the life of Philo T Farnsworth - Early Television Foundation

CLEARING THE IMAGE OF SMUDGE AND BLUR
the generated current was therefore weaker. This resulted in the
dark smudge across the center of the picture, which represented
a composite of all the steep parts of the many sine waves that
accomplished the complete scanning of the image.
This effect was anticipated by Farnsworth in his first patent
application. With his amazing ability to visualize the paths of
electrons and their effects, he had in the early theoretical conception
of his television scheme recognized that the ordinary
sine-wave scanning pulses would not be adequate for his purpose.
In this early document he stated that he would use a
straight-line,
or saw-tooth, wave form for scanning purposes.
Such a wave form was much easier to describe in a patent application
than it was to produce by his generating panels. However,
faced with the reality of a blur across the center of the
picture, the production of straight-line scanning,
which would
give even values all the way across the field, offered the only
means of correcting the blur through the middle of the image.
Saw-tooth wave pattern
The saw-tooth form of wave, with a ratio of at least ten to
one between the length of the upsweep of the wave motion and
that of the downsweep, was necessary to eliminate the double
image. In other words, the ratio in time between the scanning
from right to left and the scanning from left to right was ten
to one. This effectively blanked out the ghost image due to the
return-line scanning.
The solution of the problem
was first
worked out mathematically;
then months and months of patient effort were devoted
to the development of the saw-tooth wave form. This