On Tue, 13 Mar 2007 17:39:04 -0500, "Richard Fry" wrote:

"Owen Duffy" wrote
Richard,
The round trip time on the transmission line is 1uS+, and the period of
the highest modulating frequency is 0.2uS, so transient performance of
the line is very important.
____________

Sorry, sir, but quite a few decades of experience in the analog TV broadcast
industry show otherwise (not to mention an accurate theoretical analysis of
this condition).

For example, a reflection within an analog TV broadcast signal that is
delayed by one microsecond from the main image equates to something like a
10% horizontal displacement of that reflected, or "ghost" image from the
main image (525/60Hz TV standard).

A ghost television image amounting to 5% of the main image, and offset by
10% of the width of even a fairly small display screen is not difficult to
see (or to be objected to) by an "average" observer at an "average" viewing
distance from that display screen.

Reflected r-f power may be less of a concern to amateur radio operators than
it is to commercial operators, but that doesn't mean that reflected power is
non-existent, or even unimportant.

RF http://rfry.org

I know that Roy was heavily involved with TDR at Tektronix years ago. I began
working at the RCA Laboratories' antenna lab in 1958. I don't know what
Tektronix was doing relative to TDR at that time, but one of my colleagues at
the lab was Donald Peterson. Don was then working on TDR, and to our knowledge
then, his work on the subject was new. His experiments showed that using TDR we
could spot problems in a TV TX transmission line that was causing ghosts. Using
Don's technique, he traveled to many TV stations around the country that had
ghost problems, and with TDR he was able to determine the precise location of a
discontinuity in the transmission line that produced a reflection that caused
the ghost.

That was over 40 years ago, but I seem to remember that any discontinuity that
resulted in a VSWR greater than 1.005:1 produced a ghost that could not be
tolerated in the transmitted picture.

I'm sure this is the magnitude of reflections Richard F. is referring to.

Walt, W2DU