The Tektronix S-4 Sampling Head is a 25 ps risetime unit with a 50 Ohm input impedance. The S-4 can be plugged into the sampling unit or attached by a sampling head extender for remote use. A trigger pickoff within the S-4 provides a trigger signal output from the plug-in unit. Signal range - Variable dc offset allows signals between +1V and -1V limits to be displayed at 2mV/div. For best dot-transient response with random-sampling sweep unit, signal amplitude should be less than 500 mVp-p. Save Overload maximal +/-5V. Fits in 7S11 and 7S12.