so ive been lurking on this forum for a while and finally pulled the trigger on building my first QRP rig from scratch. went with a pretty basic 40m single band CW design, nothing fancy, just wanted to understand the whole thing top to bottom before i moved on to something more complicated. took me about three weekends in the garage but i got it oscillating and making contacts yesterday which honestly i didnt think was gonna happen that fast.

anyway the thing is putting out around 3 watts into my end fed and ive been getting some decent reports on 40m in the evenings, made it about 400 miles last night which felt pretty good for 3 watts. but im wondering about efficiency - like the final stage runs pretty warm and im not sure if thats normal or if im losing a lot as heat. im using a IRF510 MOSFET and the drain efficiency seems okay but i havent actually measured it properly, just going by feel and the fact that my 9v battery doesnt die as fast as i expected. also curious if anyone runs QRP portable and what kind of antenna situation they use when theyre out in the field because i want to take this thing hiking eventually.

sorry for the wall of text, main questions are basically: is warm = bad for the final, and whats a good portable antenna setup for QRP

warm is totally normal for the IRF510, that transistor runs hot even when everything is working right. as long as you have a small heatsink on it and its not too hot to touch after a few minutes of keying you're probably fine. if its burning your finger immediately then yeah something might be off in the bias or the matching network. the IRF510 is kind of notorious for being a little finicky but its also super common in homebrewed rigs for a reason - theyre cheap and forgiving enough that you can actually learn on them without destroying something expensive.

for portable antenna i almost always just throw up a random wire and use a small tuner. i built a little L-network tuner that fits in an altoids tin and it handles pretty much anything i throw at it. some guys swear by end feds with a 9:1 unun for hiking since you only need one feedpoint and can just toss the wire over a tree branch. honestly for QRP portable the antenna matters way more than anything else so if you havent already i'd spend as much time thinking about that as you did on the rig itself

400 miles on 3 watts is pretty solid honestly, dont undersell that. i remember my first QRP contact felt like magic even though logically i knew the physics worked out. the warm final thing i cant speak to super specifically but every QRP rig ive used gets warm to some degree, i wouldnt stress it unless youre seeing weird power output drops or the thing shuts itself down.

for hiking ive been using a SOTAbeams linked dipole and it packs down to almost nothing, little bag that clips to my pack. its cut for a couple bands so you dont need a tuner which is nice when youre already carrying a bunch of stuff up a hill. only thing is setting it up takes a little longer than a random wire but the efficiency you get from a resonant antenna on QRP is worth it in my opinion, every fraction of a dB counts when youre running low power