Norm VE3LC has come into possession of more than 60 Fair-Rite toroidal ferrite cores, part number 2643251002. See:
https://fair-rite.com/product/round-cable-emi-suppression-cores-2643251002/ .
Dimensions are shown at: https://www.fair-rite.com/wp-content/uploads/2020/03/2643251002cat.pdf
Norm wound up one of these cores as a classic 49:1 HF RF transformer ideal for feeding end-fed antennas.
With a 2470 ohm resister load on the output of the 49:1 transformer, I swept the between 2 and 30 MHz using my MFJ-259B and the SWR was less than 1.5:1 on all HF bands.
Suitable wire to wind the core for a RF impedance transformer in the prescribed way can be 18 or 20 gauge enamel insulated wire for up to 100 watts. You will need approximately 45 inches of wire to wind up this RF transformer. These cores would also be suitable for a 1:1 current balun if wound using very small diameter coaxial cable such as RG174 or RG316.
Norm VE3LC will have the toroid cores available at the April 17th meeting for anyone interested along with ceramic 100 pF capacitors. I will also have them available at the Smith Falls fleamarket and afterwards. All proceeds go the OVMRC.
Norm VE3LC
Appears in: Rambler Vol.66 Issue 8