From FB group Building Transistor Radios
Jim Glover
You asked about performance. There are factors unrelated to either type that affect the performance, one being the type of wire used. If Litz wire is used it has lower losses, and therefore higher Q than solid wire. Same holds true for silver plated wire at HFs. The area of the coil determines the amount of signal captured, but at AM broadcast frequencies the limitation is background noise, so capturing more signal also captures more noise.
The best antenna, no matter what type, is higher off the ground and away from man made noise. Outside is better – there is some signal loss inside bldgs.
Also you can reduce the number of turns in the loop and use more capacitance. But variable capacitors can be excessively large. So the air variable in older sets is a compromise, and the polystyrene variables in small radios are even lower capacitance, and demand more inductance to tune the AM band.
So all your designs face some compromises that will be made. It’s up to the designer which compromise will be made. And for most designs it’s compromises that give small size.
