Circuit Description - Alinco DJ-G1T Service Manual

CIRCUIT DESCRIPTION

1 ) Receiver System
1. Front End
2. IF Circuit
3. Demodulator Circuit
The receiver system is the double superheterodyne.
The first IF is 30.85MHz and the second IF is 455kHz.
108.00MHz~ 173.995MHz.
The receive signal is passed through a low-pass filter (L1, L2, L4, C3, C4,
C5 and C7), resonator circuit (L12, varicap D7 and D8), and input to the RF
amplifier (Q6). The signal from Q6 is passed through resonator circuit (L13,
varicap D10 and D11), resonator circuit (L15, varicap D13, D14), led to the
first mixer Q8 and the signal is converted into the 30.85MHz. The resonator
circuit (L12, L13, L15, varicap D7, D8, D10, D11, D13 and D14) is controlled
by P/D voltage. The bandwidth characteristics is obtained the frequency of
108.00MHz~173.995MHz. The diodes (D9, D12, D15 and D22) are ON at
108.00MHz~ 139.995MHz, and they are OFF at 144.00MHz~173.995MHz.
Local oscillator signal from VCO is injected to the base of mixer (Q8). The
radio uses the upper side superheterodyne.
420.00MHz~ 479.995MHz
The receive signal is passed through a high-pass filter (L10, L11, C31, C32
and C33), band switch (D16B), trap circuit (L18, C57, C58 and C59) and
input to the RF amplifier (Q12). The signal from Q12 is passed through
resonator circuits (L19 and C60), (L20, C64 and C65), led to the first mixer
Q13 and the signal converted into 30.85MHz. Local oscillator signal is
passed through the buffer amplifier (Q17), and injected to the base of mixer
(Q13). The radio uses the upper side superheterodyne at 420.00MHz~
429.995MHz, and uses the lower side superheterodyne at 430.00MHz-
479.995MHz.
800.00MHz-999.99MHz (DJ-G1E only)
The receive signal is passed through a high-pass filter (L10, L11, C31, C32
and C33), (printed coil, C67 and C69) and input to the RF amplifier (Q14).
The signal from Q14 is led to the first mixer Q15 and the signal converted
into the 30.85MHz. Local oscillator signal is input to the doubler amplifier
(Q16), and injected to the base of mixer (Q15). The radio uses the lower
side superheterodyne.
The receive signal is mixed with the local signal in the mixer to gain the
difference frequency of 30.85MHz. The unwanted frequency band of the
first IF signal is eliminated by the monolithic crystal filter (FL302), and led to
IF amplifier Q301.
FM and AM demodulators are built in the IC301(TK 10930). The AM circuit
becomes active when Pin 14 of IC301 goes low.
IF by
T h e signal is am plified
of IC301, where it is mixed with the second local oscillator signal
(30.395MHz, X303) and so is converted into the second IF signal (455kHz).
IF Q301,
th e first am plifier of
to
Pin24
an d input