On Mon, 27 Dec 2004 11:38:51 -0800, Bill Turner
wrote:

The "ghosting" I'm talking about is a very close-spaced ghost, perhaps
1/4 inch or less on the screen. It can definitely be caused by a poor
antenna. I used to install TV antennas for a living, trust me on that.

Hi Bill,

For the benefit of others, let's put this into perspective. The time
it takes to scan one line across the face of a TV screen, is 50µS
which from my Radar days would have been 5 Radar-Miles. As this is
TV, instead that scan line is 10 Miles long (for RF traveling at 5µS
per mile). All this math is going to be about 5-10% off:

If we take the TV screen to be a modern size of 30" diagonal - call it
25" across, then a ghost offset by one inch has its origins in a
reflection (somewhere) that increases the path length by 0.4 mile.
This, of course, presumes that the ghost is displaced horizontally
within the same scan line, and not offset by one vertical trace which
would add 12+ miles plus that 0.4 mile. Where did the extra 2+ miles
come from? Retrace time.

On occasion of poor coax shielding from the cable TV provider, I would
get leakage from strong local TV transmissions that would have ghosts
with huge offsets not only in time, but also picture content. It
would easily compute to 100s of miles path difference, but the lag
time (timed by jump-cuts) proved it was the difference between the
network feed and cable feed time (upwards to a second or two).

So, when we return to this ¼" ghost, for this particular TV set, the
dimension is 0.04 mile or about 200 feet. Sounds like a ringing line.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
So, when we return to this ¼" ghost, for this particular TV set, the
dimension is 0.04 mile or about 200 feet. Sounds like a ringing line.

How does that fit with the state-of-the-art theory that standing-wave
energy doesn't travel end-to-end but instead sorta sloshes from side-
to-side between nodes?
--
73, Cecil http://www.qsl.net/w5dxp


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