Toroidal cores are used in a wide variety of applications such as power input filters, ground- fault interrupters, common- mode filters and in pulse and broadband transformers.
 
These are the cores typically used in 1:49 broad band transformers for 80m-10m End Feed Half Wave Antennas, in conjunction with a 100pf capacitor. These can be used to make a nice portable EFHW transformer for SOTA operations with this kit.
 
Use 1 core for up to 100w output power SSB and 25w CW/Digital modes.
 
Dimensions
35.55mm Wide
12.70mm Thick
23.00mm Hole
 
These smaller cores are trickier to use as a common mode choke then the 240 size.