Bifilar or just an easy center tap?

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Bifilar or just an easy center tap?

Postby kb3vuk » Sat Dec 29, 2012 6:38 pm

One goal of this project is to learn more about magnetic components - the term 'bifilar' was a new one to me. After researching the term and comparing its definition to the use on the schematic, I get the impression that constructing the coils as described is just an easy way to create the center tap?
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Re: Bifilar or just an easy center tap?

Postby AE9RB » Sat Dec 29, 2012 7:37 pm

The bifilar technique is important. Especially on the toroids. If you need to prove this to yourself, experiment with T2.
73 David AE9RB
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Re: Bifilar or just an easy center tap?

Postby kb3vuk » Sat Dec 29, 2012 10:56 pm

I certainly wanted to know what made it different from conventional winding techniques and how it works.

Some stuff I found digging though the pdf collection helped explain it.

( Troubleshooting Analog Circuits )
"Tightly-coupled windings, both bifilar and twisted pairs, have much better magnetic coupling and less leakage inductance than do well-separated primary and secondary windings. As the magnetic coupling improves, the capacitance between windings increases-but high capacitance between windings is often an undesirable effect in a transformer."

( Electronics dictionary)
"bifilar transformer A transformer in which unity coupling is approached by interwinding the primary and secondary coils (i.e., the primary and secondary turns are wound side by side and in the same direction).

bifilar winding 1. A method of winding a coil (such as a resistor coil) in the shape of a coiled hairpin so that the magnetic field is self-canceling and the inductance is minimized. 2. A method of winding transformers to minimize leakage reactance."

"Broadband transformers are often called transmission-line transformers because they make use of the transmission-line properties of the windings. This is done by using bifilar trifilar-type windings rather than the conventional type of winding.
A conventional transformer usually has two entirely separate windings. That is, one of the windings is usually wound onto the core first and, then, the other winding is wound on top of the first winding. Typically, the larger winding is wound first for convenience. This winding technique is shown in the toroidal transformer diagram of Fig. 7-27. Note that an impedance transformation occurs between the primary and secondary of the transformer. The value of the transformation is dependent upon the turns ratio from the primary to the secondary. Transmission-line transformers use an entirely different technique for the windings, as shown in Fig. 7-28. First, the primary and secondary windings are made by twisting the wires together for a certain number of turns per inch (Fig. 7-28A).

This produces a certain characteristic impedance for the resulting “transmission line” in much the same manner that a coaxial cable exhibits a certain characteristic impedance which is dependent upon the spacing of its center conductor to its outer conductor. The actual characteristic impedance of the twisted pair is de- pendent upon the number of turns per inch, the shape of the windings, and the size wire used. For low-impedance lines, tight twists (many turns per inch) are used while high-impedance lines may not be twisted at all. Instead, the windings will be placed side-by-side around the core. For optimum operation, the characteristic impedance of the winding should be equal to:"

Z = Sqrt(Primary Impedance * Secondary Impedance)
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