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 a signal) and from it to the receiver. We’ll talk about this.
This is the name of devices whose main purpose is the reception or emission of electromagnetic waves. Antennas are an integral part of any radio transmitting and receiving device. It should be noted that, depending on the purpose, the functional role is changing. For example, a transmit antenna converts high-frequency current into electromagnetic wave energy. It may be such that it is multifunctional, and it may also be a reception room. In this case, electromagnetic waves are captured and converted into energy of high-frequency oscillations. This version of the device is most preferred due to its technical and economic characteristics.
This is a set of devices due to 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 range of frequencies that are transmitted along it. The feeder can also emit waves. But this is only possible in cases where adjacent sections of two wires are surrounded by currents that coincide in phase. Their fields in this case are mutually reinforcing. By the way, antennas can be implemented on this effect.
In this case, they are called in-phase, and it should be noted that they are very widespread. There can also be radiation from the feeder in cases where the distance between the wires in certain directions acquires a significant difference in stroke. It should be noted that it is possible to choose a value at which the addition of waves will occur. Antennas called antiphase also work on this principle.
Back to our device
The design of antenna-feeder devices with subsequent creation requires that individual concepts form a single 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 linear four-terminal. What is its feature? If in it the electromotive force and load are interchanged, 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. From it follows the reversibility of the processes of transmission and reception. It is thanks to this that you can do with one antenna, 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 massive use of this principle.
And 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, it is better to turn to sensible books. As the first sample, we can recommend the one written by Drabkin: “Antenna-feeder devices”. This book was published in 1961. But despite its age and rather substantial obsolescence, it can still be useful. At least by the fact that it examines the fundamental theoretical principles 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. Of particular note 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, G. Erokhin deserves mentioning, “Antenna-feeder devices and radio wave propagation” - this is a very modern and at the same time sensible book. We can advise you to pay attention to the second edition, released in 2004. The book sets out the theoretical provisions and, which I especially want to note, a lot of attention is paid to issues that directly relate 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 you need to know?
But let's get back to the topic of the article. To determine the value of the parameters, an analyzer of antenna-feeder devices is used or calculated using formulas. This is necessary to obtain a device with the desired characteristics. Here is a list of things to watch out for:
- The radiating power of electromagnetic waves. The strength and number of waves that go from the antenna to free space. Active power is meant, because the radiation is gradually scattered in the space that surrounds the antenna. It can be expressed through resistance.
- Power loss. By this is meant a value that is uselessly lost by the transmitter when passing a current antenna through the wires. The significance of the earth and objects may be taken into account, provided that they are located near the antenna. It is also an active parameter and can be expressed in terms of resistance.
We continue to list the parameters
- Power in the antenna. A value that displays the energy supplied from the transmitter. It is represented as the sum of the two previous parameters.
- Antenna input impedance. This means the value that is on the input terminals. It is characterized by the presence of re / active components. The best option is tuning to resonance. In this case, the active load is given to the generator, and the device is used with maximum efficiency.
- Directivity of the antenna. This means the ability to radiate electromagnetic waves in a certain direction. In order to judge this property, use the radiation pattern.
In addition to the above, you should know:
- Coefficient of directional action.
- Working range. The more specialized 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 high enough, and with the feeder path the coordination does not significantly deteriorate. This should be a little reflection. This is required to reduce transient noise in the channels present due to the presence of associated flows.
- Coefficient of protective action. It is used to determine the degree of attenuation of antenna signals that are received from side directions.
Installation of antenna-feeder devices is based on where and in which range they will be used. In this case, it is necessary to ensure that the directed properties are at least in one plane. With a short length, the antennas come out quite compact. This allows you to make them rotate and get a significant gain in power, while reducing mutual interference of radio stations. Well, and where without it - to communicate in any desired direction.
In the range of meter waves, 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 manually. 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 the same type of antenna can be used to work in adjacent ranges. Here is a list of them:
- Antennas of long waves. They have large geometric dimensions. But despite this, it is still significantly less than the wavelength. The height of the device rarely exceeds 0.2 of its size.
- Mid-wave antennas. They are characterized in that they are proportional to the wavelength. They have a higher radiation resistance than the previous version. Thanks to this, the efficiency can reach 80%. The radiation pattern for these devices has the form of an elongated figure eight along the earth's surface. 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 directly related to the distribution features of this range. To ensure stable communication, the carrier frequency of the transmitter is selected depending on the time of year and day.
- Antennas of ultrashort waves. They are distinguished by a high efficiency and a narrow radiation pattern. This is due to the fact that the dimensions of the antennas are approximately equal to the length of the working waves.
For the device to work without problems, it is necessary to timely prevent it. If we talk about the current inspection of objects, then they include:
- Radio relay communication.
- Foundation (this is further for large stationary objects).
- Support structures.
- Braces of masts, and also their fastenings.
- Premises (container) of the base station.
- Designs for fixing the base to the foundation.
- The adjacent territory.
In this case, attention should be paid to such points:
- The state of the equipment.
- Corrosive and mechanical damage.
In addition to the current, there is also a scheduled periodic maintenance of antenna-feeder devices. It involves a more thorough inspection, the so-called audit inspection and repair.
So it is considered what are antenna-feeder devices. 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 it.