Holidays are over so back to business. The two week heat wave is over so the weather is perfect for spending some more time in the shack.

I’m very gratefull that Owen Duffy (VK2OMD) is helping me my HWEF projects. I’ve un-published some of my HWEF pages where I refer to a 200 Ohm rule of thumb for primary impedance which was just… well… bullshit to be honest. I was calculating inductance using the simplified formula only using number of turns and Al value of the material (e.g. 330 for 52 material) but this is only valid for frequencies up to 500 kHz. From that inductance I calculated the impedance which is also wrong of course. For future projects, I’m using Owen’s calculators:

https://owenduffy.net/calc/toroid.htm
https://owenduffy.net/calc/toroid2.htm

I’m trying to convert that calculations to a spreadsheet and I’m also planning of incorporating the manufacturers material specific parameters that are required in the calculations that give a much more realistic output.

I’m still working on an optimised dual band 80/40 HWEF and a multiband 20/15/10 version. I’m experimenting with 5:35 (80/40) and 3:21 (20/15/10) transformers on a single FT240-52. I might go for 4:28 ratio on two stacked 240-52’s for practical reasons.

For these projects I’m using a true auto transformer so not using seperate (twisted / bifilar) primary turns and also no crossing over. I have reasons to believe it’s unnecessary and it makes the design over complex for no reason. Only one way to find out HI. I’ll keep you updated.

73 Pleun (PA3HHO)