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May 12th 05, 10:26 PM

Michael A. Terrell

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wrote:

Most radio and RF distribution systems for transmitters
are 50 Ohms. A lot of test equipment is 50 Ohms.
But TV uses 75 Ohms in both video and RF distribution
systems. I have dug through all of my refference books,
inclding one from 1947 and even that far back, when color
TV was still a dream, they used 75 Ohms.

75 ohm cable was used because it has lower loss than 50 ohm cable of
the same size.

I must have slept through this in class 30 years ago
becvause I am sure there is a logical explanation.
Does anyone know why TV video, antenna systems?("F" connectors),
and cable all use 75 while real radio uses 50 OHms

75 ohm cable was used because it has lower loss than 50 ohm cable of
the same size.

Bonus quesiton: How can you tell a 50 Ohm and a 75 Ohm
BNC connector apart just by visual inspection?

The diameter of the center pin and collet are different for the two
different impedances.

And guess which BNC was most commonly used in TV facilities
up until HDTV came along?

75 ohm, in equal amounts of both genders for video signals, and 50
ohm for remote control is all I saw in pre HDTV studios. The 50 ohm was
used on a audio/video router for the remote control panels.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

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