Vco; Figure 9-5 Diagram Of Vco - Hytera MD78X Service Manual

Service Manual
9.3.4

VCO

The VCO is composed of transistors (Q100, Q103, Q106 and Q110), varactors and four Colpitts
oscillators. There are four VCOs in all: two VCOs (Q100 and Q103) used to transmit excitation signals
and the other two VCOs (Q106 and Q110) to receive LO signals. U302 controls the operating
frequency of the VCO. Q102 and Q107 constitute the buffer amplifiers for the transmitter circuit, while
Q111 and Q109 for the receiver circuit. The digital-to-analog converter (U500) modulates the TX
oscillator signal.
TX PA
Q107
RX Lo
Q109
TX_L_VCO
Q103
Q102
Q100
TX_H_VCO
RX_L_VCO
Q110
Q111
Q106
RX_H_VCO

Figure 9-5 Diagram of VCO

107
UHF1 (400-470MHz 45W) Information
MOD
LPF
PLL IC （U100）