Re: Wire and ferrite baluns

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From: Karl F. Larsen (k5di@zianet.com)
Date: Sat Sep 28 2002 - 15:46:23 CDT


Hi Hugo,

On Sat, 28 Sep 2002, Hugo wrote:

> You can use ferrite to make either a voltage or current balun.
>
> With Iron powder, since the permeability is much less than ferrite, size
> does matter and you can not use a small core.
> The same turns ration don't apply. The desired bandwidth is easier to
> achieve with higher perm cores. Most of the time the price to pay is low
> efficiency, (heat loss), although you see a nice match with the network.
> Speaking of MFJ, they have a reversible L 'mobile' tuner (don't know the
> model, but you might know it), with a coil wound on two stacked ferrite
> cores about 1 1/4 " diameter that matches almost anything with a nice
> bandwidth. If you thing about it, the reason is simply the horrible losses
> in that core that makes it so easy to match to a low VSWR
>
> Also never forget that the core is only necesary for lower bands. The same
> "wideband-cure_it_all" balun (80-10M), doesn't make use of the core's
> magnetic properties on higher bands.
>
> I don't know who LBJ is nor what he or she sells, therefore I can't tell
> whether the design is flawed or you wound it wrongly.

        Sorry, my error. It's a LDG balun and it was shipped with a
powdered iron core and I ran the test where you make a load with 2
series resitors and ground the center. It failed with the powdered iron
core. And passed with the ferrite core.

>
> My point is that you can even make an efficient current (choke) or voltage
> balun with either or NO core at all.

        Yes you can and MFJ has started using no core on some tuners.

>
> It seems to be a confusion amongst some list members on this issue. The
> ARRL Antenna Handbook has plenty of info about transmission line
> transformers.
>
        Yes there is and the ARRL Antenna Book does cover this well.

> 72,
> Hugo
> AA1XV a.k.a. CX9AAK
>
>
>

-- 
                      
               - Karl Larsen k5di Las Cruces,NM Az ScQRPions -


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