Anyhow, some time back I picked up all the 15.2X8.53X5.94 toroid cores, L4517 the local Aztronics. They sell from the Altronics catalog. So these cores are not standard sizes or models that are used in HAM radio, so far that I can make out. They are pretty close to a T50-2, as they are supposed to be iron core, but are a bit larger diameter. Using 0.5mm/24bs enameled copper wire, WW4016, from Jaycar, I've spread the turns out over at least 80% of the toroid, values as follows;
- 10 turns gives 0.001mH
- 20 turns gives 0.003mH
- 25 turns gives 0.005mH
- 36 turns gives 0.012mH - for 3.5MHz BPF
I could probably squeeze on another 5 turns, but 10-36 turns covers the inductance that I need right now. Perhaps other gauges of wire will yield other usable values. These toroids as they are setup are intended for low pass filters or band pass filters. The Pixie 2 needs just one in its current configuration. I intend to build up a better filter as there is lots of AM broadcast signal there when down on the flat in Adelaide.