Kenwood NXR-700 Service Manual page 15

4-2. 1st-Mixer circuit
The unwanted out-of-band RF components produced
by Q1 are attenuated by the BPF. Only the desired signal
is transmitted to the A1 Double Balanced Mixer (DBM).
Here, the desired signal is mixed with the fi rst hetero signal.
49.95MHz is produced as the 1st Intermediate Frequency
(IF1).
BPF
L136~139
TC5~8
1st local
185.95~203.95MHz
Fig. 17 1st-Mixer circuit
L46,52
D9
SW
L47,53
D10
SW
4-4. Demodulator circuits
The desired signal that passed through the 1st-IF circuits
passes through the distributor consisting of LC parts and
is fed to the IF system IC_IC12, IC13. The signal in Ana-
log_Wide_5k/4k or Analog_Narrow mode is mixed with the
second local oscillator hetero signal by the mixer in IC12.
450kHz is produced as the 2nd Intermediate Frequency (IF2).
It passes through D15, CF2, D16, D19, CF5 and D20
path if the modulation mode is Analog_Wide_5k/4k. It pass-
es through D15, CF3, D16 and D19, CF7 and D20 path if
the modulation mode is Analog_Narrow. The baseband sig-
nal FM-detected by the quadrature detection circuit consist-
ing of L128, Q57, and Q58 and is amplifi ed to a signal level
CIRCUIT DESCRIPTION
A1
Mixer IF1
49.95MHz
L74,90
XF1 XF3
Q19 Q28
Analog Wide 5k/4k
L75,91
XF2 XF4
Q20 Q29
Analog Narrow
NXDN Narrow
NXDN Very-Narrow
Fig. 18 1st-IF circuits
4-3. 1st-IF circuits
The IF1 signal produced by the 1st-Mixer circuit is trans-
mitted through either one of two 1st-IF circuits with different
bandwidth. The signal passes through the WIDE band con-
sisting of D9, XF1, Q19, XF3, Q28 and D13 only in Analog_
Wide_5k/4k mode. Meanwhile, the signal passes through
the NARROW band consisting of D10, XF2, Q20, XF4, Q29,
and D14 only in Analog_Narrow, NXDN_Narrow or NXDN_
Very-Narrow mode.
XF1 and XF2 is 2 pole and XF3 and XF4 are 4 pole
Monolithic Crystal Filters (MCF). They are BPF for removing
spurious noise occurring close to the desired signal. The
DC switch consists of Q31, Q32, Q26 and Q25, switches the
WIDE (5k/4k) and NARROW bands of the 1st-IF circuits.
8WR
D13 Q25
8NR
SW SW
Q26
8NR
SW
D14
SW
of approximately 100mVrms by IC20 and is then transmitted
to the control unit (X53-413) from CN42 (pin 12).
The signal in NXDN_Narrow or NXDN_Very-Narrow
mode is mixed with the second local oscillator hetero signal
by the mixer in IC13. 450kHz is produced as the 2nd Inter-
mediate Frequency (IF2). Here, irrespective of modulation
modes, it passes through the CF4 and CF6 path. It is trans-
mitted as the baseband signal via IC14 to the CN43 control
unit, X53-414.
CF2, CF3, CF4, CF5, CF6 and CF7 are hexode Ceramic
Filters. They are BPF for removing spurious noise occurring
close to the desired signal.
NXR-700
+8V
Q32
8WR
SW
Q31
IF_SW
SW
15