Block Diagram - Kenwood TS-820S Instruction Manual

5.1 BL,OCK DIAGRAM
This signal is fed to the IF unit, passes through the noise
blanker circuit and the crystal filter. and is finally amplified
by the 3-stage IF amplifier, so that it is converted into AF
signal by the ring detector.
The AF signal is applied to the AF-AVR unit where it is am-
plified to th~ level to drive the speaker. The frequency cha-
racteristic of the AF amplifier is automatically changed to
suit CW or SSB operation by means of the MODE switch.
GENERAL
The block diagram of TS-820S is shown on page 24.
The transceiver is composed of the single superheterodyne
receiver and the single conversion type transmitter with a fil-
ter type SSB generator. It uses 8,830 kHz IF and its local
oscillator is equipped with a PLL (phase locked loop) circuit
controlled by VFO. Both the receiver and transmitter use
balanced type mixer circuits with dual gate MOS FET's, thus
minimizing spurious durislg transmission and preventing the
effects of strong signals and suprious signals during recep-
tion.
Taking full advantage of PLL system, the transceiver offers
IF SHIFT function (electronic system pass,band tuning) and
permit one SSB filter to provide the same effect obtained by
USB and LSB filters, The transceiver also includes a number
of latest accessory circljits such as the RF speech processor,
the digital display circuit, transmit monitor circuit. etc,
TRANSMITTER SECTION
The microphone signal is fed to the IF unit. amplified by the
microphone amplifier and is then fed to the ring modulator
composed of 4 diodes. The DSB output from the modulator
passes through buffer amplifier and the crystal filter. The
sse signal thus obtained is further amplified and fed to the
transmit mixer of the RF unit.
The transmit mixer is a double balanced type mixer with 2
MaS FETs. The local oscillator is VCO type (voltage control-
led oscillator) whose output is controlled by the PLL circuit
to minimize spurious during transmission. The sse signal
converted into the wanted transmit frequency is amplified by
the transmit driver tube (12 BY7 A) before being fed to the
two S200 1 A power amplifier tubes of the final stage.
They operate in class AB 1 because of low distortion amplifi-
cation fo sse signal.
The output signal is transmitted through a pi-network to the
antenna.
RF NFB is applied from the output of final stage to the driver
stage to further reduce the cross modulation distortion.
RECEIVER SECTION
The antenna signal passes through the RF ATT switch.
where it is attenuated by about 20 dB as necessary. and is
then amplified by the RF unit.
The amplified signal is fed to the buffer amplifier and mixed
with VCO output in the balanced mixer with 2 MOS FETs to
produce 8.830 kHz IF signal.
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