3T Toroidal Chokes
A toroidal choke design with a self-resonant frequency to enable shimming through DC on 3T RF receive loops. Able to be made by hand with a 3D printer and magnet wire.
The choke consists of a 3D-printed toroidal core wrapped with 22 AWG magnet wire. For our models, we used cores printed on the Dimension sst 1200es with ABS filament and BELDEN 8051 22 AWG magnet wire. Cores measure 8mm ID, 16 mm OD, and the wire wraps as many times as can fit on the core. In addition, each end of the wire wraps once more around the core (external to the first winding) to add capacitance and inductance.
The chokes show a consistent self-resonant frequency of 150 MHz. (NOTE: This is worth confirming when hand-winding, as we have an unsolved issue where certain chokes have an SRF of 2/3 the SRF of others with the same design.)