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• High – low TX power control circuit
The IC112 LM358M, transistor Q108 and Q109, diode D102 and external resistors and
capacitors buildup the Automatic Power Controller.
TX High power output 25 watts @ 50Ω loading:
High power mode the CPU pin25 output is low, the transistor Q105 is rest. Then adjust the
VR101 to change IC112 pin3's voltage and the Q116 collect output can automatically to
control the RF power module pin2's Gate voltage to control the power gain output.
TX Low power output 1 watt @ 50Ω loading:
Low power mode the CPU pin25 output is high, the transistor Q105 is working. Then
adjust the VR101 to change IC112 pin3's voltage and the Q116 collect output can
automatically to control the RF power module pin2's Gate voltage to control the power gain
output.
• Low Pass Filter
The Low pass filter is by three group LC buildup. There are L107 match C100, L100 match
C102 and L101 match C103.
• TX modulation path
TX modulation audio amplifier used low power quad operation amplifier IC107 LM324 buildup.
IC107 pin1 to pin3 is amplifier, other three group make the limiter for maximum modulation.
• RX Receiver
The RF amplifier stage used double turn circuit to achieved. The main part are L116, L117, Q114,
L119 and L120.
RX receiver is dual conversion super-heterodyne type with the first IF 21.4MHz and the second
IF 450KHz. PLL supplies the local frequencies below 21.4MHz to convert 21.4MHz signals.
Q114 amplifies the incoming RX signals. Q115 mixes the incoming RX signal and local to
generate IF frequency possessing audio information. There stage 450KHz amplifier circuit IC104
amplify the 450KHz signal to make enough level for discriminate the audio signal. IFT L123 and
R171 are working as a FM detector. The RX audio through Volume control coupling the audio
amplifier IC TDA2003 output to speaker.
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