I used a large coffee tin and a RF transformer on a high mu core with 90 / 4
turns.
It worked great at LF and MW, but not on the higher frequencies as the
transformer was not designed for that. You could probably try that.
I even tried the body of my car. It worked but due to the large capacitance of the bottom plate to ground, losses were too high. Best regards, Roelof Bakker