We are going to tell you how to make a log-periodic antenna. Log-periodic antennas are frequency-independent. The units operate in a wide range, covering the spectrum of broadcasting. They resemble the appearance of a wave channel antenna, only directors of variable length obeying a logarithmic law. For the first time the idea was proposed in 1957 by the article of Izbella, Duhamel. Three types of devices are known in the ordinary, readers probably saw one - lined with stores. Log-periodic antenna is made by hand. Find out the sizes, understand the importance, realize the possibility of a concession to give the maintenance of accuracy.
Types of log-periodic antennas
We rarely meet the phenomenon: a self-made log-periodic antenna. Construction. .. log-periodic antennas of three types:
- Flat. They resemble an incomprehensible circle, tracks( sectors) are randomly cut( at first glance).It turns out an unprecedented combination of the target, with the rings of the pistons of the internal combustion engine, it is not clear what. .. As a result, the thing accepts-radiates waves.
- Spatial log-periodic antenna terrible appearance. It brings a fantastic film association: space flagships hung with similar gizmos. It is not excluded, the directors were equal to sabzhektom. It looks just fantastic, it works really.
- Flat unidirectional log-periodic antennas that we see in stores. A long rod sticking forward, studded on both sides, like a mustache, with cross-beams of various lengths. Looks more orderly, understanding is unattainable.
It is a mistake to think that log-periodic antennas are suitable for catching only television. The thing is different: the design of products is complex, the first techniques suggested nomograms, guided by which, self-taught masters had to be redone many times. The first log periodic antennas were difficult to tune. That is why interest has not developed until recently, although more than half a century has been known. Designs for GSM, WiFi, and other microwave protocols are available, have long been proposed, are unknown plainly. Refusing to believe, try to find information on the Internet, correlate the results on Kharchenko’s biquadrate, you will immediately understand the situation.
Solving a problem mathematically runs into a host of integral equations, a rare botanist for teeth. The most knowledgeable authors consider: it is wise to use simply ready-made structures, independently develop, more by the method of scientific testing. Clearly, the first task on paper is tedious to solve; experienced people recommend simply using various programming languages. MathCAD and C ++ are best suited.
The design of a log-periodic antenna
The design of a log-periodic antenna is striking in complexity. Let's try to describe the device. Let's start over simplified, avoiding confusing readers.
- The rod resembles the traverse of the wave channel, provides separate power to the left and right vibrators. They are symmetrical in antiphase.
- Moreover, alternately the left-right row of vibrators vary carrier( two, closely spaced and parallel).For example, the first left vibrator belongs to the upper carrier, the first right vibrator belongs to the lower one. With the second vice versa. The left is now on the bottom, the right - on the top.
- The number of vibrators depends on the construct, the length of the largest( placed in the back) is( in the total left and right) half the wavelength of the lowest lower frequency range.
- Power is supplied to the front. It is permissible to make a wire laid inside the carrier, or immediately connect a symmetrical line to the top. In the first case, let us explain: the coaxial cable lies within one guide, with one part of the line being a guide. When you exit the nozzle of the central core closes on the second carrier. It turns out that the two-wire line plays the role of a quarter-wave balun transformer.
- Shorting of the line is made behind the longest vibrator at a distance of the eighth part of the wavelength of the lower frequency range. According to some information, made for reasons of coordination. By the way, the method is good because the vibrators turn out to be closed to the ground, therefore, when the lightning strikes the first, the cable braid burns out( in the absence of a lightning rod).
Action of the log-periodic antenna
According to the theory, in a log-periodic antenna there is always some active region formed by vibrators, where the current level is above 10 dB.The frequency starts to decrease, the zone moves in the direction of the vibrators longer. Increase provokes the reverse process. Few line items work equivalently. Some rest. It turns out phenomenal broadband. The peculiarity of the line is that the wave first comes to vibrators having a size different from the resonant one( smaller).As the signal moves to the “ideal” vibrator, some of the power dissipates. It is possible to shorten the longest radiator, reducing the size of the log-periodic antenna.
So, we present a simple thing to readers: today, a simple, simple method of calculation has not been invented, amateurs who delve into the integrals are invited to publish Log-period dipole antennas of 2005: details are exaggerated. Several sections are devoted to programming. We avoid digging up the intricacies of MathCAD, cite the calculation of a log-periodic antenna, preferring C ++, show the conclusions so that readers can get into the design:
- The range of the antenna is 470-790 MHz.
- The number of vibrators 9 pieces per side.
- The coefficient of geometric progression of 0.895.
- The distance between the vibrators is 0.17 meters.
- 75 Ohm input impedance.
- Feed impedance of the feed line 97.143 Ohms.
- The diameter of the feeder line conductors is 8 mm.
- The distance between the conductors( carriers) 10,768 mm.
- The distance from the longest vibrator to a short circuit of 72.556 mm.
Explain about the data: the length of the longest vibrator( left + right total) should be equal to half the wavelength of the lowest frequency( theory).Find the parameter. The wavelength is calculated by the formula used from the school bench 299792458/470000000 = 637.85 mm. Divide by four, trying to find the length of one( left, right) vibrator, we get 159.5 mm. Each subsequent vibrator find, multiplying the number of the coefficient of the data. All the ends lie on a line drawn from some imaginary center, located along the axis of the antenna, in front. Distances are multiplied by a factor. The initial is 17 cm.
As the author of the idea explains, different thicknesses of vibrators went out according to the formulas, some did not receive portions of energy during the work( mentioned above), as the UHF log-periodic antenna was created, it was decided to take the wire 6 mm thick, distancesthe lengths are as follows:
- Distance 0 mm, length 145.1 mm.
- The distance of 98.7 mm, length 128.4 mm.
- The distance of 186 mm, length of 113.6 mm.
- The distance is 263.3 mm, the length is 100.5 mm.
- The distance is 331.7 mm, length is 89 mm.
- Distance 392.2 mm, length 78.78 mm.
- Distance 445.8 mm, length 69.7 mm.
- Distance 493.2 mm, length 61.7 mm.
- Distance 535.2 mm, length 54.6 mm.
Adjustable antenna by changing the distance between the carriers. Varies the removal of a short circuit line from the longest vibrator. Take the dimensions of the table, the author knew better, probably took into account the distances between carriers and so on. The considered log-periodic antenna perfectly fits the digital multiplex, and it will capture everything, check Wikipedia in more detail. To work on the reception of television should be positioned design to vibrators were in the horizontal plane. In a big city, the beam may not come at all from the direction of the tower, also at an angle. Be afraid to catch - try to tilt the log-periodic antenna to achieve the desired effect.
They told about the power supply, pass the cable into one of the carriers, in the area of the spout, connect any of them with a braid, the second one - with the vein. Closes the line behind the longest vibrator. Now each reader can independently make a log-periodic antenna according to the given information. A separate line are design considerations. Earlier, the director was welded to the traverse, today you will find other methods.
We wish the audience good luck in experiments. Now you know how the log-periodic antenna is made by hand. We remind you that the considered design is far from being idle and you need to see the range for all used frequencies. No need - create quarter-wave vibrators( for digital multiplexes), avoiding the wilds. It is easier to assemble a wave channel that differs from a log-periodic antenna by equal sizes of vibrators.