I decided to post this after several e-mails about ducting.
I'm not convinced ionospheric ducting is anything beyond pure
speculation. Even the experts admit there is no way to measure the
effect, that means it is pure conjecture.
Here in Georgia, the path to Europe is further from the lossy polar
regions, but the bulk of the path is along the poorly conductive and
ray scattering Appalachian range. European signals are ALWAYS
disappointing on 160, while a quick drive a few hundred miles east
puts nearly the same path over salt water. 250 miles east signals are
consistently much stronger, and this is always evident when I'm mobile
on 160 making regular night time trips back from a race track about
fifty miles inland from Savannah, Georgia.
In Florida mobile trips, signals from Europe and VK are MUCH
stronger, but signals from JA are about the same as here in Atlanta.
In Ohio, signals from VK and JA are nearly the same as here in
Atlanta, but the shorter and more conductive land mass towards
Europe produces better signals up there, but Ohio sure doesn't
provide the signals like it does to those living in Massachhooosis or
New Yawk. The JA path is more consistent here in Georgia than Ohio
(probably because the path is away from the polar region), but even
with more frequent openings signals from JA almost NEVER get real
strong.
In southern California, over salt water paths, JA and VK signal
levels are VERY strong. When I was working in California two years ago
(a two month stint at an amplifier manufacturer with weekend trips
home) I connected a receiver to small amplified loop. The JA's were
well over S 9, and so were several VK's. The SAME type of antenna
produced dismal S3 signals from VK and JA here in Atlanta.
Think about how the signals typically are night after night. Does the
ionospheric duct suddenly stop at land's beginning? It sure seems like
IF ducting produces these very strong signals, it stops above the less
conductive earth! The sudden consistent lack of "ducting" is too
coincidental to be true, in my opinion. Unless someone can prove the
saltwater ionizes the air and creates the duct!
There certainly are exceptional nights at every location, when
ionospheric losses are low (when the MUF and OWF are low). But
even during propagation "hot times" east coast salt-water-path-boys
have several dB advantage over us poor saps who have to launch
multi-hop propagation that depends on poor soil for half the bounces.
Where on earth is a duct when an inland fellow needs one? Hiding over
the salt water? I think not.
I suspect ducting is NOT part of normal 160 propagation, since
ducting would completely eliminate the effects of lossy terrain
along several hundred or thousand miles of the path. If ducting were
common, the 250 mile east south east single night move I sometimes
make would logically NOT consistently enhance Eu signals, and 500 mile
southerly trips would just as logically NOT enhance VK's along with
the Eu's.
I think the Canadian station simply enjoys a good path totally away
from lossy polar regions, since the entirety of that path is salt
water. Half his loss is greatly reduced, since the bottom portion of
the multi hops are made with a saltwater re-radiator. I enjoy such a
path to Africa from Atlanta, but I never once though the loud signals
from that direction were ducts.
If I recorded signals from Africa, the "in-ducteees" would be
enamored by the obvious "ducting" that takes place from Atlanta to
Africa. But if I recorded European signals following the Appalachian
range, everyone would be amazed at how weak the strongest signals from
Europe are.
All areas of the country, even areas separated by a few hundred
miles, enjoy greatly different signals. These signals mainly appear to
be influenced by the presence of a salt water non-polar path. If we
all enjoyed ducting as much as claimed we would be thrilled at signals
from transcontinental paths across the USA, and not just those signals
reflected by salt water during multiple hops from VK.
73, Tom W8JI
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