RECOMMENDATIONS FOR USE
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RECOMMENDATIONS FOR USE
6. TYPES OF THE WIRE EAVESDROPPING DEVICES
6.1. WIRE DYNAMIC AND ELECTRET MICROPHONES
Purpose:
interception of the voice information in the room with the subsequent transfer via
cables.
Dynamic (electrodynamic) microphones
are the most common type of microphones. They
do not require power to operate. The design of microphones lacks a preliminary power amplifier.
Information is transmitted via two wires (or one pair of multi-wire cable). The transmission
range can be several hundred meters.
Electret microphones
(one of the varieties of condenser microphones) are often used in
eavesdropping equipment due to their low price and suitability for use in "cramped conditions".
The microphone design includes a preamplifier, for the operation of which a constant voltage of
a certain polarity is required. This is achieved by applying “phantom” power to the microphone
(simultaneous transmission of power and information signals over one wire). Some electret
microphone models have an autonomous power supply.
Method of connection to the cable – parallel.
Power supply – 3 - 20 V
6.2. HIGH-FREQUENCY WIRE TRANSMITTERS
Purpose
– interception and transfer of the voice information on power mains or low-current
cables in the high-frequency range (0.1 - 30 MHz).
The transmission range of information on power mains, as a rule, does not exceed 500 meters
within one or several buildings powered by one low-voltage bus of a transformer substation.
When using telephone cables or LAN cables (at frequencies of 5 - 30 MHz), the transmission
range of information exceeds 500 meters.
Sometimes, high-frequency transmitters use coaxial cables of terrestrial or cable television as
a channel for transmitting information (audio and video).
Method of connection to the cable – parallel.
Power supply – from the cable or an autonomous source.
6.3. TELEPHONE TRANSMITTERS
Purpose
- interception of voice information transmitted over a telephone cable and its
broadcast per а radio channel.
Telephone transmitters (low-power radio transmitters) modulate the reference frequency with
electrical pulses that occur in the cable when talking on the phone. Most telephone transmitters
turn on automatically when the handset picks up. Information (telephone calls) is broadcast
outside the room via a radio channel.
