[opendtv] Re: 200 Mile 8VSB Reception
- From: Richard Hollandsworth <holl_ands@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 17 Jan 2007 15:19:20 -0800 (PST)
A couple comments re. "Ducting".
The San Diego to Santa Barbara path is almost all over water and
hence relies on the SURFACE Ducting effect, wherein the signal
is trapped in a fairly low loss "waveguide" formed by the ocean's
surface and a low lying reflective layer.
This also explains many extremely long DX events, such as report
of 2500 miles FM from Tijuana to Hawaii, found in the Wiki article...
Things get more "interesting" when TX or RX sites are at or above the
reflective layer.....such as attenuating coupling into the "waveguide"....or
forming a less efficient secondary duct above the surface duct...such as the Mt
top to Mt top links...
Another, oftentimes overlooked, aspect of long distance DX is the
need for an on-channel noise floor close to the receiver's thermal
noise floor.....which can be very difficult to achieve if there are high
power transmitters generating intermod noise in your front end.
Hence, these long distance DX reports are almost always from
extremely rural locations....and rarely from the outer suburbs...
holl_ands
====================================
John Willkie <johnwillkie@xxxxxxxxxxxxx> wrote: v\:*
{behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:*
{behavior:url(#default#VML);} .shape {behavior:url(#default#VML);}
st1\:*{behavior:url(#default#ieooui) } The ducting effect
along the Southern California/Northern Baja coast is well known. There?s a
mountaintop just north of Ensenada (90 miles south of the border) where people
with analog cell phones can get native LA analog cellular (no roaming.)
John Willkie
---------------------------------
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On
Behalf Of Mark Aitken
Sent: Wednesday, January 17, 2007 11:00 AM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: 200 Mile 8VSB Reception
Ducting... an Anomaly. Well understood over some bodies of water (some
countries have a schedule, take Kuwait for example...from the island of Failaka
broadcasting to Iraq!).
Pine needles as big as a UHF wavelength???? 15-25"???? Where is this place???
Mark
the Mark that can often differentiate the norm from the rare
John Willkie wrote:
At the risk of putting Bob Miller back in the hospital ?
(try this with low power COFDM)
http://www.flickr.com/photos/docsearls/342324583/in/set-72157594453965824/
(click next to advance)
(Cadged from Bob Gonsett?s newsletter)
John Willkie
P.S. Yet someone else who doesn?t know that ?OTA is dead? and ?8-VSB doesn?t
work.? When will they ever learn?
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