[Amps] simple balun (101) questions

[Will Matney]

Dan,

It could be your not using enough core area if it's running hot, etc. The XL for most I would think should around 200 ohms. Calculate that from the inductance of the winding. You are correct though on the math that the turns ratio is 1.41 to match 50 to 25 ohms. However, I've read some on this in some PDF publications on the net about transmission line transformers and seen that that's not quite the case sometimes. The best thing to do is do a google search for Transmission Line Transformers and look for all the PDF files that show up. Most discuss this very thing. There's also a book out named that too and is about making these very transformers. One last thing, look at using a yellow or white core as really red isn't rated for the full band of 2-30 MHz if I recall. Some manufactures dont have white, a few do. I cant remember the details without looking on each.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 3/4/06 at 7:59 AM Dan Sawyer wrote:

>All,
>
>This is a simple balun question. I wish to make a 100 watt 50 Ohm to 
>about 25 Ohm balun for 2 to 50 MHz, I realize that spread may be too 
>large and both ends may not perform well. The input is coax and the 
>output is effectively a dipole.
>
>What core material should I select? (I believe 43)
>
>About what OD diameter core?
>
>How many windings should be on the 50 Ohm side?
>
>How many windings should be on the 25 Ohm side?
>
>Should this be wound as independent windings or as an autotransformer?
>
>I have tried to make a balun with 'red' cores with 10 windings on the 
>input and 7 on the output. This does not behave well at all. There is 
>some signal at the output however impedance measurements are very strange.
>
>Thanks in advance - Dan
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