RTTY calibrator indicator

RTTY calibration indicator To calibrate an RTTY (radio teletype) decoder correctly in accordance with the marks and spaces, an oscilloscope is needed. The mark and space signals are applied to the X and Y inputs of the instrument respectively, when, on correct calibration, the screen of the oscilloscope displays the well-known RTTY cross. If an oscilloscope is not available, the circuit shown here can be used. It consists of two amplifiers with high- impedance input, T1and T 8, that are followed by driver stages T2...T 4 and T5...T7. The driver stages control three LEDs, D 1... 0 3 direct. Diode Di (red) is the mark indicator, D 2 (green) is the space indicator, and D 3 (amber) indicates whether the decoder has been calibrated symmetrically. Preset potentiometers P1and P2 determine the amplification of the field-effect transistors. Proper setting of these components enables the indi- MARK cator to be matched with the filter outputs of any RTTY decoder. After the indicator has been...