The device of the antenna-feeder system should be known to everyone who is interested in signal transmission in radio engineering systems (broadcasting, radio communications, television). It should be noted that in this case, the possibility of communication in both directions is provided. The feeder transmits electromagnetic waves from the transmitter to the antenna (which emits/receives the signal) and from it to the receiver. Let's talk about that.
About antennas
This is the name of devices whose main purpose is to receive or emit electromagnetic waves. Antennas are an integral part of any radio transmitter and receiver. It should be noted that depending on the intended purpose, the functional role changes. For example, a transmitting antenna converts high frequency current into electromagnetic wave energy. It may be that it is multifunctional, and may also be a reception. ATIn this case, electromagnetic waves are captured and converted into high-frequency vibration energy. This version of the device is the most preferred due to its technical and economic characteristics.
Pro feeder
This is a set of devices through which energy is supplied from the transmitter to the antenna and from it to the receiver. Often they are also called the feeder path. The design directly depends on the frequency range that is transmitted over it. The feeder can also emit waves. But this is possible only in those cases when adjacent sections of two wires are flowed around by currents that coincide in phase. Their fields in this case are mutually reinforcing. By the way, antennas can be implemented on this effect.
They are in this case called in-phase, and it should be noted that they are very widespread. There may also be feeder radiation in cases where the distance between the wires in certain directions acquires a significant path difference. It should be noted that it is possible to choose a value at which the addition of waves will occur. Antennas, which are called anti-phase, also work on this principle.
Back to our device
Designing antenna-feeder devices with subsequent creation requires that individual concepts develop into an integral system. So, if there is a radio channel formed from transmitting and receiving antennas, as well as a propagation path, then it can be considered as a passive linearquadripole. What is its feature? If the electromotive force and the load are interchanged in it, then the system parameters will not change. That is, the receiving antenna can be made transmitting and vice versa. This property is called the principle of reciprocity. It implies the reversibility of the processes of transmission and reception. It is thanks to this that one antenna can be dispensed with, which acts in both roles. And this has a positive effect on the technical and economic indicators of the radio communication system, which contributed to the mass use of this principle.
What to read on this topic?
Looking ahead, it should be recognized that this topic is very extensive. Therefore, if after reading the article there are questions, then it is better to turn to explanatory books. As a first sample, we can advise the one that Drabkin wrote: "Antenna-feeder devices." This book was published in 1961. But despite its age and rather significant obsolescence, it can still be useful. At least the fact that it discusses the fundamental theoretical provisions that are useful to study for everyone who is interested in this topic.
Drabkin's book is a textbook on antenna-feeder devices. Actually, it is intended for radio engineers and students of radio engineering faculties, but if the topic is really interesting, then almost anyone can figure it out. Particularly noteworthy is the consideration of the theory of antennas, wire, microwave and aircraft samples, the specifics of measuring electrical parameters. Although only this, of course,the list is not limited.
Of the more modern authors, Erokhin G. A. deserves mention, "Antenna-feeder devices and radio wave propagation" - this is a very modern and at the same time sensible book. It is advisable to pay attention to the second edition, released in 2004. The book outlines the theoretical provisions and, what I would especially like to note, much attention is paid to issues that are directly related to the design and operation of television, radio communications and broadcasting systems. For this, praise should be given, which Erokhin fully deserves. "Antenna Feeder Devices…" by this author is a really useful book.
What antenna parameters do I need to know?
But let's get back to the topic of the article. To determine the value of the parameters, an antenna-feeder device analyzer is used or calculated using formulas. This is necessary to obtain a device with the desired characteristics. Here is a list of things to look out for:
- Emitting power of electromagnetic waves. The strength and number of waves that go from the antenna into free space. Active power is implied, because the radiation is gradually dissipated in the space that surrounds the antenna. It can be expressed through resistance.
- Power loss. By this is meant the value that is uselessly lost by the transmitter when current passes through the wires of the antenna. The value of the ground and objects can be taken into account, provided that they are located near the antenna. Also activeparameter and can be expressed in terms of resistance.
Continue listing parameters
Also remember:
- Power in the antenna. A value that represents the energy supplied from the transmitter. Represented as the sum of the two previous parameters.
- Efficiency.
- Input impedance of the antenna. By this is meant the value that is on the input terminals. It is characterized by the presence of re / active components. The best option is tuning in resonance. In this case, a resistive load is given to the generator, and the device is used with maximum efficiency.
- Directionality of the antenna. This refers to the ability to radiate electromagnetic waves in a certain direction. In order to judge this property, use the radiation pattern.
Other parameters
In addition to the above, you should know:
- Directional Coefficient.
- Working range. More specifically, the concept of antenna bandwidth is used. This is the name of the frequency interval where the width of the main lobe of the radiation pattern does not go beyond the established limits, the gain is characterized as sufficiently high, and the matching with the feeder path does not deteriorate significantly. There should be little reflection. This is required to reduce channel crosstalk due to co-current.
- Coefficient of protective action. It is usedto determine the degree of attenuation of signals from the antenna, which are received from side directions.
Working with waves
Installation of antenna-feeder devices is carried out based on where and in what range they will be used. In this case, it is necessary to ensure that the directional properties are at least in one plane. With a short length, the antennas come out quite compact. This allows you to make them rotating and get a significant gain in power, while reducing the mutual interference of radio stations. Well, where without it - to communicate in any desired direction.
In the meter wave range, a variety of non / symmetrical vibrators are often used for ease of use. Although this is far from the only option. Due to the size of the meter band antenna, it is quite problematic to move it by hand. Let's take a closer look at this.
What is the difference between waves of different lengths?
You can distinguish by purpose by specific features. It should be noted that in some cases it is possible to use the same type of antennas for operation in adjacent bands. Here is their list:
- Long wave antennas. They have large geometric dimensions. But despite this, it is still much less than the wavelength. Device height rarely exceeds 0.2 of its height.
- Medium wave antennas. Characterized by the fact that they are commensurate with the wavelength. They have a higher resistance to radiation than the previous version. Due to this, the efficiency ratioaction can reach 80%. The radiation pattern for these devices has the form of a figure eight elongated along the surface of the earth. True, because of this, the signals coming from the atmosphere are significantly weakened.
- Short wave antennas. They have specific requirements. But this is not from scratch, but is directly related to the distribution of this range. To ensure stable communication, the carrier frequency of the transmitter is selected depending on the time of year and day.
- VHF antennas. They are characterized by high efficiency and narrow radiation pattern. This is due to the fact that the dimensions of the antennas are approximately equal to the length of the operating waves.
Maintenance
In order for the device to work without problems, it is necessary to deal with its prevention in a timely manner. If we talk about the current inspection of objects, then they include:
- Antennas.
- Feeders.
- Radio relay communication.
- Foundation (this will continue for large stationary objects).
- Support structures.
- Guy masts, as well as their fastenings.
- Premises (container) of the base station.
- Designs for fastening the base to the foundation.
- Surrounding area.
In this case, attention should be paid to the following points:
- The condition of the hardware.
- Corrosion and mechanical damage.
In addition to the current one, there is also scheduled periodic maintenance of antenna-feeder devices. Itinvolves a more thorough inspection, the so-called audit inspection and repair.
Summing up
Here it is considered what the antenna-feeder devices are. The information provided is most likely not enough to build your own working device. But to provide the necessary theoretical minimum in order to move on, we hope we succeeded. And if the reader is savvy in these matters, then perhaps he has already figured out what and how to do.
