PA 50 MHz AFT05MS031N

Sergey, EX8MLE, has designed a very cost effective 25 W PA for 50 MHz that matches the drive power from the RFzero. The PA makes it extremely easy to build a beacon for 50 MHz either as a stand alone beacon or to take part in the Synchronized Beacon Project. The PA also features an on-board low pass filter and bi-directional coupler.

The PA, fully assembled and ready-to-use, is available for only 75 USD plus shipping directly from Sergey. All you need to add is a suitable heat sink. Please contact him directly using the email address from

If you are not already familiar with Sergey’s PA designs you may take a look at the 4 metres Website. Sergey is a really skilled PA designer from low power to kilowatt. This PA uses a 2SK3475 as driver and an AFT05MS031N in the output.

Why not use the RA30H0608M power module from Mitsubishi? Well, the second harmonic on 100 MHz is only -5 dBc. This means that 6 W of RF, and even more on DC, is wasted continuously. Even if you add a good low pass filter the second harmonic power is reflected back into the power module meaning it is subject to a permanent minimum SWR of 3. This is neither good nor efficient from an electrical bill point of view.

Parameter12 VNotes
Frequency range50 - 54 MHz
Output power48 W
Input power13 dBmOn-board 15 dB input attenuator pad. Resistors' wattage limit the drive power
Gain, max50 dB
Second harmonic suppression>60 dBc
Current6,35 A

Spectrum performance. Picture courtesy Sergey, EX8MLE.

The PA schematic. Picture courtesy Sergey, EX8MLE.