K
keep-alive electrode An electrode in a mercury-arc rectifier which maintains the vapour in a partially-ionised state.
Kell factor In TV a factor expressing the ratio of horizontal to vertical definition. Suppose each of the n lines of a TV picture is made up of alternate black and white elements. If these elements are assumed to be square-which is equivalent to regarding horizontal definition as equal to vertical definition-then there are 4n/3 elements in each line, the aspect ratio being 4:3. The lowest video frequency which will enable such a row of elements to be resolved is one in which one half-cycle represents a white element and the other half-cycle a black element. This is the upper video-frequency limit for the system and it gives ...
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