Air (Notes) ... (a Wired Design)

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I've done it for making coils for crystal radios and Tesla coils but it works for any coil that's cylindrical in shape. This is also useful is you're going to be using your coil in an LC tank resonant circuit. An inductance calculator is provided below for making it easy.

Inductance is often what you are trying to achieve when designing a coil i. Coils have a property called inductance. When electrical current changes as it flows through the wire of a coil, it produces a changing magnetic field that induces produces a voltage, or emf electromotive force , in the wire that opposes the current.

That is called induction and inductance is a value quantifying the ability of the coil to induce that voltage. The symbol for inductance is the Henry and the unit is H. Here we're actually talking about the coil inducing the voltage in itself, which is self-induction, but we'll just say induction. If it's a hollow cardboard or plastic tube then the cardboard or plastic counts as air and you can use 1. Materials like iron and ferrite have higher relative permeabilities in the hundreds and thousands.

For an iron core, a rough number to use is though it really varies depending on the alloy. The same goes for ferrite which can have value anywhere from 20 to but if you're at a loss as to what to use then is a rough compromise. Since it's multiplied by the rest of the formula, that means using those materials will give a higher inductance value.

Cores for crystal radio coils are sometimes plastic or cardboard, and therefore are air core coils, and sometimes they're ferrite core. The cores for Tesla coil secondary coils are usually plastic, and smaller ones may be cardboard, and therefore count as air core coils.

In the s and s Europe the Nazis used barbed wire in concentration camp architecture, where it usually surrounded the camp and was electrified to prevent escape. Barbed wire served the purpose of keeping prisoners contained. Infirmaries in extermination camps like Auschwitz where prisoners were gassed or experimented on were often separated from other areas by electrified wire and were often braided with branches to prevent outsiders from knowing what was concealed behind their walls.

The demonstration showing cattle restrained by the new kind of fencing was followed immediately by invitations to the Menger Hotel to place orders. Gates subsequently had a falling out with Washburn and Moen and Isaac Ellwood. He moved to St. Louis and founded the Southern Wire Company, which became the largest manufacturer of unlicensed or "bootleg" barbed wire. An US District Court decision upheld the validity of the Glidden patent, effectively establishing a monopoly.

This decision was affirmed by the US Supreme Court in This led to disputes known as the range wars between open range ranchers and farmers in the late 19th century. These were similar to the disputes which resulted from enclosure laws in England in the early 18th century. These disputes were decisively settled in favor of the farmers, and heavy penalties were instituted for cutting a barbed wire fence.

Within 2 years, nearly all of the open range had been fenced in under private ownership.

Inductance calculator

For this reason, some historians have dated the end of the Old West era of American history to the invention and subsequent proliferation of barbed wire. Barbed wire fences remain the standard fencing technology for enclosing cattle in most regions of the United States, but not all countries. The gaps between posts vary depending on type and terrain. On short fences in hilly country, steel posts may be placed every 3 yards 2.

However, many farmers place posts 2 yards 1. Barbed wire for agricultural fencing is typically available in two varieties: Both types are galvanized for longevity. High-tensile wire is made with thinner but higher-strength steel. Its greater strength makes fences longer lasting because it resists stretching and loosening better, coping with expansion and contraction caused by heat and animal pressure by stretching and relaxing within wider elastic limits.

It also supports longer spans, but because of its elastic springy nature it is harder to handle and somewhat dangerous for inexperienced fencers. Soft wire is much easier to work but is less durable and only suitable for short spans such as repairs and gates, where it is less likely to tangle.

In high soil-fertility areas where dairy cattle are used in great numbers 5- or 7-wire fences are common as the main boundary and internal dividing fences. On sheep farms 7-wire fences are common with the second from bottom to fifth wire being plain wire. In New Zealand wire fences must provide passage for dogs since they are the main means of controlling and driving animals on farms.

As with any fence, barbed wire fences require gates to allow the passage of persons, vehicles and farm implements. Gates vary in width from 12 feet 3. One style of gate is called the Hampshire gate in the UK, a New Zealand gate in some areas, and often simply a "gate" elsewhere. Made of wire with posts attached at both ends and in the middle, it is permanently wired on one side and attaches to a gate post with wire loops on the other. Most designs can be opened by hand, though some gates that are frequently opened and closed may have a lever attached to assist in bringing the upper wire loop over the gate post.

Gates for cattle tend to have 4 wires when along a three wire fence, as cattle tend to put more stress on gates, particularly on corner gates.

The fence on each side of the gated ends with two corner posts braced or unbraced depending on the size of the post. An unpounded post often an old broken post is held to one corner post with wire rings which act as hinges. On the other end a full length post, the tractor post, is placed with the pointed end upwards with a ring on the bottom stapled to the other corner post, the latch post, and on top a ring is stapled to the tractor post, the post is tied with a Stockgrower's Lash or one of numerous other opening bindings. Wires are then tied around the post at one end then run to the other end where they are stretched by hand or with a stretcher, before posts are stapled on every 4 feet 1.

Most gates can be opened by push post. The chain is then wrapped around the tractor post and pulled onto the nail, stronger people can pull the gate tighter but anyone can jar off the chain to open the gate. Most barbed wire fences, while sufficient to discourage cattle, are passable by humans who can simply climb over the fence, or through the fence by stretching the gaps between the wires using non-barbed sections of the wire as hand holds.

To prevent humans crossing, many prisons and other high-security installations construct fences with razor wire , a variant which instead of occasional barbs features near-continuous cutting surfaces sufficient to injure unprotected persons who climb on it. A commonly seen alternative is the placement of a few strands of barbed wire at the top of a chain link fence.

The limited mobility of someone climbing a fence makes passing conventional barbed wire more difficult. On some chain link fences these strands are attached to a bracket tilted 45 degrees towards the intruder, further increasing the difficulty. Barbed wire began to be widely used as an implement of war during World War I. Wire was placed either to impede or halt the passage of soldiers, or to channel them into narrow defiles in which small arms, particularly machine guns , and indirect fire could be used with greater effect as they attempted to pass.

Artillery bombardments on the Western Front became increasingly aimed at cutting the barbed wire that was a major component of trench warfare, particularly once new "wire-cutting" fuzes were introduced midway through the war. As the war progressed the wire was used in shorter lengths that were easier to transport and more difficult to cut with artillery.

Other inventions were also a result of the war, such as the screw picket , which enabled construction of wire obstacles to be done at night in No Man's Land without the necessity of hammering stakes into the ground and drawing attention from the enemy. During the Soviet—Afghan War , the accommodation of Afghan refugees into Pakistan was controlled in Pakistan's largest province, Balochistan, under General Rahimuddin Khan , by making the refugees stay for controlled durations in barbed wire camps see Controlling Soviet—Afghan War Refugees. The frequent use of barbed wire on prison walls, around concentration camps, and the like, has made it symbolic of oppression and denial of freedom in general.

For example, in Germany the totality of the complex German Democratic Republic border regime is commonly referred to with the short phrase "Mauer und Stacheldraht" that is, "wall and barbed wire" , and Amnesty International has a barbed wire in their symbol. Recently, Britain and France have begun restricting the use of barbed wire due to the risk of injury it poses to trespassers. Movement against barbed wire can result in moderate to severe injuries to the skin and, depending on body area and barbed wire configuration, possibly to the underlying tissue.

Humans can manage not to injure themselves excessively when dealing with barbed wire as long as they are cautious. Restriction of movement, appropriate clothing, and slow movement when close to barbed wire aid in reducing injury. Infantrymen are often trained and inured to the injuries caused by barbed wire. Several soldiers can lie across the wire to form a bridge for the rest of the formation to pass over; often any injury thus incurred is due to the tread of those passing over and not to the wire itself.

Injuries caused by barbed wire are typically seen in horses , bats , or birds. Horses panic easily, and once caught in barbed wire, large patches of skin may be torn off.

Barbed wire - Wikipedia

At best, such injuries may heal, but they may cause disability or death particularly due to infection. Birds or bats may not be able to perceive thin strands of barbed wire and suffer injuries.

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For this reason horse fences may have rubber bands nailed parallel to the wires. More than 60 different species of wildlife have been reported in Australia as victims of entanglement on barbed wire fences, [33] and the wildlife friendly fencing project is beginning to address this problem. Barbed wire has been reported as a tool for human torture. Because of the risk of injures, in Norway prohibited making new fences with barbed wire for limiting migration of animals.

Consequently, Rolls-Royce Motor Cars is using Norwegian hides for producing leather interior in their cars, since the hides from Norwegian cattle have fewer scratches than hides from countries where barbed wire is used. The most important and most time-consuming part of a barbed wire fence is constructing the corner post and the bracing assembly. A barbed wire fence is under tremendous tension, often up to half a ton , and so the corner post's sole function is to resist the tension of the fence spans connected to it.

The bracing keeps the corner post vertical and prevents slack from developing in the fence. Brace posts are placed in-line about 8 feet 2. A horizontal compression brace connects the top of the two posts, and a diagonal wire connects the top of the brace post to the bottom of the corner post. This diagonal wire prevents the brace post from leaning, which in turn allows the horizontal brace to prevent the corner post from leaning into the brace post.

This has the function of a corner post and brace assembly but handles tension from opposite sides. It uses diagonal brace wire that connects the tops to the bottoms of all adjacent posts.

Heavy livestock and crowded pasture demands the smaller spacing. The sole function of a line post is not to take up slack but to keep the barbed wire strands spaced equally and off the ground.

Coil design and inductance calculator

Once these posts and bracing have been erected, the wire is wrapped around one corner post, held with a hitch a timber hitch works well for this often using a staple to hold the height and then reeled out along the span of the fence replacing the roll every m. It is then wrapped around the opposite corner post, pulled tightly with wire stretchers, and sometimes nailed with more fence staples, although this may make readjustment of tension or replacement of the wire more difficult. Then it is attached to all of the line posts with fencing staples driven in partially to allow stretching of the wire.

Barbed wire is usually placed on the inner pasture side of the posts. Where a fence runs between two pastures livestock could be with the wire on the outside or on both sides of the fence. Class I has the thinnest coating and the shortest life expectancy.

A wire with Class I coating will start showing general rusting in 8 to 10 years, while the same wire with Class III coating will show rust in 15 to 20 years. Aluminum-coated wire is occasionally used, and yields a longer life.

Barbed wire

In Canada spruce posts are sold for this purpose. Iron posts, if used, are a minimum 2. Bracing wire is typically smooth 9-gauge. Conversely, steel posts are not as stiff as wood, and wires are fastened with slips along fixed teeth, which means variations in driving height affect wire spacing. During the First World War, screw pickets were used for the installation of wire obstacles; these were metal rods with eyelets for holding strands of wire, and a corkscrew-like end that could literally be screwed into the ground rather than hammered, so that wiring parties could work at night near enemy soldiers and not reveal their position by the sound of hammers.

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