RF output DOES NOT equal Composite!!!!

From: Gary Hildebrand <ghldbrd_at_ccp.com>
Date: Sun Jun 16 10:04:02 2002

Sellam Ismail wrote:
>
> This has always been an area of confusion for me. Can someone recommend a
> good reading that will explain video as far as composite vs. RF and
> modulation and all that?
>
> Would Don Lancaster's Video Cookbook have what I want?
>
> Web articles would be preferred.
>
> Sellam Ismail

Okay, composite video is the complex waveform that defines NTSC as found
in any television station. It includes horizontal & vertical sync
pluses, and if it is color, it also has a burst flag and subcarrier
information that is a phase modulated 3.579545 signal, all interwoven.
YOu can easily see this on any good oscilloscope. Bandwidth is usually
about a few cycles to about 4 mHz, sometimes higher.

This is usually fed through 75 ohm coax and BNC connectors (really old
stuff uses UHF/PL259s). Consumer home gear uses RCA/phono connectors as
a rule, although other connectors are sometimes used.

The RF modulated signal is a carrier signal on a standard TV channel,
usually Chs 2-4, that has the video modulating it AM style, and the
audio sound is FM modulated 4.5 mHz higher in frequency. Commercial TV
uses vestigial sideband transmission, where the lower sideband is
partially removed with filtering and amplifier tuning to conserve
bandwith. The common RF modulators used with game consoles, etc. does
not have this filtering, but relys on the tv set to filter that out in
the front end. In rare cases it can affect the signal/picture quality.

RF also is fed through 75 ohm coax, but 300 ohm twinlead used to be the
norm. F connectors are as a rule used for anything RF, but phono
connectors are quite often used as they are in stock and cheap as well.

Hope that clears up any questions out there.

Gary Hildebrand
St. Joseph, MO
Received on Sun Jun 16 2002 - 10:04:02 BST