HYT TC-610P Service Manual page 14

In Tx mode, the oscillator frequency of VCO is generated by Q100; in Rx mode, it is generated by Q101.
U202 generates, via the phase comparator, a control voltage to control varactors (D100 and D101 in Tx
mode; D102 and D103 in Rx mode), making the oscillator frequency of VCO be consistent with the
preset frequency of MCU within a wide frequency range.
Q652 performs switching between transmission and reception under the control of T/R: in Tx mode, T/R
is set to low level and Q653 is turned on, making Q100 operate; in Rx mode, T/R is set to high level and
Q653 is cut off, making Q101 operate. The outpuf from Q100 and Q101 is amplified by Q102 and then is
fed to the buffer amplifier for further processing.
If the PLL is unlocked, the LD pin of U202 outputs low level. If the microprocessor detects such situation,
Tx/Rx operation is prohibited, and an alarm sounds.
2. RF Power Amplifier Circuit (Tx Section)
The block diagram of the RF power amplifier circuit is shown in the figure below:
3 Amplifier
Q104
1
2SC5108 1
To obtain the required RF power, the RF signal from VCO goes to the buffer Q104 and to the driver
amplifiers Q400 and Q401. Then the amplified RF signal goes to the driver Q402, which pre-amplifies
power of the input signal to drive the final-stage power amplifer Q403. The input RF signal is then further
amplified by Q403, and goes to the LC low-pass filter (LPF) through the Tx/Rx swithing diode D401.
Finally, it is transmitted from the antenna after high-order harmonics are removed by LPF.
3. Rx LNA and Mixer Circuit (Rx Section)
1） Rx LNA and RF BPF
To allow better frequency range selectivity, the Rx bandpass filter adopts the multi-stage electrically
tunable circuit, as shown in Figure 3.
Q402
2SK3475
Q400
2SC5108
1
Q401
2
2SC4988
RF PA
Q403
RQA0002
MATCH
2
APC
Figure 2
12
TC-610P Service Manual
ANTENNA
R/TSW LPF
RX
L453
1u
0