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Wireless covert earpiece
- this page is a stub
LD-5 is a miniature in-ear earphone or
earpiece, manufactured between 1995 and 2012 by
Sonic Communications International Ltd. in Birmingham (UK).
It is intended for use with covert radio systems
that are hidden under the user's clothing, and communicates with the covert
radio via an induction loop. It was commonly supplied with a concealed
Sonic body-wearable radio harness.
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The device consists of a pickup coil, an amplifier powered
by a miniature battery, and a speaker element, packed in a plastic
skin-coloured enclosure that fits entirely inside the
ear canal.
From the outside, only the end-panel – with the battery compartment lid
that acts as the on/off switch – is visible. In practice, this could easily
be concealed by combing the user's hair over it.
The device is powered by a standard 10AE (PR70) button-type battery,
that was typically swapped every day at the start of a surveillance task.
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The molded plastic enclosure is shaped for the left or right ear. 1
Depending on the environment and the circumstances,
the user wears either the left
or the right earpiece, or both. For hygienic reasons, they were usually issued
to individual operators, rather than as part of the equipment.
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Each user was given
a black pinch wallet marked SONIC, in which the earpiece(s),
spare batteries, a special cleaning
tool and the instruction were stowed.
The cleaning tool holds a metal pick, a hard brush and a magnetic stub
that can be a useful aid when placing or removing a battery.
The earpiece is used in combination with an induction loop
fitted around the user's neck, or
an induction coil that is hidden under the user's clothing, close to the
ear that holds the earpiece. It is connected to the radio and sends the sound
to the earpiece in the form of magnetic waves.
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Unlike the compatible Danavox 131-CD/TELE,
which is based on a regular hearing aid, the Sonic LD-5 does not have a volume
control knob. Instead, the audio level has to be adjusted with the volume
control of the radio itself. Because the LD-5 does not have a volume control
and uses a smaller battery, the device is smaller than the
Danavox and can be inserted deeper into the ear canal,
making it more suitable for covert surveillance. A short nylon cord is present to retract the device.
The LD-5 was commonly supplied with the covert radio body harnesses that
were also made by Sonic. It was eventually succeeded by even smaller devices
that were virtually invisible.
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The one shown here is molded for the right ear.
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Commonly known as an Audio Frequency Induction Loop System (AFILS).
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The image below shows four Sonic LD-5 inductive in-ear units of which the
rightmost three show the function of the battery door that also acts as
the on/off switch. In the first device, the 10AE battery is installed at
the inside of the battery door. The door is then toppled so that the battery
disappers inside the device. When the door is fully closed (rightmost example)
the device is ON. To turn it off again, tilt the door slightly,
by pressing the raised edge with a finger nail.
The units have a universal shape that fits most ear canals. The oval
end-panel measures just 8 by 10 mm, as a result of which it can be
inserted deeper into the ear canal that most regular earpieces and
hearing aids. The nylon cord is present to retract the device easily
when finished.
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Covert radios that use this earpiece
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Below is the block diagram of a typical setup. At the left is the
receiver-part of the (covert) radio, to which an induction loop with
several windings is connected instead of the loudspeaker. The loop converts
the audio frequency (AF) signals from the receiver to a magnetic field that
varies in the rythm of the AF signal (sound). If the induction loop is
worn around the neck, the magnetic field is wide enough to reach the
pickup coil inside the earpiece, where it is then amplified.
The advantage of using a neck loop, is that the magnetic field is identical
at either side of the body, so that the user can wear the earpiece in the
left or right ear, or even wear earpieces in both ears as shown in the block
diagram below. This is especially useful in noisy environments.
Although a induction loop (neck loop) offers the best performance, it is
sometimes inconvenient, as it has to be hidden under the user's clothing
before it can be connected to the radio. In such cases a flat induction
coil with a wide stray field could be used as an alternative. It can
easily be attached to the inside of, say, a coat by means of a safety pin.
The disadvantage is that the stray magnetic field is much narrower, as a result
of which it has to be placed close to the earpiece.
Flat inductors are often used with pre-wired radio harnesses or with
bullt-proof vests, that are worn under the clothing, and allow for quick
deployment. The inductor has to be placed
at a strategic position close to one of the shoulders,
near the ear in which the earpiece is worn.
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© Crypto Museum. Created: Monday 21 June 2021. Last changed: Tuesday, 22 June 2021 - 05:06 CET.
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