Theory
The output audio signal from a Walkie Talkie, Tetra radio or Presenter's earpiece Box is passed through a conductor typically a personal neck loop or Shoulder Pad. When the signal is passed through the neck loop it produces a magnetic field.
The magnetic field produced by the neck loop varies in strength according to the audio wave form being passed through it.
This variation in the magnetic field causes a small current to be induced in a tiny coil housed in the wireless earpiece. This is then amplified (hence the need for a small pill battery to power the amplifier) and passed into a transducer which converts the signal from the coil to an audible sound. The sound is then passed down the molded delivery tube out of a little apeture hole and into the ear.
A blue wax guard may be present at the sound outlet hole in the earpiece. This helps prevent wax blocking the sound outlet. Under very hot conditions any wax present can liquify and via the process of capillary action run up the sound passage into the transducer, coil and amplifier to solidify. The earpiece quickly becomes an expensive write off and the warranty does not cover this damage. Not even the wax guard can prevent this so this is an important reason to maintain good ear hygiene before inserting a wireless earpiece into your ear.
Key points of Induction Loop Earpieces
The process involves no radio frequencies.
The sound level heard by the listener of the earpiece is dependant
- The output level of the radio (volume control on radio)
- The match between the radio output (or other device) and the neck loop or shoulder pad.
- The amplifier gain setting in the earpiece.
Showcomms' neck loops and ICM 40 earpieces have been tailored by our manufacturer to provide consistently good results in most conditions on most radios. The neck loops use high efficiency coils and the amp is optimised for a higher output.
Interference.
This is generally encountered as low level buzz or hum and can increase the closer the proximity to the source of interference. Induction loop earpieces are susceptible by their very nature to unwanted magnetic signals that can be produced by other electronic devices. Sources of possible magnetic include High Volltage, Electronic, switching equipment, electric motors, fluorescent light fittings dimmers and computers.
