Kenwood TS-2000 Service Manual page 12

TS-2000/X
The signal is then amplified by the first IF amplifier (Q18)
and is converted to the second IF frequency of 10.695MHz
in the second receive mixers (Q19, 20). The tuning fre-
quency of each stage, the second local oscillator frequency
and others are changed according to the receive frequency
to respond to the changeover of the previously stated first IF
frequency.
A circuit for changing over the IF signal from the units of
the VHF, UHF and 1.2GHz bands and IF signal from the HF
band is provided on the output side of the second receive
mixer. That is, the circuits following this stage are com-
monly used circuits, regardless of the receive frequency on
the main side.
In addition, there is a semi-fixed volume (VR4) on the out-
put side of the first receive mixer. The volume is used to
eliminate the gain differential generated due to the
changeover of the first IF frequency.
The signal for the noise blanker is extracted from this
point by passing through Q22. The noise blanker circuit is
based on the same principle of operation as the conven-
tional one, but can change the threshold level by changing
the emitter potential of the noise detection stage (Q29).
The 10.695MHz signal is amplified by Q26 which also
serves as a noise blanker gate circuit and passes through a
10.695MHz IF filter. It has three bandwidths, 2.7kHz, 6kHz
and through, and when it is combined with the 455kHz filter
group, the same continuous band change function (analog IF
throughput: operation in modes other than FM) as in con-
12
CIRCUIT DESCRIPTION
2nd Mixer
Q19,20
D46
10.695
MHz
Q18
LO2
65.230MHz X57-606 X57-607
58.390MHz RIF
12RIF
FM IC
D68
FM
FM
ALT
DET
IC1
AF
IC2
CF4
455kHz
Q709
ventional analog devices is implemented. The band in this
analog stage does not affect the operation of the digital IF
filter in the IF DSP and is automatically set to the optimum
band for removing unwanted signals outside the band.
Then, the signal is converted to the third IF frequency of
455kHz in the third receive mixer (Q700, 701). The 455kHz
filter has three bandwidths: 2.7kHz, 9kHz and 15kHz. In FM
mode (main band side) the 15kHz filter is selected for WIDE
and the 9kHz filter is selected for NARROW, and signals
passing through the filter are sent to the FM IC (ICI), ampli-
fied and detected. IC1 processes squelch, S meter, etc.
As a characteristic operation in this stage, a tuning error
detection voltage for the ALT function operating in the
1.2GHz band FM mode is generated. It utilizes the DC volt-
age that is overlapped with the ICI detection output.
In a mode other than FM, the receive signal is amplified
by the next third IF amplifier (Q38) and operational amplifier
(IC18) and converted to the final 12kHz IF frequency by the
fourth receive mixer (IC3). The converted IF signal in FM
(audio signal) and non-FM mode (IF signal) is selected by the
multiplexer (IC7) and the signal is sent to the DSP of the
control unit for processing. The signals processed in the
control unit become audio signals in all modes and return to
the TX-RX1 unit (X57-605). These audio signals are power
amplified to the level that drives the speaker with the AM
amplifier (IC9).
A speaker separation function is available as an acces-
sory circuit. The bands can be changed as shown in Table
14.
Q25
D60,64
Noise blanker
D49,55
Q22 Q26 Q28
SW
Q29~Q31 D50,53
CF1
D69 D67
CF2
Q38 D71 D70
IC18
CF3
4th Mixer
IC3
12kHz
DSP
Q42
X53-391
Q41
RCAR
467kHz
TX-RX 1 (X57-605 A/9)
Fig. 4
10.695MHz
D52,56
XF5
D57,61
XF6
D58,62
3rd Mixer
Q700,701
Q32
LO3
11.15MHz
AF PA AMP
IC9