On Mon, 06 Aug 2007 13:46:21 -0400, Jack Smith wrote: >I would be amazed if a single 50 ohm barrel would "stop" a digital video >signal.
This IS way off topic, but the right answer lies in studying reflections and losses. Any real world video cable will have significant loss in the GHz range, so reflections are unlikely to travel very far from one termination to another and still be strong at the other end. In other words, lets say you had two video monitors on a line, one at the end, terminated, and the other bridging somewhere along the line. The bridging one would see reflections from a mis-match at the end monitor, attenuated by the loss in the line between the two monitors at the frequency at which the mismatch was significant (>500 MHz), and the monitor at the end of the line would NOT see its own mismatch. And I'm talking small mismatches here -- a 50 ohm connector instead of a 75 ohm one, not a MISSING 75 ohm term, or a double one. And a double term would be far less problematic than a missing one. In his EMC lectures, Henry Ott correctly observes that a mismatch produces a reflection that is observable only at a distance from the mismatch, not at the point of a mismatch. So if I were building a precision video or data plant that might need to work well into the hundreds of MHz range, I would be pretty careful about connector impedance at passive patch points, but not at terminations. And the input of an ACTIVE router is a termination! 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
