Band pass filter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Filters and matching devices

 Comments on the article

Bandpass filter (BFT), shown in Fig. 1, is a more advanced design of the filter, published earlier in the journal "Radioamateur" [1]. The prototype had noticeable losses in the range of 160 meters. In the proposed modification, this shortcoming is eliminated.

Fig. 1 Band pass filter of a homemade transceiver

The filter bandwidth is determined by the ratio Af=l,4f/Qe, where f is the center frequency of the range; Qe - quality factor of the circuit. For calculation on all amateur bands, it is chosen equal to 30.

Due to the high quality factor of the circuits in the 80 m range, the filter bandwidth is approximately 150 kHz, so it had to be divided into two sub-bands 3,5 - 3,65 MHz and 3,65 - 3,8 MHz.

Fig.2 Single-range 3-loop band-pass filter

The DFT contains only two main coils, which makes it possible to significantly reduce its overall dimensions and not to make shielding between the elements of the ranges. It is possible to offer two options for the circuit design of the DPF - to switch the ranges with biscuit switches or small-sized relays RES-60.

Figure 3 shows a sketch of the layout of the DFT (author's version), switched by a ceramic 4-way switch. The filter dimensions can be somewhat reduced using PGZ-type switches with a biscuit diameter of about 30 mm. The LCB coupling coil is wound on a rod of insulating material with a diameter of 8 mm. Coils L1 and L2 can be wound on suitable frames with a diameter of 12 ... 20 mm.

Fig.3 Sketch of the placement of bandpass filter elements

To determine the number of turns, it is appropriate to give the calculation formula for a single-layer coil

w is the number of turns; L is the inductance of the coil, μH; 1 - winding length, cm; D is the coil diameter.

The filter can be calculated for any frequency, the capacitances of capacitors C1 and C2 are determined by the formulas

where f is the desired operating frequency.

The filter is designed for resistance Rin=Kout=75 Ohm. Coil inductance L1 and L2 = 2 μH, LCB = 15 μH.

In the DFT version on biscuit switches, it is convenient to place the 10-28 MHz ranges on the petals facing up and to the sides, and make the capacitors C1 composite of parallel-connected trimmer ceramic capacitors KPK-M and ceramic capacitors of constant capacitance. Trimmer capacitors for structural rigidity are installed and soldered on strips of foil fiberglass, which, in turn, are rigidly soldered between the petals of the biscuits.

Capacitors C2 are immediately soldered between the switch petals and the ground bus, also made of foil fiberglass, screwed to a vertical carrier screen. The values ​​of the capacitors C2 are chosen closest to the calculated values. When setting up a filter, they are usually not selected. Taps in coils L (point A) are made from the middle.

Filter setting

The filter is tuned according to the usual method, using a GSS and an RF voltmeter, or, which is much faster and clearer, using a frequency response meter (XI-38, XI-48, etc.). The filter output is loaded with a 75 ohm resistor. The DFT is tuned in two ways. On ranges where trimmer capacitors are installed, the setting is as follows.

First, the connection between the circuits L1 and L2 is forcibly weakened - a capacitor is soldered in parallel with the coupling coil, the value of which is approximately equal to 2/3 of the capacitance of the compensating capacitor in each range, they are indicated in brackets in Fig. 1.

Thus, each circuit, independently of each other, can be tuned to the middle of the range for the maximum GSS signal. Then the compensating capacitance is removed and the frequency response is taken, which turns out to be shifted higher in frequency. The frequency offset value is determined, the compensating capacitance is soldered again, and the tuning procedure is repeated, but at a lower frequency, taking into account the offset value. After soldering the compensating capacitor, a final check is made of the resulting frequency response. An example of setting the filter to one of the amateur radio bands

We tune the 10-meter band at a frequency of 28,5 MHz. Desired bandwidth 27,85 ... 29,15 MHz, center tuning frequency 28,5 MHz. The originally measured bandwidth turned out to be 28,2 ... 29,5 MHz, i.e. shifted up at 350 kHz. Then we re-tuning at the center frequency of 28,15 MHz and the A frequency response of the range is in place.

On those ranges where there are no tuning capacitors, it is more convenient to tune in a way that is somewhat different from the previous one.

The GSS signal is applied to the DFT input, the RF voltmeter is connected to point A of the tuned circuit, and the opposite point A is grounded. GSS-ohm is determined by the resonant frequency of the primary circuit. By switching the HSS from the input of the DFT to its output, the resonant frequency of the second circuit is determined in a similar way. By selecting the value of the capacitor C2, the second circuit is tuned to the resonant frequency of the first circuit.

We restore the filter to its working position, load it with 75 ohms and record the resulting frequency response (see example). We repeat the tuning procedure taking into account the shift frequency, tune the circuit again, selecting capacitors C1 and C2, and correct the final frequency response.

DFT into 50 Ohm

If you need to make a DFT with Rin \u50d Kout \uXNUMXd XNUMX Ohm, then you can use the following formulas to calculate capacitors

3-loop DFT

For those who want to make an even better DFT, with a greater steepness of the slopes (it should be noted that in this case, the attenuation in the passband will slightly increase, approx. RW3AY), we can offer a more complicated version. The filter turns into a three-circuit system with more complex switching, Fig.2.

The inductance of the middle coil should be half the inductance of the outer coils - 1 μH. In the middle circuit, it is enough to switch only one capacitor on each range. Its value can be determined by the formula

С = 2С1С2/С1+С2

Literature

1. "Simple DFT" N. Smirnov, Radio Amateur Magazine No. 1-95

Author: N.Smirnov, UA3TW, Nizhny Novgorod; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Knots of amateur radio equipment. Filters and matching devices.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

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 ... >>

Random news from the Archive Recharging through the asphalt 01.03.2004 The authorities of Genoa (Italy), fighting exhaust air pollution, decided to put a battery electric bus on one of the routes in the center. The choice fell on the new buses of the Italian company Eco Power Technology, which are recharged at the final stops without being connected to wires. Three electric buses run along the 2400-meter route. At the final stop, where the bus arrives approximately every 20 minutes, an induction coil with a diameter of one meter is embedded in the asphalt, in which an alternating current with a frequency of 20 kilohertz circulates. The same coil is lowered from under the bottom of the car, and the distance between them can be up to 40 centimeters. An in-cab monitor shows the driver how exactly the two coils match up. Charging takes 10 minutes. Rain and snow do not interfere with the transmission of energy. Previously, the same system was adopted in one of the cities of New Zealand, and after Genoa, perhaps Turin will acquire it.

Other interesting news:

▪ Water-cooled capital

▪ Memory cards with backup function

▪ Biological magnetoreception

▪ The bus recognizes the pedestrian

▪ NEC LaVie GZ 800g Ultrabook

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the website Audiotechnics. Article selection

▪ article Measures to improve the sustainability of the functioning of the object of the economy in an emergency. Basics of safe life

▪ article What was the role played by the four actors who died of smoking-related illnesses? Detailed answer

▪ article Locksmith for the manufacture and assembly of metal structures. Standard instruction on labor protection

▪ article Liquid compositions for cleaning canvas and canvas shoes. Simple recipes and tips

▪ article Babies from the stroller. Focus Secret

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024