180W Pallet Amplifier Using MRF9180

This is my first time to play with the 180W pallet amplifier kit from China. The kit comes with only a printed schematic but there was no details for the input transformer and the coaxial balun. The bias for the LDMOS is not also indicated so I have to download the datasheet of the MRF9180 from the internet.

The input transformer has a 9:1 impedance ratio so it has a 3 turns in the input while a single turn in the output. Connected to the drains are the 25 ohm teflon cables. This coaxial transformer is responsible for stepping up the low impedance drain to approximately 25 ohms. Next is a 50 ohm cable used to combine the 25 ohm balance signal into 50 ohm unbalance at the output. I choose to cut this cable to 15cm so that pallet operation would be optimal at the fm broadcast band.

The datasheet says that for MRF9180, gate voltage bias may be set anywhere between 2 to 4V but in my amplifier the VGS was set to 2.2V. At full output power, the pallet amplifier is consuming around 8 to 10 amps at 24V dc supply.

After the test, I was getting 150W at 144MHz (2W) drive and 200W at 100MHz (1.5W) drive and this pallet amplifier is remarkably broadband. The test was conducted without the LPF at the output.
--- 73 de du1vss.