> Perhaps the reason that a sunrise peak sometimes enhances signals only
> slightly is that it is not really a peak at all, but a drop in ambient
> noise level at one's sunrise time. This may be because noise is no
> longer propagated in from the east at sunrise and weak signals from the
> west can be more easily heard.
Noise level very clearly does drop from directions of daylight and even from
directions of poor propagation. The more directional the antenna system, the
less noticeable any noise change when pointed into the dark.
This is one effect that makes low directivity antennas, such as low dipoles
and omni-verticals, work better than predictions at sunset and sunrise.
> I have always used low-angle vertical polarization, but those with
> high-angle horizontal antennas may have different observations.
Using low angle antennas here the 160 band often gets a second S/N peak well
after sunrise. Sometimes as late as 45min past. But at that time noise has
also dropped. The same level of signal would be impossible to copy with the
dark noise level, so the absolute strength, like you said Earl, is actually
less. It's more an upward swing of abn otherwise downward trend than an
actual peak, at least most days it is.
There are many things going on at the same time, but we sure like to single
in on one cause and one explaination...often based on next to zero time
actually spent working DX with even the smallest directional antennas. Most
propagation theories seem to be incubated and hatched in local ragchews, or
one night stands, perhaps with the aid of a little brew.
73 Tom
|