Kirisun PT4208, Service Manual

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PT4208 Service Manual
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receiving; flashes red while in low battery power.
2. Channel Selector Knob
Rotate the knob to select channel 1-16.
3. On/Off/Volume Control Knob
Rotate clockwise to turn on the radio, and keep turning
to adjust the volume. To turn off the radio, rotate the knob
anticlockwise till a sound of click is produced.
4. PTT (Push-To-Talk) Key
Press the PTT key and talk to the microphone to send the
voice to the recipient.
5. Side Key 2 (Programmable key)
6. Side Key 1 (Programmable key)
7. Top Key (Programmable key)
8. Speaker/Microphone Jack
Jack for connecting external speaker or external
microphone to the radio.
Chapter 3 Circuit Description
3.1 Frequency Configuration
Figure 3.1 Frequency Configuration
The reference frequency of the frequency synthesizer is
provided by crystal oscillator X4 (TCXO, 16.8MHz). The
receiver adopts double mixing. The first IF is 49.95MHz and
the second IF is 450kHz. The first local oscillator signal of
the receiver is generated by the frequency synthesizer. The
second local oscillator signal adopts the third harmonic
(50.4MHz) of the crystal oscillator X4 (TCXO, 16.8MHz).
Transmitter signal is directly produced by the frequency
synthesizer.
3.2 Principle of Receiver (RX)
Figure 3.2 Principle of Receiver
Front end
The signal coming from the antenna passes through the
RX/TX switch circuit (D1, D2, D4 and D5), and passes
through a BPF (C37, C227, L8, L15, C70, C126, D30, C218,
L9, C230, C128, D26, C217, L10, C229, C127 and D24) to
remove unwanted out-of-band signal, and is routed to the
low noise amplifier (LNA) consists of Q20 and its peripheral
components where it is amplified.
Output signal from the LNA passes through a BPF (L7,
C228, C47, D23, C219, L6, C182, C124, D22, C216, L5,
C132, C32 and D21) and goes to the first mixer (Q19).
PWM wave is output from pin 12 of the MCU. The wave
is filtered and rectified into adjustable voltage, which can
control the center frequency of the band pass filter through
changing capacity of the varactor diode (D21, D22, D23,
D24, D26 and D30).
First mixer
The receiving signal from LNA is mixed with the first
local oscillator signal from the frequency synthesizer to
produce the first IF signal (49.95MHz). Then the first IF
signal passes through crystal filter (XF1 and XF2) to remove
the adjacent channel signal and signal outside the adjacent
channel.
IF circuit
The first IF signal from the crystal filter is amplified by
the first IF amplifier (Q21), and is routed to the IF
processing IC (IC5, TA31136).
IF IC consists of the second mixer, second local
oscillator, IF amplifier, limiter, discriminator, and noise
amplifier.
The 16.8MHz frequency produced by TCXO (X4) is
multiple-amplified and then adopts the third harmonic
(50.4MHz) as the second local oscillator signal source. The
second local oscillator signal (50.4MHz) is mixed with the
first IF signal (49.95MHz) in IC5 to generate the second IF
(450kHz). And then the second IF signal is amplified and
limited in IC5, filtered in the ceramic filter (CF1, 450kHz),
and demodulated in IC5. After that, the demodulated signal
is routed to the audio circuit to output audio signal.