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Wide band class-A power amplifier

  I designed a simple and compact wideband power amplifier circuit for HF. Depending on the operating point, an output of 4~5 W can be obtained with input ~ 0.1 mW.
diagram

Configuration

Driver：MMG3H21NT1
  Gain 17dB、OP1dB 20.5 dBm
  It is also used for TX circuits in IC-9700. Input and output impedance are almost completely matched at 50Ω without any matching circuits.

Final：AFT05MS004NT1
  VDSS = 30 V, PD = 28 W
  A LDMOS FET for RF power amplification with small feedback capacitance and high gain in the HF band.
diagram
In May 2021, they are in mass production and you can get them easily. Since both devices are designed for RF use, they can be applied to the HF to VHF bands by adopting matching circuits. (Class-A power amplifier for the 144MHz band (5W) is here.) This two-stage configuration is recommended as a power amplifier circuit up to 5W class because it is simple and versatile.

Characteristics

  Adjust the bias current with a variable resistor not to clip output waves. The frequency dependence shown in the photo shows gain in 7~25MHz is within ± 1dB.
Since the heat sink cannot be attached directly, you should take care to heating. Here, heat is made to escape to the heat sink through the PCB.
diagram

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