Throat mic Vox unit Throat mic Vox unit plugged into PMR500
Throat Microphone-Earphone with VOX
The EM-800 vox unit will enable hands-free operation with this throat mic on most commercial and amateur radio
handheld transceivers ( Yeasu, Icom ,standard, etc ) that have the facility to connect an
external mic via a 2.5 mm mono jack and an external speaker via a 3.5mm mono
jack . It consist of a small contact transducer ( electret microphone) the size of a 10 cent coin
that is held in place on the side of the throat at the level of the voice box by
an adjustable stainless steel neck band. The microphone has an impedance of 2.2k
ohm The assembly has a small
conventional earphone that is fitted into the users ear
The earphone has a nominal impedance of 32 ohms and an audio
level of 90db SPL at 1 khz and 1mW. The control electronics is based on
the NJM2072 ic designed for signal level sensor systems and used commonly in vox
circuitry for small Dictaphones , it is in a small match box
sized unit that is powered by a single 1.5v "AAA" battery. The unit has a high,
low sensitivity and off (PTT) mode. The speaker plug is a 3.5mm mono jack and the
microphone a 2.5mm mono jack (tip is audio positive and sleeve earth) .The earphone volume is controlled by the volume
control of the transceiver.
Throat mic Vox unit
Throat mic Vox unit plugged into PMR500
The 3.5mm speaker plug is inserted into the transceiver, while the 2.5mm mic plug goes
into the external mic socket. The unit is placed on the side of the neck and the
mic position adjusted for comfort ( to the side of the "adams apple")
. The mic needs to be about 3.00 cm to the side away from the voice box. adjust
for best clarity. The unit is switched on and the vox sensitivity adjusted to cater for the ambient
noise level of the immediate surroundings, ie High (-93db) or Low (-83) db sensitivity.
There is an acoustic difference of about 10 dB between the mic sensitivity settings.
The users voice level is modified to allow the radio to automatically
transmit. There is a built in delay of about 0.8 seconds to allow the radio to stay
in transmit mode in between words, any delay of over 0.8 seconds and the radio will drop
back to receive. The mic jack is switched by an NPN transistor to earth (the emitter is
connected to earth) The resistance across the 2.5mm mic jack goes from meg ohms on
"receive" to about 3k ohms on "transmit".
If you wish, the unit may be operated in manual mode. On the same side of the control
box as the sensitivity control can be found the small PTT (push to talk) switch.
This switch is active at all times even when the unit is turned off. (There will be no
current drain when the unit is actually turned off)
Throat mics are NOT Hi Fi units, however they produce communications
quality audio, the audio they produce does not sound as good as the
average acoustic microphone, but are excellent in certain circumstances
where an acoustic mic is unusable and verbal communications must be maintained.
PRICE: $150 plus gst (doesn't include radio)
Pinfold Health Services Ltd., 1172 Arawa St. ,Rotorua , New Zealand ph +64-7-3488850 fax +64-7-3486555 pinfold@xtra.co.nz