7S12

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The Tektronix 7S12 is a Time Domain Reflectometer / Sampler plug-in for 7000-series scopes. It occupies two mainframe plug-in bays (one vertical, one horizontal).

The 7S12 has two bays for S-series plug-in modules ("heads"). The right bay accepts a pulse generator or a trigger recognizer plug-in, whereas the left bay accepts a sampling plug-in.

The typical configuration is to have an S-6 on the left and an S-52 on the right for time domain reflectometry, or a sampling head like the S-4 on the left and an S-53 on the right as a generic sampler.

The 7S12 can also control an optional 7S11 through its left side contacts, adding a second input channel.

Y axis can be scaled in voltage (mV) or distance (ρ) units, X axis in time or distance.

Key Specifications

Sweep modes	Single / Repetitive / Manual / External input
With S-6 and S-52	Pulse: 200 mV into 50 Ω Rise time: < 35 ps for incident step, < 45 ps for displayed reflection Jitter: < 10 ps
With S-5 and S-54	Pulse: > 400 mV into 50 Ω Rise time: < 1.5 ns for displayed reflection of a shorted line Jitter: < 20 ps
Sweep modes	free-running single manual external input
Air Dielectric Range	15 m (49 ft) 150 m (490 ft) 1500 m (4900 ft)
Weight	2.13 kg (4.7 lbs)

Links

Tektronix 062-1244-00: Time-Domain Reflectometry Measurement Concepts, James A. Strickland, 1969. pages. PDF, OCR, 6.2 MB
Service Scope No. 45, August 1967 - Time-Domain Reflectometry Theory
Tek 7S12 @ amplifier.cd
Tek 7S12 @ barrytech.com
Evaluation of 7S12 performance (video)
7S12 extender board by Dave Partridge

Pictures

Front view without sampling head plug-ins
Front view with S-6 sampling head and S-52 pulse generator
7S12 TDR "self portrait" in 7613 storage mainframe
7S12 as a sampler, displaying a 1 GHz sine using a S-6 sampling head and S-53 trigger recognizer, 2^nd channel (top) on a 7S11 with S-4 sampling head.
Metric dial tape

Inside

Left side
Left side with cover. Side contacts to interface 7S11 are exposed.
Right side
Top view
Horizontal board
Vertical board

Measurements

TDR

TDR "Self Portrait" — pulse reflected on S-6 "through" path (approx. 120 ps one way)
7S12 displaying the incident pulse from an S-52 (nom. < 25 ps) through an S-6 head (nom. < 30 ps). Displayed rise time ~35 ps confirms spec.
7S12/S-6/S-52 displaying pulse reflection from ~ 5 in semi-rigid SMA cable. Stored display of two traces. Left trace: cable only, right trace: cable plus SMA-to-BNC adapter (~ 25 mm)
7S12/S-6/S-52 displaying reflected pulse from end of 5 in semi-rigid SMA cable. Stored display overlaying multiple traces, left to right: cable alone, SMA-to-BNC adapter added, BNC f-f adapter added, (cheap) 50 Ω terminator added.
Full pulse pattern of a 7S12/S-52 in real time (top trace) and sampled (bottom trace) shown simultaneously on 7844. 7S12 trace at slowest possible sweep.
S-52 pulse in real time (top trace) and sampled (bottom trace) shown simultaneously on 7844. Approximately equal time scales.

Probe rise times

Rise time of a P6202 500 MHz FET probe measured on a 7S12 with S-52 and S-4 (in a 7844 mainframe), at 1 ns/Div
Rise time of a P6202 500 MHz FET probe measured on a 7S12 with S-52 and S-4 (in a 7844 mainframe), at 100 ps/Div
P6230 Rise time, no ground lead
P6230 Rise time, no ground lead, enlarged – 9.2 * 20 ps = 184 ps (equiv. to 1.9 GHz bandwidth)
P6230 with "low inductance" ground lead – rise time 400 ps, bandwidth 875 MHz

As a generic sampler

7S11 with S-4 and 7S12 with S-6 and S-53 displaying a 1 GHz sine in normal mode without storage. Sampling is evident.
7S11 with S-4 and 7S12 with S-6 and S-53 displaying a 1 GHz sine in high-res mode with variable-persistence storage on a 7613.