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.
| Parameter | 12,6 V | 13,2 V | Notes |
|---|---|---|---|
| Frequency range | 50 - 54 MHz | 50 - 54 MHz | |
| Output power | >44 dBm/25 W | >47 dBm/50 W | |
| Input power | -6 dBm | 0 dBm | On-board input attenuator pad. Resistors' wattage limit the drive power |
| Gain, max | 50 dB | 47 dB | |
| Harmonic suppression | >70 dBc | >70 dBc | |
| Current | 5,0 A | 6,5 A | |
| Efficiency | 39,6% | 58,2% | |
| Class | AB | AB |
Spectrum performance. Picture courtesy Sergey, EX8MLE.
Frequency response. Picture courtesy Sergey, EX8MLE.
The PA schematic. Picture courtesy Sergey, EX8MLE.
