TRANSMITTERS - "SPIES"

We bring to your attention several designs of miniature transmitters.

Necessary devices and tools:

1. Ammeter voltmeter (AVOmeter) with a linear scale (pointer) with measurement limits 30V, 150V, 15V, current 15 Ma, 150 Ma.

2. Wavemeter - the diagram is shown below:

Coil L1 contains 4.5 turns of wire with a diameter of 1-1.5 mm, wound on a mandrel with a diameter of 16 millimeters. The withdrawal is made from 2 turns. A piece of coaxial cable is used as an antenna. The braid and the inner core are soldered together. The length of the segment is 100 millimeters. Microammeter - 50-100 microamperes. Structurally, the wavemeter is made in a metal case.

It is better to calibrate the wavemeter using a high-frequency generator, but you can use an auxiliary generator and a radio receiver with a digital scale for this purpose. The generator can be assembled according to one of the schemes described below. First, on the scale of the receiver, we find the frequency of the auxiliary generator, then we set the wavemeter to the same frequency and make a mark opposite the pointer of the wavemeter capacitor. So we consistently perform the entire calibration for operating frequencies in the range of 88-108 megahertz.

3. Control transmitter.

The control transmitter circuit is shown below:

This transmitter is assembled according to a typical scheme and has maximum repeatability.

About the details: Microphone - type MKE-332...333A, transistor - KT3102A-B, KT315 can be used, but they have a large generation current spread. The coil has 6 turns, PEV 0.45-0.7 wires on a blank of 6 millimeters (winding - close), tap - from 2 turns (counting from above according to the scheme). The frequency of the assembled circuit is 82 ... 90 megahertz. The frequency is changed by a variable capacitor. Antenna - a piece of stranded wire, 200-260 mm long.

Setting: We connect the power source (9 volts!), Turn on the milliammeter in series with the source. Current consumption should be within 8-10 milliamps. We select the current consumption using the resistor R2. Next - connect the antenna and tune the transmitter to the desired frequency.

The control transmitter can also be used for pre-selection of transistors (in mass production). To do this, you need to solder the socket to the place where the transistor is connected and insert the transistor to be checked into it (it is clear that before changing the transistor, you must turn off the power source!).

Transistors are selected for the same current consumption. It is also useful to use several (for example, 43, 51 and 62 kilo ohms) resistors and a switch for the appropriate number of positions in place of the resistor R2. Later, during mass production, the nominal value corresponding to the optimal one for this instance of the transistor is soldered in place of this resistor. To manufacture a transmitter in one copy, you can not do a preliminary check of the transistor, but then you may have to select a resistor in the finished design - and this is not very convenient, given the miniaturization of the design ...

4. Tools for installation work (tweezers, wire cutters, soldering iron with accessories).

5. Materials: foil fiberglass, winding wire, paraffin - for fixing the turns of the coils after tuning, "zapon" type varnish.

A little about antennas: in the descriptions there will be antenna designations A1 and A2. Antenna A1 is a piece of wire about 300 millimeters long, antenna A2 is a piece of wire about 1 meter long.

A typical transmitter circuit with an A2 antenna provides a communication range in the city - up to 500 meters (manufacturer's data). To operate the transmitter at a fixed frequency, the capacitor C6 is replaced by a constant capacitor of the appropriate rating.

The high power transmitter circuit is shown below:

The range of the transmitter with the A2 antenna is 1-1.2 kilometers at a power supply voltage of 9 volts. Current consumption - about 28 milliamps.

This transmitter consists of a typical one and is supplemented with a power amplifier based on a VT2 transistor. The circuit is characterized by increased frequency stability and less dependence on external factors. This allows you to wear the transmitter on your body...

About the details: L1 - 6 turns, wire 0.47, on a mandrel, with a diameter of 3.5 mm, L2 - 4 turns, on a mandrel 2 mm, wire with a diameter of 0.3 mm. L3 - on a mandrel 2.7 mm - 7 turns, wire diameter - 0.3 mm. When laying out the transmitter, the coils L1 and L3 should be positioned mutually perpendicular! Coil L2 is placed inside coil L1. Other details - as in a typical transmitter.

Setting: First, we set up the master oscillator on the transistor T1 - by changing the value of the resistor R2, we achieve a current consumption of 10 mA. Next, we assemble the output stage on the transistor T2. With the antenna connected, by moving the L2 coil, we achieve a current consumption of approximately 26-28 mA. Further - along the wavemeter we achieve the maximum output power (by selecting loop capacitors - roughly and moving apart the turns of the coils - smoothly).

The telephone line powered transmitter is shown below:

To work in telephone lines, the transmitter must have a current consumption of 10-12 mA in lines without a blocker and 16-18 mA in lines with a blocker. The transmitter is assembled according to a typical scheme. To obtain the desired current consumption, it is necessary to put transistors in the circuit with a selected current consumption of 7-8.5 mA with a base resistor 2 times smaller than the one used when selecting the transistor. A microphone is not needed in this circuit. Modulation is carried out by power supply during a conversation... Transmitter setup does not differ from the typical one. The capacitance of capacitor C2 is 0.022 microfarads. A few words should be said about the design of the antenna. For the manufacture of the antenna, a piece of insulated single-core wire, 210-240 mm long, was used. At one end, the insulation is stripped for soldering. A piece of winding wire, approximately 200 mm long, is soldered to the stripped end, and it is wound onto the wire of the main antenna, approximately 20 mm wide in several layers. The opposite end of the wire is soldered into the circuit. After manufacturing, the winding should be fixed. It turns out an antenna with a distributed inductance. This measure made it possible to significantly reduce the dimensions of the antenna with little or no reduction in the radiated power (in this design, for obvious reasons, they sought to obtain the smallest possible dimensions). The range in the city (declared by the manufacturer) is 200-350 meters. The transmitter turns on when you pick up the handset.

The transmitter coil L1 is wound on a 3 mm blank turn to turn and contains 6 turns, wires with a diameter of 0.3-0.4 mm. The setup is practically the same as that of a typical transmitter. We adjust the frequency by selecting a loop capacitor and moving apart the turns of the coil.

The FET transmitter circuit is shown below:

The circuit is characterized by low power consumption. The selection of transistors is not needed. The output power is equal to the output power of a typical transmitter with half the current consumption. Frequency drift when the supply voltage changes from 3 to 9 volts - no more than 0.2 megahertz (declared by the manufacturer). Coil parameters - as in the basic transmitter circuit. The outlet for connecting the antenna is made from the second turn. The circuit can be used as an independent transmitter, or as a master in a more powerful one (similar to a transmitter circuit with increased output power).

All of the above transmitters operate in the frequency range of 88-108 megahertz (FM band). To tune to the FM range (64-72 megahertz), you need to correspondingly increase the number of turns of the loop coils by 1.4 times. The length of the antennas should also be increased by 1.4 times. You can not increase the length of the antenna, but this will slightly reduce the range of the transmitters.

A few words should be said about the installation. To give the design sufficient rigidity and reliability, all transmitters should be manufactured on printed circuit boards. When designing a printed circuit board, it is necessary to strive to reduce all conductors to a minimum. The length of the leads of the parts is reduced to the minimum possible. Theoretically, it is possible to manufacture a transmitter according to a typical scheme on a board with an area of ​​no more than 1 square centimeter. After tuning, the transmitter should be coated 2-3 times with quick-drying varnish - to increase the rigidity of the structure. The coating is best done by dipping (you must first solder all external conductors). The length of the power and microphone wires should also be kept to a minimum. After assembly, it is useful to place the transmitter in a sealed metal casing, which should be connected to the common ("negative") conductor of the board at one (!) point. All these measures improve the reliability of the transmitter during operation.

The acoustic generator is designed to induce interference in places of confidential negotiations. It generates "white" noise in the entire range audio frequency. The transmission of acoustic vibrations occurs through piezoelectric vibrators and acoustic speakers

This transmitter is designed to transmit telephone conversation information to a VHF receiver in the 68-108 MHz range. The range of the repeater is 50-100m

The detailed scheme is very easy to repeat by any novice radio amateur and is able to register vibrations of walls up to 0.5 m thick or a whole riser of radiators

Usually, radio bugs operate at one frequency in the range of 30 ... 500 MHz with a low radiation power of not more than 5 mW. More advanced radio bugs can work in standby mode and start radio transmission in the presence of a threshold noise level, which reduces their likelihood of detection. Many radio bugs like to "dwell" in telephone or 220V sockets, as they do not require their own power source.

A selection of simple homemade designs of radio bugs powered by a single 1.5 volt cell, with very low current consumption. Such a radio bookmark can work offline for a very long time with the transmission of a radio signal at a distance of 30-60 meters.

This method of protection against laser devices consists in using special devices to make the glass vibration amplitude much greater than that caused by a person's voice. At the same time, difficulties arise on the receiving side in detecting the speech signal.

An excellent selection of good circuitry solutions for television video transmitters for wireless transmission video signal from video cameras, satellite receivers, game consoles and many other devices. Video transmitter circuits operate in the standard frequency range of 470-580 MHz and can be received from channels 21-34 by almost any TV. The video signal is capable of being transmitted over a distance of 50-100 meters using a short antenna made from an ordinary piece of copper wire.

The presence of a video camera in modern realities is not particularly surprising to anyone. It can be used to reflect important moments in our lives, the lives of our loved ones, as well as our competitors in our professional lives. In this review article, we will consider the main schemes and connection methods for different purposes, their advantages and disadvantages.

To exclude work mobile phone and mobile internet in certain places such as theaters or educational institutions during the exams, you can use homemade GSM signal jammers for cell phones.

This bug scheme is recommended for repetition by novice radio amateurs and young spies. Firstly, it is not difficult to assemble, it consists only of available radio components and is powered by a 9 volt crown battery. The radius of its action is up to 200 meters, in the conditions of the city it can be even less, it all depends on the transistor used in the bug circuit. I borrowed the scheme from an English-language site, but it is fully functional, because it was tested in the assembly.

Likbez > How to find a spy

S. Chertoprud

Fans of shortwave radio broadcasts often stumble upon mysterious stations broadcasting endless sequences of numbers. An incomprehensible code is monotonously read out in different languages ​​by male, female, and sometimes even children's voices. Strange broadcasts first appeared on the air about forty years ago; The signal of such stations is very strong, but they never report either their location or the audience for which the broadcast is intended. Usually, listeners, having stumbled upon such a transmission, for some time still try to make out the endless "three-five-two-nine ...", and then, confused, turn the tuning knob further.

It is extremely rare for such radio stations to transmit individual phrases or texts. For example, a few days before the dissolution of the East German foreign intelligence service, the Stasi, a discordant choir of male voices constantly sang a song about a little duckling. It was broadcast on the same frequencies as the usual instructions to the "fighters of the invisible front."

Only numerous "illegals" and agents from the GDR all over the world could appreciate the vocal abilities of officers of one of the most effective intelligence services of the Cold War period: for them, the transfer meant the end of their careers. Meanwhile, the song was heard not only by scouts and counterintelligence officers, but also by numerous radio amateurs, who, in all likelihood, did not understand the meaning hidden in it, but meticulously recorded the time of each session and the frequency of "spy stations".

Loners vs Spies
Since about the mid-1970s, with the advent of new receivers with digital devices to track transmitters, shortwave enthusiasts took up “number stations” seriously. By that time, it was already clear that the mysterious radio points belonged to spy centers and transmitted encrypted messages to their agents in other countries. work, but also engaged in radio direction finding to establish their bases.

As you know, radio communication in the short wave range ensures the transmission of messages over the longest possible distances, connecting even diametrically opposite points of the globe. Accordingly, HF broadcasts are an ideal tool for anonymous one way communication. An intelligence agent anywhere on the planet can receive messages from the authorities using a small, publicly available and unmodified radio receiver.

It has long been known from numerous documentary books and memoirs of retired intelligence officers that so-called one-time pads are used to encrypt such messages - a cryptosystem that is absolutely unbreakable when it is correct use. True, history also knows cases of fatal errors, when a "one-time" cipher was used repeatedly, which led to its opening, reading secret correspondence and the arrest of agents.

The most famous story of this kind is the American "Venona Project" (http://www.nsa.gov/docs/venona), which led to the exposure of the extensive Soviet intelligence network in the 1940s and 50s. The cryptanalysts of the NSA (National Security Agency, National Security Agency, the American analogue of the Russian FAPSI) managed to decipher some of the messages exchanged between the Soviet legal residency and the Center.

For those who want to outdo the NSA, there is the original Project Conet website on the internet. It was initiated by a small British company Irdial-Discs, which back in 1997 released a set of four CDs with recordings of spy "number stations" broadcasts over the past thirty years. Now, inspired by a series of well-known RSA Challenges competitions popular cipher algorithms conducted by RSA), Project Conet (http://www.ibmpcug.co.uk/~irdial/conet.htm) encourages everyone to engage in the opening of encrypted intelligence transmissions. located in Britain, USA and Germany.

It is unlikely that the intelligence services of these countries will suffer any damage from the actions of the Internet "cryptanalysts". An amateur cannot open a cryptosystem of this level. Most likely, with such a peculiar action, the company is simply trying to revive interest in a somewhat stale product. The fact is that any radio amateur can record the latest broadcasts of "number stations" himself or buy a CD-ROM with such a selection. It is interesting, however, that, having announced the competition, the organizers for some reason forgot to name the amount of the prize.

Radio intelligence (Communication Intelligence, COMINT) - the most old view electronic intelligence. Its main content is the detection and interception of open, classified, coded transmissions of communication radio stations, the direction finding of their signals, the analysis and processing of the obtained information in order to reveal its content and determine the location of radiation sources. Radio reconnaissance information about enemy stations, their construction systems and the content of transmitted messages makes it possible to reveal the plans and intentions of the enemy, the composition and location of his groupings, to establish the location of their headquarters and command and control posts, bases and missile launch sites, and so on.

Here are three typical examples of messages from the electronic intelligence unit:

Russian military network No. 1.

The traffic consists of control radio sessions every two hours, although once an encrypted message was accidentally transmitted.

Callsigns: RINK-17, RINK-22, RINK-25, RINK-44, RINK-46, RINK-55, RINK-74, RINK-80, RINK-86, RINK-93, RINK-94, RINK-100, SMALL BIG.

Frequencies: 2650 kHz (Night), 5855 kHz (Day).

Russian military network No. 2.

The traffic on this network consists of messages in the format "5 digits word 4 digits 4 digits". Perhaps this is a type of encrypted message.

For example: "54828 SVINTUS 0064 0392" or "11233 ARMOR 2207 7720".

Call signs: KAZAK-24, VIRUS-11, UROZHAI-24, ETHER-12.

Frequencies: 4517 and 5794 kHz.

Russian military network no. 3.

The traffic in this network consists of the exchange of information between aircraft, ships and the flight control center (air traffic controller).

Callsigns: KLAD-86 (air traffic controller), METEOR-24 (aircraft), NAGAN-58, KLEN-38, VETER-41, LEADER-24, HYPNOSIS-60, ZIMA-158 (ship).

Frequencies: 5360 and 5888 kHz.

These data are taken from one of the sites of radio amateurs - http://www.wunclub.com. These people are fanatically looking for any secret radio stations, from the armies of all countries of the world to aerospace agencies. It is clear that the list also includes radio stations of agents and illegal intelligence officers, be it Israeli, American or Russian. Many radio amateurs are engaged not only in listening and recording transmissions of "numerical stations", but also in ordinary radio intelligence. If in the first case the damage from their activities is minimal (counterintelligence technical units themselves closely monitor all communication sessions), then in the second they sometimes turn out to be more effective than the military. After all amateurs perform the same tasks that radio intelligence solves, but at the same time they have a unique opportunity to compare data obtained from operators that are independent of each other, which the military cannot afford.

A little about ghosts
The international club of radio amateur interceptors "Spooks" ("Ghosts") prefers not to advertise itself. By their own technical capabilities"ghosts" can easily compete with the radio intelligence of the world's leading powers. The activity of the club began in the 1980s, when many radio amateurs around the world began to actively communicate with each other. In the mid-1990s, some of them became interested in radio intelligence. interested not only in the location and parameters (transmission schedule, call signs, frequencies) of individual radio stations, primarily for military purposes, but also in the content of messages.

Unlike the USSR and subsequently Russia, in the USA there are no frequencies prohibited for listening (moreover, they even publish directories indicating the frequencies of ground services of airports, police, and the army). As a result, over many years of broadcast monitoring, the club members have accumulated information about how the detected transmitter worked during what period. That is, in fact, everyone for himself was engaged in what, in the language of electronic intelligence, is called "drawing up an activity schedule." And this is a full-fledged part of the work of intelligence, which makes it possible, subject to the analysis of many data, to predict events.

Here is what, for example, Viktor Suvorov wrote in Aquarium about the capabilities of the GRU electronic intelligence: “A file is opened for each radio station, for each radar: type, purpose, where it is located, to whom it belongs, at what frequencies it works ... Whether the messages are clear to us or not, an activity schedule is set up on the station and each of its broadcasts is recorded ... If each broadcast is recorded and analyzed, then it soon becomes possible to predict its behavior. As a result of many years of analysis, it becomes possible to say: “If RB-7665-1 went on the air, then in four days there will be a massive take-off in Ramstein.” This is an inviolable law. And if the station we call C-1000 suddenly starts working, here and it is clear to the child that the combat readiness of American troops in Europe will be increased…”.

Who uses the information obtained by "ghosts"? In addition to numerous sites of radio amateurs, of which there are now more than thirty, these are journalists, analysts and everyone who needs reliable information about the situation in a particular region. Although the analytical capabilities of "ghosts" are far from the professionals from the GRU but they can do something. As an example, the story of the discovery of a group of Russian agents in the United States, former citizens of Cuba.

Phantoms against Cubans
On September 28, 1998, a message appeared on the Spooks club's electronic bulletin board: "Two weeks ago, the Miami Herald newspaper reported that a group of Cuban spies, 12 people, were detained by FBI agents in Miami who were trying to infiltrate the American military base in South Florida." The radio amateurs were given the task of establishing how the arrest of Cuban spies affected the activity of radio transmitters operating from the territory of Cuba (it is tasks of this kind in such situations that are performed by counterintelligence services)

A week after the arrest of the Cuban spies, Andy Bell reported that the station, which had been given the number S7 Russian Man by amateurs, had suddenly switched to a daily operation. As it was established by the ghosts, before the arrest of the spies, the transmitter went on the air only twice a week. Based on this, the hunters suggested that the duplication of messages may mean that the recipient of the information is not responding to the signal. Since the S7 Russian Man transmitter was previously held as belonging to the FAPSI (under this designation, in addition to the transmitters of the FAPSI itself, the radio stations of other Russian intelligence services - the SVR and the GRU) are listed), it was concluded that the Cuban group may have worked for the Russians. Further (especially for those interested) was made public Technical information, namely the frequencies on which the S7 Russian Man transmitter worked: 5937 kHz, 7737 kHz and 9337 kHz. According to some experts, most of the broadcasts for Russian intelligence agents were conducted from Cuba, where until recently the Lourdes radio interception center was located. The choice of location is not accidental: short distance to the United States allowed the use of low-power compact radio stations for receiving and transmitting messages.

Radio amateurs of all countries
“Ghosts” is not the only organization of this kind. In January 1995, the WUN (WorldwideUTENews) club, which we already wrote about above, began to operate. The letter combination “UTE” means that members of the club are interested in radio stations operating in the frequency range up to 30 MHz. The WUN headquarters consists of 11 people from the USA, Europe, Japan, New Zealand, and there are already many more than a hundred ordinary participants. To date, there are almost no places on the planet that would not fall into their field of vision.

Such organizations are a structure that any counterintelligence or radio intelligence can only dream of. First, they are elusive: they use only email, usually work under a pseudonym, never go on the air themselves, using only radio monitoring equipment, since in many countries its registration is not required. In cases where registration is officially required, as in Russia, necessary equipment always available on the black market.

Secondly, "ghosts" and the like work against other countries and thus do not come into conflict with local law enforcement. For example, Americans prefer to listen to transmitters located in Cuba, Chinese citizens prefer US radio stations, and Russians prefer the Chinese. This is connected not only with a sense of patriotism or self-preservation instinct, but also with technical features organization of secret radio communications.

Thirdly, "ghosts" are characterized by high level efficiency and reliability. Thanks to the World Wide Web, any fresh information becomes known to all members of the club almost instantly. Fourthly, radio amateurs are extremely professional and carefully study all available information on the organization of radio intelligence and electronic warfare (EW).

Free download book:
"Spy passions. Dual-use electronic devices"

Given circuit diagrams, descriptions, features of the design and operation of small-sized dual-use transceivers - used both for communication purposes and for unauthorized access to confidential information- electronic espionage. More than 200 schemes of devices and nodes are presented, sharing which allows you to create more than a thousand electronic designs. On the example of the simplest experiments are described possible ways interception of information but some channels of its formation, processing and transmission (sound, radio, telephone, computer). Simple recommendations on the protection of information are given. The book is intended for a wide range of readers who design means of communication, as well as those who are interested in the possibilities of electronics and are concerned about the protection of their own and others' secrets.
Development and use of achievements modern electronics¦ led to the emergence of new radio elements and devices based on them with new (often unique) remarkable parameters and consumer properties. The widespread introduction of these elements and devices, especially in the 5th, led to a radical transformation of living conditions.

High-sensitivity high-quality small-sized radios, televisions, and tape recorders appeared. The possibilities of modern personal computers are amazing. Audio and video, laser dis- \ And, multimedia, virtual reality - new concepts, new opportunities, a new level that improves the quality of life. Means of communication have entangled the whole world. This is accompanied by a significant expansion of communication services. Through a computer, you can watch TV shows, listen to the radio, shop without leaving your home, and almost instantly communicate via the Internet or similar systems with anywhere in the world. It's crowded on the air: DV-, "V-, HF-, VHF-devices, - television channels not enough space. Satellite and cable systems, radio and fiber optic communication lines are becoming commonplace. A cellular radiotelephone no longer seems to be something outstanding. All this is admirable.

However, the wonders of electronics can cause not only delight.

The radio transmitter as a means of communication expands the possibilities not only of ours, but also of our friends, colleagues and partners. For a number of users of products of modern microelectronics, some goals and methods for achieving them may be not only honest and noble. And they do not always look only at the TV and computer screens, or through a telescope at the stars and beauties of firoda, but, to our deep regret, also through keyholes. And they listen not only to their own phone, but also to someone else's - and not out of idle curiosity caused by a lack of tact and culture. And the damage from all this can be not only moral, but also economic.

Information acquires value and becomes a commodity. And how it is produced, stored, and sold as a commodity. And how the goods are stolen, copied and resold without the permission of the rightful owner, violating his rights and causing him economic damage.
And all this is called - industrial, more precisely economic, espionage, carried out, as a rule, using all the achievements of modern microelectronics: amplifiers, receivers, transmitters, repeaters, tape recorders, televisions. Eavesdropping, spying, intercepting messages. All information transmission channels used can be monitored: sound, telephone, radio, etc.

There are currently many special electronic means, designed for unauthorized access to someone else's information - for electronic espionage. Such devices differ in technical parameters, consumer properties, price. In most cases, in the design of these tools, as a rule, there are enough simple principles and circuit solutions.

Some schemes of such electronic devices or their individual fragments will be given and described below, recommendations for design and configuration will be given. However, the goal is not to stimulate "enthusiasts" of industrial electronic espionage (or intelligence - whichever you prefer). The goal is to illustrate the possibilities of modern microelectronics, the achievements of which can be used for various purposes.

Using high-quality components and modern circuit solutions, you can create highly efficient and compact communication facilities. However, on the basis of the same elements and the same schemes, it is possible to create electronic espionage devices in a matter of minutes (or hours) with average qualifications, “on the knees”.

For those who are concerned about the protection of secrets - their own or others, small or large, personal or industrial - this material is intended. It is also intended for those who, without violating legal and moral laws, would like to get acquainted with some circuit solutions and use them to repeat some of the above devices or create their own radio designs, of course, for communication purposes.

Main elements of transceivers

Antenna amplifiers (radio and TV), antennas

Briefly about antennas

Antennas for transmitters

Using indicator meters

Antennas for receivers

AM and FM radio converters

VHF FM and AM radios

FM and AM radio transmitters

Walkie talkies (transceivers)

Alternative means connections

Telephone repeaters

General issues

Unconventional use of radios

Power supply of stationary and autonomous devices

Data protection

Professional means of information protection

Basic stationary means of information security

Search equipment

VHF micro transmitter for telephone

When you want wireless remote listening telephone conversations on one's own (someone else's) telephone set, then you will need a circuit for a miniature frequency modulation transmitter designed to operate in the VHF band at frequencies of 63 ... 80 MHz in conjunction with any household radio.

The circuit is powered by the telephone line only during a conversation when the handset is picked up.

The conversation is listened to by the radio receiver in the section of the range where there are no broadcasting stations. The range of the transmitter without the use of the WA1 antenna is up to 50 m, and to increase the range, in addition to using the antenna, it is necessary to use a receiver with high sensitivity. So, increasing the sensitivity of the receiver by 2 times increases the reception range by the same amount. When connecting the device to a telephone line, observe the polarity indicated in the diagram. Setting up the circuit consists in rebuilding the generator with the core of the coil L1 to the desired frequency of the VHF band, and after that, with the capacitor C3, it is necessary to adjust the transmitter, controlling the reception by the quality of the transmission by ear. Frequency modulation in the transmitter is obtained by changing the internal capacitance of the transistor when the supply voltage of the circuit fluctuates due to the flow of current in the TA line during a conversation. Before setting up the transmitter, you must connect it to the telephone line and, with the receiver off-hook, measure the voltage across the resistor R4. It should be in the range from 2 to 3.5 V, and if the voltage is higher, then the resistance of this resistor should be reduced. The transmitter circuit is assembled on a one-sided printed circuit board 20x40 mm in size, to the contact pads of which the elements are soldered. The dimensions of the board allow it to be placed in a standard telephone jack housing.

Capacitor SZ of the KPKM type, and the rest of the resistors and capacitors used can be of any type, small-sized. Coil L1 is wound on a frame with a diameter of 5 mm with a PEV wire of 0.23 mm and contains 5 + 5 turns. The KT315G transistor can be replaced with a KT3102A, and it is not recommended to use other transistors, since this greatly increases the level of harmonics that can interfere in other ranges. With the details indicated in the diagram, the level of the second harmonic of the transmitter is 40 ... 45 dB less relative to the fundamental frequency. As an antenna, you can use a piece of any stranded wire 30 ... 40 cm long. Tuning to the desired frequency, if there is no high-frequency ferrite core, can be done by selecting the capacitance of the circuit shown in the diagram by a dotted line. Capacitors C1 and C2 can have ratings of 0.022 ... 0.068 uF. Connecting these circuits does not affect the quality of the phone.