"Richard Clark" wrote in message
...
On Wed, 20 Oct 2004 12:31:41 -0500, "jakdedert"
wrote:

With a system set up as described, I'm surprised he doesn't get some
ghosting on channel 13 from the reflected signal coming off his main
antenna. If so, trapping that channel before the splitter (combiner)
would
reduce the effect.

Hi jak,

Reflected signals on a nearby antenna (like one on the same mast) is
going to be totally invisible. The scan line crosses the screen in
62µS and an RF signal will travel 10 Miles in that time. For a ghost
to be observed the original and the reflection must exhibit some
significant portion (or multiple plus offset) of that value. Let's
arbitrarily call your TV 10 inches wide and set the reflection with a
1 mile path difference. Thus the two images (original and ghost)
would be offset by one inch.

Now let's ramp that 1 mile difference down to a couple of feet (those
two adjacent antennas). You should then appreciate that 1 inch ghost
offset will shrink to sub mm (to mix units). Conventional TV
bandwidths could not resolve the difference.

You misunderstood me. I didn't mean the reflections from the antennas
themselves. I was talking about reflected signals picked up by the off-axis
'main' all channel antenna. Of course, for the reflections to occur, there
would have to be some geographical or architectural feature for them to
reflect off of. In my neighborhood (near center of a metro area), rooftop
antennas have to be rotated for each individual channel. Many times, the
optimum direction is more a function of achieving fewer ghosts than aiming
directly at the station.

jak

73's
Richard Clark, KB7QHC