A simple crystal filter
Quartz filter at the present time, the most convenient frequency-selective element for tract FC Amateur radio receiving and transmitting equipment. The lack of such a filter makes the design simple designs with satisfactory parameters. At independent manufacture of quartz filters from the individual resonators required measuring equipment and some experience of such work. In General, requires an investment of time, effort and some money. As a result, according to the observations of the author, only a small part of ham radio is able to produce quartz filters.
According to the author, most easy to manufacture and have high repeatability stair quartz filters. In Fig.1 shows a diagram of a simple chetyrehjadernogo ladder filter, designed and manufactured by the method described in . It requires a small number of resonators and has a quite acceptable parameters for use in a simple receiving and transmitting equipment, for example, described in [2, 3].
The author filters were manufactured from quartz resonators from the radio RSIU A-136 (6,180556 MHz) and A-460 (7,680556 MHz) without pre-selection by parameters.
The best form of the frequency response of the filters turned out with the same capacitors. On this basis, it can be expected that the use 34 of the intermediate values of quartz from No. 136 to 460 series "A" will get the same results. Probably the same is true for quartz higher and lower frequencies, and for quartz series "B" number 283 (6,194444 MHz) at room 601 (7,666667 MHz). If you want to use quartz resonators of other types, as well as to other frequencies, it is necessary to use the method  for the design of the quartz filters, and be sure to explore the frequency response of the received filter.
In Fig.2 shows a printed circuit Board (view from the side conductors), which is the basis for the design of the quartz filter on the resonators from the radio RSIU. It is made of bilateral fiberglass. On the side of the quartz resonators were left with just the wires at the edges, a longitudinal conductor in the center from edge to edge, and two conductors corresponding to the vertical dashed lines.
Prior to the installation of quartz resonators by means of soldering to install the side walls with a total height of 53 mm, of which are 10mm lower cost. In addition, you need to install internal partitions: longitudinal - in the center (top and bottom) and transverse (top-only) shown by dashed lines. The lower longitudinal wall has a cutout on the bottom for conductor connecting the terminals of the quartz resonator tori B2, B3, C3. The side wall is absent only at the top, opposite the entrance and exit. As a result, the filter is inside a shielded enclosure, which is very convenient for its use in Amateur practice as a separate unit.
Shielding quartz filter is necessary not only because of the reason the Torah from the radio RSIU made in plastic housings are quite large, but due to the need to eliminate interference and penetration of the signal from input to output due to the parasitic relationships.
In the manufacture of the housing can be used any measurable soldering materials such as tin or coated fibreglass. To know the frequency of a quartz resonator by its number can refer to [4, 5].
1. Bunin S. G. Yailenko L. P. Handbook of Amateur radio-shortwave. - 2-e Izd., revised and enlarged. K.: engineering, 1984, Pp. 17-25.
2. Bahmutov M. SW receiver. Radio, 1975. No. 11, Pp. 21-22.
3. Stepanov B., G. Shulgin Transceiver "Radio 76 M2". Radio, 1983, No. 11, P. 20; N12, P. 16.
4. Radio, 1970, No. 5, P. 60.
5. Solodovnikov, E. P. program for calculating the frequencies of the quartz from the radio RSIU. - Ham, 1994, No. 1, P. 47.
Author: E. Solodovnikov, Krasnodar; Publication: N. Bolshakov, rf.atnn.ru