> Consider U-cores, such as those in TV set flyback
transformers. These are
> usually high-mu Mn-Zn cores. Check the junk box and ham
swaps, or ask for a
> dead flyback at the TV repair shop (if you can find one
these days!). Ditch
> the burnt-out transformer coil, and you have a large split
core.
I know it's a common hint to use flyback or deflection
cores, but if you measure impedance you'll find the
available 43, 44 and 33 cores are actually much higher
impedance at HF.
You can find high-mu materials in fairly thin wall smaller
diameters that might fit over a small wire or cable, but not
in what we need for larger cables. I know it was suggested
RadioWorks has 73 material snap on beads but I looked and
sure didn't see any. If they were large, I really doubt they
would be effective at HF.
I'm afraid about the best we can do at HF in a large snap-on
bead is 33 material. That why if you look through
manufacturer's catalogs you can't find larger suppression
cores with high impedance. It isn't that they don't want to
make them, they just can't.
The reason we can't buy anything but small-diameter
thin-wall high mu cores that work at high frequencies is
because MnZn cores develop internal resonances that cause
impedance problems. This is why 73 materials and such are
not available in snap-on styles that fit the size harness we
are dealing with. 73 material already has a negative
impedance slope at mid-HF when in a very small core. It's a
disaster in a core large enough to slip over a cable much
larger than RG58.
73 Tom
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