3 kW linear amplifier with four ART1K6 LDMOS fets

The purpose of the project is to build a linear LDMOS amplifier for HF bands 160-10 m. The amplifier must withstand a continuous power of 1.5 kw, because of reliability, I have ended up using several separate amplifier modules. Implemented with four modules, only less than 400 W of power is taken from one module. It is possible to get a power of more than 1 kw from each module, so the amplifier will not be overloaded in any situation.

The amp does not have WARC bands, maybe I will add them in the future?




 Circuit boards of the RF part


 Drilling holes in copper plate

 Fets soldered in a cooling plate


 Two RF modules with a heatsink



 Each module is tested separately


Heat sink datasheet



 Four modules with cooling plates and combiner and divider


RF amplifier unit and power switches

Control board


UI at rear panel



Simulation vs. real world


 Diplexer looks good!

Why diplexer? The diplexer directs the desired signal to the antenna, but harmonics to the dummy load (the so called harmonic load). In the LDMOS amplifier (push-pull), the third harmonic can be only 10-12 dB weaker than the useful signal, This means if you drive 1.5 kW antenna, and 150 W go to dummy load! 


20 m Diplexer



More diplexers....

Testing a diplexer with network analyzer



Output without diplexer



With diplexer.... 3rd harmonic -50 dB@ 2 kW...


Dummy load spectrum


6-band HF diplexer


Test at 1,5 kW per band

160 m



40 m without filter and with filter

20 m

15 m


10 m


Need more attenuation for 3rd harmonics at low band.



WaveNode SWR sensor added inside of amplifier

Installed Diplexers

Thermal cam tests


Diplexer and harmonic load


Harmonic load with FAN-control






9 kW 50 V three-phase power supply ESP120


Power connectors 


 Power switch v1.0

LDMOS power switch


LDMOS Control board v1.0


Arduino controller on board


Control board v4.0


TFT-touchscreen UI


LDMOS power switch v2.0


TRX-relay board




Input step attenuator










Almost ready to use

Added handles, weights approx. 30 kg

The amplifier was in real operation for the first time at the WPX CW 2023 contest. No problems found.






Latest UI


Three phase power supply

Three-phase power supply from three Huawei R4850G2 power supplies connected in parallel. Maximum power about 9 kW.Why three power sources when one or two would be enough? In three phase system, loading one phase would cause a so-called bias load to the power grid.


DC output connectors and D15 connector CAN bus for control 





Linear + power :)