How do I get the transmit side of ESP-SDR actually putting out a signal?

I got mine transmitting last weekend, so I can tell you what my setup looks like. First thing I'd check is whether the pin is actually toggling at all. I put a meter on the output pin and watched the voltage while it was keyed, and on mine the whole thing was dead because I'd left the transmit enable flag out of the build config. The readme mentions it but it's easy to skim past. Rebuilding with that turned in was what got me actual output, so double check your config file before assuming the code is the problem.

Second, a single wire jammed onto the pin will radiate something, but it's a terrible match and most of the energy just turns into heat in the pin driver. Mine started working properly once I added a simple low pass filter between the pin and the antenna, just a few wound coils and caps on a scrap of board. Without it you're dumping a square wave full of harmonics into whatever wire you've got. It also cleans up the signal alot if you ever listen to yourself on another receiver. Power wise, laptop USB is usually fine. I've run mine off a cheap phone charger and off a hub with no brownouts. But watch the serial console while it transmits, if the board is browning out you'll see it reset mid transmission, and that's a dead giveaway. If that happens, try a different cable, half the USB cables people have lying around are charge only or just bad.

For the antenna itself I'm using about a quarter wavelength of wire cut for the band I'm testing on, with the other end floating. Even that crude setup gets a usable signal across the room into a cheap SDR dongle. Before I cut it to length, when it was just a random length of wire, the signal was much weaker and I almost thought the transmit stage was broken.

So in short, check the config flag first, then look at the pin with a meter, then sort out the antenna side. It does work on the current code, mine's been running fine.

One thing that tripped me up for an embarrassing afternoon was the pin numbering, because the silkscreen on my board does not match the GPIO numbers in the datasheet, so I had my wire on the wrong pad entirely and the code was happily toggling a pin I never touched. Worth cross checking which variant of the module you actually have, since the diagrams floating around the repo seem to assume one specific board. I also found that holding the wire near the laptop screen gave me a much better signal into a nearby radio than leaving it hanging, which told me the ground path was doing half the work.

Adding to the antenna talk, don't forget you need some kind of return path. Mine was barely audible til I clipped a second wire to ground as a counterpoise, then it jumped up noticeably. A single floating wire alone is fighting an uphill battle.

Also curious what band you're testing on, since mine behaves differently depending on frequency. Works great low, gets flaky up higher.

Tried this last night with a random bit of wire and got nothing on my little handheld radio, but then I noticed when I held the bare end of the wire with my fingers the signal suddenly came through faintly. Is my body acutally acting like part of the antenna or is that just me picking up stray noise? Feels like a wierd way for it to work better.