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

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