HYT TC-700 Ex PLUS, Service Manual

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TC-700 EX PLUS Service Manual
17
Fig. 3 Receiver Section Configuration
1) Front-end RF Amplifier
The signal from antenna is amplified at RF amplifier (Q207) after passing through a
transmit/receive circuit and a band pass filter. Before passing the first mixer, the amplified
signal is filtered through another band pass filter to remove unwanted signals.
2) First Mixer
The signal from RF amplifier is mixed with the first local from PLL frequency synthesizer circuit at the fix
mixer (IC202) to create a 49.95MHz first IF signal. The first IF signal is then fed through a crystal filter
(XF203) to further remove unwanted signals.
3) IF Amplifier
The first IF signal is amplified by Q206 before passing through crystal filter and by Q204 after crystal
filter and then enters IF processing chip IC204. The signal from IC204 is mixed with the second oscillator
signal again in IC204 to create a 450 KHz second IF signal. The second IF signal then passes through a
450KHz ceramic filter (wide: CF201
，
narrow: CF202) to eliminate unwanted signals before it is amplified
and detected in IC204.
4) Narrow/Wide Switch Circuit
Pin WCON and pin NCON of IC500 outputs wide (high level) and narrow (low level) channel spacing
signal respectively to turn on corresponding diode-connector, and to choose ceramic filter CF201 (wide)
or CF202 (narrow) to filter useless spurious signal.
5) Audio Amplifier
The resulting audio signal from IC204 enters baseband processing chip IC408. The processed audio
signal is then amplified by an audio power amplifier (IC401) to drive the speaker.
ANTSW
BPF
RF AMP
Q207
BPF
1st Local OSC
(PLL)
IF AMP
Q206
MCF
XF203
IF AMP
Q204
IF,MIX,DET
IC204
CF201,202
AF AMP
IC401
SP
Audio
Processor
IC408
VCXO
X3
multiply
16.8MHz
APC
ANT
2nd Local OSC