This page discusses the VHF and UHF pallet amps commonly found on eBay that use pulled MRF-186 LDMOS finals...
Documents for these amps are next to none other than the photo of a generic schematic. I will show you how I built both the VHF and UHF amplifiers and hope to make it easier to understand..
First of all these amplifiers are different from some of the ones you are use to.... to properly drive them to get the rated output you will need a power supply capable of providing 24-28 volts dc at 4-5 amps of current. these can be run with a 12vdc supply but its output will be less than half of the design.
The chip used is a MRF-186 RF MOSFET chip. originally it was designed for 800Mhz to 1Ghz applications but it suites nicely in the VHF and lower UHF ranges as well. this design sets the amplifier up in a push pull configuration. the nice thing with push pull amplifiers is that the even harmonics are suppressed, but the odd harmonics remain so we will still need filtering on its output side to keep the amp in FCC specs (minimal 60 dB total suppression).
Still more to write here soon with full instructions and photos of the build...
soldering of the smd capacitors and the transmission line forward and reverse signal metering
Installing of the transformer and chokes
completed 2m mrf-186 120w Amplifier 24vdc 4a. Will need extra LPF filtering on output to reduce harmonic spurs.
Closeup of the input side of the amp showing the input coupling transformer and the MRF-186 MOSFET
Right: finished amp installed on heat sink with minimal LPF.
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