REPEATER_TONE_BURST_GENERATOR

Published:2009/6/18 3:52:00 Author:May | From:SeekIC

Integrated circuit gates IC1-a and ICl-b form a monostable, whose time constant is determined by C2 and R3. When the transmitter is dekeyed (and then almost immediately rekeyed) point TX+ goes low and takes pin 1 low for a short time. This triggers the start of the timing period controlled by C2/R3, The capacitor C2, charges via R3 until the trigger point of gate ICl-b is reached. At this point, the monostable changes state and pin 3 goes low again. On the prototype, this time was about 700 ms. The pulse occurs each time after dekeying and it is normally inaudible. If, however, point TX+ goes high again (as in immediate rekeying) the monostable is still in the enabled state and the oscillations of ICl-c are present in the transmission. During this time period, the buffer gate, ICl-d, is enabled and the tone is therefore passed to the output.



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