Encyclopedia of radio electronics and electrical engineering / Civil radio communications
Comments on the article
On fig. 1 shows a single-stage low-pass filter (LPF) with a cutoff frequency of 35,6 MHz. The filter is designed for input and output impedance of 50 ohms. The inductance of the coil L1 is 0,45 μH. It is frameless and contains 8 turns of PEV-2 wire with a diameter of 1,6 mm, wound on a mandrel with a diameter of 10 mm (ordinary winding, turn to turn).
When removing the frequency response of the filter assembled according to this scheme, deviations from the calculation were revealed. The loss in the filter at the maximum operating frequency (29,7 MHz) was 3 dB, while such attenuation should have been only at the cutoff frequency (curve K in Fig. 2). Perhaps this happened due to the finite quality factor of the circuits, or due to inaccurate correspondence between the parameters of real elements and the calculated ones. The fact that this is not an error in measuring the frequency response is indicated by the dependence of the SWR on frequency. The increase in SWR occurs at the same frequencies as the increase in losses, i.e., these two curves are clearly correlated.
Losses in the transparency band can be reduced by choosing an inductor L1 or choosing a slightly higher cutoff frequency when calculating the elements. In this case, the frequency response will, as it were, shift to the right and the attenuation in the stopband will slightly decrease. With an increase in the cutoff frequency, the SWR will also improve in the frequency band of 27 ... 30 MHz.
On fig. 3 shows the circuit of an m-type notch filter, the notch frequency of which is chosen to be 57,2 MHz. Near this frequency is the frequency band of the first television channel. Coil L1 is the same as in the P-filter, only it has 7 turns and an inductance of 0,35 μH.
To increase the filtration efficiency, these filters were combined (Fig. 4).
The frequency response of the combined filter and the dependence of the SWR on the input frequency when a 50 Ohm load is connected to the output are shown in fig. 5.
The inductance of the coil L1 is 0,45 μH, and L2 is 0,35 μH. Instead of capacitors C2 and C3, you can install one with a capacity of 150 pF.
The filter is best done in a metal case. The filter sections must be separated by a shielding partition. The distance between the filter walls and the inductors must be at least twice its diameter. Since the design of the filter greatly affects its parameters, and it is impossible to take into account all the parasitic factors, each instance of the filter needs to be adjusted. The cutoff frequency (and hence the attenuation at the top of the transparency band) can be indirectly determined using an SWR meter. To determine the notch frequency, you will need an RF generator and an RF voltmeter. During adjustment, the filter is loaded with a dummy load with a resistance of 50 ohms.
When removing the frequency response, one should take into account the possible dependence of the output voltage of the RF generator on the frequency due to the fact that in the stop band the input impedance of the filter differs from 50 ohms and has a complex character.
Author: O. Dolgov, Moscow
See other articles Section Civil radio communications.
Read and write useful comments on this article.
<< Back
<< Back
Latest news of science and technology, new electronics:
Air trap for insects
01.05.2024
Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>
The threat of space debris to the Earth's magnetic field
01.05.2024
More and more often we hear about an increase in the amount of space debris surrounding our planet. However, it is not only active satellites and spacecraft that contribute to this problem, but also debris from old missions. The growing number of satellites launched by companies like SpaceX creates not only opportunities for the development of the Internet, but also serious threats to space security. Experts are now turning their attention to the potential implications for the Earth's magnetic field. Dr. Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics emphasizes that companies are rapidly deploying satellite constellations, and the number of satellites could grow to 100 in the next decade. The rapid development of these cosmic armadas of satellites can lead to contamination of the Earth's plasma environment with dangerous debris and a threat to the stability of the magnetosphere. Metal debris from used rockets can disrupt the ionosphere and magnetosphere. Both of these systems play a key role in protecting the atmosphere and maintaining ... >>
Solidification of bulk substances
30.04.2024
There are quite a few mysteries in the world of science, and one of them is the strange behavior of bulk materials. They may behave like a solid but suddenly turn into a flowing liquid. This phenomenon has attracted the attention of many researchers, and we may finally be getting closer to solving this mystery. Imagine sand in an hourglass. It usually flows freely, but in some cases its particles begin to get stuck, turning from a liquid to a solid. This transition has important implications for many areas, from drug production to construction. Researchers from the USA have attempted to describe this phenomenon and come closer to understanding it. In the study, the scientists conducted simulations in the laboratory using data from bags of polystyrene beads. They found that the vibrations within these sets had specific frequencies, meaning that only certain types of vibrations could travel through the material. Received ... >>
| Random news from the Archive Graphene will be used in a quantum computer
04.01.2014
The amazing material graphene is now the object of study in many laboratories around the world. Researchers at the Massachusetts Institute of Technology (MIT) have uncovered additional potential for using a single layer of carbon material, discovering unexpected properties it exhibits under certain conditions. According to experts, these properties can be used in quantum computing.
As it turned out, under the influence of a very strong magnetic field and a very low temperature, graphene filters electrons along the spin - the electronic devices we are used to are deprived of this quality.
If you apply voltage to a piece of graphene under normal conditions, a current will flow through it. However, as soon as a magnetic field is applied, the lines of force of which are perpendicular to the plane of graphene, its behavior changes: the current flows only along the edge of the piece, and the central part becomes a dielectric. Moreover, the current flows in only one direction, depending on the direction of the magnetic field lines. This effect is known as the quantum Hall effect.
The researchers took the next step by applying a second magnetic field parallel to the graphene sheet, and this again changed its behavior. Electrons were able to move in both directions, with positive spin electrons moving in one direction and negative spin electrons moving in the opposite direction.
Spin segregation of electrons is characteristic of topological insulators, but it is not observed in conventional conductors. According to the scientists, they managed to create a special kind of conductor by making one material behave like another. Moreover, by changing the magnetic field, it is possible to control the detected edge effect. As stated, this principle can be used to build transistors and more complex circuits that have not yet been possible to implement using existing materials.
In particular, scientists see the potential of graphene in relation to the creation of a quantum computer in the discovery. Of course, the effect is still far from practical application: it is observed at a magnetic field induction of 35 T, which is approximately an order of magnitude greater than in MRI, and at a temperature that is only 0,3°C above absolute zero.
However, scientists have already managed to detect a similar effect in a field with an induction of only 1 T and at higher temperatures.
|
Other interesting news:
▪ Water from the air
▪ Color vision of bats
▪ Fortinet Software Defined Network Security
▪ Greenlanders came from Siberia
▪ The influence of foods on a person's mood
News feed of science and technology, new electronics
Interesting materials of the Free Technical Library:
▪ section of the site Data transfer. Article selection
▪ article In the hanged man's house they don't talk about the rope. Popular expression
▪ article Who painted the nude version of the Mona Lisa? Detailed answer
▪ article Hyssop officinalis. Legends, cultivation, methods of application
▪ article Electronic refrigerator defroster. Encyclopedia of radio electronics and electrical engineering
▪ article Mains voltage LED indicator. Encyclopedia of radio electronics and electrical engineering
Leave your comment on this article:
All languages of this page
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua
2000-2024
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese