Hi Rich,
You can get a commercial choke showing in excess of 5K Ohm at 28 Mhz, up to 3Kw:
https://myantennas.com/wp/product/cmc-130-3k/
If you prefer to build it yourself, you just need to follow Jim´s Cookbook:
http://k9yc.com/2018Cookbook.pdf
73,
Máximo EA1DDO
www.EA1DDO.es
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Richard
Smith
Sent: martes, 27 de diciembre de 2022 0:53
To: towertalk@contesting.com; Jim Brown <jim@audiosystemsgroup.com>
Subject: Re: [TowerTalk] Wireman W2DU Current Type Balun
I can see that my initial request included far too few details. Thanks for the
many good responses.
The responses were very helpful for me. I'll try to refine my request.
1) Approximately 5000 ohms choking resistance at 10 Meters.2) A design that can
easily handle 1500 Watts into a 2.5:1 max SWR load.
In preparation for my next contest effort, I already have about 30 tasks on my
Task List. I was hoping that a suitable commercially made choke balun would be
available so that I would not have to design and build them. From the responses
to my initial request, it looks like no one on TowerTalk can share any
first-hand experience with the Wireman W2DU choke balun. Also, the Balun
Designs 1115t (which I have purchased in the past) does not have good
performance at 10 Meters.
It seems that I should investigate the commercial offerings, asking:
How many beads or cores?Physical size of the beads or cores?Are they Mix 31 or
43?What type of coax or wire is used internally?What is the Rs of the choke at
10 Meters?
Does that sound about right?
TNX and 73, Rich, N6KT
On Sunday, December 25, 2022 at 12:00:57 PM PST, Jim Brown
<jim@audiosystemsgroup.com<mailto:jim@audiosystemsgroup.com>> wrote:
On 12/25/2022 8:15 AM, Lux, Jim wrote:
> The material datasheet claims 20% uncertainty in the properties
> (although I don't know if that is "run to run" or "piece to piece
> within a run") - They're sintered from a powder, and having just
> looked a a bunch of micrographs of gas line filters made using a
> similar process, i was surprised how much variation there is in that process,
> within a batch.
I accumulated a stock of 100 or so cores purchased from different vendors over
almost 15 years. They included one that was a pre-production sample from
2004-5. As part of my process, I characterized all of those cores by measuring
the "same" winding on each of them, and tabulating complex data at selected
frequencies. Cores were generally not labeled by purchase date, except for
group of recently purchased cores.
After completing work on the Cookbook, I decided to try to evaluate Steve's
recommendations for chokes on #52 material, and purchased 40 of those cores,
buying 10 from four industrial vendors over about 8 weeks.
I repeated the characterization process, selected four cores at limits, wound
and measured chokes based on Steve's designs for single core and two core
chokes. I could not repeat any of Steve's recommendations with those "limits"
cores.
73, Jim K9YC
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