so i finally finished my first scratch built QRP rig, its a 40m CW transceiver based loosely on the Wilderness Radio SST design but i made a few changes along the way because i couldnt source a couple of the original parts. took me about 3 weekends spread over a month and a half to get it done.

the thing that surprised me most is how well 5 watts actually works. ive been licensed for about 4 years but always ran 100w into a dipole and kind of assumed QRP was for people who just wanted a challenge for its own sake. went out to a park last saturday with a wire antenna thrown up in a tree and worked 6 stations in like 2 hours, including one in ontario which felt pretty crazy for what is essentially a mint tin with a few toroids in it.

efficiency wise i was getting maybe 60-65% from the PA stage which i know isnt great, the IRF510 gets warm but not hot. wondering if anyone has played around with different transistors for the final or if its worth messing with the bias to squeeze a bit more out. also curious what antennas people are using for portable operation, i just used a random wire with a tuner but im thinking about winding my own EFHW transformer.

the IRF510 running warm is pretty normal honestly, those things are workhorses but they aint exactly the most efficient FETs on the planet. some guys swap in a BS170 based design for lower power or go with a 2N7000 but if youre pushing anywhere near 5w you kind of need something beefier. have you checked your drive level? sometimes the efficiency suffers because the gate is being overdriven and you get weird crossover distortion that just turns into heat. a little less drive sometimes gives you cleaner output AND better efficiency, counterintuitive but true.

for the EFHW transformer idea, absolutely do it. i wound one on an FT140-43 core, 49:1 ratio, and it works fantastic with about 30 feet of wire. super portable, just a transformer and a wire and youre on the air. takes 10 minutes to put up in a park. thats the whole point of this stuff really, just get out and play radio.

congrats on the build, thats awesome. i'm still kind of nervous to build my own rig, been doing kits (built a KX1 kit last year) but scratch building feels like a different level. ontario from a park with 5 watts though... that's making me want to try harder with my little setup. what state were you in if you dont mind me asking? i always wonder how distance maps onto signal reports with QRP.