Circuit Description; General Realization Method - HYT TC-580 Service Manual

TC-580 Service Manual

Circuit Description

General Realization Method

TX Section: The audio signal from MIC is amplitude limited and amplified by U203. After that, the
signal feeds to the AGC circuit and then to the baseband processor U202 in AK2347, where the signal
is filtered, compressed, pre-emphasized and amplitude limited. The signal from AK2347 goes to VCO
for frequency modulation (the PLL system is composed of U101, Q100 and Q101). After modulated
onto the RF carrier, the signal is processed by the buffer amplifiers Q104 and Q106. Then the signal
passes through the TX/RX switch D401, and goes to the front-stage power amplifier for
pre-amplification. After that, the signal is further amplified by the driver amplifier Q402, for obtaining the
power to drive the final-stage amplifier. After the signal is amplified by the final-stage amplifier (Q403),
the signal with required power is generated. Then it passes through the TX/RX switch D403, and feeds
to the low-pass filter circuit. Finally, the signal is transmitted via the antenna after high-order harmonics
are removed (The TX/RX switch circuit is composed of D401, D511, D403, D501 and D502).）
RX Section: The RF signal from the antenna passes through the low-pass filter, and then feeds to the
bandpass filter (composed of D514, D515 and D516) to filter out undesired out-of-band interference
signal. Then the desired RF signal enters the high-frequency low-noise amplifier Q501, where it is
amplified. The amplified signal goes to the bandpass filter (composed of D509, D510 and D513) to filter
out out-of-band interference signal again. The desired RF signal is mixed with the first local oscillator
signal from VCO at Q502. The newly generated signal is processed by the crystal filter (Z1, Z2 or
XF501) to generate the first IF signal. After amplified at Q505, the first IF signal goes to the IF
modulator (U201), where it is mixed with the second local oscillator signal from X101 to generate the
second IF signal (it is filtered by CF201). Then U201 demodulates the second IF signal, and outputs
audio signal, which is divided into two flows and sent to the baseband processor U202 in AK2347. One
flow of audio signal is amplified, and then goes to the low-pass filter to filter out high-frequency audio
signal (CTCSS/CDCSS signal is kept). The CTCSS/CDCSS signal is sent to MCU (U611) for decoding.
The other flow of audio signal is filtered, de-emphasized and expanded, and then is sent to the audio
amplifier (U205), where the audio power of the signal is amplified to drive the speaker directly.
Power Supply Section: The 7.4V battery voltage goes to the LDO IC (U601), and generates 5V DC
voltage, which is divided into two flows. One flow is converted into 4.5V voltage via the dual LDO IC
(U602) (under the control of MCU, one flow (4.5T) supplies power for the TX circuit; one flow (V_SAVE)
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