[TowerTalk] Balun dimensions

[Jim Lux]

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 at 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

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