|LC combinations can be done with different type
of coils. Most used are cilinder, honeycomb and spiderweb coils. But you
can also make your coil using a toroidial coil. But there are lots of
toroids available made out of different kind of materials. Some are
Iron, Ferrite Mumetal, and lots of compositions of different materials.
For crystal radio use the most used are ferrites, like the FT240-61. Meaning: Ferrite Toroid 2,4inch outer diameter, No61 material. The No61 material is for the frequency range of 0,2-10Mhz.
There are a lot of materials available, with all kinds of final outcome when made a coil useable for the 531-1600Khz AM broadcast band.
A toroid mostly used is the 4C65 or the FT140-61, I tested these toroids, wound using 300/44 litz wire. Combined with my best variable C to get a LC network and measured for Q on different frequencies across the BCB band.
Here i`ve wound toroid type 4C65 using 300/44 litz wire and
type R40C1 with the same litz, but the R40C1 has a second contra wound
Best results in Q where measured using the 4x stacked
R40C1, size 37x23x7mm (small one). A Q of around 1300 at 600Khz and a Q of
around 800 at 1600Khz. But litz wire used in that combination was 660/46.