qrp-gaijin has been working on a 1-meter-diameter small transmitting loop for 7 MHz:
I’ve decided to try constructing a smaller, more traditional loop of 1-meter diameter. A smaller loop means smaller radiation resistance, and that means that small values of loss resistance become more significant. Great care must be taken in all aspects of construction to minimize the loss resistances.
This series of articles will detail the progress of the project.
Project info at qrp-gaijin blog.