Directional microphones. Directional Microphones with Parabolic Reflector Professional Directional Microphone

Today we continue articles about spy technologies, namely, today we will try to assemble a directional microphone - for listening to neighbors behind the wall. Sometimes a bug is less useful for eavesdropping and there are places where it is simply impossible to drop a radio transmitter for various reasons. Or let's say you really need to listen to the conversation of some person, but you don't have access to his house ... And here a microphone comes to the rescue, which is specially made for such purposes. The device itself will be mounted in a silicone gun.

The directional microphone is powered by a low-voltage power supply of 3 - 6 volts. Convenient use of lithium batteries from mobile phone with a voltage of 3.7 volts and with a capacity of about 800 mA. The operating current of the device is from 50 to 120 mA, depending on what type of transistors we use. The whole design of the directional microphone fits perfectly in the specified housing and has a small size. The piezoelectric head receives the signal, then the signal is amplified by a preamplifier assembled on transistors VT1 and VT2, later passing through the filter, cut off from the signal low frequencies and the processed signal goes to the final amplifying stage. The degree is so high that it allows us to hear even the whispers of our neighbors. The device uses an ordinary piezoelectric head. See the diagram of a directional microphone below:

Almost any high-impedance speaker with a resistance of at least 25 ohms is suitable as a headphone, in this case a small head with a resistance of 32 ohms is used. All transistors can be replaced with imported ones - this will reduce the size of the board and may positively affect the overall quality of the directional microphone. It is possible to use SMD components. Instead of the final amplifying stage, you can also use an amplifier, for example, on a microcircuit, assembled according to the bridge version, but when using microcircuits, the sensitivity can be halved, but it's easier. It is possible to power the common circuit board of the directional microphone from two AA batteries with a voltage of 3 volts, but the use of a battery is convenient because it can be charged and reused, and in addition, the battery ensures long-term and reliable operation of the device.

A piezo head-microphone is placed in a specially made umbrella in order to center the sound waves at a single point - this, in turn, preliminarily increases the spectrum of the speech stream. The main thing is not to confuse the polarity of the head by connecting the central part of the head to the plus according to the scheme.

It is better to isolate the battery from the common case in order to avoid background sound, and it is also necessary that the earpiece be at a certain distance from the device, which is exactly 1 meter. If the piezoelectric head is replaced with an electret microphone, then the device will turn into a directional microphone, it is able to pick up human speech at a distance of about 15 meters. True, in this case, you will not be able to hear conversations behind the wall.

Directional microphones

If a window or transom is open (ajar) in a dedicated room, directional microphones can be used to listen to the conversations taking place in it. Reconnaissance can be conducted from neighboring buildings or vehicles located in parking lots adjacent to the building.

Three types of directional microphones are mainly used: parabolic (reflex), tubular (interference) and flat microphone arrays.

parabolic microphone(Fig. 1) has a parabolic reflector, in the focus of which is placed a microphone capsule with an omnidirectional or unidirectional directivity (XD). Such microphones are sometimes called reflex microphones.

Rice. 1. Scheme of a parabolic directional microphone

Sound waves coming from the axial direction of the parabola are reflected from the reflector and, due to the properties of the parabola, after reflection, are concentrated in phase at its focus, where the microphone capsule is located. Sound waves arriving at an angle to the axis of the parabola are scattered by the reflector without reaching the microphone. In a reflex system, the CI is highly frequency dependent and varies from almost non-directional at low frequencies (with a reflector diameter less than the sound wavelength) to a narrow lobe at high frequencies. The frequency response of the sensitivity of such microphones has a rise towards high frequencies with a steepness of the order of 6 dB per octave, which is usually compensated either by an electronic method (for example, an equalizer) or by a special capsule design.

The appearance of some parabolic microphones is shown in photos 1 - 3, and the main characteristics are in Table. 1 − 3 .

The simplest in design is the Super Ear - 100 directional microphone (photo 1).

The parabolic reflector is made of plastic. An electret microphone connected to the input of a low-noise low-frequency amplifier is placed at the focus of the reflector. The built-in 8x binoculars allow you to accurately point the microphone at the target.

The microphone measures 29015090 mm and weighs 1.2 kg. The microphone is powered by a battery type "crown". Operating time from the internal battery - up to 60 hours.

Photo 2. Appearance of parabolic directional microphones

Photo 3 Appearance of parabolic directional microphones

Table 1. Main characteristics of the directional parabolic microphones PKI 2915 and PKI 2920

Table 2. Main characteristics of parabolic microphonesSupersoundZoomandPR-1000

Table 3. Spectra G50 and Big Ears BE3K Parabolic Microphone Key Features

Listening to intercepted conversations is carried out using headphones. The microphone has a built-in voice recorder that allows you to record intercepted conversations.

The microphone directivity pattern is 10, the gain is 70 dB, which ensures the interception of conversations in open areas at low noise levels up to 100 m. The microphone frequency range is from 100 to 14,000 Hz.

The quality of a directional microphone is estimated by the gain ratio in relation to "signal-to-noise" due to spatial selection K nm, dB.

For a parabolic microphone, this coefficient K pm, dB, is calculated by the formula:

Kpm ≈ 10lg(1.2×10 -4 ×S neg × f 2 ), (1)

where S neg is the area of ​​the microphone reflector, m 2; f is the signal frequency, Hz.

As can be seen from formula (1), the larger the area of ​​the reflector, the greater the value of the coefficient K pm.

Therefore, the range of interception of conversations largely depends on the diameter of the reflector. For example, for the same conditions, with a reflector diameter of 60 cm (PKI2915 microphone), the conversation interception range is 100 m, and with a diameter of 85 cm (PKI2920 microphone) - 150 m. Parabolic microphones are most often disguised as satellite television antennas and installed on the balconies of houses .

Traveling wave (interference) microphones, often referred to as tube microphones, consist of a tube with holes or slots, at the rear end of which is an omnidirectional or unidirectional microphone capsule (Fig. 2) .

Rice. 2. Scheme of a tubular (interference) microphone

The holes (slots) in the tube are closed with a cloth or porous material, the acoustic impedance of which increases as it approaches the primer. Exacerbation of chronic insufficiency is achieved due to the interference of partial sound waves passing through the holes of the tube. When the sound front moves parallel to the axis of the tube, all partial waves arrive at the moving element simultaneously, in phase. When sound propagates at an angle to the axis, these waves reach the capsule with a different delay, determined by the distance from the corresponding hole to the capsule, while partial or complete compensation of the pressure acting on the moving element occurs. A noticeable worsening of CI in such microphones begins at a frequency where the length of the tube is more than half the wavelength of the sound wave. With an increase in the frequency of HN, it becomes even more aggravated. Therefore, even with a significant length of such microphones, which can reach a meter or even more, the frequency response at frequencies below 150–200 Hz is determined only by the capsule and is usually close to a cardioid or supercardioid.

Tubular directional microphones are more compact than parabolic ones and are used mainly in cases where it is necessary to ensure the secrecy of listening to conversations. With the use of such microphones, reconnaissance can be conducted both from a car and from a window located opposite a building.

The appearance of some tubular microphones is shown in photos 4 - 7, and the main characteristics are in Table. 4, 5.

Typical tube microphones include the PKI2925 directional microphone (photo 4). The total length of the microphone with a 35 cm tube is 85 cm, weight - 525 g. The microphone is powered by battery supply voltage 3.6 V. The microphone has built-in high and low pass filters.

Photo 4. The appearance of a tubular directional microphonePKI 2925

Photo 5. The appearance of a tubular directional microphoneYKN

Photo 6. The appearance of a tubular directional microphoneSennheiserMKH 70 P48

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Directional microphone"hunt" is directional professional microphone and allows you to hear sounds at a distance of up to 300 m., in absolute silence, as well as a microphone for listening at a distance has a monocle that allows you to view the tracking object, complementing the overall picture. This one can transmit good sound only in direct line of sight, there should not be any obstacles such as a wall or a building. If the barrier is single-layer glass, then the range will be reduced to 10-15 meters, tree branches and bushes will also reduce the range. Such directional microphone greatly facilitates the hunt for the beast, helps to orient its location. The sound that will be received by the directional microphone for hunting can be recorded to the internal memory and then listened to. This is a kind of voice recorder function.

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Working hours directional microphone from the crown 9 V. to 3 hours. Absolutely any headphones are suitable for this device, since the microphone has a standard audio input in case the headphones in the kit suddenly do not suit.

Technical characteristics of the directional microphone for wiretapping:

Built-in voice recorder - play and record buttons on the case.

Audio output 3.5 mm jack

The directional microphone has a range of recorded sound waves - up to 100 meters

Monocular magnification - 10 X

Equipment:

Directional microphone - 1 pc.

Stereo headphones - 1 pc.

Instruction manual - 1 pc.

Buy a directional microphoneright now You can by calling:

How to make a simple directional stereo microphone out of junk?

I have already described one design of a microphone designed for the DPC, but its operation revealed a number of shortcomings, which are described below. So I tried to make a better model.

The result is two different microphones, one mono and the other stereo.

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Prologue.

My first homemade microphone had a too uneven frequency response due to the resonance that occurs in the tube. In addition, it allowed recording only monophonic sound. It was decided to build a more perfect model of the microphone, but, as always, do without turning and milling.

In the course of reflection, several ideas came up for making a slot microphone tube without the use of machines, and even the tube itself.

Washer slit microphone tube.

The slot microphone tube can be made from large diameter washers. If two holes are drilled in each washer, then you can use two pins to assemble a multilayer sandwich, and adjust the size of the slots with small washers.

This idea, in my opinion, has only one significant drawback. In order to drill holes in each washer with sufficient accuracy, a small jig would have to be made.

Tube slot microphone from transistor clamps.

If instead of washers you use clamps from old-type transistors, then you won’t have to drill anything at all. It remains only to collect the tube.

The disadvantage of a pipe assembled from standard clamps from transistors of the type P213 ... P217 is a lot of weight. If you use duralumin clamps from transistors of the KT801 type, you can get a fairly light tube. True, it will be difficult to place two microphone capsules in such a tube at once, so for a stereo wet phone you will have to look for another solution.

Slit microphone tube made of metal tape.

The slit microphone tube can be made from a narrow metal tape by rolling it into a helix on a template of the desired diameter. Then the width of the slots can be adjusted by changing the pitch of the screw.

Based on these ideas, I made two microphones - monophonic and stereophonic.

This time I omitted some details regarding the assembly of microphones and the manufacture of parts, since I have already covered them in detail.

Slit microphone from clamps from transistors.

This is a drawing according to which a slit microphone was made from transistor clamps.

1. Collar from transistors - duralumin.
2. Nut - steel, M2.
3. Grover washer - steel, M2.
4. Hairpin - steel, M2.
5. Gasket - cambric.
6. Shielded cable - Ø2mm.
7. Bushing - rubber Ø11mm.
8. Body - medical syringe - 5g.
9. The back wall is a medical syringe - 5g.

It turned out to be easy to assemble a microphone from clamps from transistors. Here's what was used for the build.

1. Grover washer - steel, M2.
2. Shielded cable with 3.5mm Jack connector.
3. Helical spiral - solder Ø2mm.
4. Velvet.
5. Capsule electret microphone– Ø10x7mm.
6. Clamp from transistors such as KT801, KT602, KT604.
7. Medical syringe - 5 gr.
8. Stud, nut - steel, M2 (studs were made from a bicycle spoke).

To do appearance more presentable, I wrapped the body of the microphone, made from a syringe, with heat shrink tubing. First I seated the front part, and at the end of the assembly I inserted the cover and seated the tail part.

Here's what happened.

Directional slit stereo microphone made of metal tape.

This is a drawing from which a directional stereo microphone was made from a metal tape.

1. Screw - M1.6x5.
2. Nut - M1.6.
3. Collar - steel, S0.3mm. (tin from a tin can).
4. Tape - steel, S0.5x8x50mm.
5. Screw - M1.6x5.
6. Partition - medical syringe 20gr.
7. Bushing through passage - rubber Ø11mm.
8. Cargo - solder Ø2mm.
9. Krpus - medical syringe 20gr.

Very few parts were needed for this microphone.

1. Shielded mono cable - Ø2mm.
2. Shielded stereo cable - Ø3mm.
3. Screw - M1.6x5.
4. Bushing through passage - rubber Ø11mm.
5. Collar - steel, S0.3mm. (from a can).
6. Screw, nut, washer - M1.6.
7. Cargo - solder Ø2mm.
8. Electret microphone capsule - Ø6x6mm.
9. Syringe medical 20gr.
10. Tape - steel, S0.5x8x50mm.
11. Heat shrink tube – Ø8mm.

In order not to deal with painting, I covered the steel tape with heat shrink tubing, and then rolled it into a helical spiral pos. 1 on the body of a 10 gram syringe.

From the body of a 20-gram syringe, I made the microphone body pos.3, and the baffle pos.2 from the piston of the same syringe.

At this stage, you can drill three holes for attaching the tube to the body and cut the threads.

To reduce the length of the unshielded wires going to the microphone capsules, I extended the stereo cord with two small pieces of mono cord. The picture shows how it was done. Thick paper is used as insulation.

The microphone housing, as in the previous design, was covered with heat shrink tubing.

Another picture explaining the assembly order.

Here's what happened.

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And here's how it works.

Small details.

When testing the first pair of microphone capsules, it turned out that their frequency response differed too much. In anticipation of the market day, I even assembled a small stand to test microphones without using soldering. I bought a few more capsules for $ 0.4, so that I had plenty to choose from. But, the very first pair taken from this purchase turned out to be consistent in frequency response. I didn't experiment anymore.

In this article, we will look at the main types and mechanism of operation. remote devices wiretapping.

Manifold

The technology of microphones for listening at a distance varies depending on their type. According to the principle of operation, one can distinguish three categories of remote listening devices:

1. Directional microphone;
2. laser microphone;
3. Listening device through the wall.

Directional microphone

A directional microphone is used for remote listening in open areas and recording telephone conversations. the main problem directional microphones - the distance to the sound source. Already at a distance of one hundred meters, the sound will weaken so much that it is almost impossible to separate speech from interference.

There are 4 types of directional eavesdropping mechanisms:

Professionals use a whole kaleidoscope of directional listening devices. However, most of this list is not for sale. Parabolic microphones are available to "mere mortals", which you can buy in special online bug stores.

laser microphone

With a laser listening device you can hear what's going on in the room. It reads the vibration of the window in the room. The device sends a laser beam to the glass. Reflected from the glass, the laser changed by oscillations returns to the device. The device decodes the signal and we hear the sound.

The range of the laser is up to 0.5 kilometers. You don't have to give out your position to the listening object. Without suspicious bugs, you can listen to any secret conversation on the phone.

The cheapest laser microphone in Moscow costs about half a million rubles. It is possible to buy cheap artisanal versions, however, they will not work properly. If they work at all.

Listening device through the wall

If you and the purpose of wiretapping are separated only by a concrete wall, then choose this particular device. The microphone picks up the slightest vibrations of the wall and converts it into sound. According to the principle of operation, it is similar to a laser. The only exception is you have to be at least in the next room.

For the device to work properly, you need to adjust the sound. To do this, lean the microphone against the wall and adjust the sensitivity. As soon as you hear understandable speech, you can use it.

Directional wiretapping device through the wall is cheap. You can buy it in special bug and phone stores for about five thousand rubles.

We looked at the types of listening devices at a distance. You have probably already chosen for yourself what kind of devices to replace the notorious bugs. In the next paragraph, we will look at popular models of listening devices.

Favorites in the market

Parabolic Microphone Super Ear 100

As with all parabolic devices, it uses plastic concave parabolic dish. AT this device There are headphones and binoculars with an eightfold magnification. The built-in voice recorder allows you to record short conversations. You can connect headphones so that nothing interferes with listening to the target.

A microphone with a dish allows you to listen to a conversation at a distance of up to one hundred meters. Up to 70 dB of sound amplification makes Super Ear 100 extremely sensitive, while you can set it to a maximum output of 105 dB and record any conversation on the phone.

This handsome man is powered by a 9-volt "crown", which will live 55 hours. Weighs a little over a kilogram. Thanks to the resistant design, it is able to listen to the environment and phones in any frost and heat.

The price of Super Ear 100 ranges from 3500 to 5 thousand rubles.

Directional microphone Yukon

Like the previous instance, can pick up sounds from a hundred meters away. However, it does not have a special dish, and it is smaller in size than a stage microphone. Battery life - up to 300 hours.

The wind with it will not be a hindrance, since the Yukon is equipped modern system noise reduction. You can adjust the volume and volume of the sound yourself.

The microphone can be attached to binoculars, spyglass or camera. It will be convenient for you not only to listen to the target, but also to observe it. There is also a tripod mount.

Such a device is eagerly used reporters and cameramen in sound studios because it's easy to record professional-quality sound with it.

Price Yukon - from 4200 to 6 thousand rubles.

Conclusion

We looked at listening devices that can replace bugs. They can be afforded by a person of any income and profession. In this case, you do not need to be near the target, and the bug will not arouse suspicion.

However, remember that illegal espionage is a criminal offense. You can get to places not so distant for a long time just because, without the consent of the goal and the law, you installed a bug or recorded a secret conversation. So make sure you don't break the law. Let your conscience guide your actions.