The Tektronix 4S2 is a two-channel sampling vertical plug-in for the 661. Signals enter the 4S2 through GR-874 connectors on the front panel. Unlike the 4S1, the 4S2's signal path does not contain a delay line between the input connector and the sampler. This has the advantage of maintaining higher pulse fidelity and thus higher bandwidth, but the disadvantage of making it impossible to see the leading edge of the triggering event unless a pre-trigger is used.
The 4S2, which was designed in 1962, uses a four-diode sampling bridge. The 4S2A, designed in 1965, uses a two-diode sampling bridge. This design change is discussed in the 4S2A Engineering Spec document linked below. The 4S2 does not provide trigger pick-off. The 4S2A provides trigger pick-off for channel A.
The 4S2 and 4S2A front panels look the same, but they use different GR-874 input connectors. The 4S2 uses a short airline unique to the 4S2. The 4S2A uses the connector-to-board system described in US Patent 3,426,311, and has some parts in common with the 3T7.
|Bandwidth||DC to 3.9 GHz|
|Rise time||90 ps|
|Deflection||2 mV/Div to 200 mV/Div, 1−2−5|