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the design of toroidal baluns - request for resources

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odyseus

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Does anybody have any links/articles on te the design of toroidal baluns used for impedanced transformations (ie balanced to unbalanced)??
 

Chinaski

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Hi Odyseus,
Nice to talk with you again :smile:
In FM Chinasky folder you can find two app. notes about the design of broadband HF transformers using ferrite cores. The main parameter is Al (inductance/turns) and it depends on the shape of the ferrite core.
You have to go to the sites (amidon, philips, etc...) and select the material and the shape.
The _BOOK_ about this is
"Transmision Line Transformers"
Jerry Sevick, W2FMI
Noble Publishing
It's a cheap book ($39)and you can buy it through the ARRL (www.arrl.org)
There is another little book from the same author
"Building and using BalUns and UnUns"
but I cannot say anything about it because I havn't got it. It's cheaper ($19.95) and it seems to be a practical approach
To buy ferrites I use Barend Hendriksen site
(www.xs4all.nl/~barendh/)
Hope this helps
 

odyseus

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Hi Chinasky

Thanks for! that I also use Barend Hendrikson in Holland as they are the best place in Europe to get RF parts....
 

unkarc

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Dear Odyseus,

I would like to tell two Motorola Application Notes on this topic, as an addition to Chinasky's very good offerings from the Philips side. See url
http://www.maneapc.demon.co.uk/motorola/appnotes.htm and look for AN758/D at the very bottom of the long list. Also see url http://e-www.motorola.com/rf/apnotes/rfifappnotes.html and look for AN721/D.

In building wideband RF baluns, the main difficulty usually is to make a transmission line with the needed characteristic impedance. For up to a few tens watts of RF power these lines can be made from twisted enameled copper wires. The point is how tightly you twist 2 or 3 paralled enameled wires because the characteristic impedance varies with the tightness of the twist. The more tightly you twist, the less characteristic impedance you get and also as the wire diameter increases, the char. impedance also decreases. The practical lower limit that is reachable with a diameter of 0.6-0.7mm wires which are very-very tightly twisted together is around 18-20 ohms. To receive lower than this characteristic impedance for a line, you have to use copper stripes unfortunately. Of course, if the toroidal core (what you have or can afford or have space for a higher size core) takes two identical twisted lines mechanically, you can connect them paralel and this way you can half the characteristic impedance.
These are in nutshell on the practical aspects.
On the lower impedance side of a toroid transformer (or balun) you can measure the inductance of that side with the other side open. (Of course if the balun is 1:1 in ratio, then both sides are equal in inductance.) The rule of thumb here is that the inductive reactance (X-L) of the lower impedance side should be 4-5 times ohms larger than the the lower impedance itself. This gives the lower limit on the permeability of the core. Practical wideband transformers with frequency ranges from 2MHz to a few tens of MHz should have a toroidal core with u(mu)=around 700-800. For higher frequencies the u is around 120-200.

I hope these thoughts are of some further help.

Regards

unkarc
 

Chinaski

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Hi all,
That's rigth, I forgot Motorola :sad:. Diving into my old catalogs I have found another app. note from motorola book "RF Application Notes" It's AN749 -> "Broadband transformer and power combining techniques for RF" I think it's not available in electronic form so I'll scan it tomorrow or perhaps netx monday.
Good luck
 

Chinaski

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Hi all,
That's rigth, I forgot Motorola :sad:. Diving into my old catalogs I have found another app. note from motorola book "RF Application Notes" It's AN749 -> "Broadband transformer and power combining techniques for RF" I think it's not available in electronic form so I'll scan it tomorrow or perhaps netx monday.
Good luck
 

Chinaski

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Hi all,
an749.pdf scanned and uploaded to Chinasky folder.
Good luck


<font size=-1>[ This Message was edited by: Chinasky on 2001-11-16 11:20 ]</font>
 

Chinaski

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Just to pop this topic up :smile:
 

unkarc

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Hi all,

That is right, the AN749 so far has not been available in any file format but in print. Thanks for taking the burden of preparing it to PDF, so I can also add it to my collection.

To revise my thoughts, I was a bit optimistic on getting as low as 18-20 ohms characteristic impedance with tightly twisted enameled copper wires. The correct value unfortunately is around 25-27 ohms.
Also a small revision: I did not mention that the frequency to be considered in calculating the minimum inductive reactance at the lower impedance side is the lowest frequency to be covered by the balun/transformer.

Regards

unkarc
 

Needbias

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Whoever has advice of making a pratical microwave balun used in microwave mixer just like WJ's M14,thx
 

bingoboy

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Hi, i have any pdf-s.
I upload them when i recive access to FM.

Regards.
 

Needbias

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Hi,bingoboy:
Thx you very much,but I want to get it now ,can you pm it to me?
 

dr_amos

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Hi IBall
thanks for the PDF files !
 

Needbias

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Hi IBall ,
Good job,thx for your help!
 

darksky041257

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Have a look at the ARRL handbook.

This is a great source of all kinds of info.
 

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