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Re: Consoles old and new
Date: Fri, 22 Sep 89 14:01 PDT
From: Donald Leo Kaiser <email@example.com>
What does the PE stand for in "100MHz PE video signal"???
Boeing Advanced Systems
"Phase-Encoded". Phase encoding (also called phase modulation) is a technique
similar to frequency modulation; it works by shifting the phase of a
constant-frequency carrier, such that a 0 can be represented as an unmodulated
carrier, and a 1 bit can be represented by a 90 degree phase shift. (I do not
know what the exact modulation scheme is; these figures are examples only.)
The circuitry required is simple and (relatively) cheap.
Sending straight video signals through a long cable, especially
high-resolution monochrome signals, creates too much electrical noise; worse
yet, it's broadband noise, which requires too much shielding and filtering to
attenuate to the levels required by Federal Communications Commission
By phase-encoding the video signal onto an 80 MHz (or 100 MHz) carrier, the
potential interference is confined to a smaller band, thus filtering and
shielding can be substantially simpler. This more than makes up the cost of
the modulation and demodulation circuitry.
-- Chuck Fry (Chucko@Riverside.SCRC.Symbolics.COM)
Symbolics Software Support