In facsimile, a frequency modulationsystem where one frequency represents picture black and another frequency represents picture white[?]. Frequencies between these two limits may represent shades of gray
An intentional frequency change used for modulation purposes
... - spent 12 years starting in 138 BC exploring much of Central Asia for Emperor Han Wu Di[?]
Zheng He, (1371-1435), Chinese admiral who travelled widely over the Indi ...