Current transformers with resistive loads are examined experimentally to determine some of the limitations to high frequency response. Coil resonances are avoided by placement of damping resistors around the secondary winding. This permits a relatively large number of secondary turns (50 or 100), improving low frequency response and increasing thei×tproduct, even for the highest frequency transformers. Uniform response to several gigahertz is obtained in a transformer with 6.4 mm window, while a range ∼1 Hz to ∼300 MHz is found in a larger transformer (12.7 cm diam and 2.5 cm window). Both ferrite and iron alloy cores are utilized.