William Sommerwerck wrote:

"Dave Plowman (News)" wrote in message
...
In article ,
William Sommerwerck wrote:

But I'm still not sure what you mean by 'non linear group delay'.

Phase shift in which the shift is not linearly proportional to the
frequency, along a straight line that passes through the origin.

Right. And just where would you get this?

From less-than-well-designed transmission systems.

The US had microwave systems which generally had low group-delay errors. In
the late '50s, Europe had coax systems which generally did not. Which was
one of the reasons PAL was selected. According to the books, anyhow.


I knew an old ATT guy who worked in both cross country coaxial &
microwave video feeds. He told me how much of a pain it was to equalize
a section of cross county coax used for network TV feeds, and keep it
that way as the temperature changed.

The emergency lashup to cover the JFK assignation was via coax that
wasn't properly equalized, and you could tell from the muddy video.
There was barely enough extra capacity to do it without notice, but all
of the three networks were able to get the live feed at all of their
stations. Some sections of failing coax had to be used, since it was all
that was available without dumping other customers.

That was at a time they were working to eliminate the last of the
cross country coaxial trunklines. They still used coaxial feeds from
the nearest microwave tower to the TV station. Now most of the
microwave sites are gone, having been replaced with fiber optic cable.


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