W9SCH described this small loop in Sprat 60 and it has proved useful to the QRPer, especially where space is at a premium.
It is basically a variant of the usual magnetic loop, using a toroid balun to get a reasonable match on the three bands.
A slow motion drive would prove useful on the tuning capacitor, which is a 100 pF airspaced variable. The lamp is used to tune the loop.
Depending on local environment, it may be necessary to experiment with the dimensions of 33" square and the turns on the toroid.
Using this indoors, the author worked several thousands of miles with QRP.