I’m very exited to tell you that I’m working on a new 100W HWEF transformer design based on smaller 52 mix ferrite cores. I’m also happy to inform you that Owen Duffy (VK1OD) himself is helping and advising me in the process. As I’m still experimenting I will not publish any results yet but I it’s looking very promsing.
To bring core losses down to 0.2 dB (theoretical), I’m using the lower permeability mix 52 ferrite cores instead of the popular 43 mix. Problem with 52 mix is that the magnetising impedance on lower frequencies is lower. To overcome this, I’ve stacked 2x FT140-52 (36mm, AL=283) cores and put 4x FT82-52 (21.5mm, AL=151) inside. This compilation should theoretically boost up the total AL to 1170 which is higher than a 3xFT240-52 QRO design. Of course it will not be able to handle as much power, but in Europe, many hams do use their rigs barefoot (100W PEP).
I’ve wound the core with 3:21 ratio to get even more magnetising impedance on lower bands. Tests of the prototype seems to work very well on 40m but still needs to be tested with a capacitor on the input to control the flux leakage on higher frequencies. I’m planning on doing that first, then maybe add another FT140-52 and two more FT82-52’s to get total AL=1755 boosting up the magnetising impedance on 80m.
Here’s the HWEF test center on “the 4th floor” of my house HI.
Will keep you updated!