The lower the frequency of radio transmission, the more antenna that will be needed in general. [OM0ET] wanted to work the 80M to 20M ham bands and decided to turn to a frame antenna. You can see the project in the video below.
The antenna looks a lot like a magnetic loop antenna. The one in the video has seven loops forming a 520mm square. The loop is, of course, an inductor and by removing some insulation, the operator can clip a lead at different points to control the inductance. A variable capacitor resonates the antenna, so there is definitely tuning required.
The physical support for the antenna is 25mm PVC. It isn’t that hard to build, but does it really work? The video shows quite a bit of detail on the construction, but we are waiting for part two which will show the operating tests. From past experience, we will guess it will work well enough, but the tuning will be sharp, meaning you’ll have to retune a lot when changing frequencies.