Receiving Circuit - Kenwood TS-120S Operating Manual

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RECEIVING CIRCUIT
The signal from the antenna is fed to the 8.83 MHz IF trap
circuit. This signal is stepped up about 10 dB and
impedance-converted by a wide-band transformer before it
is applied to the bandpass filter (BPF). The BPF is common
to transmission and reception, eliminates the need for a
preselector, and makes the RF section compact in design.
The signal from the BPF is fed to the dual-gate MOS FET
wideband RF amplifiers consisting of a 3SK74 (Q1) and a
2SC1815 (Q2), where the 2 MHz to 35 MHz signal is
amplified about 20 dB.
The RF amplifier output is through a wide-band transformer
to the input balanced transformer of the balanced mixer (two
3SK74s, Q3 and 04), where it is mixed with the VCO output
from the PLL and converted to the 8.83 MHz IF. This signal
is applied to the IF unit through the ceramic filters, NB gate
circuit and the crystal filter. The NB circuit is controlled by
the NB switch on the front panel.
The signal, passing through the crystal filter, is amplified
about 90 dB by the three-stage 3SK74 MOS FET IF
amplifier (Q1, Q2, and Q3) and is demodulated into audio by
the four-diode ring detector.
From the final IF stage, the signal also passes through a
buffer amplifier and is fed to the AGC circuit where it is
detected and amplified. Receiver gain is controlled by this
AGC voltage applied to the second gates of the RF and IF
amplifiers, with the time constant determined by R38 (2.2
MQ) and C40 (1 uF). Input levels of 2 dB and 34 GB are in-
dicated as S1 and SQ on the S-meter. The AF signal is
amplified by Q1, a 2SC2240 (GR), gain controlled, and
further amplified by an HA1366W (Q7, the power-amplifier
IC, to drive the speaker. This signal, which is transistor-
coupled with Q14, a 2SC1815(Y), and Q15, a 2SA1015(Y),
is sampled for ANTI-VOX control, so the VOX circuit is not
tripped by the speaker output. This new system is a depar-
ture from the conventional transformer-coupled sampling
systems.
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TRANSMITTING CIRCUIT