Kjell,
When I'm in a mood for QRPp, I haul out my Zachtek "Flea" transmitter and the ATS-25 general coverage receiver I use with it. It's only 300mw, on 20, 30, and 40m. It doesn't have to be that particular receiver, I just chose that one because Harry from Zachtek used it for his own Flea and knows it works properly. The Flea handles antenna swapping between the receiver and transmitter, and it has a very imaginative frequency spotting feature that makes it dirt simple to find the transmitter frequency. It's a VERY small transmitter, about the size of an index card. The receiver is actually larger than the transmitter in my case. I power the transmitter using a USB-C Power Delivery battery bank and a 12v trigger cable with the correct DC coaxial barrel plug on it. I have a link dipole for 20/30/40m that's resonant in the CW portion of each band, so I don't even need to tune the antenna, just make sure the correct links are connected.
I used this setup at Field Day a couple of years ago, and was making contacts 800+ miles away from our ham radio club's usual Philadelphia-area camp in a local State Park that has camping. I was being heard quite effectively near the Illinois-Wisconsin border and thereabouts.
For those concerned, the PD setup I use is not plagued with birdies or other noise. I routinely operate out and about using such power supplies. I do have a couple of LiFePO4 12v batteries that I can bring to bear, but they're heavy and bulky, and need special chargers. (Not as heavy as the Sealed Lead-Acid Batteries I was using prior to LiFePO4 availability, but still heavier than a 10-20Ah USB-C PD power bank. I've even operated using the 4,000mAh PD bank I keep in a pouch in my pocket. Works great. I had an article in QRP Quarterly some years ago that showed my first PD trigger board (I found it on Tindie) connecting a compatible PD power bank to one of my original QCX radios. As long as I used the correct size of barrel plug, it always worked like a champ.
But I do seriously recommend the Flea as a very useful QRPp transmitter. It's also relatively inexpensive.?
The software for the Flea was created by Kevin Loughin, KB9RLW. He has a whole series of YouTube videos on the Flea project, from various stages in development. He also operated at Field Day, using a Malahit receiver. Kevin hasn't been doing a lot since he caught Covid and was laid low with Long Covid and is still having difficulty getting back into the swing of things. Here's his video relating his Field Day operations.
Worth a look, even if you never get your own Flea.
73,
Gwen, NG3P
Gwen Patton