How to record a telephone conversation. Landline phone recording devices Telephone line recording diagram
In various dispatch services, in enterprise offices, and in some everyday situations, it may be necessary to record telephone conversations. Of course, there are now various digital “recorders”, but this is equipment that needs to be purchased specifically. Despite the fact that almost any obsolete and no longer used cassette tape recorder capable of recording an audio signal, at least with mediocre quality, can be used to record telephone conversations.
How to record a telephone conversation
The website shows a diagram of a matching device that provides automatic recording of telephone conversations on a cassette recorder. The circuit connects to the telephone line anywhere and can record conversations from any number of parallel telephone sets. The recording device, as mentioned above, is any working cassette recorder. From this circuit, an audio signal is supplied to it, and the contacts of relay K1 are connected to the open circuit of the power supply circuit of the tape drive motor of the tape recorder.
If the tape recorder circuit has a 9V DC source, this circuit can be powered from it. Otherwise, from any separate current source with a voltage of 912V.
The system operates as follows. You need to connect the system to the telephone line, turn on the tape recorder for recording (turn on its power, press the “record” or “record” button).
Since the power supply to the tape recorder's motor will be turned off, recording will not occur. When you pick up the handset on any of the telephone sets connected to this line, the contacts of relay K1 will close and recording will begin. An important point is that if the tape recorder has an auto-stop that does not allow the mechanism to remain stationary for a long time, it must be turned off or dismantled.
Now about the operation of the circuit. When the line is not busy, there is a relatively high DC voltage (usually more than 40V). The stabilization voltage of the zener diode VD7 is much lower (12V), so its reverse resistance decreases and through it and resistor R3 a certain constant voltage is supplied to the base of transistor VT1, at which transistor VT1 opens. In this case, the voltage at the collector VT1 is low and transistor VT2 is closed. No current flows through the relay winding, its contacts are open and no power is supplied to the tape recorder's electric motor.
When you pick up the handset, the line voltage drops to 5-10V, sometimes lower (depending on the telephone). This is lower than the stabilization voltage of the zener diode VD7, so the current through it stops. The voltage at the base of VT1 gradually drops as capacitor C2 discharges, as a result of which transistor VT1 closes. But at the same time, transistor VT2 opens, because the voltage at its base increases. Current flows through the winding of relay K1 and its contacts turn on the power supply to the tape recorder's motor. Recording begins.
After the end of the telephone conversation, the voltage in the line rises again and the power to the LPM electric motor is turned off. The audio signal for supply to the recording path of the tape recorder is generated by the circuit C1R1 VD5VD6. Separating capacitor C1, resistor R1 and diodes VD5 and VD6 form a signal limiter. When setting up, resistance R5 should
choose one at which the recording quality will be optimal.
Relay K1 is an old relay from the remote control of domestic TVs. It can be replaced by any other relay with a 12V winding with a resistance of at least 200 Ohm. Zener diode VD7 is any low-power zener diode with a stabilization voltage of no lower than 12V and no more than 35V. The remaining parts can be replaced with any available analogues.
Many people wonder why special devices are needed that record conversations from landline phones? This is necessary in order to ensure the security and confidentiality of various information. For some offices and various companies, this is a very necessary device that can easily identify the culprit of leaks of various information that should not be distributed under any circumstances and under any circumstances.
Therefore, many companies, for security purposes, install special devices for recording telephone conversations, and this recording can be used as evidence in court or to fire a person who made a mistake. Previously, when these devices did not yet exist, you could use a personal computer that had a Dial-Up modem. By connecting a telephone cable to the modem and installing special software on your computer, you can intercept a telephone conversation from one line, listen to everything that is said on the phone or make a recording, including setting the program so that it starts recording when the handset is answered. the other end.
But now, at the moment, when the technology industry is moving upward, you can find special devices on the market that automatically intercept telephone conversations and save it on the computer. There is no longer a need to buy multiple modems for several telephone lines - now there are special boxes for several ports, which simplifies the task.
If you are interested in these devices, then you can purchase them in special stores that sell special devices that ensure confidentiality, security and safety of various information. By purchasing this device, you will be able to make recording of telephone conversations. For the company This is a very necessary and useful equipment that will allow you to record and listen to various telephone conversations and determine who is responsible for leaking confidential information.
However, everyone can use this device at their own discretion. Some people buy these models in order to simply record information in digital form that they can listen to and think about the entire conversation. Prices for such devices vary from four thousand rubles and above, depending on the number of incoming telephone ports.
Telephone adapter
To record telephone conversations, devices are used that automatically connect recording devices when the telephone is picked up. One of the diagrams of such an adapter is shown in Fig. below.
The operating principle is as follows: When the handset is not picked up, there is a voltage of about 60 V in the telephone line. Through a divider assembled on resistors R1-R3, it enters the gate of field-effect transistor VT1 type KP10ZM and locks it. This leads to the closure of transistor VT2 type KTZ15 and transistor VT3 type KT814. Relay K1 type RES22 is de-energized and its contacts K1.1-K1.4 are open. When the tube is lifted, a voltage of 5-15 V is established in the line, which leads to the opening of transistor VT1 and, consequently, transistors VT2 and VT3. Relay K1 is activated, which, with contacts K1.3 and K1.4, supplies 220 V power to the tape recorder, which is previously turned on for recording, and at the same time, with contacts K1.1 and K1.2, connects the telephone line through capacitors C1 and C2 to the input of the tape recorder. The tape recording of the conversation begins. The SZ capacitor smoothes out ripples and noise induced in the line, which can cause false alarms of the device. When connecting the device to the line, the power polarity must be observed. The device can use any power transformer that reduces the voltage to 12 V and is designed for a load current of more than 0.1 A.
This reference guide presents materials on industrial designs of special equipment of domestic and foreign production intended for information protection.
Information about methods of collecting and monitoring information using technical means is provided in an accessible form.
More than 100 schematic diagrams of information and object protection devices are presented, the logic and principles of operation of these devices are described, and recommendations for installation and configuration are given. Methods and means of protecting the information of personal computer users from unauthorized access are considered. Brief descriptions and recommendations on the use of software products and restricted access systems are given.
The book is intended for a wide range of readers, trained radio amateurs who want to apply their knowledge in the field of protecting objects and information, and specialists involved in information security issues.
It is of interest for heads of government and other organizations interested in protecting commercial information.
Telephone adapter
To analyze information leakage through open telephone communication channels, it is necessary to have records of telephone conversations of all company employees. Listening to recordings allows you to establish the nature and source of information leakage and draw appropriate conclusions.
To record telephone conversations, devices are used that automatically connect recording devices when the telephone is picked up. The schematic diagram of such a telephone adapter is shown in Fig. 3.26.
Rice. 3.26. Telephone adapter
When the handset is not picked up, there is a voltage of about 60 V in the telephone line. Through a divider assembled on resistors R1-R3, it enters the gate of field-effect transistor VT1 type KP103M and locks it. This leads to the closure of transistor VT2 type KT315 and transistor VT3 type KT814. Relay K1 type RES22 is de-energized and its contacts K1.1-K1.4 are open.
When you pick up the handset, a voltage of 5-15 V is established in the line, which leads to the opening of transistor VT1 and, consequently, transistors VT2 and VT3. Relay K1 is activated, which, with contacts K1.3 and K1.4, supplies 220 V power to the tape recorder, which is previously turned on for recording, and at the same time, with contacts K1.1 and K1.2, connects the telephone line through capacitors C1 and C2 to the input of the tape recorder. The tape recording of the conversation begins. Recording stops when the handset is lowered onto the telephone arm. The SZ capacitor smoothes out ripples and noise induced in the line, which can cause false alarms of the device.
When connecting the device to the line, the power polarity must be observed. The device can use any power transformer that reduces the voltage to 12 V and is designed for a load current of more than 0.1 A or a ready-made network adapter with the same parameters. Relay RES22 can be replaced with two relays of type RES9.
Adapter for voice recorder
Currently, imported voice recorders with a built-in VOX system, i.e., with a voice control system, are widely used for recording audio information. This allows you to use film more economically, because in the absence of a signal, the voice recorder motor is turned off and the current consumption of the device is minimal. Below are two diagrams of adapters for working with voice recorders.
The first diagram is shown in Fig. 3.27.
Rice. 3.27. Adapter with transformer
This circuit is extremely simple, because it contains only one part - transformer T1, which is connected to the line break. Transformer T1 is homemade. For its manufacture, the winding of the RES15 or RES49 relay is used.
The standard relay winding serves as the II winding of the transformer. Winding I is wound on top of it, which contains 400–500 turns of PEV 0.1 wire. The winding threads are fastened with Moment glue.
The adapter is connected to the break of any of the line wires without observing polarity.
How to record a telephone conversation? It would seem that nothing could be simpler - just connect any tape recorder to the telephone line...
However, not everything is so easy and simple here: if you need record a telephone conversation, then do not rush to send a signal from the telephone line (TL) directly to the input of the tape recorder. This will lead to the appearance of a background with a frequency of 50 Hz in the line (due to the penetration of pulsation from the tape recorder’s power supply), which will affect speech intelligibility and the quality of the conversation recording, and the subscriber with whom the conversation is taking place may suspect illegal wiretapping of the telephone line. In addition, such a connection can damage the input stage of the tape recorder and disrupt the operating mode of the TL. At the moment the subscriber calls, the voltage amplitude in the line exceeds 120 V.
Below is scheme device that eliminates all these problems and, if necessary, can be used for automatic recording of phone conversations.
The device is powered from a 220V network. In standby mode, it consumes minimal energy - the no-load current of transformer T1. The tape recorder turns on only when the handset is picked up after 1 second and turns off after the handset is put on the SLT. The delay is necessary so that the circuit does not trip from short-term power surges that occur when dialing a number on the telephone.
For these purposes, it is better to use a tape recorder with electromagnetic clamping of the sound head to the tape, for example YAUZA-220. If you use a portable tape recorder with a mechanical clamp, then it will have to be constantly in recording mode (without turning on the power), which will lead to the rubber roller pulling the magnetic tape being pushed through, as well as the tape sticking to it, which can damage it (the “chewing” effect tapes).
The circuit is connected to the telephone line in any convenient place, observing the polarity indicated on the circuit. The device consists of an off-hook indicator (VT1...VT3, their operation is described in the article above), an optocoupler switch (U1), transistor switches (VT4, VT5), a circuit switching relay K1, K2 and a power supply (T1, VD2.. .VD5).
The use of an optocoupler LED pair U1 makes it possible to obtain electrical isolation of the TL from the control circuit and the 220 V network. Capacitors C1 and C2 provide decoupling of the tape recorder circuits from the DC component in the TL; SZ - performs a delay in turning on relays K1 and K2.
For ease of use of the device, the SA1 power switch is set to three positions. This allows you to turn on the tape recorder without turning on the machine circuit when listening to the recording.
The circuit uses resistors of type C2-23; capacitors C1, C2 type K73-16V for 100 V, SZ - K52-1 for 6 V, C4 - K50-24 for 63 V; relay K1, K2 type RES9 RS4.524.200; switch SA1 type PG2-18-ZP4N. Plug X1 is a standard telephone plug, X2 is widely used in household radio equipment for transmitting audio signals, XZ is a power plug of any type, sockets X4, X5 type G4.0 or similar.
As transformer T1, you can use any small-sized one that provides sufficient voltage (16... 25 V) in the secondary winding for the relay to operate.
When setting up the circuit, you may need to select resistor R6. To control the operation of the machine, the HL1 LED is used, which lights up when the machine’s power is turned on and goes out when the handset is lifted from the phone (at the same time, the main power supply of the tape recorder is turned on by the contacts of relay K1.2).