HYT TC-610P Service Manual page 15

TUNE FROM MCU
C526
After out-of-band signals are removed by the electrically tunable bandpass circuit (D503, D504, L501,
L502, C503, C505 and C507), the signals from the antenna go to the low-noise amplifier (LNA) Q500 for
amplification. Then the amplified signals go to the three-stage bandpass circuit (mainly composed of
D505, D506, D507 and peripheral components) to effectively eliminate out-of-band interference and to
obtain pure RF signals. Finally, the signals go to the mixer circuit.
MCU provides the electrically tunable control signal (its level can be obtained via table lookup or
calculation), making the varactor operate within an appropriate voltage range. It forms a bandpass filter
with the peripheral inductors/capacitors. The capacitance of the varactor changes as the control voltage
of MCU, to satisfy the requirements of preset Rx sensitivity and out-of-band rejection.
2） Mixer Circuit and BPF Circuit
The block diagram of the mixer circuit is shown in the figure below:
AN29160
C521
C524
D505
D507
D506
C523
C519
L508 L507
L506
TUNE BPF
1stIF BPF
38.85MHZ
XF1
LNA
Q500
1
C505
D504
C506
L502
TUNE BPF
Figure 3
C534
Q501
RF MIXER
Figure 4
13
TC-610P Service Manual
TUNE FROM MCU
D503
C504
L501
22nH L530
C531
C532
C533
C528