Kenwood TS-2000, Service Manual

Page: 11 / 171

11
TS-2000/X
HF Receiver System and Main IF System
Three antenna terminals used for the HF and 50MHz
band reception are ANT1, ANT2 and HF RX ANT.
After the incoming signal from ANT1 and ANT2 passes
through the transmission/reception changeover relay in the
filter unit (X51-315), and is sent to the HFRX terminal of the
TX-RX unit (X57-605). There is an HF RX ANT terminal there,
and one of the antennas can be selected from the menu for
reception .
The HF RX ANT terminal is used to connect a dedicated
HF-band low-band receiving antenna, such as a Beverage
antenna, and operates at frequencies up to 30MHz. (If an
antenna, such as a solid wire antenna, is connected to this
terminal, unwanted radio signals in the shack may be picked
up. It is recommended that a 50 (coaxial cable be used for
routing in the shack.)
The signal passes through an RF ATT, an image filter and
a limiter for surge absorption and enters the RF BPF for both
transmission and reception. The division of the RF BPF is in
the range shown in the block diagram. For 6.9~7.5MHz,
13.9~14.5MHz and 49~54MHz, a dedicated BPF (adjustable
type) is used and particularly effective for eliminating un-
wanted signals in the low band. Other BPFs (non-adjustable
type) are designed as circuits with independent armature
bands, except that the 24MHz and 28MHz bands are
shared. Signals pass through these BPFs at the time of
transmission, so they are useful for producing radio signals
with little radiation.
Although the conventional RF ATT had an attenuation
level of 20dB, the attenuation level of the current RF ATT is
12dB. It can, however, be changed to approximately 20dB
by removing the jumper (CN2) near the ATT within the unit.
The pre-amplifier (Q12, Q705) have been changed to a
power MOS FET from the combination of the conventional
cascade amplifier and MOS FET amplifier. This element is a
FET that is used in a younger stage for transmission and has
excellent large input characteristics. The actual circuit con-
tains two amplifiers using this FET. Large input characteris-
tics with a low gain are given priority on the low band (Q12)
with respect to 21.5MHz, and sensitivity is given priority on
the high band (Q705). circuit on the low band side bordering
21.5 MHz favoring a gain with moderately large input char-
acteristics and that on the hybrid side (Q705) favoring .
When the pre-amplifier is off, the signal from the RF BPF
enters the receiving first mixer (Q7~Q10) in the next stage
as it is.
The receiving first mixer circuit uses a double balance
type mixer with four joint type FETs. The signal is converted
to the first IF frequency by the first local oscillator signal.
The TS-2000S has adopted a method that changes the first
IF frequency according to the receive frequency. For this
reason, it has two sets of roofing filters (MCF) that deter-
mine the selectivity of the first IF. Table 1 shows the rela-
tionship between the receive frequency and the first IF fre-
quency. The central frequencies for the reception and
transmission of the first IF frequency are different from each
other by 100kHz because the transmission and reception is
performed simultaneously during satellite communication.
–12dB
ATT
LPF
L1
TX-RX 1 (X57-605 A/9)
HPF BPF
1.705~2.5MHz
49.0~54.0MHz
D12 D13
BPF
D33 D34
30kHz~1.705MHz
1.705MHz~
60MHz
D7 D8 D10
D11
RF BPF
D38 D39
D705 D704
PRE AMP
Q12
30kHz~21.5MHz
ANT1 ANT2 HF RX ANT
Q705
21.5MHz~60MHz
D35 D36
1st Mixer
Q7~Q10
XF1
69.085MHz
XF2
75.925MHz
X51-315
FILTER
X57-605
TX-RX1
Q18
2nd Mixer
Q19,Q20
D42 D41
10.695
MHz
Q13
LO1HF
75.955~
129.085MHz
RX/TX frequency (MHz) RX 1st IF (MHz) TX 1st IF (MHz)
0.03~ 9.0 75.925 75.825
9.0 ~17.0 69.085 68.985
17.0 ~24.0 75.925 75.825
24.0 ~26.0 69.085 68.985
26.0 ~30.0 75.925 75.825
30.0 ~37.0 69.085 68.985
37.0 ~49.0 75.925 75.825
49.0 ~60.0 69.085 68.985
Table 13 RX frequency and 1st IF frequency
Fig. 3
CIRCUIT DESCRIPTION