- a bigger loop is a more efficient loop
The optimum diameter of a loop is frequency dependent
- You can make loops using standard plumbing parts
Yes, you can but the more solder you use the higher the resistance of the loop i.e. the higher the losses and the lower the efficiency. There should be a minimum of soldered joints and silver solder or brazing should be used instead of normal solder. Thais also applies to connections to the capacitor.
- You can use an ordinary variable capacitor
You can but there will be losses where the rotor connects to the terminal tag. Solder coax braid to bridge the connection.
- Loops can be made to cover 80m – 10m
They will tune over a wide range assuming that you can find a capacitor of the correct range but the efficiency will be ridiculously low at the longer wavelengths. For best performance you need to have loops optimised for specific bands, 80m&40m, 30m,20m & 17m and another for the higher HF frequencies. And remember just because a loop ‘tunes’ does not mean it will work as a radiator of RF.