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Quartz filters. Setting up quartz filters. Diagram, description Homemade water filter

Simple and cheap filter for SSB

Vorontsov A. RW6HRM proposes, as an alternative to EMFs, to use a simple and, most importantly, cheap quartz filter circuit. The article is relevant due to the scarcity and high cost of these elements.

Recently, very often in Internet publications there are “tears” of beginning radio amateurs, they say, it is difficult to get an EMF, it is expensive, a quartz filter is difficult to make, instruments are needed, etc. Indeed, it is now quite problematic to get a good new EMF, what is offered on the market is deep used without a guarantee of normal operation, and to build a quartz filter even on commercially available quartz at 8.86 MHz without having the appropriate control and measuring equipment, “at peephole,” impossible. At first glance, the situation is not so great...

However, there is an option to make a simple quartz filter for a low-frequency SSB transmitter or transceiver quite simple and, most importantly, inexpensive. It’s enough to walk through radio stores and see “two-legged” quartz crystals for sale for remote controls for frequencies from 450 to 960 kHz. These parts are made with fairly large tolerances on the generated frequencies, which gives us the right to choose both the intermediate frequency used and the bandwidth of the filter being made. Let me make a reservation right away: the idea is not mine, it was previously tested by the Swedish radio amateur HARRY LYTHALL, SM0VPO, and I’m just letting you know about it (after making several filters for myself).

So, what we need to select quartz is a simple three-point generator and a frequency meter or a radio receiver with a frequency meter covering the amateur band of 160 meters. From a bunch of quartzes, we need to select two with a spacing of generated frequencies of 1 - 1.5 kHz. If we use quartz at a frequency of 455 kHz, then it is most convenient to tune to their fourth harmonic (about 1820 kHz, achieving a spacing of 4 - 4.5 kHz), and if 960 kHz, then to the second (1920 kHz, spacing 2 - 2, 5 kHz).

Circuit CL1 in this example is the load of the previous amplifier stage; this is a standard 455 kHz circuit from any foreign manufactured AM receiver. You can also use data from amateur radio literature for homemade circuits at a frequency of 465 kHz, reducing the number of turns by 5%. The dots indicate the beginning of the communication coils L2 and L3; 10–20 turns are enough for them. It is quite possible to install a filter immediately after the mixer, for example, a ring one with four diodes. In this case, you will already get a 1:1:1 transformer, which can be made on an F600 ring with an outer diameter of 10 - 12 mm, the number of turns of twisted triple wire PEL-0.1 - 10 - 30. Capacitor C in the case of a transformer, of course, is not needed. If the second stage of the amplifier is made on a transistor, then a 10 kOhm resistor can be used in the current-setting base circuit, then a 0.1 μF isolation capacitor is not needed. And if this filter is used in a simple radio circuit circuit, then the resistor can be eliminated.

Now from the remaining pile of quartz we need to select one suitable for the reference oscillator. If we select quartz at 455 kHz to the values ​​indicated in the diagram, then at the filter output we will get a lower sideband, if at 454 kHz we will get an upper one. If there are no more quartz left, then it is quite possible to assemble a reference oscillator using a three-point capacitive circuit and, by selecting its frequency, adjust the resulting filter. In this case, the generator must be made with increased measures regarding its thermal stability.

Tuning can be done even by ear, using radio station carriers, but we will leave this pleasure for more or less experienced “musicians”. For setup it would be nice to have a sound generator and an oscilloscope. We feed a signal from the sound generator with a frequency of 3 - 3.3 kHz to the microphone amplifier (assuming that the filter is already in the transmitter circuit), connect an oscilloscope to the output of the filter and shift the frequency of the reference oscillator until the output signal level after the filter decreases minimally . Next, we check the lower limit of the filter’s transmission by applying a frequency of 300 Hz from a sound generator to the microphone input. By the way, to increase the lower limit of the transmission bandwidth of a microphone amplifier at audio frequencies, it is enough to install transition capacitors with a capacity of about 6800 pF or less, and for the upper limit, in any case, it would be good to install at least a single-link low-pass filter.

That's all. As you can see, you will not incur large costs in the manufacture of this filter, and the signal will be quite presentable. Of course, due to its simplicity, it is no longer advisable to use it in transmitters of the second category, but for 1.8 - 7 MHz it will be more than enough. According to the measurement results, this classical design completely coincides with that described in reference books (for example, the Shortwave Handbook of Bunin and Yaylenko) - the lower part of the characteristic is somewhat tightened. Attenuation in the passband is about 1 - 2 dB, it depends on the quality of the resonators used. But if you find an even cheaper way to go on the air with SSB (except phase) - let me know

Improving the frequency response of the "Leningrad" quartz filter

S. Popov RA6CS



Purifying water with homemade filters is a standard activity for camping and field conditions. After all, it is unwise to carry huge bottles on yourself due to the incredible physical costs. In addition, this is irrational due to the almost ubiquitous presence of the liquid component of the earth’s shell necessary for the body.

The liquid people need is indeed available everywhere, but its sanitary condition is not always compatible with consumption. But you can make a very effective water filter with your own hands even on a multi-day route, being far from populated areas, with a minimum of available tools.

We will introduce you to the most effective and easy-to-implement devices for purifying dirty water. Here you will find diagrams, recommendations and a detailed description of manufacturing technology. The material offered for review is systematized, supplemented with visual illustrations and video instructions.

How to choose filter media?

When choosing a container for a filter, you need to carefully calculate everything, because the cleaning properties primarily depend on the correctly formed “filling”. The volume of the filter container must be such that it can easily accommodate all components.

Natural materials are widely used as absorbents, such as quartz river or washed quarry sand, gravel, activated carbon and zeolite. As you know, any filter begins with a primary coarse layer. Often this role is assigned to cotton-based fabric materials.

The water in the filter must undergo several stages of purification. The upper layers trap large inclusions and contaminants, the lower layers prevent the penetration of small particles

Natural materials are very impractical from a hygiene point of view. Firstly, in a humid environment, such a filter layer is subject to rotting processes, which causes an unpleasant odor. Secondly, the structure of the fabric implies very rapid contamination of the filter with unwanted particles, which increases the need to change the layer.

Much better performance is observed in synthetic analogues. More preferable in this regard is lutrasil. The material has moisture-resistant qualities and is more resistant to contamination than cotton or bandage.

Non-woven polypropylene fabric - lutrasil can be used as a bottom layer intended for final water purification

A completely budget option for a fabric filter can be considered a synthetic layer, which is used in making coffee.

Quartz sand does an excellent job of retaining small particles, as well as filtering heavy chemical compounds. While gravel, on the contrary, will better screen out large inclusions of unwanted materials. A mineral called zeolite has an incomparable cleansing effect.

Zeolite is widely used in water purification. It extracts heavy metals, organic compounds, phenol, nitrates, ammonium nitrogen, etc.

The active action of the substance will successfully cope with water pollution with metal and salt suspension, and also neutralize pesticides and other processed products of the agricultural industry.

Activated carbon cleaning devices

The most common group of homemade filters involves the use of activated carbon. The drug can be purchased at any pharmacy in unlimited quantities. Its reserves will practically not increase the weight of the luggage and will not take up much space in the backpack.

But in terms of cleaning power, coal has few rivals. It perfectly adsorbs toxic substances, absorbs an impressive range of heavy metals, and mercilessly fights harmful microorganisms.

Small-sized camping varieties

Perhaps the best quality filtration results are shown by homemade options based on activated carbon. The absorbent will equally successfully cope with the retention of both mineral formations and toxic substances.

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The properties of the material include the ability to impart transparency to liquids, as well as eliminate unpleasant odors and waste products of microorganisms.

When choosing coal, you need to pay attention to the structure of the mineral. Too fine and powdery will penetrate into the water, while coarse, on the contrary, will not provide the proper level of purification. (Granular starting material should be preferred).

Activated carbon is the most popular material in homemade filter devices. It is advisable to fill it in layers so that there is powdery material below, granules on top, and the fractional composition increases in height

An important factor is the degree of so-called “roasting” of the coal. If you overdo this procedure, the absorbent will quickly lose all its valuable qualities.

Coal can be bought at any supermarket, or made at home. The best absorbent qualities are observed in deciduous wood, in particular birch.

To obtain coal, you need to load wood into any metal container and heat it over a fire (preferably put it in a stove). After the wood gets red hot, remove the container and let it cool - that’s it, the charcoal is ready for use in the filtration system.

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A completely camp option would be a homemade carbon-based filter for water from the ashes of a burnt-out fire. If necessary, it is better to use whole pieces approximately 4 cm in length.

As a rule, anything can serve as a housing for such an improvised system, but mainly a plastic container or bottle is used for convenience.

Making a carbon water purifier

Before assembly, you need to select a more optimal housing option.

For this you will need:

  • Several plastic containers (bottles or PVC pipe, in some cases you can use food containers. Due to their strength, they will serve well as the base of the cartridge).
  • Tools for processing plastic (various sharp objects: awl, scissors, stationery knife, screwdriver).
  • Absorbent material (in this case activated carbon).
  • Additional filter granules (quartz sand, gravel).
  • Material for the primary fabric filter (medical bandage, gauze or coffee filter).
  • Plastic covers or plugs.

To ensure the tightness of the structure, polymer substances should be used at the junctions of the modules (if the filter is multi-level and consists of several parts). Moisture-resistant silicone glue or insulating tape work well.

To install the hanging structure, you need to first cut off the bottom of the plastic bottle using a stationery knife. Then make two holes opposite each other to attach the hinges. Now the improvised body can be hung, for example, on a tree branch.

Next, you need to make an outlet valve from where the filtered liquid will flow. At this stage, the design feature depends on individual preferences. You can organize something according to the principle of a shower - make many small holes in the lid, or you can drill one large one.

The next step will be the actual installation of the components. After screwing on the perforated lid, the body is turned over or hung by the hinges. Then, the first step is to place a bandage or gauze folded several times. The use of a coffee filter is also encouraged.

In some cases, you can find designs where the role of the primary filter material is played by a fabric cover, sewn specifically to the size of the housing. This greatly simplifies the task of changing the absorbent and saves time.

It is worth paying attention to the fact that the installation of absorbent components should be done in a “pyramid” type. This means that the first step is always a fine-grained absorbent (coal), then comes a layer of quartz sand, and then comes the turn of river pebbles or gravel.

Each subsequent filter layer has a different, most often finer, structure than the previous one. This promotes more thorough cleaning

For greater efficiency, it is recommended to alternate several layers of pebbles, however, do not forget that excess material can impede the flow of water. It is better to cover the filler hole with some kind of cloth or lid to prevent unwanted objects from getting inside the cartridge.

The principle of operation of such a filter is the passive flow of water through all layers. Under the action of the granules, the contaminated liquid is cleaned and flows out of the perforated hole. Initially, you need to pass several liters of water through the filter. The first filtering procedure will wash the layers and remove contaminants.

The disadvantages of the system include the rather slow cleaning speed and the need to constantly add new liquid after completing the filtration procedure.

The disadvantages of homemade water filters with natural fillers include low speed, the need to frequently change filter layers, and not very high cleaning quality

Useful homemade PVC pipe

To purify water in a suburban area, you can also make an effective purifier that can compete with. It will be needed to process water collected in or into, but will be especially useful if the water is drawn from a river, pond or lake.

To build the structure you will need a piece of plastic water pipe and 2 containers. You can connect two bottles, where the upper segment will act as a coarse filter.

The filter can be made from improvised materials without the help of special equipment. Everything you need can be found in everyone’s home

As expected, a primary layer of gauze or cotton wool is first placed inside, while some kind of mesh backing, for example, made of plastic, is constructed so that the layers do not mix. A plastic cap that can be glued into a PVC pipe is well suited for this, then drill several small diameter holes around the circumference.

Perforations in the plastic baffle are necessary to retain synthetic or natural fibers in the primary filter

After this, close the module again with the lid, only this time you should not resort to using glue, because this part must be removable in order to be able to replace and clean the filter material.

The filler should be laid tightly, but at the same time not too much so that the layer does not interfere with the passage of water

Then the turn of the plastic pipe begins. You need to cut off the neck of the bottle and secure it inside the pipe so that you can use the thread.

It should be secured tightly to avoid leaks (silicone glue works well). It is recommended to wrap the outer side and edging of the neck with several layers of electrical tape for greater strength.

The insulation must also be wound in several layers in order to prevent the possibility of leakage

As usual, you need to insert a cap into the other end of the tube and make a perforation. A fabric layer should be placed on the inner surface of the improvised cassette.

After all the manipulations, the structure is ready to be filled with granulate (in this case, activated carbon). For better efficiency, you can alternate layers of minerals inside the pipe.

It is best to use synthetic material as a filter layer, because... it is more durable and does not need frequent replacement

Once complete, the primary filter and carbon module are screwed together using threads. Then plastic bottles are added on both sides. That's it, the cut PVC carbon filter is ready for use.

The homemade design does not require special conditions of use and does not take up much space when disassembled.

Water filter for aquarium

As you know, for the normal functioning of aquatic inhabitants, it is necessary to clean the tank in a timely manner and maintain the purity of the water. Owners of small aquariums will come in very handy with instructions on how to build a filter at home.

The body of a homemade filter for purifying hard water can be any plastic tube of a suitable diameter, including, in the absence of one, 2 syringes will work well.

Before assembly, you need to prepare some additional parts: a spray bottle (often used in bottles with detergents), a sponge with a high degree of rigidity, as well as a mechanism by which the structure will be attached to the wall of the aquarium (suction cup).

The main advantage of the design is ease of manufacture. All components can be easily found at home

The first step is to remove the moving part of the syringe; it will not be useful. Then, using hot glue or other sealant, connect the blanks to each other, after cutting off the spouts.

For water flow it is necessary to make perforations. An ordinary soldering iron will do an excellent job of this, and if you don’t have one, you can heat any metal object, such as a nail, over the fire and make holes over the entire area of ​​the syringe.

To optimize the speed of water passage through the filter, it is recommended to make holes at an even distance from each other

In some cases, you can put some granules into the filter capsule; the best option would be to use zeolite, because The absorbent does a good job of filtering nitrates. Next, you need to place the atomizer inside the housing, and its flexible tube should run evenly along the entire length of the cassette.

Then the improvised cartridge should be completely wrapped with a sponge and the outer layer should be secured so that it does not unwind. That's all, the power of such a filter is quite enough to purify water in a small aquarium.

The design is quite compact and can fit into any small tank

Sand option for the pool

As already mentioned, the process of constructing small-sized variations of filter systems is quite simple, however, if we are talking about a large reservoir, it is necessary to think through all the nuances of the purification system.

Many people have probably encountered the problem of “blooming” water. Most often, this process is observed in the warm season, and if it is also equipped with a heating system, such an incident can occur at any time.

It’s fair to say that the problem of green water can be completely solved with improvised means, namely, removed mechanically, but sometimes a layer of algae can sink to the very bottom and removing the surface film will not solve the problem.

In order for the water to circulate through the filter, an inexpensive vortex pump is included in the circuit. Install it after the filter


Before turning on the pump, the filter must be closed with a lid so that conditions for normal suction are formed inside it.

In addition, not only algae can act as a pollutant, but also fallen leaves, as well as sand and all kinds of microparticles if the pool is located outside.

Faced with problems of this kind, people begin to frantically buy all sorts of detergents and cleaning products in the hope of getting rid of annoying green islands. But the active chemical action of substances can only help with the pollutant that is on the surface and in order to clean the tank to the very bottom, completely different methods are needed.

There are special ones for completely cleaning the pool. They work on the principle of a “vacuum cleaner”, namely, they pump liters of contaminated liquid through a compressor. The filtration process is a repeated transfer of water from one part of the pool to another.

This mechanism is often used in large municipal or private institutions, where the volume of the pool sometimes reaches thousands of liters, so the best solution is an automated filtration system.

But it is not profitable for the average user to invest in such bulky equipment if, for example, it is necessary to clean only a small seasonal inflatable tank.

Just for such reservoirs there are instructions for constructing a sand filter.

The body of the device contains a filler with filtering properties (sand). You can replace the material with any other

During the assembly process, you will need any container that can serve as a cartridge. The water tunnel from the primary filter can be made from a plastic pipe 2 meters long (if the pool is large).

You also need to take into account that the tunnel design involves a 90-degree rotation, so a PVC corner is needed. The inner diameter of the cartridge and pipe should be about 50 mm.

A threaded bushing with a diameter of M10 can be used as a support pin for cleaning modules. The convenience of this design allows you to connect several filter cassettes into one, which turns a regular filter into a multi-level one. This increases absorption efficiency and ultimately results in cleaner water.

At the first stage, you need to make two holes (it is better to use a hammer drill).

The first is in the filter plug, and the second is in the PVC corner, then connect the two parts using a pin and nut. A water compressor should be attached to the other end of the tube. The power of the equipment should be selected based on the volume of the pool.

In order for the filter to float, it is necessary to make a special foam backing.

The purification process is circular, and occurs by taking water from the lower layers of the pool and pumping it through the filter using a pump.

The advantage of this design is the absence of additional elements for releasing filtered water, as well as the possibility of replacing the cartridge. It is better to carry out the rinsing procedure over a separate container to avoid dirty liquid getting back into the pool. It is better to use a bucket for this.

In addition, the cost of this installation is significantly less than branded analogues. Everything you need can be purchased at specialized retail outlets, for example, a compressor is sold in any pet store, PVC pipes and corners in construction supermarkets, and a replacement cartridge in the markets in the plumbing department.

A big advantage when creating a floating filtration system is the freedom of design. If you have decorative components on hand, you can disguise the filter as any object that fits into the composition of the pool, for example, a ship.

Homemade water filter

At home, anyone can build an installation consisting of three containers connected in series. Such a water filter works only under a certain pressure of the water supply system.

Plastic or glass containers can be used as future cassettes, and the segments must be connected using a ¼-inch adapter nipple.

The filter is connected directly to the water supply system and does not require installation of additional communications

For convenience, the adapters have entry/exit guides. They will make sure that the assembly process is successful. Another important point is the tightness of the installation. To avoid leaks, it is recommended to wrap each thread in Teflon tape and seal the joints with synthetic material.

A filter of this type is connected to the system as a tee and connected in series with the water supply pipes. The same coal can be used as granulate. It will clean raw water from harmful microparticles and prevent the appearance of scale on the heating elements of an electric kettle and washing machine.

Conclusions and useful video on the topic

After some time, you will have to replace the homemade system with a more professional one. This is due not only to the wear and tear of old parts, but due to their low absorption and purification efficiency in relation to microorganisms contained in water.

To ensure the sterility of the reservoir, modern filters are equipped with a mineralizing system. Before buying equipment, it is worth testing the water in laboratory conditions for mineral content and then, based on the results of the examination, choosing a filter with the appropriate mineral composition.

Homemade equipment does not have such a function, so after the cleaning stage it is recommended to boil the filtrate. Also compare the power of the filter with the water pressure. Incorrect calculation of the water pressure intensity in relation to a homemade filtration system can affect the performance of the equipment.

Video #1. The process of making a simple filter from a plastic bottle:

Video #2. This video will help those who want to make a miniature version of a water filter:

Video #3. Construction of a filter for a personal pond:

There really is no limit to people’s ingenuity, and this is clearly confirmed by the variations of the presented filters. A wide selection of materials, fillers and an abundance of shapes are suitable for any case where you need to quickly purify water.

Quartz filters "Desna"

Eight-crystal quartz filter “Desna”. Assembled, configured, without housing (shielded box). Quartz filter at a frequency of 8.865 MHz. The filter is assembled on a 75x19 mm printed circuit board. The kit includes 2 reference quartz (SSB, CW). Squareness coefficient at levels 6 and 60 dB – 1.5; attenuation beyond the passband more than 80 dB; unevenness in the passband no more than 3 dB; 6 dB bandwidth – 2.4 kHz; Rin and Rout. from 200 to 280 Ohm (indicated in the passport). It is possible to produce several CFs for one frequency with a spread of no more than 20 Hz.

Four-crystal quartz filter "Desna". Assembled, configured, without housing (shielded box). Quartz filter at a frequency of 8.865 MHz, Kp. 2.1; bandwidth 2.4 kHz. The kit includes 2 reference quartz (SSB, CW). The filter is assembled on a 35x19 mm printed circuit board. It is possible to produce several CFs for one frequency with a spread of no more than 20 Hz.

Four-crystal (cleanup) quartz filter “Desna”. Assembled, configured, without housing (shielded box). Manufactured at the frequency of the main HF. Possibility of changing the band from 2.7 to 0.7 kHz. The filter is made on a 30x15 mm printed circuit board. The kit includes 3 varicaps KV-127.

Radio amateur set "Desna"

The Desna set is intended for the manufacture of quartz filters: an eight-crystal main selection and a four-crystal eraser with a variable bandwidth (0.7 - 2.7 kHz) for devices with one frequency conversion used in amateur radio communications.

For the manufacture of quartz ladder filters, identical quartz resonators from PAL/SECAM television set-top boxes are used. As measurements have shown, these quartzes have a high quality factor, the resonant gap is about 12 - 15 kHz. The manufactured eight-crystal quartz filter from such resonators has the following parameters:

    squareness coefficient at levels 6 and 60 dB ~ 1.6;

    attenuation beyond the passband more than 80 dB;

    unevenness in the passband – 1.5 - 2 dB;

    6 dB bandwidth – 2.4  0.15 kHz;

    input and output resistance - 20210 Ohm.

The set includes:

    selected quartz resonators « NEW» (C = 5 Pf) – 12 pcs.;

    quartz resonators of reference oscillators (marked – G) – 2 pcs.

    Capacitor KM-12-15pF – 2 pcs. Capacitor KM-91pF – 2 pcs.

    Capacitor KM-39pF – 2 pcs. Capacitor KM-110pF – 2 pcs.

    Capacitor KM-47pF – 2 pcs. Capacitor KM-120pF – 2 pcs.

    Capacitor KM-56pF – 2 pcs. Printed circuit board – 2 pcs.

    Varicap KV-127A (B) – 3 pcs.

* Capacitor ratings are given for quartz resonators only of this “NEW” type.

P
Conceptual diagrams of CF and PKF:


C1, C7-39pF, C2, C6-12-15pF, C3, C5-47pF, C4-91pF, C8, C11-120pF, C9, C10-110pF. C1, C3-56pF, C2-91pF.

Filters are implemented on printed circuit boards. One of the terminals (marked *) of the outer resonators, and in the PKF and all four, cannot be cut off on the boards; they will be the input/output of the KF and PKF, as well as for connecting additional capacitors in the PKF.





Connection diagram for a four-crystal cleanup filter

Fig. 1 Quartz filters with “parallel” capacitances

Arrows AA and BB show the second option for switching on the KPI. Resistors R1, R4 (0 ... 300 Ohms) are installed in the presence of large emissions in the frequency response. Capacitor C4* is selected in the range from 0 to 30 pF.

In order to minimize the number of capacitors, filter circuits containing only parallel capacitances were selected, Fig. 1. Since the filters are symmetrical (with respect to their input-output), it turned out to be possible to use dual KPIs from broadcast receivers with a capacity of 12 - 495 pF. In addition, you will need another single-section variable capacitor, pre-calibrated in pF.

Setting up the filter is as follows.

To configure, you may need a device for measuring amplitude-frequency characteristics X1-38 or similar. I use an oscilloscope and a homemade attachment (see below).

Initially, all capacitors are installed in a position corresponding to a capacitance of 30 ... 50 pF. By controlling the frequency response of the filter on the device screen and rotating the capacitors within small limits, we achieve the required bandwidth. Then, by adjusting variable resistors (use only non-induction ones, for example, SP4-1) at the input and output of the filter, we try to level the peak of the frequency response. The above operations are repeated several times until the desired frequency response is obtained.

Next, instead of each individual section of the KPI, we solder a pre-calibrated capacitor, with the help of which we try to optimize the frequency response of the filter. Using its scale, we determine the capacitance of the permanent capacitor and replace it. Thus, all sections of the KPI are, in turn, replaced with capacitors of constant capacity. We do the same with variable resistors, which we will later replace with constant ones.

The final “finishing” of the filter is done directly on site, for example, in the transceiver. After installing the filter in the transceiver, it may be necessary to correct the values ​​of these resistors; in this case, for optimal matching of the filter with the output of the mixer and the input of the amplifier, the frequency converter and the oscilloscope must be connected according to the diagram shown in Fig. 2.

Fig.2 Connecting a quartz filter for final settings

Several filters were manufactured using the described method. I would like to note the following. Setting up three or four crystal filters with some skill takes no more than an hour, but with 8 crystal filters the time investment is much higher. At the same time, attempts to pre-set first two separate 4-crystal filters, and then connect them, turned out to be fruitless. The slightest scatter of their parameters (and this always occurs) leads to a distortion of the resulting frequency response. It is also interesting to note that theoretically equal capacitances (for example, C1=SZ, in Fig. 1a; C1=C7; SZ=C5, in Fig. 1b) after tuning with a graduated KPI according to the optimal frequency response had a noticeable scatter.

In my opinion, the advantage of this technique is its clarity. The device screen clearly shows how the frequency response of the filter changes depending on the change in the capacitance of each capacitor. For example, it turned out that in some cases it is quite enough to change the capacitance of one capacitor (using a relay) in order to change the filter bandwidth without significantly deteriorating its squareness.

As noted above, to configure the filter, an S1-77 oscilloscope and a converted attachment for measuring frequency response are used.

Why S1-77? The fact is that on its side wall there is a connector on which there is a sawtooth voltage of the scan generator. This makes it possible to simplify the set-top box itself and eliminate the sawtooth voltage generator (RVG) from its circuit. Therefore, there is no need for additional synchronization and it becomes possible to observe a stable frequency response at different sweep durations. Obviously, other types of oscilloscopes can be adapted, perhaps with a little modification.

Since the simplified attachment is used only when working with quartz filters near a frequency of 8 MHz, all other subranges were excluded from it.

Also, in the set-top box you are using, you will need to slightly increase the output voltage. To do this, it is enough to convert the output stage into a resonant one. It must be tuned to resonance each time a new filter is connected to its output.

Fig.3 Attachment to an oscilloscope for setting up quartz filters

Literature.

  1. V. Zalnerauskas. Series of articles “Quartz filters” Radio magazine No. 1, 2, 6 1982, No. 5, 7 1983
  2. S. Bunin, L. Yaylenko “Handbook of shortwave” ed. "Technique" 1984
  3. V. Drozdov “Short-wave transceivers” ed. "Radio and Communications" 1988
  4. Radio magazine No. 5 1993 “Swinging frequency generator”

When implementing frequency filters, it is necessary to take into account the specifics of their application. We have already discussed earlier that active filters (most often) are convenient to use for implementing relatively low-pass filters. It is convenient to use in the frequency range from hundreds of kilohertz to hundreds of megahertz. These filter implementations are quite convenient to manufacture and in some cases can be tuned in frequency. However, they have low parameter stability.

The resistance value of the resistors in the filter is not constant. It changes depending on temperature, humidity or when elements age. The same can be said about the capacitance value of the capacitor. As a result, the tuning frequencies of the filter poles and their quality factors change. If there are filter gain zeros, then their tuning frequencies also change. As a result of these changes, the filter changes its . They say about such a filter that it “falls apart”

A similar situation occurs with passive LC filters. True, in LC filters the dependence of the pole or zero frequency depends less on the value of inductance and capacitance. This dependence is proportional to the square root, in contrast to the linear dependence in RC circuits. Therefore, LC circuits have greater parameter stability (approximately 10 −3).

By applying certain measures (such as the use of capacitors with positive and negative TKE, thermal stabilization), the stability of the parameters of the described filters can be improved by an order of magnitude. However, when creating modern equipment, this is not enough. Therefore, starting from the 40s of the 20th century, more stable solutions were searched for.

During the research, it was found that mechanical vibrations, especially in a vacuum, have lower losses. Filters were developed on musical tuning forks and strings. Mechanical vibrations were excited and then removed by inductors using a magnetic field. However, these designs turned out to be expensive and cumbersome.

Then the conversion of electrical energy into mechanical vibrations began to be done using magnetostrictive and piezo effects. This made it possible to reduce the size and cost of filters. As a result of research, it was found that quartz crystal plates have the greatest stability of vibration frequency. In addition, they have a piezoelectric effect. As a result, quartz filters are by far the most common type of high-quality filter. The internal structure and appearance of the quartz resonator are shown in Figure 1.


Figure 1. Internal structure and appearance of a quartz resonator

Single crystal resonators are rarely used in crystal filters. This solution is usually used by radio amateurs. Currently, it is much more profitable to buy a ready-made quartz filter. Moreover, the market usually offers filters for the most common intermediate frequencies. Manufacturers of quartz filters use another solution to reduce dimensions. Two pairs of electrodes are deposited on one quartz plate, which form two resonators interconnected acoustically. The appearance of a quartz plate with a similar design and a drawing of the housing where it is placed are shown in Figure 2.


Figure 2. Appearance of a quartz plate with two resonators, drawing of the housing and appearance of the quartz filter

This solution is called a quartz pair. The simplest quartz filter consists of one pair. Its graphical designation is shown in Figure 3.


Figure 3. Graphic designation of a quartz pair

The quartz double is electrically equivalent to the bandpass filter circuit with two coupled circuits shown in Figure 4.


Figure 4. Double-circuit filter circuit equivalent to a quartz twin

The difference lies in the achievable quality factor of the circuits, and therefore the filter bandwidth. The gain is especially noticeable at high frequencies (tens of megahertz). Quartz filters of the fourth order are made on two pairs connected to each other using a capacitor. The input and output of these twos are no longer equivalent, so they are denoted by a dot. The diagram of this filter is shown in Figure 5.


Figure 5. Fourth order quartz filter circuit

Filters L1C1 and L2C3, as usual, are designed to transform the input and output resistance and bring them to a standard value. Eighth-order quartz filters are constructed in a similar way. To implement them, four quartz twins are used, but unlike the previous version, the filter is made in one housing. A schematic diagram of such a filter is shown in Figure 6.



Figure 6. Schematic diagram of an eighth-order quartz filter

The internal design of an eighth-order quartz filter can be studied from the photograph of the filter with the cover removed, which is shown in Figure 7.



Figure 7. Internal design of an eighth-order crystal filter

The photo clearly shows four quartz duals and three surface mount capacitors (SMD). A similar design is used in all modern filters, both penetrating and surface mounted. It is used by both domestic and foreign manufacturers of quartz filters. Among domestic manufacturers, we can name JSC Morion, LLC NPP Meteor-Kurs or the Piezo group of enterprises. The list of references shows some of the foreign manufacturers of quartz filters. It should be noted that the design shown in Figure 7 can easily be implemented in surface-mounted (SMD) packages.

As we can see, now there is no problem buying a ready-made quartz filter with minimal dimensions and at an affordable price. They can be used to design high quality receivers, transmitters, transceivers or other types of radio equipment. To make it easier to navigate the types of quartz filters offered on the market, we present a graph of typical dependences of the amplitude-frequency response on the number of resonators (poles), given by SHENZHEN CRYSTAL TECHNOLOGY INDUSTRIAL


Figure 8. Typical shape of the frequency response of a quartz filter depending on the number of poles

Literature:

Along with the article "Quartz filters" read:


http://site/Sxemoteh/filtr/SAW/


http://site/Sxemoteh/filtr/piezo/


http://site/Sxemoteh/filtr/Ceramic/


http://site/Sxemoteh/filtr/Prototip/