Tektronix delay line, dual channel with input signal pick-offs

Description

Tektronix delay line (from TekWiki)
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The purpose of delay lines in oscilloscopes is to allow observation of the leading edge of the trigger event. In the vertical signal path, before the delay line, there is typically a trigger pick-off which supplies an undelayed copy of the vertical signal to the trigger and sweep circuitry. Trigger and sweep circuitry need about 60ns to react when presented with the trigger event. Without a delay line, the trigger event would already have come and gone before the scope can trigger and sweep. By sending the input signal through a delay line, the scope will have triggered and begun sweeping by the time the trigger event emerges from the delay line. Thus, the trigger event is drawn on the screen where the operator can see it, photograph it, or record it by other means.
The first Tektronix scope to contain a delay line was the
513D
, which uses an L-C network. Soon after, the
517
appeared, using 51 feet of RG-63U coaxial cable as a 65 nanosecond delay line. 7000-series scopes use special twin-lead delay cables. The delay line in the
519
is a large coil of low-loss air-dielectric semi-rigid coax.
The location of the delay line in the instrument block diagram varies:
Delay before any active electronics:
4S1
,
1S1
Delay between amplifiers:
517
,
7000 series scopes
,
315
,
547
,
524
Delay between amplifier and CRT:
516
,
533
,
545
,
551
,
555
Delay Lines in Sampling Oscilloscopes (TekWiki)
The purpose of delay lines in sampling scopes is the same as for conventional non-sampling scopes. Since sampling scopes are often used for observing fast pulses, delay lines are often problematic since they have dispersion, and therefore distort pulse waveforms. For example, the
4S1
contains a delay network while the
4S2
does not. Because of this, the 4S2 is a less convenient instrument, but has faster rise-time than the 4S1. One way around the trade-off between pulse response and convenience is to use
random sampling
.
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