This means that a version of this antenna using copper rather than the specified aluminium is likely to be more efficient than the prototype. Soldering the loop element directly to the variable capacitor will also improve performance and long-term reliability, especially if the antenna is used outdoors. The reason why this wasn't done in the prototype was due to the difficulty in soldering to aluminium. Use a single piece of metal for the conductor to reduce resistive losses. Make the loop a circle or octagon instead of a square.
Square loops are the easiest to make, but cover less area for a given perimeter than other shapes.
This lowers efficiency. Make the antenna rotatable. The loop's deep nulls can be used to advantage in nulling out interference from power lines, TV sets and other stations. Use a larger loop. Efficiency increases rapidly with loop size.