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Tektronix S-42
Optical Sampling Head
S42 Head

Compatible with 7000 and 3S series sampling heads

Produced from 1989 to 1990

(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix S-42 is a sampling head for 1300 nm optical signals. It has an FC/PC fiberoptic connector for the input signal. It is essentially an S-4 sampling head with a photodiode at the input.

Specified accuracy is for connections through 8/125 μm single-mode fibre, although a lens in front of the photodiode allows connections using multi-mode fibre as well, at some degradation of response speed.

The manual shows it being used in a 7S12-driven TDR setup with an external OT503 electro-optic converter as the optical signal source.

Key Specifications

Pulse response 55 ps
Bandwidth 6.4 GHz (equiv.)
Spectral response 1000 – 1700 nm
Deflection 50 μW/Div to 50 mW/Div @ 1300 nm
Noise equivalent power 42 μWRMS max.
Max. nondestructive input 10 mW mean, 125 mW peak
  • Mean power meter, dynamic range 5 nW to 5 mW (60 dB), bandwidth 100 Hz


The S-42 borrows heavily from the S-4 sampling head, re-using the S-4 strobe, sampler and preamp boards. It uses the same six-diode traveling-wave sampling gate, strobed by 125 ps pulses generated using a snap-off diode driven by an avalanche transistor.

The S-4's SMA input connector is still present internally, and driven electrically in some of the calibration procedures, with the photodiode removed.

To accommodate the photo diode, the S-42's case is longer than the S-4's. When inserted, the S-42 therefore protrudes from the base unit by about two centimeters.