[opendtv] Re: 200 Mile 8VSB Reception
- From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 17 Jan 2007 15:23:15 -0800
It should also be noted that the effect is generally more pronounced in
summer than winter, and that this is a particularly cold winter, and last
weekend was very cold. For Southern California.
John Willkie
_____
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On
Behalf Of Richard Hollandsworth
Sent: Wednesday, January 17, 2007 3:19 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: 200 Mile 8VSB Reception
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:
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
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