Ajetrays AJ447, Service Manual, Page: 9 / 16

PAGE 8,TOTAL 16 PAGES
CIRCUIT DESCRIPTION
1.
IC DESCRIPTION
The RDA1846 is a highly integrated single-chip transceiver for Walkie Talkie applications. The
RDA1846 has a powerful digital signal processor, which makes it have optimum voice quality ,flexible
function option ,and robust performance under varying reception conditions.
2. RECEIVER SYSTEM
2-1 Front End (RF AMP)
The signal coming from the antenna passes through the Transmit / Receive switching diode circuit,
passes through a BPF ( L7 and L10), and is amplified by the RF amplifier (Q2). The resulting signal p
goes to RF signal processing IC6 (RDA1846)..
2-2 RF input
Received from the antenna to the RF signal amplified by the LNA(Q2) into IC6 (RF signal processing
IC).RF signals in the chip (IC6) within the amplification, mixing, analog / digital conversion, digital
signal processing (DSP) and analog / digital converter, the output audio signal through the chip PIN
9,enters the microprocessor MCU(IC3).
2-3Receive Signaling(CTCSS/CDCSS)
The output signal from IC6(RDA1846) enters the microprocessor(IC3). IC3 determines whether the
CTCSS or CDCSS matches the preset value, and controls the SP MUTE and the speaker output sounds
according to the squelch results.
2-4 AF Amplifier
The AF signal from the IC is amplified and decoded by MCU (IC3), and the signal passes through AF
VOL circuit and enters the audio power amplifier IC4 (TDA2822) to drive the speaker.
2-5 Squelch
RF signal strength testing done by the IC6. Detecting level values are compared with the default values,
will determine the output to the microprocessor(IC3) to control the audio power amplifier(IC4) is
working. To output sounds from the speaker, microprocessor(IC3) sends a high signal to the MUTE and
turns IC4.
3. TRANSMITTER
3-1 Transmit Audio
The signal from the microphone passes through the IC3. The signal passes through the SOFTWARE
PROGRAM
for the maximum deviation adjustment, and goes to the IC6 modulation input.
3-2 CTCSS/CDCSS Encoder
A necessary signal for CTCSS/CDCSS encoding is generated by the IC6, and transmits through RF
circuit.
3-3 RF Amplifier
The RF signal from the IC6 RF Output is amplified by Q12,Q11and Q14 to the sufficient level to drive