I use 31 mix up to 30 MHz (and higher) to good effect.
The real part of the impedance keeps going up to 1GHz (that's the lossy
component)
The imaginary part peaks at about 30 MHz, is decent to 100 MHz, and then falls
off. (that's the pure inductance)
https://fair-rite.com/31-material-data-sheet/
don't forget that Z is mu*frequency, so even though both real and imaginary
parts of my start to roll off at 2MHz, the *impedance*, which is what you want
for a choke, keeps going up.
On Wed, 25 Jun 2025 18:40:46 +0000 (UTC), Kirk Kleinschmidt via TowerTalk
<towertalk@contesting.com> wrote:
John,
The type 31 material is optimized for 160-80 meters. Type 43 is generally used
on the upper HF bands.
I use 8-12 turns through FT-240 cores.
Various online cookbooks may weigh in on that, but it has worked well for me.
Regards,
Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com
and on the Amazon Kindle (soon)
On Wednesday, June 25, 2025 at 12:42:19 PM CDT, John Geiger via TowerTalk
wrote:
The balun I was using on my TGM Communications MQ-26 miniquad died a couple of
months ago. I came up with the idea today of making one myself since I have
some extra RG58 I salvaged from a mobile antenna mount. I plan on running some
turns of it on a FT240-31 ring torrid. Maybe 2 rings, one on top of the other.
I need it to cover 14-50mhz. Any good idea as to how many turns through the
ring I need?
I have found some plans using a FT140-43 torrid but that looks pretty small to
work with.
73 John AF5CC
Sent with [Proton Mail](https://proton.me/mail/home) secure email.
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