Rf Power Amplifier Circuit (Tx Section); Rx Lna And Mixer Circuit (Rx Section) - HYT TC-508 Service Manual

TX signal or RX first local oscillator signal.
2) VCO
The VCO section is realized by the three-point capacitor oscillator circuit. TX VCO and RX VCO share
the same oscillator circuit. Q103 controls the switch between TX VCO and RX VCO.
Note: If the PLL is unlocked, the LD pin of U101 outputs low level. If the microprocessor detects such
situation, TX/RX operation is prohibited, and an alarm sounds.

2.2 RF Power Amplifier Circuit (TX Section)

The modulated carrier signal from VCO is pre-amplified at Q104 and Q406, and controlled at D404 and
D405. Then it is amplified by the front-stage amplifier Q401, the pre-driver Q402 and the final-stage
amplifier Q403 orderly. Finally it goes to the LC low-pass filter (LPF) and is transmitted from the antenna
after high-order harmonics are removed by LPF.
APC circuit is composed of Q404, Q405 and U401. U401 controls the bias voltage at the gates of Q402
and Q403, to control TX current and to further regulate power.

2.3 RX LNA and Mixer Circuit (RX Section)

SQUELCH DET
CIRCUIT
R562
C597
NOISE FILLER
CIRCUIT
R509
C553
R510
W /N
IF2 FILLER
CF501
450 KHz
N-DET DEMODULATING IC
U611
BA4116FV
FIL OUT
FIL IN
DEMODULATING
AF AMP
CIRCUIT
AF
U 613
CD501，R502，
TA75S01F
C536
Figure 3
VDD
3 4
Crystal
XT 101
38.4 MHz
2 1
IF1 AMP
Q506
MIXER
Q 502
2SK318
IF1 FILLER
XF501
38.85MHz
QT- AF
AF PROCESSING
CIRCUIT
AF
U 610 ，C554，R538
Figure 4
9
TC-508 Service Manual
ANT LPF
BPF1
LNA
BPF2 Q 501
AT41511