19 November 2021

Looking for clean SS HF PA w/QSK - part 8 (KM3KM Mercury IIIS LDMOS kit)


Hi all,

here is another way how to get the SSPA for HF. The question is - if it meets all of our requirements and needed features...
In that case it is a bit special stuff as it is sold as the kit which has to be assembled and tested before using it in the hamshack.

As you know my preview parts talked about:
ACOM 1200S
LINEAR Amp Gemini HF-1K

Azden AZR-1000

Elecraft KPA1500

KM3KM Mercury IIIS LDMOS kit

This solid state HF amplifier uses a single LDMOS for fully automatic operation from 160m to 6M making 1200W with input power between 50 and 90W depending on your ALC setting. Protected against antenna SWR over 2 to 1 and also against excessive input power. Built-in power supply for 120 or 240 VAC without changing taps in the transformer, just changing the power cable plug.

Fans work silent and color front panel display. Output to three antennas selectable in the display with operator finger.
This is a kit that you put together at home but assembly is very easy to do.

• Solid state amplifier (BLF189XRA)
• 1.8 - 54 MHz
• All Protections
• RF Band Decode
• FWD / SWR Meter
• Output Digi 700 Watts
• Output SSB/CW 1200 Watts
• Antenna Selector Switch
• 7 Inch Touch Color Screen
• Di Voltage / Di Current Meter

• Integrated Power Supply 120-240v

• W12 x L13.5 x H5.5 inch

• Weight 26 pounds


Maintains linearity under full output power (1200watts). 

Low harmonic content (below -43dBc on HF & -65dBc on VHF bands) thanks to an efficient Chebyshev filter. 

Fast and effective protection systems maintain the amplifier’s safety from operational damage.
Compact linear amplifier with 1200 watts SSB/CW & 700 watts DIGI-MODE of output power on all amateur bands from 1.8 to 54MHz (<800watts 50 to 54MHz) 

Auto sensing power supply from 120 to 240VAC.

There is nothing said about the T/R switching but it looks like relay T/R switching is used so no QSK unfortunately. 

The powerful PSU is built-in. Also extremely low noise fan cooling system is designed for that amp so you will not feel like sitting on the tarmac waiting for the jet to take off. (compare to KPA1500 or Palstar LA-1K or the SPE 1.5K amps...)

No ATU unit built-in just three antennas switch installed. So compare to other SSPA like B26-PA RF2K-S there seems to be disadvantage.

This amp provides a COOL SOLID 1 KW output on CW. It is the best bang for the buck on the market. This amp is high tech simplicity. Everything is modular and easily replaced if repair is needed which is not likely. Running 1 KW all the time leaves 200 watts of head room and because you are running near max the amp is more efficient and produces less heat than other amps designed to run at 1500 watts when you run them at 1 KW.

Five stars overall rating on eHam from currently 48 reviews is really promising... 

KM3KM website:

Assembly manual:

Operating manual:

73 - Petr, OK1RP
"auf die Dauer hilft nur Power" (Erich, HB9FIH)

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