENCY
FRx [MHz] F2nd
LO
[MHz]
25-
89.9999
768
1025-1089.9999
90- 249.9999
768
1090-1249.9999
250- 519.9999
768
1250-1519.9999
512- 999.9999
256
1512-1999.9999
Table 4
A double-balanced mixer IC7 converts 1st IF signals
to 2nd IF (10.7MHz) signals.
A LPF consisting of C142-C144 attenuates higher
harmonics of 2nd LO signal from IC7. Q18 amplifies
2nd IF signals from IC7, and the output of Q18 is fed
to the IF UNIT.
A part of 2nd IF signals from IC7 is buffer-amplified
at Q19, then is applied to a LPF consisting of L60
and C114-C116. These signals are then fed to the
[10.7MHz IF OUTPUT] JACK.
4·1·9 TUNED CONTROL CIRCUIT (RF UN!n
This circuit converts the lock voltage from the PLL
UNIT to tuned voltages for the LO trap (tuned notch)
circuit and BPF1-BPF4.
Fig. 1 shows the relation among receive frequencies,
the control voltage, the tuned voltage for BPFs and
the tuned voltage for the LO trap circuit.
I I
j
I
~~
:: y:
'.VJ:V1
1
V '
~-
I I I
..Jo
I
CL
>
I
I
0
I I
0 250 512 762 1000
frequency [MHz]
frequency [MHz]
frequency [MHz]
Fig.1
IC3(A) DC-amplifies the CV from the PLL UNIT, and
IC3(A) supplies IC1(A), IC1(B), IC2(A), and IC2(B) with
control voltage.
IC1(A) supplies E!PF1 with a tuned voltage. The gain
and offset voltage of IC1(A) are controlled by R68
and R66, respectively.
IC1(B) supplies BPF2 with a tuned voltage. 053 and
R157 adjust the gain of IC1(B) to fit the characteristics
of BPF2.
IC2(A) supplies BPF3 with a tuned voltage.
IC2(B) supplies BPF4 with a tuned voltage. The gain
and offset voltage of IC2(B) are switched by Q9 and
Q10, respectively, to convert the variations of two PLL
lock voltages to a continuous tuned voltage.
IC3(B) supplies a tuned voltage with the LO trap
(tuned notch) circuit. The offset voltages of IC3(B)
are switched by Q11 to convert the variations of
two PLL lock voltages to a continuous tuned voltage.
4·1·10 POWER SOURCE SWITCHING CIRCUIT
(RF UNln
IC5 switches the power source of each RF amplifier
and attenuators by signals from the LOGIC UNIT.
Q21 and 052 are voltage converters and regulators of
the power source for IC5.
An inverter circuit consisting of Q12 and R106 reverses
ATT signals from the LOGIC UNIT to make THROUGH
signal.
Q14 and Q15 are power source switches for RF
relays RL1 and RL2. Q14 and Q15 turn ON via BPF4
signals.
BPF4 signals control IC4, and IC4 outputs positive
voltage to pin 7 (when the receive frequency is
25-511.9999 or 1025-151.9999MHz) or pin 1 (when
the receive frequency is 512-999.9999 or 1512-
1999.9999 MHz).
4·1·11 AGC BUFFER CIRCUIT (RF UNln
An AGC voltage buffer Q20 converts AGC voltage
variation (4-0V) to the voltage variation that is
required for Q1-Q4.
4-1-12 FM (wide) CIRCUIT (IF UNln
In FM (wide) mode, 2nd IF signals (10.7MHz) from the
RF UNIT are impedance-converted at
L1,
and fed to
Fl1. 2nd IF signals from Fl1 are amplified at Q2 and
IC1. The gain of Q2 and IC1 is approximately 40dB.
2nd IF signals are then applied to IC2, and are limiter
amplified and then detected to obtain AF signals.
AF signals from IC2 are applied to buffer amplifier
Q4. This circuit switches AF signals and matches
the level of AF signals with other modes.
4-3