7J20: Difference between revisions

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The '''Tektronix 7J20''', which only appears in the 1975 catalog, is a "rapid scan" optical spectrometer for the 250 nm to 1100 nm region.
The '''Tektronix 7J20''', which only appears in the 1975 catalog,
Rapid scan means that it can capture the spectrum quickly enough to show spectral changes at temporal resolution of a few milliseconds.
is a "rapid scan" optical spectrometer for the 250 nm to 1100 nm region.
Rapid scan means that it can capture the spectrum quickly enough
to show spectral changes at temporal resolution of a few milliseconds.


The instrument is based on a [https://en.wikipedia.org/wiki/Monochromator Czerny-Turner Monochromator],  
The instrument is based on a [https://en.wikipedia.org/wiki/Monochromator Czerny-Turner Monochromator],  
in essence a narrow slit followed by a [https://en.wikipedia.org/wiki/Diffraction_grating diffraction grating].
in essence a narrow slit followed by a [https://en.wikipedia.org/wiki/Diffraction_grating diffraction grating].
A [https://en.wikipedia.org/wiki/Vidicon vidicon tube] scans the optical spectrum and produces a periodic electric signal which is then displayed by the scope mainframe.  
A [https://en.wikipedia.org/wiki/Vidicon vidicon tube] scans the optical spectrum
and produces a periodic electric signal which is then displayed by the scope mainframe.  
[[File:7J20-principle.jpg | thumb | 400px | center | Operating principle (click to enlarge) ]]
[[File:7J20-principle.jpg | thumb | 400px | center | Operating principle (click to enlarge) ]]
The spectrometer is packaged in two enclosures linked by an umbilical cable. The 7J20 is a 2-wide plug-in for [[7000-series scopes]] containing the sweep timing and mainframe interface circuits. The external enclosure is labeled "J20". It has controls for the optical components (grating, filters etc.) on one side and an input aperture on the other.
The spectrometer is packaged in two enclosures linked by an umbilical cable.
The 7J20 is a 2-wide plug-in for [[7000-series scopes]] containing the sweep timing and mainframe interface circuits.
The external enclosure is labeled "J20".
It has controls for the optical components (grating, filters etc.) on one side and an input aperture on the other.
 
The internal vidicon horizontal scan voltage corresponds to wavelength,
but not in a linear way.
To provide a linear nm/div horizontal display on the 7000-series mainframe,
the vidicon horizontal scan signal is passed through a function generator IC,
the [[155-0106-00]],
which implements an interpolated lookup table.
Inside the 7J20, there are 40 trimmer potentiometers that allow the lookup function to be tweaked
so that the horizontal scale of the system is accurate.


The 7J20 is very rare. According to Dennis Tillman, ''Best estimate is ~40 were actually built.''
The 7J20 is very rare. According to Dennis Tillman, ''Best estimate is ~40 were actually built.''

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