I want to made a broadband receiving loop. It will be a one turn
shielded loop of around 2 meters in diameter. The frequencies I want to
be able to receive are the broadcasting band in Europa, LW (153 - 279
kHz), MW (531 - 1620 kHz) and SW (2310 - 25820 kHz). The antenna will have enough gain for the
SW, but less gain on the 2 other bands.

At the base will be a little box with the connection to the loop and a first balun 1:1 symmetrical to asymmetrical. The signal will just do a few centimeters to another box (a big one), and to an adjustable capacitor (a tuning cap from an old vacuum tube radio, so I can have a little motor to tune remotely the frequency of the loop).

I plan to have a preamp, but only for LW and MW. It will have a higher maximum gain at low frequency, and this gain will be adjustable remotely with a voltage.

Is it possible to do a such 1:1 balun with a bandwidth from 150 KHz to around 25 MHz and if yes, how?

Another question is the size of the loop. I try a few coaxial cables to do the loop, and get a self resonance frequency of the loop between 8 to 11 MHz. So, the tuning cap work very well under this frequency, but its effect is hard to define above this frequency. If I decrease the size of the loop, I will get less signal, but the cap will work in a linear fashion on all the SW band. If I keep the same size, it work well, but the effect of the cap is hard to define above the self resonance frequency of the loop. And what about if I increase the size of the loop?


Cheers,
Dominique