Spam ? - Winding High Q Toroid Inductors

[Richard O'Neill]

"The toroids will be wound with Litz wire so we don't want to waste any expensive Litz if possible."

Hi Mike,
 Several members of the crystal set building fraternity have experimented with ferrite toroid core coils for LF and MW frequencies. Our experiences have demonstrated a significant variation in core properties among different production runs and manufacturers. Our MW ferrite toroid coil Q's typically measure in the 250-350 range but some have measured as low as 150.
 
 I suggest winding with solid wire first, then rewinding the same core with litz - once the correct number of turns have been determined. If your goal is a specific inductance and high Q this procedure should be done for each core to avoid the need to tweak the number of turns and possibly waste expensive litz wire.

 Another important factor to consider is the introduction of a small space between toroid and wire (litz or solid). This space helps to reduce proximity losses and maintain a higher Q at the upper end of the frequency range. Without the space coil Q can be relatively high at the low end but drop dramatically as frequency is increased. As always YMMV.