
6. RF Power Amplifier Circuit
(Main unit)
7. Antenna Switch Circuit
(RF unit)
8. A PC Circuit
(RF unit)
3) PLL Circuit
1. Summary
2. Reference Oscillator Circuit
(Main unit)
3. Loop Filter Circuit
(VCO unit)
4. VCO Circuit
(VCO unit)
IC2 is the power module, which obtains stable output power (50W T/E, 35W TE1/
TE2) within the band. The signal of younger amplifier is amplified by the PA
amplifier (IC2), and then led to the antenna switch circuit.
When transmitting, D11 and D9 are ON in the antenna switch circuit, L14 becomes
parallel components. This causes the output signal of IC2 not to go to the RX
circuit. The signal is led to the antenna connector passing through the low-pass
filter (L15 ~ L18, C76 ~ C80, C148).
When the TX signal is passed through the low-pass filter, matching voltage and
mismatching voltage are detected by the D14 and D15. When the antenna
impedance is 50£2, the detected voltage of D14 and D15 are minimum. But when
the antenna impedance is not 50ft, the detected voltage becomes higher. The
detected voltage is passed through the power setting potentiometer (VR1), and the
signal is amplified by Q17, Q16 and Q14. The transmitting power is controlled by
the voltage of V1 (IC2) and collector voltage of Q13. When the temperature of the
unit goes high, the powerdown circuit (R104, TH2) prevents the device from being
damaged.
The PLL circuit uses PLL IC (IC201) equipped with built-in dual modulus prescaler.
The PLL IC serial data is sent from CPU.
The VCO output frequency divided by N is compared with reference frequency in
the phase comparator.
The reference frequency is obtained by X3 (12.8MHz), and its output is led to the
VCO unit.
The phase error of phase comparator is integrated to DC voltage by loop filter
circuit, and supplied to D201, D202 of varicap diode jn VCO unit. The time
constant of the active loop filter (consisting of Q202 and Q210) is determined by
C211, C212, R228, R210. The output is passed
th ro u g h th e
lag
filte r
(R213,
C208), and input to VCO unit.
The circuit is the Hartley oscillator circuit (Q201), and the signal is output passing
through the buffer amplifier (Q204). C247 is switched by D205 to vary the capaci
tance, and the oscillating frequency range is shifted.
Содержание DR-140E
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