Having operated in Western and Central Europe a few times over the years on
160-40M from average to better stations Ive observed something else.
With the typical 5-7 hour time difference the East Coast hears EU well
before sunset in the winter and its hard to impossible to attract a QSO.
This is the prime evening time in EU where activity is highest adding to the
across the band din making weak signals poor copy. Also there is band
sharing with commercial and other stations that drops down considerably as
the evening progresses. Some of those signals are wide with TX generated
noise.
As it approaches EU bed time the consumer noise generators are shut off,
more hams are in bed and the bands "seem" to open to NA.
A good part of EU is also under the auroral curtain at times which adds to
the band noise and signal attenuation.
Whatever real or imagined propagation anomalies exist just add to the
problem.
The only cures I know of are running a remote TX a lot closer to EU; or a
tube with handles and a 10dB+ boost over 1500W such as he who is often
complaining about others comments on here.
Carl
KM1H
----- Original Message -----
From: <k9la@frontier.com>
To: <topband@contesting.com>
Sent: Monday, December 03, 2012 1:09 PM
Subject: Topband: one-way propagation
Jim K9YC asked about other possible mechanisms besides atmospheric noise
to account for one-way propagation on 160-Meters. For the record, I also
believe atmospheric noise (and even man-made noise as experienced by the
PT0S ops) is a big player in these observations. By the way, I also would
like to extend a big THANK YOU to the PT0S ops, especially for their
topband effort.
One-way proapgation was an interesting topic in the AM broadcast industry
in the 1970s (I do not know if it still is). The issue was tied to
allocation of frequencies and the difference in loss depending on whether
it was an east-to-west path or a west-to-east path. John C. Wang of the
FCC measured signal strengths of 18 MF broadcasting stations (540 – 1630
KHz) at 4 receiving sites throughout the continental US to compare the
measurements to the CCIR model.
Subsequent analysis of this data by Douglass D. Crombie of the Institute
for Telecommunication Sciences in Boulder found that for paths between 200
km and 3000 km, the east-to-west path loss is some 9 dB greater than in
the west-to-east direction. Further analysis shows this is highest for
frequencies above 830 KHz. The data did not show any such difference on
north-to-south paths and south-to-north paths.
The second-to-last sentence in the previous paragraph suggests that the
ionosphere, being immersed in the Earth's magnetic field, is anisotropic –
in other words, the ionosphere looks different for RF going east-to-west
versus west-to-east. But if you run ray traces with Proplab Pro (it
includes the effects of the magnetic field and electron-neutral
collisions) for both directions, you will see no significant difference –
at least I have not for my runs). We have to watch it here, though – the
model of the ionosphere in Proplab Pro is a monthly median model (as it is
in all of our propagation prediction programs) – so it does not capture
the day-to-day variability, which may be involved in these observations.
So I believe there is a possibility that there are other mechanisms at
play to give us one-way propagation. Unfortunately, as far as I am aware,
we do not understand them.
Carl K9LA
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