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Low-pass filter

A project log for Simple Digital Mode Transmitter

A low-power, all-digital transmitter.

RobGRobG 07/14/2021 at 09:310 Comments

I have now cobbled together a low-pass filter to try to suppress the PA harmonics. This one has a corner frequency of 28MHz (to allow me to use it up to 10m band), using the following components (left to right):

shunt C: 100pF

series L: 12T on T37-6 core, making about 485nH

shunt C: 180pF

series L: 13T on T37-6 core, making about 580nH

shunt C: 180pF

series L: 12T on T37-6 core, making about 485nH

shunt C: 100pF

28MHz LPF

Performance simulated in LTSpice, and then confirmed with a nanoVNA. I'm now feeling a bit happier about winding the power up without annoying the neighbours...

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