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GPT5 Reads Schematics,Does Simple RF Analysis!

 GPT5 helped me understand how the Tuna Topper ][ amplifier in Project TouCans operates yesterday. It started from just this clip of the schematic!


While debugging the power supply relay of Project TouCans a few days ago, I noticed an interesting thing. With the Pico-W rig controller plugged into the supply brick TouCans itself was only being doled out twelve volts by the phone charging brick in its base, not the fifteen volts its USB-C adapter was asking for. That mattered the most to the Tuna Topper II amplifier that drives the five watts to the antenna.

I changed the rig so that, for now,  the Pico-W runs on three AA batteries. That upped the supplly to the rig back to its intended fifteen volts. I wanted to understand in broad terms what that meant for the power output of the rig. I tooled around for a bit on paper and spreadsheets before it occurred to me to ask GPT5. I didn't expect to get an answer at all. I definitely didn't expect it to be able to read the schematic above when asked it, 

"For the attached schematic of a class C amplifier using a single FET and the transormer shown, what is the voltage swing at the output of C14?"

But, it came back with 


When I asked about the bandwidth-gain product for the specific transistor, it came back with 



it continued



and we were off to the races.

About half an hour later, I had learned about class C amplifiers, I'd learned that the experimental observations we'd made—that increasing the bias voltage on the gate of the transistor had increased output power—were correct, and that the STP16NF06 isn't actually intended to be an RF amplifier, but it will do at lower frequencies. I knew what the conduction angle was and why increasing the bias increased the angle which in turn increased the power output while at the same time decreasing the efficiency of the amp! I was reminded what transductance was and why it mattered. I learned a lot!


GPT5 also created graphs from a model of the transistor that show how output power varies with gate bias voltage and input frquency—we operate the amplifier at 14.0574 MHz—at both power supply levels, the 15 volts the radio was supplied with this week and

the  12 volts that we were unintentionally using for the last year or so



GPT5 knows a bit about RF engineering and can read schematics! Frankly, i didn't expect it to be able read the schematic!

If you'd like to play with the model, and I'm very interested in any issues that I missed, please do here.


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