300W FM Broadcast Reference Design using the BLF278

The FM300v2 is a broadband 300W amplifier for the FM broadcast band. We've recently managed to source a quantity of used BLF278 transistors at a great price, so have provided a reference design so that a low-cost, high performance amplifier can be constructed from the plans provided here. 

This design is available as a paid download. Files will be available once a purchase is made. 

Features

• Broadband 300W FM broadcast amplifier operating from 87.5-108MHz
• Only 0.5-1W input drive required
• Microcontroller controlled on-board 2-stage thermal and SWR protection 
• Fault output to power down exciter during a fault
• High efficiency - cool running
• High reliability - designed for years of continuous use at 100% duty 
• Low harmonic content, suitable for direct connection to an antenna
• PCB Gerber files and full construction details with parts list provided as a digital download 

Specifications

• Power gain 25dB typical
• Gain flatness +/- 1.3dB
• Output power 320W typical
• Efficiency 68-78% (73% typical)
• Output power 270-345W (320W typical)
• DC Current consumption (main supply) 48V, 8.5-10.5A (9.5A typical)
• DC Current consumption (pre-drive) 12-15V, 1A
• Input power 0.5-1W
• Harmonic output -74dBc typical 

We sell many of the parts to make this amplifier, and full details are provided on the parts list. 

A limited number of PCBs are available here. 

A programmed microcontroller for this design is available here.