Posted by
Brett Howard on
Jul 31, 2010; 2:35am
URL: http://elecraft.85.s1.nabble.com/Balun-Questions-tp5328810p5357293.html
Where be your tutorial? I've got a couple 4" #2 cores that I was
thinking of using... Not sure if it'll be the right material but they
sure are big enough that I shouldn't have to worry about power
handling! ;)
It'll probably be a bit before I get to building the Balun project. I'm
in the process of building a full few sets of W3NQN band pass filters.
So far I've built one all the way through and I've got 82dB of second
harmonic rejection. Now I'm in batch mode and I've just finished
getting the connectors on a bunch more project boxes. Also about 91
cores just arrived on the front door step! ;)
Then on top of that I'm working on making a band decoder
(
http://k3decoder.googlecode.com). Needless to say I'm keeping busy
with those projects and the full time job. ;)
~Brett (N7MG)
On Fri, 2010-07-30 at 11:13 -0700, Jim Brown wrote:
> On Fri, 23 Jul 2010 11:53:33 -0700, Brett Howard wrote:
>
> >Interesting enough his high power one uses two cores and appears to be
> >made the same as the "budget" one that is wound on one core... Seems
> >like stacking them on top of one another is going to just couple them
> >and hinder your isolation but maybe I'm wrong there....
>
> No, the only coupling between chokes wound on different ferrite cores
> that provide a complete path for current (like a toroid) is the stray
> capacitance that results from their physical proximity. Virtually ALL
> of the flux stays in the ferrite core -- there is virtually NO leakage
> flux (that is, coupling between coils wound on different toroids).
>
> This is generally true of ALL coils wound on closed ferrite paths.
> Leakage flux (and thus coupling outside the core) occurs when the
> ferrite does NOT complete the path (for example, a coil wound on a
> ferrite bar, also known as a loopstick receiving antenna).
>
> If you want a very good 4:1 impedance tranforming balun for less than
> about 500 watts, consider building one from two of the 12-turn or 14-
> turn THHN chokes shown in my tutorial. Each choke is wound on a #31
> 2.4-inch o.d. core. Total cost about $20 (two cores plus some wire and
> connectors).
>
> 73, Jim Brown K9YC
>
>
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