I have used my old 400W PA for 432MHz for several years, but since it never was built into an enclosure, it was obvious to make a brand new 1000W PA instead. I had a surplus Plish 2000W water-cooled PA ready to rebuild for 432MHz. It’s quite large, and imposible to find enough room for on the shelfs in my little shack. So I decide to make a more compact version. -and 2000W is also more than needed.
I found what I was looking for, – a 1000W 432MHz PA based on LDMOS for 50V. I also found a Huawei R4850G 3000W 50V SMPSU.
During the fall 2021 I found an nice heatsink I believe will fit perfect for 600W dispatched from the amplifier, but fans will be needed for sure.
After some blue smoke from the first 2 x 600W pallets, I decided to buy a ITALAB MD1K-432 pallet. Unfortunately an expensive solution, but this pallet is used in TAJFUN 1000 432 MHz for some years, I therefore assume quality is proven to be okay. LDMOS used in this pallet are MRFE6VP61K25HR5.
I have experienced during tests that RG400 is to losy for 432MHz 1kW, and get’s extremely hot, so I’ll replace it with some 1/4″ semirigd that was left from my 1296MHz PA project. Enclosure has also been found. For this project I decide not to use a surplus solution, as the surplus enclosures I had, was either too big, or too small. I found a 19 “rack-mounted enclosure at RS that just fits perfect into this project. Link to the enclosure by clicking on this line
At the shelf I had other good parts for this project:
- High power directional coupler (same as used at my 1296MHz PA)
- High power coax realy “RCT RDL-SR012” rated for 800W at 432MHz
- W6PQL sequenzer “The Ultimate Amplifier Control Board” version 6.3
Amplifier is now up running, hope it can withstand the harsh handling when I participate in NAC and hunting DX 🙂
Below is some pictures from the project
25-30W Input give 750-850W output in CW
Update 13.04.2025: I have now burned two MRFE6VP61K25H LDMOS and decided to try something different. I purchased an ART1K6FH and mounted it on the ITALAB pallet. I chose this because I found that it is used in the Gemini 70-1K (1000W, 432MHz). Both LDMOS types are unmatched versions, but data on the ART1K6FH indicates it’s more robust than the older MRFE6VP61K25H.
After testing and a lot of adjustments of both the inlet and outlet striplines, I ended up making only minor changes. The inlet stripline remains unmodified, and the SWR is around 1:1.6, which is acceptable. On the outlet stripline, I removed the 15 pF capacitor near the LDMOS and added a 3.3 pF ATC capacitor next to the 1 pF capacitor near the output end.
Current Data:
- Input: 22W → Output: 1000W = 16.6 dB gain
- Bias: Set to 2 x 600 mA, it increases to 2 x 1500 mA as temperature rises
- DC Input: 30A @ 55V = 1650W
- Efficiency: 1000 / 1650 × 100 = 60.6%
Special Thanks: A heartfelt thanks to Knud OZ1DGN for providing many valuable inputs and for his patience with my limited technical skills throughout the tests and changes.