PA 50 MHz RD70HVF1

Sergey, EX8MLE, has designed an up to 50 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 86 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 QRZ.com.

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 an AFT05MS004N as driver and a RD70HVF1 in the output. Thus the output FET is very rugged for 25 W continuous operation.

Why not use the RA30H0608M power module from Mitsubishi? Well, the 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.

Parameter12,6 V13,2 VNotes
Frequency range50 - 54 MHz50 - 54 MHz
Output power>44 dBm/25 W>47 dBm/50 W
Input power-6 dBm0 dBmOn-board input attenuator pad. Resistors' wattage limit the drive power
Gain, max50 dB47 dB
Harmonic suppression>70 dBc>70 dBc
Current5,0 A6,5 A
Efficiency39,6%58,2%
ClassABAB

Spectrum performance. Picture courtesy Sergey, EX8MLE.

Frequency response. Picture courtesy Sergey, EX8MLE.

The PA schematic. Picture courtesy Sergey, EX8MLE.