Planning a portable field setup and evaluating transformer options for my EFHW antenna. The Fair-Rite 2643251002 has been found to be more efficient than the FT240-43 across the entire HF band, while also being able to handle 100w of high duty cycle modes (such as FT8 or PSK31) for extended periods. The 2643251002 is also considerably smaller at 1.5" diameter versus 2.4" for the FT240-43. Has anyone done direct comparisons between these cores? Looking at efficiency measurements and heat dissipation under continuous digital modes.

Built transformers with both cores last year. The Fair-Rite definitely runs cooler during FT8 sessions - measured 15°C lower after 30 minutes continuous at 75W. Size advantage is huge for backpack portable work.

Colin, MM0OPX's video "Best Ferrite Core For a 100w End Fed Half Wave Antenna" covers this extensively. The efficiency difference is measurable - about 0.3dB less loss with the 2643251002. Worth the upgrade cost for serious portable ops.

Using the Fair-Rite core in my POTA setup with excellent results. No saturation issues even during contest weekends running digital modes. The smaller form factor fits perfectly in a 3x2x1 enclosure versus needing the bulky 4x4x2 box.