In the past I have used magnetic loop antennas with QRP. Although the RF voltage can be very high in magnetic loops, requiring special high voltage capacitors, this is not an issue with QRP. I have used ordinary variable capacitors or a length of coax if the loop is fixed in frequency.
Loops can be effective antennas when you are restricted for space.
The video is an example of a homemade magnetic loop although there are lots of examples on YouTube.
