Jimmy and all,
I wanted to get to this question earlier, but have been swamped.
W2FMI in his latest book does a superb job of going over the history of
baluns. Everyone should at least get this book if for nothing else then
to learn about baluns.
I am guessing that Mr. Weierich is asking the question based on this
book.
The Baluns Dr. Sevick recommends for current baluns is actually the W1JR
Reisert design. This uses low permeability ferrite (61 material) that
has very very low loss at HF, unlike the beaded balun design which must
use high permeability beads to achieve the choking reactance in a small
length.
Due to the Torroidal design of the W1JR design you get a N**2
transformer turns ration multiplier to achieve the choking reactance,
and you can do it in a very small space, as well as being able to use
the proper low permeability ferrite.
I am not going to go into the hybrid bead argument, or other wierd balun
designs.
The coiled up coax is a very good design as well if done correctly as
discussed by Tom W8JI. It just takes up more area. The reliablity is
there, as well as in the W1JR desgin. Beads are problems waiting to
happen. But fitted to the proper matched antenna they will work too.
Now Dr. Sevick continues in this book to show how you can use an UN-UN
RF transformer such as a 2:1 properly designed unit and mate it to a
properly designed BAL-UN 1:1 to make a hybrid UN-UN-Bal-UN to feed say a
25 or 100 ohm antenna element to 50 ohm coax. This is a different
subject. But can be done with very low loss if the RF transformer uses
the correct ferrite and transmission line winding. It will also have low
flux and not saturate, nor heat. But done wrong, you will have loss and
heat, and possibly exceed the curie point. Just like the beaded baluns
will do on a mismatched antenna.
Jay, WX0B
Jimmy Weierich wrote:
>
> Tom,
>
> I rarely see transmission line transformer baluns, a la W2FMI,
> mentioned on this reflector. Is there a reason for this other than
> their relative construction complexity? How, in your opinion, do they
> fare versus bead or coaxial cable baluns?
>
> Best regards,
> Jimmy
>
> --
> Jimmy Weierich, KG2AU <kg2au@stny.rr.com>
> Vestal, NY USA FN12xa
>
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Jay Terleski
Array Solutions - RME Filters
Phased Arrays - Horizontal and Vertical
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