There are several methods used to 'listen in'
to a room. A popular method is to fit a microphone in
the area, e.g. in the ceiling or another convenient place
in the room and run wires back to the LP, (listening post)
at a convenient place in the building.
It is not possible to just fit a microphone and run a
length of cable back to the listening post, the signal
from the microphone will be reduced and become noisy if
the cable is too long. A special amplifier is connected
to the microphone allowing a long length of cable to be
used back to the listening post.
Normally, such systems need to have four wires, two for
power and two to carry the audio signal.
Our audio room monitor only needs two wires which carry
the audio from the microphone amplifier back to the listening
post, and also carry power back to the microphone.
This system is known as the TWO-WIRE room listener.
Another popular method of listening into a room, is to
use a special module connected across the telephone line
in the room to be monitored. After fitting this module
across the phone line, all room conversations can be listened
to by connecting the main amplifier across the phone line
at some other place.
TWO WIRE ROOM MODULE (TWM)
This is the module with attached microphone to
be fitted in the room to be listened to.
TAPE COPYING ADAPTOR
Whilst a duplicate copy of a tape is often needed, e.g.
a duplicate tape of telephone conversations, it is not
possible to copy a tape by simply connecting the headphone
output of one tape deck to the microphone input of another
It is possible to duplicate a tape using two standard
cassette recorders after fitting the COPYING ADAPTOR between
the headphone output of one machine and the mic input
A headphone socket on the copying adaptor allows you to
listen to the tape whilst making the copy.
RADIO TRANSMITTERS (BUGS)A 'BUG' is a radio transmitter that can be left
in a room allowing the user to listen into room conversations
by tuning into the 'bug' with a radio receiver. This bug
can be received on a normal fm radio.
Line of sight range is about 400m, and battery life is
around 48hours. FM BUG, - RT1
For secure 'bugging', it is not advisable to use transmitters
that can be picked up with a normal fm radio.
For more 'professional' applications a bug with a matching
radio receiver is used. THE TX33/UX33
is a transmitter and receiver
combination operating outside the normal fm radio band.
The receiver and transmitter operate on a fixed frequency,
no tuning is necessary as the receiver is matched to the
transmitter, i.e. the TX33 can only be received by using
the UX33 receiver.
Line of sight range is 150-200m.
UHF BUG, -TX33/UX33 Transmitter/Receiver pair THE TR33/UR33 WIRELESS RECORDER
a telephone transmitter system, but the receiver is built
inside a tape recorder, making it simpler to use.
The transmitter is attached to the line and the recorder
is placed within range. The recorder is put onto record
but will only start recording when the phone is used,
and switch off automatically when the phone is put down.