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. With minor changes the PA can also be used on one of the 40 MHz, 60 MHz, 70 MHz or 144 MHz bands. Three of these PAs are used at GB3MCB.

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
Dimensions80 mm x 100 mmI.e. same as a Eurocard PCB size

Spectrum performance. Picture courtesy Sergey, EX8MLE.

The PA schematic. Picture courtesy Sergey, EX8MLE.