signal and controls the enabling of ic 3 dit oscillator 78 when dah input 16 is referenced to dit dah reference input 18 as a result of dah lever 104 of telegraph sending instrument being closed transistor q 1 turns on completing the ground path for pin 7 of ic 1 dah oscillator 74 as a result a fixed oscillation occurs on pin 8 of ic 1 dah oscillator 74 ic 1 dah oscillator 74 has an oscillation frequency of 3000 hertz as determined by capacitance c 1 and resistance r 5 when dah lever 104 of telegraph sending instrument is opened transistor q 1 turns off opening the ground path for pin 7 of ic 1 dah oscillator 74 causing the fixed oscillation on pin 8 of ic 1 dah oscillator 74 to stop similarly when dit input 20 is referenced to dit dah reference input 18 as a result of the dit lever 102 on telegraph sending instrument being closed transistor q 6 turns on completing the ground path for pin 7 of ic 3 dit oscillator 78 as a result a fixed oscillation occurs on pin 8 of ic 3 dit oscillator 78 ic 3 dit oscillator 78 has an oscillation frequency of 5000 hertz as.