wrote:
I've constructed a choke balun from a big toroidal core I had lying
around, abt 3.5 inch O.D., 2 inch ID, unknown material, measures about
125 ohms pure inductive at 7 MHz with 3 turns on it, so I figured that
10 or 12 turns would be an effective 7MHz choke*.

The coax is RG-55 double shielded RG-58 size, solid center conductor,
solid polyethylene dielectric.

I am assuming that this means that the O.D. is about .2 inch.

I wound the coax pretty tightly for neatness; each turn is probably
only 1 inch inner diameter.

Is this too tight? With a 47 ohm resistor in series with the output
wires (I figure about 0.05 microhenries there, it's a few inches of
wire), I get what I think are more or less expected results right now.
I've been playing with one of Reg's programs to see if the impedance at
the input side of the balun jives with the termination, and I think it
does, but I can't just go up up up in frequency with the MFJ-259 to see
if I've affected the *cable* impedance unless I cut off my weather
sealed, heat shrinked, and Anderson Powerpoled coil tap wires and put
on a BNC and terminator.

So I wonder about the longevity of the thing. How tight do you coil
your toroidal choke baluns?

I recently wondered about how such tight turns might affect the
longevity of cable in sunlight, but my concerns were dismissed.

*Another question, figured I'd put it at the end. What's the
impedance/length of the 43 material core that fits over RG-58 down at
7-10MHz. Amidon and Fair-Rite sites have some spot measurements higher
up that I've found, but I'm not turning up charts for all of HF.

Fair-Rite has an impedance versus frequency curve for most of their
shield beads.
http://www.fair-rite.com/newfair/pdf...log.pdf#page=1


I know 43 material is not used so much for low-power HF choke baluns
because of reduced per-bead impedance, but I got a big box of them for
free, so it's just stringing effort on my part to make a bead choke for
40m.

What are their dimensions?

Size 2643012702 (.38" O.D., .25" I.D., .25"L) has a Z of about 12 ohms
at 7 MHz, 15 ohms at 10 MHz.

Size 2643625103 (.625" O.D., .312" I.D., 1.125"L) has a Z of about 80
ohms at 7 MHz, 100 ohms at 10 MHz.