...under perpetual construction.
Under construction...
This is a hybrid coupler similar to the design presented in the ARRL handbook; only I did not have an FT-23-77 core as recommended in my junkbox, so I used an FT-23-43 with more turns (15 turns instead of 10, as recommended for the 77 material), to keep at least the low-frequency response unchanged.
No pretty PCB was built, I just jury-rigged some right-angle SMA together...
I have measured the coupler S-parameters on a multiport network analyzer:
Its performances are not bad, works well until about 400 MHz.
This is the hybrid coupler directivity: