All-wave antenna is not easy. It is known that the dimensions of the receiving devices for the conversion of aetheric oscillations into electricity depend on the wavelength. Range and gathered to change within wide limits. Let's open a little secret: all-wave antennas consist of at least two simple ones. As the two subsystems combine, the topic is discussed separately. For example, in a log-periodic antenna there are areas from a number of directors by regions. Starting from the rear and as the frequency increases, the active part shifts forward to the spout. In this case, integration is provided by a two-wire power line, which sets the correct phase distribution. Let's see how to make a full wave antenna with your own hands.
Log-period all-wave antennas
Note. Does not happen in the light of all-wave antennas. Any device is limited to the operating range. When you see advertising on the Internet, we are talking about devices for receiving television broadcasting. The area occupied by the channels, previously shared on the MF and UHF, now the frequency shifted entirely above 500 MHz.
In order to get out of the difficulty caused by the bandwidth of the vibrators, enthusiasts invented a structure formed by a multitude of arms. Any length operates at a fixed frequency, the result is summed up. The system forms a line along which the electromagnetic oscillation runs. The device is called the wave channel. You will see on the roofs of old houses without fail.
How to make a full-wave antenna. Look at the construction in the network. As a rule, it is difficult to make an all-wave antenna yourself. Easier to buy in the store. In addition, an outdoor all-wave antenna will allow to catch the reception, as a rule, of one tower. For separate designs it is chosen in one direction on television and radio. For placement on the roof will need an all-wave antenna with a signal amplifier. For the room, we will avoid extra energy waste if the wave power is sufficient.
Log-periodic all-wave antennas were invented more than half a century ago, and there is still no acceptable way to calculate the size of a device. You can find special nomograms on the network, but according to the professionals, the assembled equipment still needs to be adjusted and fine-tuned, and the dimensions do not look exactly required. The authors of a number of special books propose solving differential equations in MathCAD.This topic is devoted to the 2005 edition, which was already mentioned earlier. If the computer is not at odds, and talents do not lie in the field of programming, experts advise deliberately:
Take the already prepared, tried and tested factory sizes for designing a log-periodic antenna.
Where to find out the required. The Internet is wide, to write a review, we find a good site, take what we need. Read the article.
By the way, avoid suggestions that are often found on online forums. The essence is of the same type - the forum member asks where to find the homemade antenna circuit. In response, recommend schemes for links. More often, such answers lead to paid portals and it’s good if the result really does get as a result. More often, just send a text message from a mobile phone, lose 200 rubles and you know that you have become a victim of fraudsters. Stay tuned! Look for available free options, not “buying” for fake positive reviews.
Log-Periodic Antenna Design Resolved: Do-it-yourself an all-wave antenna is assembled from scrap materials. Where to get the right size. Type in the search engine "log-periodic antennas drawing" and choose the picture you like. Already found a suitable and happy to place such a useful source. If you do not like the selected option, find yours and build on the existing sample. On the used drawing( and any sample) it is visible that lengths of radiators and distances between them vary. The image is clear and understandable. We reduce in the table the sizes.
. What is bad in the picture. The diameter of the wire for the shoulders is shown - 6 mm - but the diameter of the bearing masts is not indicated. And the distance between the outer edges vertically is 8 mm. Just imagine. .. six millimeter rods. .. do not fit in this opening, and the supporting tubes should not touch. We believe that the distance is given between the centers of the carriers. Then the rows of shoulders lie vertically at a distance of 2 mm. Bearing tubes are selected 6 mm, and. .. withstand the wind load?
The first unpleasant surprise. .. Drawing with an obvious error( because the image will not load).Where crept in - find out with the help of the CWS meter. The log-periodic antenna is brought to mind by changing the distance between the carriers and varying the distance to the plate closing the line( in the drawing there is a jumper in the left part).In addition, a coax supply cable must be routed inside the upper carrier tube. And now let's think about whether it fits inside the cylinder with external walls of 6 mm. We believe that the RK 75 will not get through unequivocally, even if you remove the outer protective insulation. .. How to be. Choose carrier tubes to fit the cable, and shoulder the shoulders on the inside( at the top carrier bottom, at the bottom - top).
Let then the initial distance between the centers of the "directors" be 8 mm, then, if necessary, vary the parameter. Now a few words about the power cable. To feed the shoulders in antiphase, you need to skip the cable inside the upper tube and fluff at the exit of the spout. Then the screen in this place is electrically connected to the upper carrier, and the core from the lower one. This provides power to the halves of the shoulders in antiphase. The rear edge of the carrier is interconnected. It is clear that the characteristic impedance of the log-periodic full-wave antenna is far from 75 Ohm, it will be necessary to coordinate the design.
Harmonization of the log-periodic all-wave antennas
The amateur radio operator RU3UJ solved this problem with a quarter-wave 1: 4 transformer. Cable took 50 ohms. Lay a piece of cable between the internal traverse cable and the power point for matching. Not all of the wave impedance of the design coincides with RU3UJ, the scheme is not always suitable. It will be necessary to coordinate the device. We add that the impedance of a log-periodic antenna depends on:
- The distance between the crossheads.
- The length of the matching line behind the longest vibrator and the distance between the wires.
It is useful to recall that the power cable with a multiple quarter-wavelength transmits the resistance of the antenna to the output unchanged. Fact is used to measure by any method. In addition to special devices, a sequence of actions is found in the literature:
- . It is necessary to find a generator of high-frequency oscillations from the range of a log-periodic antenna.
- The length of the power cable is made the minimum and multiple quarter of the wavelength.
- A high-frequency rheostat is being sought without inductive resistance.
- A high frequency voltmeter is required. Chinese multimeter is not suitable.
The procedure starts with a voltmeter calibration, setting the scale to 100% relative to the generator power. For experience, you need to turn on the antenna through the resistor. The high-frequency voltmeter takes readings from the rheostat, and by adjusting the resistance you need to ensure that the scale shows 50%.The found point is fixed. In it, the resistance of the rheostat is equal to the characteristic impedance of the antenna. The downside of the technique is the difficulty of matching. Rheostat connect without loss, it is quite difficult. It is clear that in the laboratory all devices have the same resistance, energy reflection will not occur. In practice, the agreement will bring difficulties.
As for the method of rendering quarter-wave transformers, they have already given a detailed excursion. The device is made of segments of coaxial cable. Recall that the resistance of a quarter-wave transformer is equal to the square root of the products of agreed values. For example, if both devices are 50 Ohms each, the value found is also 50 Ohms. No need to agree. If you know the resistance of the antenna, you will need to calculate the line. To do this, calculators are posted on the Internet, where you have to choose the thickness of the core, the dielectric material and the diameter of the braid. According to this information, whoever can, can make the necessary quarter-wave transformer.
Use and wire pieces purchased or found separately. Insulation is taken from the cables, if necessary, the radius is reduced or increased. Braid is allowed to replace the copper tube. In this case, the master spins, as you can, you will not find factory solutions for all occasions. In our opinion, an all-wave television antenna is easier to buy in a store. The autographic product is designed for non-typical purposes, for example, reception of HF.Log-period wave antenna for this range is difficult to get.