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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING The main parameters of disk EMF at a frequency of 500 kHz. Reference data
Encyclopedia of radio electronics and electrical engineering / Reference materials Electromechanical filters appeared more than forty years ago, but are still used in communications equipment and, in particular, in amateur radio designs. Konstantin Aleksandrovich Shulgin (U500DA), one of the main creators of domestic EMFs, talks about the main characteristics of the most common filters for a nominal frequency of 3 kHz on the pages of the magazine. The priority of his work in this area is secured by a dozen copyright certificates and patents from seven foreign countries (including the United States). The article presents the data of commercially available electromechanical filters (EMF) with disk resonators at a nominal frequency of 500 kHz. Currently, they are found in three modifications of the case: cylindrical with a diameter of 14 mm, cylindrical with a diameter of 11 mm, rectangular with a width of 11 and a height of 12,5 mm (excluding leads). The body length is determined by the number of disk resonators included in the filter's mechanical oscillatory system. The parameters of these EMFs (they are divided into four groups according to their functional characteristics) are summarized in the table.
The EMF bandwidth shown in the table is measured at -6 dB. For all filters, the attenuation in the passband does not exceed 15 dB, and the attenuation unevenness in the passband for the first group of EMF does not exceed 6 dB, and for all the others - 3 dB. The squareness coefficient K is the ratio of the filter passbands by levels - 60 and - 6 dB. The temperature coefficient of EMF frequency does not exceed 15·10-6 in the temperature range from -60 to -30°С and 10·10-6 in the range from -30 to +85°С. For the second temperature interval in absolute value it will be no more than 0,5 Hz per degree. The input and output impedances of all EMFs are determined by tuning their circuits to the average frequency of the filter. The average frequency of filters designed to highlight one sideband is not standardized, and it is given in the table for reference only. The load resistance of the filter must be at least 3...5 times its output resistance. All filters are sealed. They can be used at ambient temperatures from -60 to +85°C and atmospheric pressure up to 10 mm Hg. Art. The article retains the symbols of the filters that the developers assigned to them and which they have been wearing for many years. The following abbreviations are accepted in these designations: EMF - electromechanical filter; D - disk; P - rectangular; C - cylindrical; the number with the letter P - the number of active resonators in the mechanical oscillatory system of the filter; 500 - nominal frequency (kHz); a number with the letter H, B or C - the bandwidth (kHz) and its position relative to the nominal frequency (lower, higher or symmetrical, respectively). The designations of the filters of the fourth group contain, additionally, through a hyphen, the combination T85, which indicates the thermostating temperature (not indicated in the table for brevity). The number of disks N contained in the filter is given in the table in order to be able to evaluate the nature of the EMF and determine its length. For example, consider the fourth filter of the third group - EMFDP-5R-500 0,5N. Based on the designation, the following can be said about it. This is an electromechanical filter, disk, rectangular shape. Its oscillatory system contains 5 active resonators, the nominal frequency is 500 kHz, the bandwidth is 500 Hz and it is located below the nominal frequency. The first group of EMF is intended for single-sideband communication systems and other electronic equipment. Their body is cylindrical with a diameter of 14 mm. Petals are welded to the end sides of the case, serving for its "grounding" (Fig. 1). The input and output of the filter are not galvanically connected to the housing. The conclusions from the coils are made in the form of rigid wire segments with a diameter of 0,8 mm. When installed in apparatus, they can be bent, but with care so as not to damage the bushings.
All filters of this group 9 are resonator, symmetrical, i.e. their input and output have the same parameters. As an input, it is customary to consider that side of the EMF, from which its symbol begins. The active resistance of the coils is 105 ±10 Ohm, the capacitance of the connected capacitors is 60...100 pF. The input and output resistances are 20 ± 5 kOhm, the quality factor of the circuits is about 10. The considered filters are interesting in that they were the first domestic EMF introduced into mass production as products of wide application. The first to master their production was the plant. N. G. Kozitsky (Leningrad) in 1961. In the summer of 1962, the jubilee, 5th "EMF-D-500-ZV" was released with appropriate honors, which the factory workers handed over to the author of this article. The second group of EMFs includes filters designed for special equipment. All of them are 11-disk, symmetrical. Among them, a set of narrow-band EMFs for passbands from 0,3 to 1,5 kHz (developed in 1962) should be noted. They differ from other filters in that, in order to increase the mechanical strength of the oscillatory system, the connection between their active resonators is made according to a complex scheme in which detuned ("passive") disk resonators are used. The overall dimensions of the filters are shown in fig. 2. Their input and output parameters are the same as for the filters of the first group.
The third group of EMF is a unified series of filters for wide application for bandwidths from 0,3 to 35 kHz. The filters included in it are designed for printed wiring, so their housing has a rectangular shape (Fig. 3). The EMF case with 11 disks has a length of 62 mm, with 9 and 7 disks - 54 mm, with 5 - 47 mm.
The active resistance of the coils of this EMF group is 50 ± 5 Ohm, the capacitance of the capacitors is 60 ... 150 pF. For convenience of matching with transistor circuits, a tap is made from part of the turns of the coils. As a result, the EMF data input and output have three pins each. The entrance is marked with a dot. Capacitors are connected to terminals 1 - 3 and 4 - 6. Between the same terminals, the total input and output resistance of the EMF is measured. It is equal to 16 ± 5 kOhm. The input resistance between pins 1 and 2 is 20,6 kOhm, the output resistance between pins 4 and 5 is 0,5 ± 0,15 kOhm. It should be borne in mind that such a decision is private. Therefore, one should not exclude the possibility of fully including filters in the circuit through pins 1 - 3 and 4 - 6. Filters of the fourth EMF group (Fig. 4) were developed for equipment operating in a wide temperature range. They are intended for use in temperature-controlled equipment (t=85°C). In the table, their parameters correspond to just such a temperature.
All filters contain 11 discs, have the same length and diameter. The bandwidths of narrow-band EMFs included in this group range from 0,3 to 1,1 kHz. The remaining filters have bandwidths from 3 to 7,8 kHz and are characterized by increased selectivity. As in the third group, their coils are made with a tap. The input of the filters has 3 outputs, the output - 4. The last output is made from the housing and does not have a bushing. In terms of input and output parameters, these filters are identical to rectangular ones. In fact, most filters of all groups have better parameters than those indicated in the table. Various firms, including developers, produced disk EMFs that differed somewhat from those considered in terms of bandwidth, number of resonators, nominal frequency, input and output impedance, external design, etc. If these firms followed the technology proposed by the developers and applied the recommended by them materials specially developed for EMF, selective properties (with an equal number of active resonators), as well as the temperature coefficient of frequency for such EMF should be similar to those given in the article. Over time, some departments and enterprises changed the names of the EMF they produced. As a result, until now, the same filters with different names are found in everyday life, which can cause certain difficulties. Let's dwell on this issue briefly. According to the price list of the Ministry of Electronic Industry, EMF of the third group were renamed. The new notation does not show the number of active resonators and moved the letter indicating the location of the bandwidth relative to the nominal frequency. It is placed right after it. So, for example, the EMFDP-9R-500-2,75V filter was renamed EMFDP-500V-2,75. Such filters are quite widespread among radio amateurs. The designations of the EMF included in the first group have not changed. Filters of the second and fourth groups are not included in the price list. Approximately 12 - 13 years ago, a new departmental system of symbols was introduced, common for EMF of four groups (OST 11 206 801-87). Symbols of filters in this system consist of the following elements: the first element is the letters FEM (electromechanical filter); the second is a number characterizing the filter according to the type of resonators used; third - registration number; the fourth is a number equal to the nominal filter frequency in kHz; the fifth is a number equal to the bandwidth in kHz; the sixth - the letters H, B or C, showing the position of the passband relative to the nominal frequency; the seventh is a number indicating the type of converter, and the eighth is the letter B, indicating the all-climatic version of the filter. Between the 2nd and 3rd, 3rd and 4th, 4th and 5th, as well as the 6th and 7th elements, a hyphen is put down. The number 1 of the second element shows that the resonators are dumbbell, 2 - disk, 3 - tuning fork, 4 - lamellar, 5 - cylindrical. In the seventh element, the number 1 corresponds to electromagnetic transducers, 2 - piezoceramic, 3 - magnetostrictive, 4 - combined. The considered system makes it possible to unambiguously evaluate the existing disk EMF and, taking into account its overall dimensions, determine all filter data using this article. For example, the FEM2-045-500-2.75V-3 filter is equivalent to the EMFDP-500-2,75V filter and belongs to the EMF of the third group. A number of EMFs with the latest marking are given in the reference book by A. I. Ladik and A. I. Stashkevich "Electronic Products. Piezoelectric and Electromechanical Devices", released in 1993 by the publishing house "Radio and Communication". Unfortunately, there is not enough information about disk EMFs in it to get a complete picture of specific filters. If an EMF falls into your hands, on which something incomprehensible or unmarked is written, then try to evaluate its characteristics yourself. To solve the problem, a GSS with a low output resistance (50 ... 75 Ohm), a high-frequency millivoltmeter (MVL) with a high input resistance and two variable capacitors of 100 pF are required. It is also desirable to have a frequency meter. Connect everything as shown in Fig. 5.
Turn off the modulation at the generator, set the carrier level to about 1 V. Set the initial capacitance of capacitors C1 and C2 to 60 ... 70 pF. Further, by changing the generator tuning frequency in the region of the expected nominal frequency, find the filter response and, using capacitors, adjust the EMF circuits according to the maximum MVL reading. Then, as detailed as the instruments used will allow you, take the frequency response of the filter point by point. It will allow you to evaluate the filter taking into account the shape and dimensions of its housing, find out which EMF group described in the article it belongs to and determine its parameters. Author: K.Shulgin (U3DA)
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