## How To Make A 4-1 Balun On A Single Core

4-1S Inductive-loop dilution-finding antenna, where

A is the length of each side in centimeters (cm) B is the width of the coil in centimeters (cm) N is the number of turns in the coil (close wound)

ft* and AT„ are 0.008, 1.4142, 0.37942, and 0.33113 respectively.

Whenever conductors are placed side by side, as in the case of the loop-wound coil, there is a capacitance between the conductors (even if formed by a single loop of wire, as in a coil). This capacitance can be significant when dealing with radio circuits. The estimate of distributed loop capacitance (in picofarads) for square loops is given by Bramslev as about 6G4, where A is expressed in meters (m). The distributed capacitance must be accounted for in making calculations of resonance. Subtract the distributed capacitance front the total capacitance required in order to find the value of the capacitor required to resonate the Loop-wound coil.

Binocular- ("balim" or "bazooka") core inductors

The toroidal core has a certain charm because it is easy to use, is predictable, and is inherently self-shielding because of its geometry. But there is another core shape that offers very high inductance values in a small volume. The binocular core (Fig, 4-1G) offers very high A\, values in small packages, so you can create very high inductance values without them being excessively large. A binocular core that uses type 43 ferrite, and is about the same weight arid size as the T-50-43 (A\, — 523), has an value of 2890. Only 8,8 turns are required to achieve 225 on I his core.

There are actually two different t.y|>es of binocular core Ln Pig. 4-lfi. The Type 1 binocular core is shown in Fig. 4-1GA. It is larger than the type 2 (Fig. 4-16B) and has larger holes. It can, therefore, be used for large rvalue inductors and transformers. The Type 2 core can be considered as a two-hole ferrite bead.

l.D,

4-16 Bazooka baJun cores: (A) Type 1 arid (B) Type 2

Table 4-8 shows several popular-sized binocular cores and their associated A^ values. The center two digits of each part number is the type of ferrite material used to make the core (e.g., BN-xx-202), and the last digits refer to the size and style of the core.

Three different ferrite materials are commonly used in binocular cores. The type 43 material is a nickel-zinc ferrite and has a permeability of 850, it is used for wideband transformers up to 50 MHz and has high attenuation, from 30 to 400 MHz. It can be used in tuned RF circuits from 10 to 1000 kHz. The type 61 material is also nickel-

Tfebie 4-8. Binocular cores

Part no. Material 4 L value Size Style

BN-43-2Q2 43 2890 A 1

BN-43-2402 43 1277 C 1

BN-43-3312 43 5400 D 1

BN-61-202 61 425 A 1

zinc and has a permeability of 125, It offers moderate to good thermal stability and a high Q over the range 200 kHz to 15 MHz. It. can be used for wideband transformers up to 200 MHz. The type 73 material has a permeability of 2500 and offers high at-tenuation from 500 kHz to 50 MHz.

The binocular core can be used for a variety of different RF inductor devices. Besides the single, fixed inductor, it is also possible to wind conventional transformers and balun transformers of various types on the core.

Figure 4-17 shows TVpe 1 binocular cores wound in various ways. The normal manner of winding the turns of the inductor is shown in Fig. 4-17A; the wire is passed from hole to hole around the central wail between the holes. The published Al values for each core are based on this style of winding, and it is the most commonly used.

An edge-wound coil is shown in Fig 4-17B. In this coil, the turns are wound around the outside of the binocular core, To checK the difference, E wound a pair of BN-43-202 cores with 10 turns of no. 26 wire; one in the center (Fig. 4-17 A) and one around the edge (Fig. 4-17B). The center-wound version produced 326 p,H of inductance, and the edge-wound version produced 276 jlH with the same number of turns.

Counting the turns on a binocular core is a little different, than you might expect, A single U-shaped loop that enters and exits the core on the same side (Fig. 4-17C) counts as one turn. When the wire is looped back through a second time (Fig. 4-17D), there are two turns.

### Winding the binocular core

Some people think that it is easier to use these cores than toroids, and after spending a rainy weekend winding LF and AM BCB coils (after pumping groundwater out of the basement workshop!}, 1 am inclined to agree partially. The "partially" means that they are easier to work than t oroids if you do it correctly. It took me some experimenting to figure out a better way than holding the core in one hand and the existing wires already on the core in another hand and then winding the remaining coils with a third hand. Not being a Martian, 1 don't have three hands, and my "Third Hand" bench tool didn't seem to offer much help. Its alligator clip jaws were too coarse for the no. 36 enameled wire that I was using for the windings. So, enter a little "mother of invention" ingenuity (it's amazing how breaking a few wires can focus one's attention on the problem). In fact, I came up with two related methods between gurgles of my portable sump pump.

The first method is shown in Fig. 4-18. The binocular core is temporarily affixed to a stiff piece of cardboard stock such as a 5 X T card or a piece cut from the stiffener used in men's shirts at the laundry. The cardboard is taped to the work surface, and the core is taped to the cardboard. One end of the wire that will be used for the winding is taped to the cardboard with enoi^gh leader to permit working the end of the coil once it is finished (2 to 3"). Pass the wire through the holes enough times to make the coil needed and then anchor the free end to the cardboard with tape. If the device has more than one winding, make each one in this manner, keeping the ends taped down as you go. Once all of the windings are in place, seal the assembly

4-1? Winding styie for Bazooka baton cores; (A) through the center; (B) around the edge (less-predictable inductance); (C) single turn winding (note: no doubling back); and (D) tw<>-tum winding.

with Q-Dope or some other sealant (RTV silicone, rubber cement, etc.). Q-Dope is intended /or inductors and can be purchased from G C dealers or by mail from Ocean State Electronics {P.O. Box 1458, 6 Industrial Drive, Westeriy, Rl 02891; phone 1-800-866-6626 (orders only), 401-596-3080 (voice) or 401-596-3590 (faxM.

The second method involves making a header for the binocular core. This header can be permanent and can be installed into the circuit just like any other coii with a header. When built correctly, the header will be spaced on 0.100" centers, so it is compatible with DIP printed circuit boards and perforated wiring board. I used

Tape to

Tape to

perforated wiring board of the sort that has printed circuit, pads (none of which connected to each other) at each hole.

Figure 4-19A shows the basic configuration for my homebrew header (a DIP header can also be used). These connectors are intended to connect wing or other components to a DIP printed circuit board designed for digital integrated circuits. I found that a small segment of printed periboard, 0.100" centers on the holes, that contained five rows by nine columns of holes (see unset to Fig. 4-19B) was sufficient for the 0,525 X 0.550" BN-xx^OS. Lai^ger or smaller hole matrices can be cut for larger or smaller binocular cores.

The connections to the header are perfhoard push terminals (available any place that perfboard and printed-circuit making supplies are sold). 1 used the type of perf-board that had solder terminals so that the push terminals can be held to the board with solder. Otherwise, they have a distinct tendency to back out of the board with handling.

When the header is finished, the binocular core is fastened to the top surface of the header with tape, then the pins of the header are pushed into a large piece of perfboard. This step is done to stabilize the assembly on the work surface. It might be a good idea to stabilize the perfboard to the table with tape to keep it from moving as you wind the coils.

Once the header and core are prepared, then it is time to make the windings, Scrape the insulation off one end of the wire for about 1/4". An X-acto knife, scalpel,

Binocular core

Binocular core

9 holes

 1 f° G o o o o o o o 6 b O o o o o 0 o o holes J O o o o o o o o o o o o 0 0 o o 1 u o o o o B o o Q o

4-19 Construction of a perfboard carrier or header for Bazooka balun cores.

or similar tool can be used to do this job. TUrn the wire over several times to make sure that the enamel insulation is scraped around the entire circumference. Some people prefer to burn the insulation off with a soldering iron, which tins the end of the wire as it burns the insulation away. IVe found that method to be successful when the smaller gauges are used, but when good-Quality no. 26 or larger wire is used, the scraping method seems to work better. If the scraping method is used, then follow the scraping by tinning the exposed end of the wire with solder. Each winding of the transformer can be made by threading the wire through the core as needed. As each winding is finished, the loose end is cleaned, tinned, and soldered to its push terminal. After all windings are completed, then seal the assembly with Q-Dope or equivalent.

### Homebrew binocular cores

You can build custom "binocular cores" from toroidal cores. The toroids are easily obtained from many sources and in many different mixtures of both powdered iron and fenite. You can also make larger binocular cores using toroids because of the wide range of toroid sizes. Actual binocular c ores are available in a limited range of mixtures and sizes. Figure 4-20 shows the common way to make your own binocular core: Stack a number of toroid cores in the manner shown. It is common practice to wrap each stack in tape, then place the two stacks together and wrap the assembly together. Although four toroids are shown on each side, any number can be used.

A variation on the theme is shown in Fig. 4-21. This binocular core is designed to have a single-turn winding consisting of a pair of brass tubes passed through the

 ( ' ^ t I f i \ J —"————_} I Stacking toroid cores to make a higher-power Bazooka balun. Torotd cores ft Brass tubing Brass tubing Rear panel 4-21 Construction of the high-power Bazooka bajun core with stacked toroid cores and copper (PCfc material) end plates. center holes of the toroid stacks. The ends of the stacks are held together with a pair of copper-clad PC boards. The read panel has no copper removed, and the front panel is etched to isolate the two brass tubes. The pads around the brass tubes at the front end are used to make cotuiections to the tubing (which serves as a single-turn winding). The other winding of the transformer is made of ordinary insulated wireT which is passed through the brass tubes the correct number of turns to achieve the desired turns ratio. This type of binocular core was once popular with ham operators who built their own solid-state RF power amplifiers. The higher-power transformers needed to match the impedances of the base and collector terminals of the RF transistors were not easily available on the market, so they had to ''roll their own." The binocular core is not as well-known as the toroid core, but for many applications, it is the core of choice. This is especially true when low frequencies are used or when large inductances are needed in a small package . . . and you don't want to work your arm off hand-winding the laige numiwr of turns that would be required on a solenoid-wound or toroidal core.

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### Responses

• Melissa
How to make a 41 balun on a single core?
5 years ago
• mehari
How to wind binocular toroids?
4 years ago
• Petra
How to wrap a bn43202?
4 years ago
• berhane
How to wing a 4 to 1 balun?
3 years ago
• aatifa
What is the inductance of 4 to 1 balun?
2 years ago
• quintino marino
How to wind binocular ferrite?
1 year ago
• loredana
How to wind a 4:1 current balun?
12 months ago