Kenwood TS-2000, Руководство по обслуживанию

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17
TS-2000/X
Transmit
S
ystem IF
S
ection
■
Transmission IF
The details of the processing by the DSP depend on the
mode.
• Modes other than FM
Transmission bandwidth change, speech processor and
microphone gain control are performed in the AF stage. A
12kHz IF signal is produced after PSN modulation and out-
put modulation control.
• FM mode
The baseband processing in the AF stage is carried out by
the DSP and a VCXO (voltage controlled X’tal Oscillator) is
used as a modulator.
The transmit signal output from the control unit (X53-391)
is switched by an analog SW (IC8) and is input to the bal-
anced mixer (IC6). The 12kHz IF signal and local oscillator
signal enters the IC6 and become a 10.595MHz signal. The
local oscillator signal is generated by the DDS (IC602).
The 10.595MHz IF component is amplified by the IF am-
plifier (Q54) and passes through the 6kHz bandwidth crystal
filter, then becomes a 10.595MHz IF signal by eliminating
local oscillator signals. The diode switch (D90) changes be-
tween FM modulator output and non-FM 10.595MHz IF sig-
nals.
The temperature compensation of the transmitter circuit
is done by the thermistor near the IF amplifier (Q54) and the
thermistor on the input side of the IF amplifier (Q711). They
reduce the gain at low temperatures and raise it at high tem-
peratures.
TH8
Q54
TH5
XF9
10.595MHz
TH7
IC6
Q58
X1
Q59
10.595MHz
Q604
TX-RX 1 (X57-605 A/9)
IC602
DDS
10.595MHz
SSB,CW,
AM,FSK
FM
2
3
8
IC8
O/I 2
O/I 3
O/I 1
X53-391
TX
signal
D90
Q711
D84
Fig. 10
The output signal from the IF amplifier (Q711) passes
through D84, Q40, D82, D48, D80 and D81 and becomes
the IF transmit signal for each band. D84 is a voltage con-
trolled attenuator circuit. This circuit changes the attenua-
tion level according to the control voltage (TGC), in the same
way as the TGC (TX gain control) used in the TS-870 and TS-
570 and is set to the adjusted attenuation level for each
band. Q49 is an IF amplifier circuit with an ALC circuit. The
gain is controlled by the voltage generated by the ALC cir-
cuit.
D82 is a voltage controlled attenuator circuit as D84. The
attenuation level is minimum at full power and as the power
decreases, the control voltage rises and the attenuation
level increases. When the power is reduced, the gain will
become relatively excessive if the IF gain is not lowered. It
is set to an attenuation level adjusted by the PGC (Power
Gain Control) accordance to the power of each band.
Q48 is an IF output buffer. It changes to the transmitter
section of each band with a diode switch (D80, D81) to sup-
ply a 10.595MHz IF signal.
During transmission in the 144MHz and 420MHz bands,
the signal is output to the TX-RX2 unit (X57-605), and during
transmission in the 1.2GHz band, it is output to the TX-RX3
unit (X57-605).
In the 1.8~54MHz band, the frequency is converted to
the final target transmit frequency in the TX-RX1 unit (X57-
605).
The local oscillator frequency changes according to the
band in second transmit mixer of Q46 and 47 to generate
different IF frequencies. (TX third IF: 68.985MHz or 75.825
MHz)
D703 and D715 are used to change the tuning frequency
of the local oscillator signal and D79, D78, D77 and D76 are
used change the frequency of the IF filter (L102).
The variable tuning filter containing these variable capaci-
tance diodes performs the coarse adjustment of the coil
(L100, L99, L98, L96, L102) in the band (18.085MHz) where
the IF is 75.825MHz. Then, it changes the tuning frequency
control voltage from the D/A in the band (14.100MHz)
where the IF is 68.985MHz and tunes it to the necessary
frequency by readjusting the coil.
HFLO1
75.955~
129.085MHz
D40
Q44,45
1.8~54MHz
HFLO2
58.390MHz
65.230MHz
D45
Q46,47
L96,98~100
68.985MHz
75.825MHz
HBPF
D76~79
L102
HBPF
D703,715
TX-RX2
X57-606
TX-RX3
X57-607
D80
D81
10.595
MHz
Q48
TX-RX 1 (X57-605 A/9)
Q49 Q711
D82 D84
RF
BPF
TIF 12TIF
Fig. 11
CIRCUIT DESCRIPTION