Note: This HF LNA design is inspired by Charlie Morris ZL2CTM's prior work.

Design

The idea that a single-transistor preamp with 10 dB gain is more than enough for HF comes from Gajendra Kumar (VU2BGS). As a new "designer," I am often overwhelmed by the different possible design paths, so guidance from an elmer is crucial.

HF LNA 1

HF LNA 2

It seems even MMBT2222A should work for building a HF LNA!

HF LNA 3

It doesn't feel right to dissipate ~45mW continuously in a SOT-23 package, so we will be shifting to PZT2222A (SOT-223) or PXT2222A (SOT-89).

With NXP parts:

HF LNA 4

With onsemi part:

HF LNA 5

So which transistor model is more accurate? ;)

It is a pleasure to work with onsemi .lib SPICE models; they are usable out of the box.

This LNA will be used in the RX path of the DDX Commercial series of transceivers soon!

Simulation

Simulation files: Gain-Blocks-LTspice

Please always publish your simulation files ;)

Updates

Updates (October-2025):

HF LNA 1

LNA Actual Picture 1

LNA Measurements 1

LNA Measurements 2

HF LNA Sim

As you can see, NXP's transistor model is pretty decent and mimics reality well!

NanoVNA setup notes:

  • Input ATTN: 30dB (Port 1 of NanoVNA)
  • Output ATTN: 33dB (Port 2 of NanoVNA)

References