The major functional parts of the Sampling Time Base PM 3419 Bare: 1. The trigger circuits 2. The time base circuits 3. The horizontal deflection circuits. The trigger circuits serve two important functions, viz: recognition of a certain part of the input waveform for triggering and for frequency count-down. The circuit responds to input signals with repetition rates from single pulses up to 1000 MHz. For frequencies below about 20 MHz the trigger system selects a trigger and presents a steady display even when the triggers are randomly spaced. The sampling rate is limited by the recovery time of the circuits in the Sampling Dual Trace Amplifier PM 3419 A to 100 kHz and by the time base circuits to about 30 times the sweep time/cm. Therefore, a hold-off and count-down circuit is used to provide triggering for frequencies above the maximum sampling rate. For input frequencies above 20 MHz the synchronizing mode usually gives less time jitter than the triggering mode. Each time the trigger circuits are actuated a fast ramp is started. The slope of this ramp determines the real time scale. The ramp voltage is compared to a staircase voltage in a comparator circuit. A strobe pulse is generated at the moment when the ramp voltage is equal to the staircase voltage. The strobe pulse is transferred to PM 3419 A, where it initiates the sampling pulse. It also goes into a diode pump circuit, which increases the staircase voltage one step. This means that the next strobe pulse is generated somewhat later, because it takes a longer time for the ramp voltage to reach the new level of the staircase. As a consequence of this the sampling is also delayed. The second sample therefore represents a later part of the input waveform See Fig. 2. The real time scale is changed by changing the slope of the fast ramp. The horizontal deflection on the CRT is taken from the staircase and can be varied completely independently of the real time scale. The height of the individual step determines the number of samples taken per cm of the CRT, and it can be varied in steps of 10, 100 or 1000 samples/cm. Time scale magnification is realized by attenuation of the staircase voltage before it is applied to the comparator. In that way all the samples are taken from a smaller part of the fast ramp and consequently the time scale is enlarged with constant number of samples/cm. Further possibilities for the X deflection can be achieved by replacing the staircase voltage by a voltage determined by a potentiometer. By turning the potentiometer the input signal waveform can be manually scanned. External deflection voltage or an internally generated slow sawtooth can also be used.