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The RF Workbench / U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« on: December 05, 2021, 0519 UTC »
A friend who lives in Europe asked me to design a small transmitter. He has a supply of FT-243 crystals from "the before time" and wants to use them on a small transmitter. I hadn't done much with crystals in years but after doing a bit of looking around, I started looking at the venerable and often used LULU design.
As I looked, there were a number of things that bothered me about them and I could see that there was quite a bit of “low-hanging fruit” that could be easily “picked off the tree” (improved) without a huge effort. In the end, I decided to redo and modernize the LULU for him, making it an updated LULU, i.e., the “U-LULU”. I have added a commercially-available Class-D audio amplifier to make a complete AM transmitter with approximately 20 Watts carrier power output (80 W PEP) in the 48-meter band. This is better than the original LULUs, where output is reported to be in the 10-to-15-Watt range. I decided to publish this design to make it accessible to others.
I regard this as an entry-level transmitter, suitable for those with less building and electronics experience. For the SMD haters, I have purposely used a through-hole TO-220 transistor and larger SMD components. Most capacitors are at least Imperial 1206/1210 [Metric 3212/3225] though there are some 0805 [Metric 2012] components.
Complete write-up is here: https://app.box.com/v/ty24asdfjAEF00
Gerber files zip archive is here: https://wetransfer.com/downloads/0415f9221a49b764d95fb207e143c59e20211205050846/d5a62f
BOM is here: https://wetransfer.com/downloads/9a9d186b74de847f01f336f0f2ee4b0a20211205050536/9d12ab
As I looked, there were a number of things that bothered me about them and I could see that there was quite a bit of “low-hanging fruit” that could be easily “picked off the tree” (improved) without a huge effort. In the end, I decided to redo and modernize the LULU for him, making it an updated LULU, i.e., the “U-LULU”. I have added a commercially-available Class-D audio amplifier to make a complete AM transmitter with approximately 20 Watts carrier power output (80 W PEP) in the 48-meter band. This is better than the original LULUs, where output is reported to be in the 10-to-15-Watt range. I decided to publish this design to make it accessible to others.
I regard this as an entry-level transmitter, suitable for those with less building and electronics experience. For the SMD haters, I have purposely used a through-hole TO-220 transistor and larger SMD components. Most capacitors are at least Imperial 1206/1210 [Metric 3212/3225] though there are some 0805 [Metric 2012] components.
Complete write-up is here: https://app.box.com/v/ty24asdfjAEF00
Gerber files zip archive is here: https://wetransfer.com/downloads/0415f9221a49b764d95fb207e143c59e20211205050846/d5a62f
BOM is here: https://wetransfer.com/downloads/9a9d186b74de847f01f336f0f2ee4b0a20211205050536/9d12ab
), though I have not yet tried to make one yet.