TV Ghosting (quotes below)

To elaborate, the visibility of a ghost image in analog TV systems is
related to the magnitude, phase and time displacement of the RF reflection
that produced it as compared to the original, or non-reflected waveform.

The round-trip transit time from the TV tx output to the mismatch in its
antenna system will determine the time displacement of the ghost, at the
rate of 1 microsecond of displacement per ~490 feet of distance between the
tx and the reflection plane (vp = 0.997c).

The visible part of a TV image is scanned onto the display screen at a
horizontal rate of about 1 line per 50 microseconds.* An internal
reflection from a transmit antenna connected to the tx by 1,000 feet of
transmission line will create a ghost image ~1 microsecond after the main
image -- or ~1/2" to the right side of it in a 25" wide picture. As the
narrowest vertical line that can be viewed on a display using a 4MHz video
bandwidth is a bit less than 0.35 microseconds wide, a ghost image of it
displaced by 1 microsecond is clearly and separately visible on a 25" wide
display, and will not appear as a "smear" of the main image.

Ghosts also can be produced by external reflections of the radiated TV
signal from buildings, large signs, etc. Often these ghosts have much
greater displacement from the main image than those that can be transmitted
from reflections in the TV transmit antenna system. This is the result of
the greater transit time for those reflections w.r.t. the direct ray, that
are common for reflecting and scattering surfaces where located in the
propagation environment.

Reflections with "short" time displacements are more difficult to resolve
separately as ghosts, but still affect and limit the visual quality of the
TV image. Reflections 40dB or more suppressed from the main image have no
practical, visible affect on it -- regardless of their time displacement.

R. Fry, RCA Broadcast Field Engineer 1965-1980

*allows for the H&V sync pulse intervals and some overscan

_______________________

R. Fry wrote
A 1.3:1 antenna SWR at the far end of more than
about 500 feet of otherwise matched transmission
line connected to that same transmitter WILL produce
a visible ghost.

"Cecil Moore" responded
Of course, a different-cycle reflection is what causes ghosting.