so i finally finished building my first QRP rig, went with the Pennywhistle 40 kit and honestly the whole thing took me about two weekends to put together. solder joints arent perfect but i did the smoke test and nothing exploded so thats a win i guess. getting about 4 watts out on 40m which is close enough to what the kit specs say.

took it out to the park yesterday with a random wire antenna and a 9:1 unun i had sitting around, made three contacts in about an hour which for 4 watts felt pretty amazing honestly. guy in Tennessee came back to me on the first call which i was not expecting at all.

my question is about efficiency — im running off a 3ah lipo right now and im curious if there's a sweet spot for power output vs battery drain. like does dropping from 4w to 2w actually make a meaningful difference in how long the battery lasts or is the rx current draw the bigger factor when youre doing a lot of listening between calls. i feel like i read somewhere that receive current is actually the bigger drain but im not sure if that was for a specific rig or just general

congrats on the first build, that's always a good feeling when it actually works. on your efficiency question — yeah receive current is often the bigger deal than people expect, especially if you're sitting there for 20-30 minutes scanning around between contacts. a lot of these small QRP rigs pull somewhere in the 25-60ma range on rx depending on the design, and that adds up over an hour of casual operating. your tx current at 4w is obviously higher but you're only keyed up for a few seconds at a time.

if you want to stretch your battery life the best bang for buck is usually cutting rx audio when you're not actively listening, some rigs have a standby or mute function, and just generally being deliberate about when you're keyed up vs listening. dropping from 4w to 2w will help a little but honestly going from 4w to 2w is only 3db which the other station probably won't even notice on a decent band day, so its more of a marginal gain on battery vs a pretty noticeable signal difference potentially. id keep it at 4w and just be mindful of the rx time

nice work getting it on the air. i built a similar kit last year and the park operating thing is honestly addictive, theres something about making a contact on a rig you built yourself with a wire in a tree that just feels different. what antenna length are you running with that 9:1? i had some weird tuning issues with mine until i figured out the wire length was causing problems with my specific tuner situation