Sweep Generator with Marker
Cor van Rij
This circuit is a simple sweep generator. The sawtooth is generated by the PNP transistor and the 555. The transistor together with the 2 diodes at the basis form a constant current source which charges the 330nF capacitor. If 2/3Vcc (=6V) is reached the flipflop in 555 is triggered and the capacitor is rapdily discharged via the NPN transitor in the 555. This voltage is then offered to the voltage controlled oscillator.
Opamp U1 and surrounding components are the marker generator. As long as the voltage over the 330nF capacitor is lower then voltage at wiper of the potmeter, the output of the opamp is high (9V). When those voltages become equal the output goes low and a strong negative pulse is offered via the differentiator to FET J1 and is disabled. The charging of the 330nF is paused for a short time. This creates a brigther image at the marker frequency.