Utilising LDMOS - MRFX1k80H
Having had great success with my HF LDMOS amplifier I decided to build a new amplifier dedicated to 50 MHz.
The path of least resistance led me to decide on using the VK-AMPS LDMOS HF/50MHz pallet with the MRFX1k80H device.
I decided against the VK-AMPS controller for this amp and instead purely wanted a simple way to control my amplifier and this led me to deciding upon W6PQL's controller board ( +Sequencer). I also ended up using W6PQL's LPF, input RF attenuators, LED PWR indicators, High current FET switches, Input and output relays.
By utilising W6PQL's controller / sequencer there is analog based shutdown circuitry to protect the amplifier in case of :
- High SWR / Load fail
- High / Overdrive on the Input side
The instantaneous shutdown of the amplifier under these "failure" conditions was extensively tested and should be better than any "software" controlled approach.
The amplifier was setup to run off 58V DC and will produce as much as 1200W PEP with 7.4W drive to the RF pallet at an efficiency of 65%.
Other measurements:
2.3W drive produces 400W PEP
5.1W drive produces 1000W PEP
The efficiency of the amplifier is governed to a large extent on the length of Coax between the output of the RF PA board and the input of the LPF. After much experimentation, I found 335mm of UT141 was needed between the VK-AMP HF/50MHz pallet and the W6PQL 50MHz LPF.
As with all these amplifier projects, once the electronics and RF testing was completed, a substantial amount of time is spent on the metal work!
