Chalk Hill Media's Virtual Museum

This device generated a test pattern as seen below.  The actual image was etched on a plate in contained inside the monoscope tube.  For an additional charge, it could be customized to include the station's call letters.

The Monoscope Tube.  It is very similar to a conventional cathode ray tube (CRT) except the beam scanned across a metal plate which is inside the glass where the picture would normally be viewed.  That plate has the test pattern etched into it.   It produces a test pattern as shown below.