EFHW dipole transformer enclosure

This is an enclosure for an end fed half wave dipole antenna transformer. It is sized for a Fair Rite 264351002 ferrite core and includes a post to hold the core securely. For 3-30MHz, the transformer is a 14 turn transformer wound with 16 AWG wire and tapped at 2 turns – this creates an autotransformer that provides a 49:1 impedance transformation. Ground is the end winding closest to the tap, the radio tap is the 2 turn tap, and the antenna end is the other end of the winding. A 100pF 3kV ceramic capacitor is soldered from ground to the tap. The antenna works well up to 100 Watts or so.

The 264351002 core is type 43 ferrite. For this application, this core form has better performance than FT-240-43 cores and is more compact.

The EFHW antenna is great for POTA use, which is what I designed it for. This small enclosure minimizes the size of the matching transformer. The handle allows it to be attached to a mast or easily hung from whatever support is available.

The other parts are a chassis mount SO-259 UHF connector and two stainless steel M6 or ¼ inch bolts. I used Phillips heads bolts with a washer inside. I printed it with PETG and used organic supports using a 0.6mm nozzle, 0.32 mm layer height, with 20% infill. The lid is held down with M3 inserts (5.7mm length)  and uses M3 X 8 flat head SS screws.

There are two version - one with vent holes and one without.

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