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5. VCO Circuit
A Colpitts oscillation circuit driven by Q301 directly oscillates the desired frequency. The frequency control voltage determined in the CPU (IC5) and PLL circuit is input to the varicaps (D301 and D304). This changes the oscillation frequency, which is amplified by the VCO buffer (Q302) and output from the VCO unit. Note The oscillation frequency is determined by turning Q301 0N and OFF. Displayed frequencies TX: 130.00 - 139.995 MHz RX: 130.00 - 161.695 MHz TX: 140.00 - 173.995 MHz ON RX: 161.70 - 173.995 MHz Q301 OFF
4) CPU and Peripheral Circuits CPU turns ON the LCD via segment and common terminals with 1/3 The 1. LCD Display Circuit the duty and 1/3 the bias, at the frame frequency is 85Hz.
2. Display Lamp Circuit
When the LAMP key is pressed, "H" is output from pin 45 of CPU (IC5) to the bases of Q1 then turn ON and the LEDs (D1, D3) Bight.
3. Reset and Backup Circuits
When the power from the DC jack or external battery increases from 0 V to 2.5 or more, "H" level reset signal is output from the reset IC (IC2) to pin 35 of the CPU (IC5), causing the CPU to reset. The reset signal. however, waits at C6 and R98, and does not enter the CPU until the CPU clock (X1) has stabilized. When the external power drops to 3.2 V or below, the output signal from the backup IC (IC3), which has been input to pin 34 of the CPU, changes from "H" to "L" level. The CPU will then be in the backup state.
4. S(Signal)Meter Circuit The DC potential of pin 13 of IC104 is input to pin 3 of the CPU (IC5), converted from an analog to a digital signal, and displayed as the S-meter signal on the LCD. 5. Tone Encoder The CPU (IC5) is equipped with an internal tone encoder. The tone signal (67.0 to 254.1 Hz) is output from pin 11 of the CPU to the varicap of the VCO for modulation. Page-5
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