HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: DoaJC_Blogger on August 25, 2026, 2137 UTC
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I recently built a Class D AM transmitter mostly from recycled parts aside from the FPGA board for DDS and the MOSFET driver. It was mostly just to see if I could so it doesn't have a filter and you wouldn't want to transmit for real with it. I also used slower Infineon CoolMOS MOSFET's instead of GAN FET's so it gets hot if you try to go above the lower AM band
(https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiG6FEqptJPGacTswKCnJ6W9Tt4LSvdka4IrPDJhQZo6uALwhi0or6eoPDVtrl2cJh-ubcZ4e4DO1Zv0DKLTPSUVtknbHhjNeWuqOBGPynrkpRV38YBHrD9WJmyH140ygLdqcB8vDPHRgTqsLJfdv7V4s1MLiuT7JyeBPNeJZ1waS2gKRFp9aI3NX5qkQPT/s1628/class_d_am_transmitter_schematic_rev0.webp)
An article I wrote with more pictures: https://coolsdrstuff.blogspot.com/2026/08/class-d-am-transmitter-build.html (https://coolsdrstuff.blogspot.com/2026/08/class-d-am-transmitter-build.html)
A video of the output on an SDRplay: https://odysee.com/class_d_am_transmitter_test_20260824:5b4a5b7bbbcb57dcf65cd6c86562fb9d0424d61f (https://odysee.com/class_d_am_transmitter_test_20260824:5b4a5b7bbbcb57dcf65cd6c86562fb9d0424d61f)
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Good experiment - what sort of power output were you getting before the FETs ran out of steam?
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I don't currently have a way to measure that kind of power but I assume that it was at least 50 watts with the 56-volt power supply since it got the 55-watt sodium light hot enough to start tripping the power supply. I don't think I was limited by the FET's
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Looks like youve been inspired by the construction methods from the Class E website!
To measure power, just use a scope and ohms law.
Crusty works!